Waterproofing & Its Critical Role In Construction Industry

Dr. Surendra P. Bhatnagar, Chairman & Managing Director–Tech-Dry (India) Pvt. Ltd.,Bangalore

The reform process received a boost in the year 1991, when government initiated the economic reforms programme to bring about fast and substantial economic growth. Since 1991, India is going through an exciting phase of the reform process and has opened up its economy. India has already globalised its economy by relaxing several economic policies.

As expected the construction industry is on the forefront of our economic development but unfortunately the technocrats involved in this industry are yet to understand the importance of waterproofing and they have to be prepared for a change and adopt modern technologies.

In the recent past, everybody is talking about green concrete and arresting of global heating. Even during the Indo-American Nuclear deal global heating and environment were important factors.

We entered this field in 1992 and set our company‘s mission as Our Company‘s Mission

 Saving our Environment  Saving Energy  Safety and durability of the buildings

We operate through chain of network within the concept of our company ―Smaller companies win through co-operative, without loosing their independence, the market position of today‘s large multinationals.‖

Thomas J. Peters, Management Consultants

We have spent several years in convincing the industry and the experts in this field that waterproofing is critical not only for durability and safety of the structure, but also equally important for sustainable, environment and friendly, energy saving technique. We faced lot of resistance because it is nature of human being to resist change, which is important fact of life. According to Harold Wilson― He who rejects change is the architect of decay. The only human institution which rejects progress is the cemetery.‖

We are happy to note that the experts in this field are slowly shifting towards green concrete concept and are accepting newer technologies. At the time when we entered this field brickbat coba and coatings like bitumen were in great demand, unfortunately even today there are several experts who do want to stick to the materials like brickbat coba. Inspite of all these odds, we continue with our efforts to introduce products, which are the need of 21stcentury.

Factors affecting deterioration of reinforced concrete structures as well as the mechanism of deterioration are well-understood today. The deterioration in concrete is usually manifested in the form of carbonation, corrosion of reinforcing steel, cracking, spalling, excessive deflection etc.

The effect of the environment on mineral building materials is a natural process, which has not attracted significant scientific interest until recently. The initial work in Germany around 1900 investigated the weathering of natural stones. The problem, which has now attracted is the entry of water containing dissolved toxic substances to the inner parts of the concrete by capillary action. This statement may be extended to the entry of deteriorating agents as a gas or in solution.

Later a problem associated with modern concrete construction emerged-that of steel corrosion in steel-reinforced structures causing spalling.

We have been creating this awareness through our several articles and Newsletters because unless this phenomenon of degeneration of reinforcement is not slowed or stopped, buildings will not be durable and can lead to problems of safety. Infact depending on the chemistry of the environment the malignancy can set-in as early as 3 months of the substrates exposure to the strong environment.

Steel Reinforcement Corrosion

The corrosion of steel reinforcement is by far the single most common cause of structural damage. This situation is rather remarkable, given that steel reinforcement in concrete is well protected against corrosion due to the highly alkaline environment generate from the hydration of cement.

The widespread deterioration of structures emphasizes the vulnerability of concrete protection, as reinforced or prestressed concrete interacts with severe service environments.

The key environmental factors that reduce the passivation of steel, as discussed earlier, are carbonation and chloride. Other factors which may influence either the initiation or rate of reinforcement corrosion include cracks in concrete, temperature, moisture, oxygen and inadequate concrete quality or cover.

Concrete as an Environment

The environment provided by good quality concrete to steel reinforcement is one of high alkalinity due to the presence of the hydroxides of sodium, potassium and calcium produced during the hydration reactions. The bulk of surrounding concrete acts as a physical barrier to many of the steel‘s aggressors. In such an environment steel is passive and any small breaks in its protective oxide film are soon repaired.

If, however, the alkalinity of its surroundings are reduced, such as by neutralisation with atmospheric carbon dioxide, or depassivating anions such as chloride are able to reach the steel then severe corrosion of the reinforcement can occur. This in turn can result in to staining of the concrete by rust and spalling of the cover due to the increase in volume associated with the conversion of iron-to-iron oxide.

In fact, the expense incurred in North America as a result of corrosion-induced repair numbers in the billions of dollars, without even considering the environmental toll of repeated construction and repair. Corrosion inhibitors are one of the most cost effective solutions to this problem, but little independent information is available on their effectiveness in actual use.

It is estimated that even in India approx. 50% of the expenditure in the construction industry are spent on repair maintenance and remediation of existing structures. In future, these expenditures will probably increase even more. A large portion of these expenditures are due to lacking durability of concrete structures. This implies a need to make a design for durability, where the service life is expressed explicitly. There is also a need to plan for and thus reduce the costs for further maintenance and repair by making an appropriate durability design of the structure.

Process of Corrosion

Corrosion is a process, which at times is described as Electro-chemical process. It results in the deterioration of the steel section available for load carrying in a reinforced concrete section. It is dependent on the environment in which the steel exists the level of oxygen available for the corrosion process, presence or absence of water or moisture temperature, exposure level.

1. Fe+O+ 2CO2 + H2O = Fe (HCO3)2

2. 2Fe (HCO3)2 + O = 2Fe (OH) CO3+ 2CO2H2O

3. Fe (OH) CO3+ H2O =Fe (OH) 3 + CO2 Steel once corroded causes cracks on the surface of the concrete cover. Presence of corrosion activity is not detected till such cracks become visible. These cracks then help in conduction of oxygen, moisture which act as accelerators for corrosion. Corrosion also causes the effective steel cross section to increase (swsll) initially. Such increase is followed by separation of outer laminate of steel and its disintegration. However increase in cross section results in reduction of density. Scales occur which normally start to fall off or separate from the steel core with time. Excessive uncontrolled corrosion causes the entire steel section to disintegrate and crumble, total loss of section also results. Corrosion is an irreversible process. Remedial measures cannot help restore the section. It only helps in delaying the process. Green Concrete

We often hear that India is going to become world power. It sounds musical to our ears but when you see the state of our Infrastructures, it is disappointing. In this paper, we will deal with one important aspect and that is the construction industry.

All of us know that India is now poised for growth and is going to be one of the fastest growing industries and the real backbone of our economy.

Crystallization

What is crystallization product? With the modern penetrants, knowledge of emulsifiers, you can develop modified silicates which in conjunction with calcium ions would form crystals which would block the capillaries and pores and reduce the porosity to great extent.

Protekta Base

Protekta Base, viscous liquid consisting of silicates and special proprietary chemical penetrants, is used as a penetrating sealer/surface hardener on concrete to improve its resistance to the ingress of liquid water and contaminants.

Protekta Base reacts with free Calcium and water to form a non-water soluble Calcium Silicate Hydrate gel complex in pore capillaries and cracks. This gel creates a sub-surface barrier. The crystalline product penetrates and reacts with the concrete forming a sub-surface barrier, waterproofing pores, capillaries and larger cracks against the ingress of water and contaminants.

The depth of penetration depends on the time and durability of curing to ensure that all the products penetrates inside. We call it consolidation, porosity reduction and to some extent hydrophobic step, but any claims that it can function alone are not in line with the chemistry.

Protekta Protex

Protekta Protex is a unique chemical treatment. Protekta Protex is supplied as 2 component –powder and liquid, which are mixed and the slurry is coated on the concrete surface. From Protekta Protex special penetrants are released, which get impregnated into the concrete surface to provide crystalline product.

Properties of Protekta Protex

 Waterproofs  Increases Flexibility  Reduces shrinkage and Cracking  Can seal hairline cracks upto 0.4mm  Becomes an integral part of the substrate  Allows concrete to breath  Improves workability of concrete  Can withstand positive and negative hydrostatic pressure

Protekta Consolidant

Protekta Consolidant is a solvent-based product, which consolidates the building materials like Concrete, Plaster of Paris, mortar, Masonry, stones, Marbles, granite etc. It enables to restore the strength as well as the physical properties of the decayed stone layers to the level of the sound stone that existed before degradation and without any harmful side effects.

Properties of Consolidant

 Provides 98–99% hydrophobicity  Enables to restore the strength as well as physical properties of decayed stone layers to the level of sound stone that existed before degradation without side effects.  One of the finest consolidators, which binds the concrete or other substrates.  Repels water  It penetrates and works like binder in the concrete.  As this product does not attract any dirt, surface appearance is unchanged  We have also developed water based consolidant.

Impregnants

There are many advantages of the impregnation of concrete. Reduction of water penetration into concrete through impregnation is significant since the contact angle of concrete capillary surfaces is greatly increased by hydrophobic impregnant.

Impregnants can play a key role in not allowing these outside toxic and pollutant materials and avoid initiate corrosion.Protekta G Protekta G is the first water soluble silane, silanol, siliconate co-polymer which is sprayed on the surface as two wet-to-wet applications and it penetrates into concrete or any other substrate to the depth of 3-4 mm and shows strong repellency after 8-8 hrs.

Properties of Protekta G

 Waterproofing of leaky concrete roof slabs  Waterproofing of earth, mud brick and cement block walls.  Waterproofing of external brick walls.  Waterproofing of A.C. sheet or tiled roof.  To provide damp-proof course in new buildings, in sandstone walls and pavings, in terracotta and ceramic pavements  To prevent surface staining from waterborne pollution, algae, moss, mould etc  Since Protekta G is water based it is totally harmless.  Offers permanent waterproof protection  Easy to apply  Surface appearance is unchanged  Porosity and vapour permeability are unaffected  Can be painted after treatment  Protekta Micro Emulsion- Protekta Micro Emulsion is a water based thermodynamically stable emulsion. It is stable at high pH and it is a neutral product. It is designed to be used for reducing water absorption capacity of building materials and render the substrate water repellent. This water repellent zone reduces not only the absorption of water but also efflorescence or other water borne staining materials. Protekta Micro Emulsion is supplied as a ready to use product.

Properties of Protekta Micro Emulsion

When Protekta Micro Emulsion is incorporated into low slump cementitious products such as imitation stone blocks and pavers, the permeability to water and the occurrence of unsightly efflorescence is dramatically reduced.

 Reduces water absorption by about 95%  It forms hydrophobic zone inside the capillaries, pores and gets permanently bonded to substrate and cannot be washed out  It can also be used as Stain free product.

Protekta Shower Plug

Protekta Showerplug is a unique, clear impregnant which soaks into tiles and grout, making them waterproof within 4-6 hours

 Properties of Protekta Shower Plug  Prevents mould, makes bathrooms/toilets easier to clean.  Will not discolor tiles or make them slippery  It will give beading effect within 4-6 hours.

Protekta Silane Cream

Protekta Silane Cream is an alkyltrialkoxy silane formulated as a water-based environment-friendly non-drip, thixotropic cream. The low molecular weight, low volatility and cream consistency of Protekta Silane Cream ensure deep penetration and high quality water repellency in even the most dense concrete. Once the product has been applied to the concrete surface, it penetrates into the substrate and polymerizes forming a permanent hydrophobic layer, which resists water, chloride ion and other pollutants.

Properties of Protekta Silane Cream

 Penetrates deeply into dense concrete.  Simplified application on overhead and vertical surfaces due to its thixotropic properties.  No pollution of waterways and atmosphere due to no run off and low evaporation.  Reacts chemically with the concrete to form a hydrophobic salt-resistant layers  Reduces water absorption over 94–99% depending on the surface and the chloride ion absorption rate is reduced by over 96-99% depending on the surface

Protektacrete SB

Protektacrete SB is a solvent-based silane/siloxane concentrated impregnant which can be diluted with organic solvent like white spirit or toluene, and which has been formulated to impart excellent water repellency to a wide variety of masonry building materials such as concrete, brick, blockwork, stone, mortar, render, grout and absorbent tiles.

Properties of Protektacrete SB

 Penetrate deeply into the masonry substrate water repellent.  Reduce water and chloride ion ingress by up to 95%.  Prevents deterioration of old buildings. Protektacrete WB

Protektacrete–WB is a water-based silane/siloxane emulsion impregnant which has been formulated to impart excellent water repellency to a wide variety of mineral building materials. The product is designed to penetrate into the first few millimetres of the surface and render the substrate water repellent. This water repellent zone dramatically reduces the absorption of water and water borne salts, while still allowing the free passage of water vapour. Due to the water-based composition of Protektacrete-WB, the release of hydrocarbon solvents is avoided.

Properties of Protektacrete WB

 Penetrates deeply into masonry substrates  Excellent surface beading effect  Does not change the original surface appearance  UV and alkali resistant  Reduce water and chloride ion ingress by up to 95%  Forms water repellent layer within the surface

Protekta Stainfree

Protekta Stain Free is solvent-based (solvent used is turpentine oil) stain resistant sealer and is totally hydrophobic. The substrate treated with Protekta Stain Free does not change the appearance of the substrate. Protekta Stain Free impregnates into the substrate and is breathable sealer, which guards against staining.

Properties of Protekta Stainfree

 It is a stain free impregnant  It is recommended to be used as a stain resistant or water repellent sealer for natural  Reduction in Water absorption 98-99%  Restores strength and does not allow stains of wine and tea etc., to remain on the surface  Reduces moss and mould growth  Reduces Salt efflorescence  Reduces oil and food staining  Does not change the surface colour and texture

Anti-corrosion Protekta Rust Guard

Protekta Rust Guard is based on polymer modified bitumen along with metal oxides like zinc, titanium, calcium and copper salts.

Properties of Protekta Rust Guard

 Protects the steel reinforcement of concrete from rust and corrosion.  Single pre-coating protection for severely corrosive environments (pH below 9).  Equivalent to embedded zinc anodic protection by single coating.  Protection of reinforcement from malignancy.

Protekta Silane Cream (see under impregnants) Design Considerations for Eco–Roof Waterproofing

Dr. C. S. Suryawanshi, Former Chief Engineer, (PWD) Mumbai.

It‘s a new world when it comes to commercial architecture and building construction. No longer is the focus only on expert craftsmanship, innovative design and attention to detail. Rather, all eyes are examining the process itself, the materials used, and most of all, the impact of construction on the environment. And there has been a quite a crowd jumping on the green bandwagon.

contemporary approaches to green roof technology began in the urban areas of Germany over 40 years ago. Because of ongoing water quality degradation and a limited existing infrastructure for the control of stormwater in these areas, few alternatives were available for improved stormwater management designs. Environmental and economic considerations helped spur the development of green roof systems that could provide the necessary stormwater treatment on-site. The paper discusses various design aspects related to materials properties, environment and plant requirements responsible for the waterproofing. The paper also out lines the various types of waterproofing systems useful for the purpose.

Historical Records

A relatively new phenomenon, green roofs first were developed in Germany in the 1960‘s and today, make up about 10 percent of all German roofs. The first green roofs in the United States made their appearance several decades later, but interest and popularity continues to grow as developers, building owners and government officials begin to see the environmental, economic, aesthetic, and social benefits of roof-top vegetation.

From the ancient Hanging Gardens of Babylon to the modern aesthetics of Le Corbusier‘s ―New Architecture,‖ integrating nature into the urban fabric has always been a very desirable amenity for people. The original inspiration for contemporary green roofs came from rugged Iceland, where sod roofs and walls have been used for hundreds of years. The sod roofs soon became popular throughout Scandinavia (Briggs, 2000). This Icelandic architectural style originated from a lack of natural resources, so people had to make do with the local materials of sod and stone (Briggs 2000). Roofs were usually made of turf, and the thick walls of the structures contained bottom layers of stone followed by cut blocks of sod alternating with strips of thin turf. Whenever possible, driftwood was included for timbers, as is the case in the church at Vidimyri, one of the six so-called sod churches that are still standing in Iceland. Built in 1834, it has been preserved as a monument and still functions as a parish church. Old timbers were always recycled whenever found in good condition.

Historically, engineered green roofs have originated in northern Europe, where sod roofs and walls have been utilized as construction materials for hundreds of years.

Concept of Green Building

Now a day the focus the world over is on constructing ‗Green Buildings,‘ which address environmentally sustainable issues in a holistic manner. In countries like the U.S the concept of green buildings is highly evolved, whereas in Canada and Brazil green buildings are quite prevalent. The concept is catching up even in China.

―It was around 2000 that the concept started gaining momentum across the world. In India it was going on in bits and pieces.‖

Minimize urban sprawl and needless destruction of valuable land, habitat and green space, which results from inefficient lowdensity development. Encourage higher density urban development, urban re-development and urban renewal, and brown field development as a means to preserve valuable green space.

Preserve key environmental assets through careful examination of each site. Engage in a design and construction process that minimizes site disturbance and which values, preserves and actually restores or regenerates valuable habitat, green space and associated eco-systems that are vital to sustaining life.

The ideal ―green‖ project preserves and restores habitat that is vital for sustaining life and becomes a net producer and exporter of resources, materials, energy and water rather than being a net consumer.

A Green What?

Green roofs, sometimes also called vegetative roofs, are built on top of buildings and are generally planted with vegetation that requires minimal maintenance and watering. As development replaces land with buildings and parking lots, the amount of impervious surfaces grows. The idea of green roofs is to replace the green space that was lost with the new construction. Green roofs are similar to rooftop gardens except they are not maintained and they are neither ornamental nor recreational. Green roofs are practical and beneficial to the building and surrounding site.

Green roofs slow down and clean storm water runoff, which otherwise can exacerbate flooding and increase erosion. Green roofs absorb storm water and release it slowly over several hours. They can retain 60 to 100 percent of the storm water they receive. In addition, they last longer than standard roofs because they‘re protected from ultraviolet radiation and extreme temperature fluctuations. Green roofs also provide insulation to the building. In winter the roof stays warmer than the ground, thus warming the building, and in summer the plants cool the roof and divert heat from the building.

What is Green Roofing?

Simply put it is a green space on top of a building structure developed from soil and plantings. Unlike a roof garden that utilizes plantings in containers scattered over the roof area, today‘s green roof covers the waterproofing system entirely with soil and vegetation. Vegetated roofs, orgreen roofs as they are frequently called, have been in existence for centuries. Sod roofs have kept many homes warm in the winter and cool in the summer with their grass or plant layer placed atop of the sod base. This natural, environmentally friendly roof provided the basis of construction for the green roof assemblies used on commercial buildings and homes throughout the world today.

Composition of Green Roofs

Green roofs, also known as garden roofs and eco-roofs, are made from a layered structure of components. Covering the roof deck is a waterproofing membrane, often composed of rubberized asphalt, to guarantee a tight seal. The next layer is a protective root barrier, to prevent plant roots from penetrating the roofing membrane. This layer varies in strength based on the landscape design or selection of plants. On top of the root barrier is an insulation/air barrier, composed of extruded polystyrene or other insulation material. Depending on the needs of the vegetation, the insulation layer may be topped with an additional moisture-holding mat.

Next is the drainage/water storage and aeration layer. Using specially designed retention cups and channels made of recycled polyethylene, the drainage layer allows for effective, controlled runoff of excess water. A layer of filter fabric tops this, to filter soil fines and debris, allowing water to pass through to the drainage and aeration layer.

The top layers are the soil layer and the vegetation. Lightweight engineered soil provides a stable structure for the plants‘ root system and supplies nutrients, water and oxygen while remaining as light as possible to prevent excessive loading of the root structure.

Depending on building conditions, climate and anticipated use of the roof, a wide variety of typical landscape and garden plants are suitable. Plants with shallow root systems and resistance to direct radiation, drought, frost and wind are wellsuited to all types of green roof landscaping; but even perennial flowers, shrubs, small trees and sod grasses can be used for intensive roofing landscapes.

Green Roofs

The term ―green roof‖ is generally used to represent an innovative yet established approach to urban design that uses living materials to make the urban environment more livable, efficient, and sustainable. Other common terms used to describe this approach are eco–roofs, and vegetated roofs. Green Roof Technology (GRT) is the system that is used to implement green roofs on a building. Green roofs are constructed using components that

 Have the strength to bear the added weight;  Seal the roof against penetration by water, water vapor, and roots;  Retain enough moisture for the plants to survive periods of low precipitation, yet are capable of draining excess moisture when required;  Provide soil-like substrate material to support the plants;  Maintain a sustainable plant cover, appropriate for the climatic region;  Offer a number of hydrologic, atmospheric, thermal and social benefits for the building, people and the environment;  Protect the underlying components against ultraviolet and thermal degradation. Types of Green Roofs

Green roofs are generally categorized as extensive or intensive. Extensive roofs are ideally suited for locations that will receive little maintenance or where structural capacities of the roof are a concern. Sedum, herbs, grasses and other vegetation that can withstand harsh conditions are recommended. Intensive roofs use plants that require regular maintenance, such as watering, fertilizing and mowing. These roofs must be structurally stronger, and often serve as pedestrian recreational areas. Several other variations include the shallow-intensive garden roof, which combines a lightweight roof assembly with slightly deeper soil to accommodate sod lawns and perennials, and sloped extensive applications, which can be applied to sloped roofs with a pitch of up to 45 degrees.

Intensive green roofs generally require more effort for the tending of plants, whereas the term extensive roofs call for a more passive approach. Intensive green roofs also emphasize the use of space and therefore raise higher aesthetic expectations than more functional extensive green roofs. Intensive green roofs generally need deeper substrate, more diverse plants including trees and shrubs, and proper watering schedules. Thus they involve higher costs (Dunnett and Kingsbury 2004; Peck et al. 1999). As in many design classifications, however, there are actually degrees of intensiveness in the approach to rooftop greening.

In order for plants to grow on roof tops, natural environmental conditions have to be recreated. This can easily be done by the installation of a series of functioning layers which, while retaining the necessary water to support the plants, allow excess water to drain off and protect the roof surface from plant roots and mechanical damage. A variety of systems are supplied by manufacturers which provide a stable roof-top environment for plant growth.

A typical system includes the following:

 Vegetation layer: Low growing, stress tolerant alpine and herb species  Lightweight Soil: 50-100mm in depth  Filter Mat  Drainage Layer: Aggregate or plastic cups  Root Barrier  Waterproof Membrane

Waterproofing Aspects

There are so many myths about waterproofing. The people dealing with construction are normally different from people using such facility or maintaining them. Either of them passes on the blame on each other, and this ends in an unnecessary and expensive treatment to places, hardly susceptible to leakage, while real culprit is somewhere else, and gets altogether neglected. This may be the result of inadequacy of individual‘s knowledge of behavior of parent material so far its resistance to water ingress is concerned and Porosity of building materials, especially that of concrete, and knowledge of the waterproofing treatment adopted.

Water Flow–Drainage

Roof drainage is an instructive example of water flow. If water is to drain from the surface, there must be a high point and a low point. The rule for adequate drainage is that the fall (slope) must be at least 1 in 80 and that must be achieved. Creative pessimism dictates that the falls intended- i.e. shown on drawings or specified will not necessarily be obtained. Using normal methods there is a level of accuracy to which any part of a building can be built, so a further rule that has to be emerged. Double the fall to be obtained i.e. an achieved fall of 1 in 80 is allowed for by specifying,fall of 1 in 40. It is then for the contractor to take such precautions that will ensure that normal building accuracy (or special building accuracy, if that has been specified) is reached.

Air Pressure, Gradients, Moisture, and Wind

As moisture vapor causes a partial pressure, known, as vapor pressure there will be a gradient across a construction, whenever air on one side, contains more moisture than the other. The overall steepness of that gradient will depend on the difference in the vapor pressure on each side of the construction; the shape on the vapor-resisting properties of the materials that made up the construction.

The action of the wind on the external surface of a construction, results in an air pressure. As such, pressure inside is usually different. An air pressure gradient arises. A positive air pressure externally assists in driving rain through gaps in the construction. Provision for pressure equalization to take place is a form of balancing. Its achievement can help greatly, to reduce the risk of rainwater penetration through constructions.

Garden Roof System (GRS)

Garden roof systems (GRS) are specialized roofing systems that support vegetation growth on rooftops. GRS not only add aesthetic appeal to the unused roof space that is available in most urban areas; they also provide multiple benefits in an urban context. From a building‘s point of view, the plants and soil protect the roofing membrane from exposure to ultra violet radiation, extreme temperatures and physical damage, thus contributing positively to the roof‘s service life. GRS also reduce energy demand on space conditioning, and hence greenhouse gas (GHG) emissions, through direct shading of the roof, evapotranspiration and improved insulation values. If widely adopted, GRSs could reduce the urban heat island (an elevation of temperature relative to the surrounding rural or natural areas due to the high concentration of heat absorbing dark surfaces such rooftops and pavements) which would further lower energy consumption in the urban area. From a community‘s point of view, GRS can be used as a source control tool for the stormwater management strategy in the urban area. Part of the rain is stored in the growing medium temporarily, and to be taken up by the plants and returned to the atmosphere through evapotranspiration. This delays and reduces runoff and takes a load off the city‘s storm sewage system. The plants can also remove airborne pollutants and improve the air quality in the urban areas.

In addition to the roofing membranes, a GRS consists of several major components, namely, root resistance layer, drainage layer, filter membrane, growing medium and vegetation. The components act together to provide a suitable environment that supports plant growth while not compromising the waterproofing function of the roofing membrane. GRS can be installed on both conventional and protected membrane systems.

In the roofing industry, GRS is generally categorized into extensive and intensive by the weight of the system. Extensive GRS is lightweight, consisting shallow growing medium with small plants (e.g., sedums, herbs and grasses). These systems require very low maintenance. Intensive GRS is heavyweight and contains much garden soil. The greater soil depth allows growing of bigger plants such as shrubs and trees.

Design Criteria of Roof

The main criteria for selection of waterproofing material and movement control in roofs are:

1. Integrity and durability of the weather proofing material and performance. Flat roof finishes are the most vulnerable due to low movement tolerance. 2. Integrity of the roof structure. 3. Interaction with supporting or adjoining elements of frameworks. 4. Integrity of attached ceiling finishes if any and integrity of the supporting structures.

Failure Limits of Roof Structure

The failure limits of roof construction are therefore determined by the effect on the finishes or weatherproofing membrane and secondly by any detrimental effect on the supporting or adjoining structures as well as on the roof structure itself.

As in other elements, the amount of movement, which can be accommodated without damage or failure, depends not only on the strength and durability of the affected components, but also on the manner of their assembly. This can greatly affect the stress induced by movements and can reduce the effect of movements being transmitted between layers, particularly of roof finishes.

Mechanical Properties of Waterproof Roof Covering

The resistance to movements of various types of roof coverings varies greatly depending on their form material and assembly.

Pitched roof coverings being the overlap unit type can stand considerable movements without failure or causing loss of weather tightness.

Flat Roofs:

Flat roof coverings on the other hand being continuous; rely on their complete integrity from cracks to maintain weather resistance.

Effect of Layers

The mechanical strengths of the top (water excluding) layers of multi-layer coverings will depend on the amount of stress transmitted by the base fabric and the strength of this in turn, in the case of bituminous impregnatedcoated fabrics is the strength of the fabric itself.

Most traditional roofing felts suffer from the weakening effects of repeated loadings. Sudden movements are accommodated by elasticity and longer term movement cycles can also be accommodated by a certain amount of viscous flow. The stresses in the top layer also depends on the amount of stress relaxation which can take place between the layers in the time, i.e. the rate of straining effect. It also depends on the distance from the substructure or cause of movement (see Figure 5.1) and on the amount of slip due to partial bonding. Single layer roofing systems are naturally less able to reduce strains than partially bonded layers.

Advice of Structural Engineer

A structural engineer should always be consulted prior to roof garden landscape design and construction.

Rooftop structures must typically be able to support a dead load of 150psf to commodate the construction of a garden. The roof must be completely covered by an elastomeric material and protected by a concrete topping slab.

It is recommended that a completely new waterproofing layer be added to the existing structure to insure the longevity and integrity of the waterproofing system.

A waterproof topping coat of concrete should be used to protect the waterproofing.

Properties of Concrete

The ease with which a fluid can be flow through the matrix of a solid is believed to be the ermeability. It is obvious that the size and continuity of pores in any porous material will determine its permeability. Several theories attempt to relate the microstructural parameters of cement products with either diffusivity (The rate of diffusion of ions through water filled pores) or permeability.

Compared to 30 to 40 percent capillary porosity of typical cement paste in hardened Concrete, the volume of pores in most natural aggregate is usually 3 percent and rarely exceeds to percent. From permeability date of some natural rocks it appears that the coefficient of permeability of aggregate vary as that of hydrated cement paste of W/C ratios in the range of 0.38 to 0.71.

Permeability Aspect of Concrete

Permeability of concrete should not be confused with absorption. It is not a simple function of its porosity but depends on the size, distribution, and continuity of pores. The volume of pore space, as distinct from its Permeability, is measured by absorption and two quantities are not necessarily related. Dense concrete is said to possess low permeability. Unfortunately, so far, it has not been possible for concrete technologists, to set limits for permeability which could be subjected to practical tests, and whatever tests are available, and those are of academic importance.

In practice, it is wrong notion to understand permeability and absorption in the same sense. In fact, permeability of concrete is not a simple function of its porosity but varies with the size spread i.e. distribution and continuity of the pores. The size of capillary pores ranges up to 1.3 nm and that of gel pores is too smaller than that. The volume of pores space in concrete, as distinct from its permeability is measured by absorption and these two quantities are not necessarily co-related. In body of concrete, the capillary pore structure allows ingress of water. It is generally observed concrete gel has porosity of the order of 28% but its permeability is about 7x109m/s. The permeability of cement paste as a whole is 20-100 times greater than that of the gel itself. Most concrete Technologists believe that, permeability although a complex property of concrete, depends largely on. 1. Quality of cement and aggregate. 2. Quality and quantity of cement paste in concrete (and quality of cement paste depends on amount of cement, the W/C ratio of the mix and hydration of cement). 3. Bond developed between paste and aggregate. 4. Degree of compaction of concrete & standard of curing. 5. Presence or absence of cracks or characteristics of cracking behavior. 6. Characteristics of any admixture used in the mix.

Morphological Aspects of Concrete: From decades to gather compressive strength is reckoned as most valuable Engineering property of concrete. The science of RCC and PCC totally devolves on this one aspect only. The circumstances under differing environments recently recognized as harmful to concrete surface have compelled the attention to other characteristics such as durability, impermeability, and volume stability.

The ability of concrete to oppose weathering actions, chemical attack, abrasion and other conditions during its service life have come to be identified as ―Durability.‖ Whereas capability of concrete building products, components, assembly, or construction to perform the function/s intended in design and construction is valued on its service ability, these definitions are broad enough to embrace all practical aspects in general. However, strength parameter doesn‘t give true picture of quality of concrete since it is directly related to structure of cement paste. Strength, durability, serviceability and volume change of hardened cement paste that is important element in concrete appears to depend not so much on chemical composition as on the physical structure of the products of hydration of cement and on their relative volumetric proportions. In fact, it is the presence of flaws, discontinuities, and pores, which are of significance and bear an impact on strength. Since present day knowledge of field engineers in respect of this fundamental approach is inadequate, it is essential to relate strength to assessable parameters of the structure of hydrated cement paste. It will be seen that the primary factor in this is ―porosity‖ i.e. the relative volume of pores or voids in the cement paste. Unfortunately the porosity, of the hydrated cement paste and micro cracking are difficult to assess and quantify in a manner, useful to the engineer to relate them to study the effects on strength factor. In fact, it is cement paste, whose structure is complex, which consists of several sources of flaws and discontinuities, despite proper compaction of concrete and even before the application of an external load up to 50% of the volume of Cement paste may consist of pores. Again, presence of aggregates either coarse or fine aggregates the position. The cracks from various sources, randomly distributed in the matrix vary in size and orientation. Consequently concrete renders itself weaker than the cement paste which it contains. The actual failure paths (when viewed under SE MICROSCOPE reveal) follow the interfaces of the largest aggregate particles, cut through the cement paste and occasionally also through aggregate particles.

Pore Size Distributions Throughout the hardened Cement paste there is a spread of whole range of pore sizes i.e. larger capillary pores and smaller ones of gel pores. When only partly hydrated paste contains interconnected system of capillary pores. Pastes that had been rapidly dried are noticed to be closest in structure when compared to undried pastes. The sorption test results indicated that their structures were dominated by platy particle of the formed shaped meso–pores and micro–pores. Slow drying produced small pores nearly cylindrical or spherical, has been established by various researchers. To get even distribution of pores it is essential to have sufficient higher degree of hydration of the capillary system to became segmented through partial blocking by newly developed cement gel, so that capillary pores get interconnected by the much smaller gel pores. Table 1.0 shows the min, period of curing required for capillary pores to become segmented. However, it is also established that finer the cement shorter is the period of curing necessary to produce degree of hydration at a given W/C ratio.

Moisture Movement & Creep Materials exhibiting creep as well elastic characteristics are often grouped as visco-elastic. Most building materials when subjected to sustained load undergo an instantaneous (elastic) deformation followed by a time dependent deformation generally recognized as creep. Creep strain composes delayed elastic strain (eventually recoverable on removal of load) and viscous strain, which remains as a permanent one when load is removed. In porous materials capable of absorbing or giving off moisture, the creep strains are linked in with moisture movement, which leads progressive shrinkage or expansion depending upon the nature of material, its initial moisture content and external environment. The theory of creep and shrinkage in concrete based on the migration of moisture from the cement gel can be established by a simple phenomenon. When a concrete specimen is over dried, it expands, when exposed to the normal environment of say 60% humidity. The gel is so thirsty that it eagerly takes up moisture from the hour and in doing so expands, this expansion takes place even against a high compressive strain. In fact, all porous materials display above characteristics. In fact up to a certain level creep in concrete is proportional to stress give rise to the concept of ―Specific Creep‖ i.e. creep strain per unit stress. This can be arrived at from the relation.

Specific creep c=t/(a + bt). Where, t=timing from loading, a,b=Constants determined by experiment

There are several important design and structural differences between ground level landscape development and rooftop developments. The following are the special construction requirements and considerations when developing a roof garden. Protection of the integrity of the roof and structure.

Protection of the Roof and Structure

The single most important element in rooftop garden construction is protecting the integrity of the roof and the structural components under the garden. For this reason there must be waterproofing of exceptional longevity to prevent damage and to reduce the possibility of long term expensive reconstruction. For this reason it is recommended a completely new waterproofing layer be added to the existing structure to insure the longevity and integrity of the waterproofing system.

Load Bearing Capacity

The structural engineer should verify the maximum load bearing capacity of the existing structure. These figures should be available from the records of the previous construction. Typically, a minimum additional dead load limit of 150 psf between columns is needed to accommodate the construction of a roof garden. Loads above columns and at the roof‘s edge can be considerably higher; however a structural engineer should be consulted to establish the load bearing capacity of those areas.

These higher load bearing areas should be used to accommodate larger specimen plantings and trees.

Waterproofing

As mention before, a completely new waterproofing system should be installed to protect the building‘s structure. There are several types of waterproofing systems available; however, elastomeric materials offer the greatest protection. Bituminous waterproofing should be avoided. Over time the organic components in bituminous waterproofing interact with the soils and the plant materials and therefore increase the likelihood of system failure.

A properly installed waterproofing system can last the lifetime of the building, however a single small leak may require the removal of the entire garden to find and repair the damage. Therefore, in order to insure the integrity of the waterproofing it is recommended that a protective topping coat of concrete be applied, as soon as possible, following the installation of the new waterproofing.

Recent Development in Waterproofing Methods

Demands for reliable waterproofing as well assured moisture and vapor leakage proofing methods and materials are being constantly felt. In many civil engineering constructions, traditional methods of waterproofing have not been found satisfactory. Consequently, repairs and renewals have to be taken up more often than they are required.

How Green Roofs Are Made

Green roofs are constructed in layers on top of the roof. The number of layers depends on the type and root depth of the plants selected, the slope of the roof, and the materials used in the layers. Layers can include, from the top down to the roof, the following: a filter fabric to hold the plants in place, Innovative roof garden systems the growth media and the plants, a drainage Polygum roof garden, root resistant membrane layer, a root barrier, an insulation layer, and a waterproofing layer. Sometimes more than one function is combined in a single layer.

The filter fabric holds the soil in place and prevents small soil particles from entering and clogging the drainage layer underneath. Generally, growth media is a mix of about two–thirds inorganic material (such as expanded slate or crushed clay) and one-third organic material (humus and topsoil).

This mixture provides essential drainage, soil air capacity, and organic nutrients.

The drainage layer carries away excess water and makes an extremely stable and pressureresistant sub-base. A root barrier prevents deep roots (in the case of trees, for example) from damaging the roof. The insulation layer is optional and prevents water stored in the green roof system from extracting heat in the winter or cool air in the summer. The waterproofing layer is critical and ensures that water doesn‘t seep into the roof.

System of Waterproofing

Waterproofing systems have been grouped into five types according to type of construction and characteristics of material of waterproofing. However following are widely favored. a) Protective coatings–Recently Developed Systems b) Waterproofing by injections.

The injection system of waterproofing by chemical grout has been found to be successful in stopping leakages completely even at a number of underground projects.

Recent Advancement Polymer technology and its applications in waterproofing field are the modern techniques of waterproofing using newly developed products. Benefits derived from the use of polymer in concrete for waterproofing are multifold particularly with regard to its efficiency and reliability. New generation has successfully used it for stopping leakages in building constructions, tunnels; power houses underwater structures, dams, reservoirs, aqueducts, etc.

Classification of Water– proofing Method/ Systems

The waterproofing Methods/ systems can conveniently be classified according to five major characteristics of Building materials, to oppose or resist the ingress of moisture.

Hydrolithic Water-proofing

Hydrolithic action mostly uses water as a base media and provides protective coating over the porous surface. Dampness and efflorescence, which cause formation of powdery white deposits on the surface of brick walls and masonry constructions, are common problems in most of the buildings. The likely damages are mainly due to ingress of water into masonry. Protective surface coatings; used mainly for getting a better surface finish and appearance of the structure, also offer resistance to moisture ingress.

Various coating materials such as epoxies polyurethanes chlorinated rubber acrylates etc. are available. They form a film to oppose entry of water. Some coatings give good film but have little penetration with the result in the long run they loose adhesion with concrete.

Certain coatings are vapor permeable, which allow passage to gases and vapors but exclude passage of liquids, vapor, barrier. Coatings block passage of both vapors and liquids and are suitable for underground or water logged structures also.

Plastic emulsions are particularly water-soluble. Epoxy emulsions, Acrylates, Silicones etc, have been used to stop the efflorescence and dampness. A few paints based on acrylic emulsion show better results but have failed to arrest efflorescence completely though epoxy emulsion as well as silicones being low viscosity liquids was found useful because they could travel deep. Permeability of water vapor by pressure is reduced completely by formation of insoluble mass or plastic membrane like film into pores. Performance of these emulsions are superior and allow the concrete to breath, i.e. allow entrapped water vapor to permeate out without allowing diffusion of oxygen, carbon dioxide, chlorine ion or rain water from outside. After the application of the protective coating, an additional coating of polymer emulsion mixed cementitious mortar is preferable as it provides high impermeability.

Integral Waterproofing

Waterproofing by inclusion of integral waterproofing compound in concrete in one form or the other has been widely carried out for many years since past and they are generally believed to have no adverse effect on durability provided they don‘t contain chloride. Polymer based integral waterproofing cement compounds give good performance, and provides high durability to concrete.

There are a number of integral waterproofing compounds and liquids conforming to the requirements of Indian Standards Specifications I.S. 2645-1975 These products are of two types:

(i) Water repellant materials such as stearates or oleates, which through surface tension effects discourage the penetration of dampness into and through concrete.

(ii) Fine particulate materials often used in conjunction with water reducers, which partially block and reduce the size of the pores in concrete, and lower the permeability to water.

Neither type of materials make concrete truly waterproof. The former can be beneficial in discouraging rising damp and rain penetration, but it has little effect against an applied head of water. In some circumstances, it can reduce problems of efflorescence.

The latter can be effective in lowering the permeability of low quality concrete but is unlikely to cause any significant improvement in that of better quality concrete (with a water/cement ratio less than 0.6) so called waterproof concrete, i.e. that containing a waterproofing admixture is not an acceptable substitute for a dampproof membrane for slabs–on ground.

New generation waterproofing techniques include polymer-based integral waterproofing cement compounds. These products are water soluble and have been found to provide significant eduction in the permeability of concrete due to more effective dispersion of cement particles in the mix and cause substantially high reduction in water/cement ratio. Water permeability is reduced tremendously by more than 85 per–cent.

Integral Waterproofers

Integral cement waterproofing compounds are generally mixed with cement at a prescribed dosage rate. These are broadly classified into three groups; permeability reducers, water repellents or hydrophobers and polymer modifier for cement. Fine particulate materials like round sand, whitening, bentonite, flyash, colloidal silica and flurosilicates; salts of high sulphonic acids, detergents and sulphonated carbohydrates are mostly used as permeability reducers and their major role is to reduce the water –cement ratio and hence the permeability of mortar or concrete. Another class of chloride free integral waterproofers based on air entraining plasticizers, normal plasticizers, super plasticizers, and retarding plasticizers are the most modern types to make the concrete waterproof. Such materials are specially used for marine and super structures.

Water repellents or hydrophobers are generally soaps - water-soluble and sulphonium salts of fatty acids, butyl stearate, and selected petroleum products like mineral oils, waxes, and emulsified asphalts etc. The chemicals in such waterproofers form a thin hydrophobic layer within the network of cement mass by coating the cement particles.

Polymer modifier used for cement is organic polymers dispersed in water. These are now extensively used in the country these days as they impart better flexibility, reduce water permeability, increases tensile strength and bonding behavior of cement particles and hence provide excellent waterproofing properties. The materials used are discussed in detail later in the text.

Membrane Type of Waterproofing

It affords a highly impermeable layer for durable waterproofing and protection of roofs, terraces, balconies, sun shades etc. against extreme weathering conditions, irregular temperature variations, industrial pollution, rain etc. It may be, a modified polymer based durable and elastic coating in semi- paste state, which forms a seamless, continuous watertight flexible membrane that makes the treated surface impermeable to water.

Failure Limits of Weatherproof Membrane and Base Fabric

Failure in the function of the weatherproof membrane can take in the following forms: a) Failure to discharge rainwater by ponding b) Local movement blistering ripples cockling c) Slippage or creep. d) Rupture: Local cracking or holes e) Delamination or uplift f) Puncturing. g) Degradation of surface material.

(a) to (e) can be brought about or be aggravated by movements in the substrate or structure or in the weatherproofing layer itself.

Sheeting Materials–As Roofing Membrane

Single ply roofing membrane is latest addition in the area of waterproofing. The recent advances in polymer science have benefitted the roofing technology as it has resulted into the development of number of new roofing materials during the last 20 years or so. [Flexible PVC membrane is most popular in the thermoplastic category and EPDM (ethylene propylene diene monomers) is the most popular in the elastomeric category though polychloroprene, polyisobutylene and chlorosulphonated polyethylene elastomeric membranes are also being manufactured and used; as detailed later]. Single ply membrane can be used in loose laid (ballasted), adhered, or mechanically fastened systems with insulation atop or beneath the sheet. When loosely laid the membrane remains unattached to the substrate except at the perimeter of the roof and penetration such as vent pipes. Because it is free floating, it can accommodate movement of the substrate and small amounts of entrapped moisture. However, it should be weighted down with smooth river gravel, avers of concrete blocks to prevent wind uplift. The ballast provides also additional protection against attack by wind uplift. Some obvious limitations of this system are that it can only be used on flat roofs and only on buildings that can structurally support the weight of ballast, otherwise sagging and ponding may occur.

The membrane may be attached with adhesive used alone or in combination with mechanical fasteners. In these cases, ballast is not required. Fully adhered systems may be used to advantage for covering sloped roofs. Preparation of the deck to ensure having a clean smooth, stable surface with taped joints is essential to maintain good bond. Partial bonding with adhesives alone or in combination with mechanical fasteners allows greater movement of membrane than a fully adhered system. Depending on the type of membrane, joints are made between sheets by heat fusion, torching, solvent welding, and tacky tapes or with adhesives

The major advantages of such elastomeric membranes are.

1. These are lightweight; weight is about 1.2 kg/m2 as against 9 kg/ m2 for a built-up-roofing membrane, or 4.5 kg/m2 for a single ply modified bitumen membrane, which makes them the obvious and preferred choice for lightweight constructions. 2. Work with single ply roofing proceeds cleanly and quickly and large areas can be closed in under wider range of climatic condition. Because the sheet is lightweight, it is often possible to re-roof with minimum surface preparation and frequently without having to spend the extra time and money for removal and disposal of the old roof. Also, this permits undisturbed occupancy of the building reroofing. 3. The single-ply roofing provides the architect with new degrees of freedom in color and design. 4. The improved safety aspects of the single ply synthetic roofing systems are deserving of mention in regard to both the installation crews and the structure. The potential for burns and inhalation of hot bitumen fumes is eliminated. Fire hazards are also reduced.

Epoxy Based Coatings

One of the widely accepted polymeric materials by the construction industry is epoxy resin; as epoxy based products provide solution to various construction problems in the form of coatings, sealants, mortars, adhesives, injection grouts and so on. The increasing demand of epoxy based products; (growth rate of more than 20. percent per annum) is mainly due to their good mechanical strength, adhesion with different substrates and chemical resistance. Epoxy resins modified with other polymeric systems such as polysulphides, phenolic etc. and coal tar have also been recently developed to meet out the requirements of aggressive and industrial environment.

Epoxy based coatings are mostly used as waterproofing, damp proofing and protective coatings for internal applications. Water thinable epoxy coatings can be applied on wet surfaces for damp proofing.

Epoxy grouts, though costly as compared to other polymeric grouting materials, have an edge over other chemical grouts as these can restore structural integrity by bonding cracks together, even in the presence of water and have superior chemical resistance. Effectiveness of chemical grouting is increased manifold, if grouting is followed by the application of polymer liquid membrane compatible with the grouting polymer.

Polyurethane Based Coatings

Polyurethane based coatings and compounds are the most versatile materials which have ttracted the building industry because of their efficacy in solving the commonly faced problems related to the ingress of water and protection of structures. Polyurethane based products are available either in the form of one component or two component systems. Onecomponent systems are generally solvent based while two component systems can either be solvent based or solvent free. Solvent based polyurethanes are mostly used for waterproofing, dampproofing, flooring and anticorrosive coatings while the applications of solvent free polyurethanes are as sealants, chemical grouts, insulation etc. The superiority of polyurethanes over other liquid membranes are due to their high elasticity (can accommodate expansion and contraction of substrate due to temperature variations), strong adhesion to substrate, high abrasion and cracking resistance (film can withstand erosion due to rain and wind as well as movement of people without wear and tear), higher resistance to biological defacement and UV radiation. The occurrence of moisture curable polyurethanes is another significant addition in this field.

Moisture curable polyurethanes are used for various applications such as adhesives, sealants, and damp proofing of concrete structures. They provide durable and cost-effective solution for the protection of structures in damp conditions.

Keeping in view the properties of various coating systems, their applications have been broadly summonsed in Table-1.

Sheeting Materials- Single–Ply Synthetic Roofing Membranes

Single ply roofing membranes is another latest addition in the area of waterproofing. The recent advances in polymer science have benefited the roofing technology as has resulted into the development of number of new roofing materials during the last 20 years or so. Flexible PVC membrane is most popular in the thermoplastic category and EPDM (ethylene propylene diene monomers) is the most popular in the elastomeric category though polychloroprene, polyisobutylene, and chlorosulphonated polyethylene elastomeric membranes are also being manufactured and used.

Single ply membrane can be used in loose laid (ballasted), adhered, or mechanically fastened systems with insulation atop or beneath the sheet. When loosely laid, the membrane remains unattached to the substrate except at the perimeter of the roof and penetration such as vent pipes. Because it is free-floating, it can accommodate movement of the substrate and small amounts of entrapped moisture. However, it should be weighted down with smooth river gravel, pavers or concrete blocks to prevent wind uplift. The ballast also provides additional protection against attack by ultraviolet light and may prevent tear propagation by wind uplift. Some obvious limitations of this system are that it can only be used on flat roofs and only on buildings that can structurally support the weight of ballast, otherwise sagging and ponding may occur.

The membrane may be attached with adhesive used alone or in combination with mechanical fasteners. In these cases, ballast layer is not required. Fully adhered systems may be used to dvantage for covering sloped roofs. Preparation of the deck to ensure having a clean smooth, stable surface with taped joints is essential to maintain good bond. Partial bonding with adhesives alone or in combination with mechanical fasteners allows greater movement of the membrane than a fully adhered system.

Depending on the type of membrane, joints are made between sheets by heat fusion, torching, solvent welding, and tacky tapes or with adhesives. The major advantages of such electrometric membranes are:

(i)These are lightweight, weight is about 1.2 kg/ m2 as against 9 kg/m2 for a built-up-roofing membrane or 4.5 kg/m2 for a single ply modified bitumen membrane, which make them the obvious and preferred choice for lightweight constructions.

(ii) Work with single ply roofing proceeds cleanly and quickly and large areas can be closed in under wider range of climatic condition. Because the sheet is lightweight, it is often possible to re-roof with minimum surface preparation and frequently without having to spend the extra time and money for removal and disposal of the old roof. In addition, this permits undisturbed occupancy of the building during re-roofing.

(iii)The single-ply roofing provides the architect with new degrees of freedom in color and design.

(iv)The improved safety aspects of the single ply synthetic roofing systems are deserving of mention in regard to both the installation crews and the structure.

The potential for burns and inhalation of hot bitumen fumes is eliminated. Fire hazards are reduced.

Conclusion

The waterproofing systems described above have been successfully adopted abroad and research on improvement on the subject is in progress.

References

 I.S. 3384–1965 Specification for bitumen primer for use in water– proofing and damp proofing.  I.S. 3067–1966 Code of practice for general design details and preparatory work for damp proofing and waterproofing of building.  Albrecht Dürr, Dachbegrünung: Ein Ökologischer Ausgleich translated: Green Roofs: An Ecological Balance. (Bauverlag, GmbH, Wiesbaden and Berlin, Germany 1995)  Briggs, Greg S. ―Why Should You Care About Green Buildings?‖ Skill Ward Magnusson Barkshire, Inc. 15 Sept. 2000.  Canada‘s Office of Urban Agriculture. City Farmer Publication. Urban Agricultural Notes ―Rooftop Gardens.‖  City of Olympia, Public Works Department, Water Resources Program, Impervious Surface Reduction Study, Final Report, (May 1995).  Daniels, Elizabeth. ―Green Buildings Starts at the Top.‖ Business & Industry Resource Venture 15 Sept. 2000.  Environment News Network (ENN). ―Chicago Hopes Rooftop Garden Cools Air.‖ United Press International. 17 May 2000. www.enn.com.  ―Green Groweth the Rooftops.‖ Environment Dec 2000: vol 42, p. 7.  Knepper, Claire A. ―Gardens in the Sky.‖ Journal of Property Management. Mar-Apr 2000, vol. 65.: 36-40.  Suryawanshi C.S (Dr), ―Water– proofing of Civil Engineering Structures.‖ Hand Book for Practising Engineers 2001.

How Crucial Waterproofing of Concrete Structure Is? Dr. Surendra P. Bhatnagar, Chairman & Managing Director, Tech-Dry (India) Pvt. Ltd., Bangalore.

Water is Elixir but Hydrophilic, Concrete is an Enemy

Cost of repair and rehabilitation is exorbitant.

The amount spent on repair and rehabilitation of concrete structure in US is around $ 8.3 billion per year.

Even 15 years back, the annual cost of corrosion of concrete bridges and support structures was estimated to be in the range of $165 to $ 500 million.

The annual cost of repair of parking garage due to corrosion was estimated at $300 to $400 million.

Out of 500,000 bridges in USA, 200,000 were reported to be under severe distress. Remaining 300,000 also needed repair and rehabilitation. The cost for replacement of 300,000 bridges was worked out to be around $112 billion.

As the third millennium dawns, the United States is in the midst of a ―bridge crisis.‖ Maintenance needs for older bridges have far outpaced available resources. This situation indicates the need not only for improved repair and rehabilitation techniques but also for a comprehensive approach to bridge management . In India, Repair and Rehabilitation is more expensive than the original cost of the structure. The Tsunami Housing Reconstruction Programme envisages the construction of about 1,300,00 concrete houses at an approximate cost of Rs. 1,50,000/- each.

Rapid industrialization, urbanization, and population growth in the twentieth century have greatly affected the natural environment, the effect of which is seen as climate change regionally and globally.

Major structural failures during natural calamities is an exception rather than the rule. During these calamities buildings collapse and the devastating result is the end of the hopes, dreams and future of large number of population. Needless to say the recent natural calamities like Tsumani in Tamil Nadu, heavy rains and flood in Mumbai are examples where we have no words to express our grief. Buildings are more likely to suffer a failure of the hydrophilic envelope with consequential interior damage due to the intrusion of wind and water.

The greatest threat to human life and property loss resulting from earthquakes is associated with seismic vulnerability of existing construction that was either not designed for seismic resistance or no care was taken to protect the reinforcement. Reinforcement is like a spinal cord of the building and once the malignancy sets in, these structures are highly vulnerable to the natural calamities.

Reinforced concrete revolutionized the building industry. Water, which is elixir of life, is a serious enemy to hydrophilic concrete structures. Environmental Impact on Structures

The ingress of damaging materials into structures may occur in the gaseous state or in the liquid state. This makes the design of a durable protection system all the more difficult. Gaseous damaging materials include CO2 , SO2 , SO3 and nitrogen oxides present in the pollution in the atmosphere upon entering the building material as a gas, may dissolve in water present in pores and capillaries forming a dilute acid solution. Water contacting a structure may also contain these dissolved gases and may contain salt from marine conditions or from salts used in de-icing operations (Figure 1 and Figure 2), where water contains acidic gases, evaporation of the water from the surface concentrates the acid to a very high level just before dryness. The frequency of ingress, temperature, and general climatic conditions influence the severity of the attack.

These damages result in high cost of repair and maintenance and sometimes much more than the cost of the building.

Let us address those cases where the awareness of waterproofing and its implication could have not only avoided the tragedies but also the durability of the building and the money that we spend on repair and maintenance could be used in creating infrastructure in India, which is badly needed.

Indian Railways

Indian Railways are more than 150 years old and perhaps an example in the world. The Indian Railways carry 1.40 crore passengers and 140 lakh tones of freight, operating 15,000 trains every day. Its trains cover a distance equivalent to the one between the earth and the moon four times a day! It is interesting to know that the network of 63,000 route kilometres spread across the length and breadth of the country has one lakh and twenty thousand big and small bridges. Forty- four per cent of them are more than 100 years old. There is a general perception that old bridges are unsafe for transport. The network has bridges as old as 135 years but they continue to be safe.

Although these bridges are old a proper repair, rehabilitation and protection of reinforcement by inhibiting the ingress of water can rectify these problems atleast for several years. But unfortunately this programme does not consider the modern scientific methods and the techniques to safe guard the durability of these bridges. The rehabilitation and rebuilding of old and distressed bridges, almost 3000 have been included in the planning and the expenses of about Rs. 1,530 crore have been kept for next few years. This money will go waste and repeated repairs would be required if the consultants and waterproofing experts are not familiar with the modern techniques. The interdisciplinary approach between structural engineer and waterproofing consultants is required.

Fate of Jetties and Briges

Various generations of protective products have been developed to counteract the aggressive actions of the environment against concrete. Good results have been obtained with barrierpenetrants: after penetration in the concrete they form a barrier against water and salts dissolved in it. Different families of these hydrophobic agents or waterproofs are already being used for many years in construction industry: Silicones, siloxanes, silanes. The silanes used for waterproofing are mostly alkyl-trialkoxy-silanes and thus monomer products. The siloxanes are oligomer or polymer alkyl- alkoxysiloxanes.

The starting product for all siliconorganic compounds is alkyl-trichlorosilane, the alkyl-group is represented by the symbol R. By transformation of this silane with alcohol (R‘-OH) only, the corresponding alkyl-trialkoxy-silane is produced together with separation of hydrogen chloride. The reaction with alcohol and water gives oligomer or polymer siloxanes, depending on the amount of water used. The last two products differ in their degree of polymerization.

The hydrophobic treatment reduces the absorption and transport of liquid water and salts dissolved in it. Whereas the penetration of water in liquid form should be entirely prevented, the waterrepellents must penetrate as deep as possible into the concrete substrate to obtain a guaranteed long-term durability. At the same time a maximum penetration depth is an essential prerequisite for an effective protection against chloride ingress and chloride induced corrosion of the reinforcements.

The conditions of jetties in our country in general are miserable. Few examples are given below where the structures have deteriorated and got damaged on account of not giving due importance to waterproofing at the time of construction.

 P & Oliver Port-Chennai  Port of Kandla  Ontario  Zeebrugge Harbour  Port of Saint John

We have our own experience —Mumbai Port Trust after complete testing selected the most appropriate waterproofing product, which was not finally included because of so called cost reasons. This is an important point, which I want to make that such kind of consideration will destroy our infrastructure and would continue to have Jetties or for that matter any infrastructure in the same conditions as they are today.

Tech-Dry (India) Pvt. Ltd., has been working on this subject of anti-corrosion and anti carbonation along with Tech- Dry Melbourne who are well-known experts in this field since last 23 years and we take this opportunity to mention our products, which we believe are cost effective and unique.

Role of Waterproofing in other Products

Mineral-based building materials are widely used for their excellent durability. One important characteristic of even the most durable materials is their porous surface structure and hydrophilic nature. Because these structures readily absorb water, exterior walls can quickly become discolored or damaged.

These façade coatings should be able to arrest the ingress of water, pollutants and chemical attack but unfortunately the common problem for many façade is their lack of water vapor permeability. When water enters the interface between the coating and the substrate coating, failures occur in the forms of blistering, cracking and peeling. By allowing water to escape these coatings, failures are avoided. In a well-protected façade, absorbed moisture must be allowed to escape into the atmosphere and the coating itself must last as long as possible.

―Structural integrity is of prime concern in evaluating deterioration of garages. If impaired it must be restored and steps instituted to maintain the structure in a safe condition. Structural distress may be defined as a condition where one or more elements of a building are so impaired that the structure‘s ability to carry its designed load safely cannot be assured.‖

Failure and Damage in Light Construction

Structural failures in light construction, whether bearing masonry or light framing, can be broadly categorized as those events arising from the lack of a continuous path of load resistance from the roof to the foundation, and events arising from the breaching of the envelope, pressurization of the building and consequential blowing out of the leeward walls, sidewalls, windows or roof.

Ultimately, all loads on a structure, wherever placed, will be transmitted to and must be resisted by the foundation. If there is a weak link in the path from point of loading to the foundation, that is where the failure will occur. If the roof is not adequately anchored to the walls, an excessive uplifting load on the roof will not be transferred through the walls to the foundation. At this point we will discuss the common conventional method used in India, which only aggravates the above problem and they should be avoided.

Brick Bat Coba / Surkhi Cracks due to temperature variations The brick bat coba treatment through successful in the damp heat of coastal regions cracks up completely on contact with the variations of temperature faced in North India and other such climates between day and night temperature.

Imposes Unnecessary Load

This system has the disadvantage of imposing an unnecessary load on the system. Once cracks appear they are almost impossible to repair and water as in the case of the tar felting travels below the coba and exits wherever it finds a path. It is impossible to trace the inlet point let alone repair it.

Almost Impossible to Dismantle for Repairs

Some parts of the coba stick so well to the concrete that even if an attempt is made to dismantle the system the slab gets damaged.

Disadvantages in using Brickbat Coba

 In due course numerous cracks are developed in the lime terracing. Water penetrates through these cracks to R.C.C. slab below it. Due to shrinkage of cement, lots of cracks are also formed on the plaster of the parapet walls. Rainwater seeps through these cracks into the bricks and slowly comes down to the R.C.C slab.  Because of improper compaction, often the concrete of the R.C.C. slab is full of voids and honeycombs. Once the water reaches the R.C.C. slab, it easily seeps inside and corrodes the reinforcement, thus weakening the structure itself.  Water, after seeping through the R.C. C. slab, makes the ceiling and walls damp. In severe cases water starts dripping from ceiling. All these leave ugly patches of dampness on the ceiling and walls and paints peel off in addition to the damage to structure and reinforcement.

Leakage in the building is a very common problem and they are on the top of the list of owner‘s complaints.

Rainwater intrusion into a recently completed building is one of the most traumatic of all unpleasant events for a new building owner.

The leaks can be variety of them in the whole building envelope and can be repaired and rehabilitated. But the best solution would have been if the waterproofing had been undertaken prior to the building construction these problems could have been avoided.

The cause of repair and rehabilitation covers so many factors but the major cause is water and deterioration.

Cause of Deterioration

Water, incompatible materials, and lack of maintenance are the major causes of damage to the buildings. The introduction of water is usually the result of the incorrect use of materials, particularly non-compatible repair materials, and the lack of maintenance; 95% of all deterioration can be linked to water. Once introduced and allowed to remain, water can weaken the chemical structure and encourage insect infestation. Allowed to continue, a building will eventually become unstable and collapse.

The moisture content of building materials varies in response to changes in the local humidity and will not usually damage the material or induce decay. The paradox of concrete structure is that it is a highly porous material. The concrete structure is forced to absorb high levels of water; however, its porous nature in collaboration with the warm climate allows it to adequately evaporate this to same level without harmful side effects. This cyclical feature is assured as long as the pores are not clogged by incompatible, less porous materials and the structure is being maintained.

Corrosion

Once the water enters into the structure and the reaches reinforcement –corrosion or cancer of the building starts. Concrete has a pH of approximately 12.5, and this provides a protective environment for the steel reinforcement because a thin film of passivating iron oxide forms over the surface of the steel (Hausmann, 1965). However, two processes lead to a breakdown of the passivating film and initiation of corrosion:

1. An acidic environment develops when carbon dioxide from the air mixes with water in the concrete pores (carbonation) that removes the passivating layer.

2. The passivating layer can become permeable due to the presence of chloride ions that penetrate into the concrete from marine environments and chloride in sand and aggregates.

The corrosion of reinforcements has resulted to be one of the most frequent causes of their premature failures, which can set in, as early as 3 months depending on the surroundings. Monitoring the corrosion rate, assuming the uniform corrosion and the loss in diameter decreases linear with the corrosion rate, allows calculating the remaining load carrying and the safety of the structure.

Carbonation

Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous concrete and neutralizes the alkalinity of concrete. The carbonation process will reduce the pH to approximately 8 or 9 in which the oxide film is no longer stable. With adequate supply of oxygen and moisture, corrosion will start.

The reaction of Ca(OH)2 with CO2 takes place by first forming Ca(HCO3)2 and finally CaCO3 , the product precipitates on the walls and in crevices of the pores. This reduction in pH also leads to the eventual breakdown of the other hydration products, such as the aluminates, C-S-H gel and sulfoaluminates.

The relative humidity with which the pore solution is in equilibrium greatly affects the rate of carbonation.

Consequently carbonation occurs at a maximum rate between 50 and 70 percent relative humidity. In addition to atmospheric conditions, carbonation rate is also influenced by the permeability of the concrete, and the cement content of the concrete. Cement content of approximately 15 percent produces a concrete relatively resistant to carbonation.

The two most common causes of reinforcement corrosion are (i) localized breakdown of the passive film on the steel by chloride ions and (ii) general breakdown of passivity by neutralization of the concrete, predominantly by reaction with atmospheric carbon dioxide.

The first mid-long term records concerning the effectiveness of a waterrepellent agent under in-site circumstances. A probability method for interpretation of test results and prediction of the service life of the quaywall was updated.

Rail Corrosion

Rail corrosion is the result of interaction between a damp environment and traction current leakage. The leakage is a greater problem than the humidity factor. We would like to deal with railway sleepers, which are replaced from time to time and are not durable because of the corrosion of the reinforcement.

We also need to take into consideration the crushed stone deposit around the flanges of the rails by modern public works vehicles. Graders/levellers, tamping machines, forming machines, etc., have the ability-and opportunity – to contribute to this problem when put under the pressures of increased productivity expectations and /or demands and reduced working times. In haste, crushed stones tend to be deposited around the flanges of the rails, in essence covering it. It is when there is this lack of above metal plate that it becomes a significant element/ contributing factor in the overall problem of isolating the rail in relation to the ballast. Observations made on the replaced rails confirm that the corrosion sets in where moistness from condensation or dampness is present. This condensation and dampness are crucial elements that produce a catalytic effect on the corrosion.

Railway Sleepers Corrosion

The Railway Sleepers that the Railway departments are making today are not very durable even though they use M50 grade mix. The environment and the toxic substances brought by water ingress in the seepage will definitely affect the sleepers, corrode the reinforcement causing cancer to the same and therefore it is necessary to waterproof concrete sleepers. There has been a continuous effort to produce durable sleepers, which complies with the rising requirements relating to loads on the track and traveling speeds of the trains as usual today.

Internal Environment Pollution Fungal Growth

Fungal infestation of buildings has become a significant factor in how the integrity of structures is assessed.

Large water intrusions of the building envelope, such as roof leaks and pipe ruptures have traditionally been handled by drying out and removing significantly water damaged material in the affected areas, however, little attention has been given to the effects of fungal growth. Additionally, in the past, small leaks that led to localized fungal growth were not considered significant problems. As a result, the assessment of the amount and spread of fungal growth in buildings has become a significant factor in determining the overall condition of a building.

Construction materials are not manufactured in sterile environments nor is the air brought into buildings sterile, thus fungal spores are readily available in most indoor environments. While fungal spores are ubiquitous, active fungal growth will not occur until moisture and a suitable source of nutrients are available.

The type and level of species and the presence of mycelial fragments are used as indicators of moisture damage and fungal growth in surface and dust samples. Species commonly associated with water damaged construction materials include Aspergillus, Chaetomium, Penicillium and Stachybotrys. Mycelial fragments in samples are used as an indication of active growth.

Needless to say the problem of safe shelter can be solved to great extent if waterproofing is given its due importance.

Before concluding we would like to say please give priority to waterproofing and join us in our efforts to create awareness and:

 To have a durable structure  To save energy  To save load on your building

It is only possible if we create scientific society which means people at large should look into these problems rationally and logic should prevail. Do not compromise for cheap products, look for cost effective and durable products.

Do not compromise for cheap products, look for cost effective and durable products.

Single Ply WATERPROOFING MEMBRANES The Way Forward

Upen Patel, Marketing Manager, BASF Construction Chemicals (India) Pvt. Ltd. Mumbai.

Preface

Waterproofing the concrete structures has always been a challenging task for construction industry. With the increased complexity of structures, more possibility of structural movements and settlements and growing concern on leakages in the structures has created a need for reliable waterproofing system. Current practices of rigid waterproofing barriers such as stone cladding, brick-bat koba and crystalline waterproofing has limitation if structure is designed to undergo movements during life span. Bituminous and polymer based elastic systems do enable elongations but have limiting success as they are always bonded to the substrate and does deteriorate with time. This article provides an insight to single ply synthetic waterproofing membranes which have global reputation and have gained quick acceptance in recent times in India. This article also provides insight to two of the success stories in India where the system is being employed currently.

Single Ply Synthetic Waterproofing Membranes

Single-ply synthetic waterproofing membranes are widely used in Europe and North America for the last 40 years and have proven performances. The concept is to provide a watertight liner all around the susceptible building element and to ensure the right technique to install the membrane. There are various synthetic liners available for the purpose and the selection is based on the expected performance out of them in the specific situations. The single-ply synthetic liners are designed and build to the various situational needs and normally consisting of synthetic roll of fixed thickness and width and are available in reinforced with glass or polyester fibres options. Today, PVC and TPO are the most popular choice of materials for the application in the civil industry. The synthetic liners have life expectancy of 25 to 50 years v/s 10 to 15 years as offered by bituminous membranes, a single factor which made synthetic liner the popular choice in the construction sector over the years. PVC membranes are manufactured by adding plasticiser in the PVC and this limits their life expectancy in the case of direct exposure to UV and required to be protected, as plasticizers may migrate out of the membrane making the membrane brittle. Thus, PVC membranes have become chosen material for underground and buried situations while TPO, which is expensive in comparison to PVC has excellent stability in UV and available in range of colors, has become the choice for exposed roofing situations.

FLAGON PVC Membranes for Underground Structures

The essential characteristics of a waterproofing liner for underground works are a high physical- chemical performance with minimum maintenance during its lifespan. Given the specific and critical nature of the work to be waterproofed, life expectancy should be measured in decades rather than years. FLAGON liners have been designed, formulated and manufactured according to specific application needs, based on a ―tailor-made‖ philosophy. This approach ensures optimisation of results from every perspective: mechanical resistance, resistance to ageing, flexibility, ease of installation and last but not least, environmental protection.

The main characteristics of Flag liners for underground works are:

 Excellent weldability  Softness and flexibility  High ultimate elongation (dimensional variation of the membrane when subjected to mechanical stress)  Tensile strength (the membrane can resist tensile stress without tearing)  Durability  Adaptability to irregular substrates  Maintains its integrity even in the case of structural movements or soil subsidence  High electrical resistance  Suitable for installation in humid places  Resistance to static puncturing  Resistance to dynamic puncturing  Chemical resistance  Resistance to bacteria and fungi  Resistance to micro-organisms  Resistance to roots  Fire resistance  Compatibility with drinking water  Signal layer surface (essential feature to check the liner once installed–any surface damage of the liner is immediately shown by the different color appearing from the surface underneath).

Another basic aspect is ease of application, where the sealing of the waterproofing membrane should allow for the execution of complex details and particulars, especially in difficult situations on site. This is essential for the successful result of the overall system.

The following should be considered:

 Easy weldability and workability of the material  Compatibility with special accessories  Ease of performing quality tests in the post-application stage (specifically, checking the welded seams).

Manufacturing Process for FLAGON PVC Membranes

FLAGON PVC membranes are produced by Co-extrusion or Spreading technique depending upon the configuration of the membrane.

Co-extrusion

In this process, the mixture of material components (resins, plasticisers, stabilisers, pigments, etc.) is introduced through a hopper into a cylindrical chamber. Here it is heated up and pressed by worm screws into a co-extrusion head, where the single extruders converge, and then it is laminated in a calender. The liner thickness is automatically adjusted by electronic equipment that controls the opening of the extrusion head and of the calender. The material thus obtained is a single-layer homogeneous, non-reinforced liner, with high tensile properties and high resistance to static and dynamic puncturing. This process can also produce two-color, single-layer liners with a signal layer.

Spreading

This is a manufacturing process that produces waterproofing liners in which the reinforcement becomes an integral part of the liner. At room temperature, a mixture of liquid-viscous products, called ―plastisol,‖ is spread onto a moving paper-support substrate by means of a gravity fed applicator. The mixture contains resins, plasticisers, stabilisers, pigments, etc. and determines the final characteristics of the waterproof liner. Gelation (curing) is achieved by passing the product through a series of ovens along the production line. This spreading and gelation process is repeated four times. The liners manufactured by this system are therefore composed of four differently formulated layers. Between the second and third layers, an internal reinforcement is introduced, either in polyester mesh for tensile strength or glass mesh for stability. This manufacturing system establishes a molecular bond between the four layers creating a homogenous and flexible singlelayer liner that can be combined with a thermally treated geotextile layer to improve its gripping characteristics when using adhesives or when it is laid on materials that are not chemically compatible with PVC-P. The spreading process can also produce two-color, single-layer liners with a signal layer.

FLAGON TPO Liners FLAGON TPO is a new generation synthetic liner made using an innovative formulation: EPR (ethylene propylene rubber) modified polyolefin. FLAGON TPO development has been based on experience, synergy, co-operation and manufacturing technologies:

 Experience gained by Flag who, since 1963, has developed and manufactured synthetic waterproofing liners for use in the roofing, civil engineering and hydraulic sectors.  Synergy with industry-leading manufacturers of polyolefins, who have developed and introduced these new materials to the field of waterproofing.  Co-operation with the most qualified designers, general contractors and installation companies.  Innovative manufacturing technologies for synthetic waterproofing materials.

Main Characteristics of FLAGON TPO Liners

The exclusive manufacturing system designed for this type of liner and its unique formulation have resulted in:

 Excellent weldability  Softness and flexibility  Excellent dimensional stability  High weather and UV rays resistance  Non-toxicity  Resistance to a wide range of chemical attacks  Compatibility with most insulation panels, including expanded/ extruded polystyrene  Compatibility with oxidized bitumen  High resistance to puncturing  Resistance to roots and microorganisms  Adaptability to structural movements  Environment and user friendly  Life expectancy in excess of 25 years  Proven installation history.

FLAGON TPO waterproofing membranes can be used for both newly built roof systems and for renovating existing roofs. FLAGON TPO membranes have been designed both for ballasted roof systems (protected) and for exposed roof systems (unprotected).

Manufacturing Process for FLAGON TPO Membranes

FLAGON EP/PV, FLAGON EP/PR liners are manufactured in UNI EN ISO 9001 certified plants and fully comply with the performance standards CEN European Standard, UNI 8629/6 – SIA 280 – DIN 16726. The raw material used to produce FLAGON TPO membranes is created by blending a mix of synthetic polyolefins and softening agents (EPR) with various additives that, through a catalloy procedure, are transformed into a moulded mass and then into granules. This combines:

 Resistance to ageing, weathering and micro-biological attack  The EPR compound gives softness and flexibility with a high resistance to mechanical and chemical influences in conjunction with the strong welding capacity of polypropylene.

The unique manufacturing process designed and developed by Flag combines a tri-extrusion process in a single pass encapsulating a reinforcement mesh that produces a complete homogeneous product with stability and high tensile strength and an effective dual light/dark color signal layer. The particular property of FLAGON TPO synthetic liners is the reinforcement insert embedded in the body of the liner. This reinforcement may be a non-woven glass mesh or polyester mesh, according to application needs, ensuring an efficient and aesthetically flawless end result. FLAGON TPO liners are produced by coextrusion in twocolors, known as a ―signal layer‖ system.

The upper sand-grey color, which provides lower heat absorption, increased longevity and aesthetic qualities, represents 10-15% of the membrane thickness and the black underside, which protects against UV damage, 85-90%. The major benefit of the system becomes apparent during installation; should the membrane become damaged, the black underside is immediately detected by the contractor and simply repaired.

Application Case Study – FLAGON PVC Membrane at Delhi Metro Project Project:GTB Nagar station by Cut & Cover and ramp as part of Vishwa Viadyalaya – Jahangirpuri section.

 Client: Delhi Metro Rail Corporation  Scope of Project: Water tightness of Cut and Cover section  Design & Construction: Senbo Engineering Limited  Year Completed: 2006/2007 Systems used: FLAGON BFR/SL & FLAGON PROFILE W4

Project Description

The history of planning a Metro Project for New Delhi dates back to the 70‘s. The concept planenvisaged a network of 58 km underground and 195 km surface corridors. The total network plan contains 16 sections to be implemented in a sequence based on passenger kilometre carried per kilometre length of each section,

which is expected to be completed in three phases. The BC-2 Package of Phase II, consists of Vishwa vidhyalaya - Jahangirpuri corridor containing 844m long cut and cover tunnel with cross section of 11m x 5.5 m and has one underground station at GTB Nagar.

As in the first section of metro corridor APP membranes were used as waterproofing system and have provided enough troubles, well known for bituminous waterproofing system, summarize as under:

Moisture sensitive Overlaps cannot be tested for effective water tightness Uniform heating of membrane difficult to achieve Cannot be compartmentalized for remedial measures Non-friendly to environment and application crew Hence, designers have opted for synthetic liner which can be relied upon and takes cares of all the negatives of APP membrane systems.

The Solution Offered

Considering the water head pressure and to minimize the fire potential, 2mm thick FLAGON BFR/ SL was selected as the primary waterproof liner 250 gsm geotextile was provided as slip membrane beneath the waterproof liner. On vertical surfaces (walls) FLAGON BFR/ SL was fixed using Rondel (PVC disks) and on horizontal surfaces was kept loosely laid. 50- 75mm screed was used on the horizontal surfaces as protection layer while brick wall was used to protection the vertical installation. At the construction joints FLAGON Profile W4 was used to compartmentalize the liner and all the compartments were installed with Pipetta for injection in the future on the event of any seepage. All possible overlaps were double seam welded and tested for air leakage at 2MPa pressure for 60 and 90 seconds against the specifications and any joint found with higher than specified leakage of air pressure was re-welded. All the physical damages were reinstated using PVC patch or liquid PVC patching compound.

Customers Feedback

Job was carried out to the total compliance with the QA aspects as laid by the client and consultant. Client is very much convinced about the BASF‘s Watertight System concept and has decided to extend the specifications for upcoming expansions in Phase II jobs.

Application Case Study – FLAGON TPO Membrane at Bangalore International Airport Project: Bangalore International Airport Client: BIAL, Bangalore

 Scope of Project: Roof waterproofing of terminal building  Design & Construction: Larsen & Toubro Limited, ECC Construction group  Year of execution: 2006/ 2007, under execution  Systems used: FLAGON EP/PR

Project Description

The Bangalore International Airport is a Greenfield project built by a consortium of five shareholders; three of them - Siemens Project Ventures, Larsen and Toubro and Unique Zurich airport are private, and the remaining two are the government of Karnataka and the government of India. Situated 34 kms to the north of the Bangalore city, it sprawls over an area of 3900 acres, which will house besides the regular airport services, a hotel, shopping mall, tax-free shops, food courts and other convenience amenities. The construction of first phase started on July ‘05 and is being built at a cost of Rupees 1,411 crores. This phase includes the 4-Km runway, aircraft stand, a terminal building, technical building and other airside & landside facilities. The construction of this phase is expected to be complete by April ‗08.

The roof of terminal building is made up of large precast segment, each of having 24 metre span and 10m length. In total there are more than 200 segments in the terminal building. The curve shape andcomplex detailing made client to choose most reliable waterproofing membrane which can be quickly installed and can last for the design period of the structure.

The Solution Offered

Considering the complexity of the job and life expectancy, 1.2mm thick FLAGON EP/PR was selected. FLAGON EP/ PR is polyester reinforced TPO membrane, manufactured by latest tri-extrusion process. Considering the wind loading on the structure the fasteners are designed. On the diaphragm walls the membrane is fully adhered to the substrate using special FLAGON adhesive glue.

Conclusion

Finally local availability of single-ply synthetic waterproofing membrane, an engineered watertight system shall enable building owners and structural designers to have choice of dependable waterproofing material. The experienced application team and easy access to global experts shall enable BASF to serve the construction industry better

Waterproofing of Structures:Challenges and Solutions

Dr Anil K Kar, Chairman, Engineering Services International, Kolkata.

Prologue

It rained and people sought protection against rain water falling on the head, Figure 1. The concept, the art and the science of waterproofing developed from this desire for protection against rain water.

In the beginning, most people thought that the objective of waterproofing was to prevent rain water from falling on their head. As people started using delicate and costly materials, and housing equipment, systems, etc. inside buildings, the ensurement of watertightness of building type structures became important. It will be seen that the prevention of the ingress of water into buildings is necessary for reasons more important than the prevention of an inconvenience or an architectural nuisance or for facilitating the proper utilization of the space inside. In the conventional scheme of making buildings waterproof, doors have door leaves, windows have shutters and roofs are made water-tight through specific waterproofing treatments or arrangements.

With time, it was recognized that it would be a good idea to make water retaining structures also water-tight. But it took a while to recognize that there was more to waterproofing than to prevent rain water from falling on the head or arresting water leakages through water retaining structures. It took time to recognize that the failure to waterproof structural elements, in addition to roofs of buildings, could lead to situations like that shown in Figure 2.

With delays to realize, and failures to act, buildings, bridges and other structures started becoming unusable because these were not waterproofed in time. This happened, generally and more quickly in the case of concrete structures, which were built during recent decades, than in the case of structures, which were built before 1965 or so.

The lack of durability of concrete structures has been a worldwide phenomenon. In a paper in 1991, Papadakis, Vayenas and Fardis1 stated : ―The last two decades have seen a disconcerting increase in examples of the unsatisfactory durability of concrete structures, specially reinforced concrete ones.‖

The problem of unsatisfactory durability is more acute in India where it has reached an alarming state. The alarming situation in India, caused by the early distress in reinforced concrete structures, is reflected in Technical Circular 1/99 of the Central Public Works Department, Government of India, wherein it has been stated that while works as old as 50 years provide adequate service, the recent constructions are showing signs of distress within a couple of years of their completion.

In most cases of concrete structures, the structural distress in the form of cracking in the concrete elements or collapse of the structure is an external manifestation of corrosion in the ferrous elements inside.

There are reasons behind the early or accelerated rate of distress, Figure 2, in modern day concrete structures. The rate, at which modern day structures started reaching states of early distress, accelerated with the use of High Strength Deformed (HSD) reinforcing bars (rebars) in the construction of reinforced concrete structures and also with the use of deicing salts on highways in cold climes of affluent countries.

Among other factors, contributing to the decaying process, was the lowering of the period of wet curing of concrete from 28 days to 3–7 days or none. As there is a move towards a greater use of Portland Pozzolana Cement (PPC) in lieu of Ordinary Portland Cement (OPC) in concrete, this change in the type of cement will have its effect on the durability of concrete structures, unless special provisions will have been made.

This paper addresses the problem of early distress in concrete structures and solutions thereto. As surface protection of structures by waterproofing is proposed as a viable solution to the problem of early distress in concrete structures, it is explained why waterproof structures are durable structures.

Durable and effective waterproofing systems are described later in this paper.

Early Distress and Causes

The alarming state of affairs with constructed facilities of recent decades has put civilization in peril1- 3. When humanity is in peril, God comes to show the way. In such circumstances ten years ago in 1996, Lord Ganesh, Figure 3 showed the way when the stone statues started drinking milk on offering by worshippers. Ganesh started drinking water. It was Lord Ganesh of rock or stone who drank milk and water. Ganesh, cast in metal, would neither drink milk nor water.

Lord Ganesh drank milk and water to teach architects and engineers a lesson. The lesson was : concrete, an artificial stone, would absorb water and other liquids. The rate and quantity of water would depend upon the permeability and porosity of concrete.

This absorption of water by concrete, though undesirable, is inevitable in the case of concrete structures without surface protection. This water, that enters inside the structure, creates a moist environment. When air from the environment, containing oxygen, enters into the structure and reaches rebars or prestressing elements of steel, oxidation, the most common of the different processes of corrosion of steel, takes place, if the Fe2O3 protective layer of passivation on the surface of rebars and prestressing elements will have been destroyed due to carbonation (by carbon dioxide from air) or chloride intrusion or due to pozzolanic reaction from the use of PPC or High-Volume Fly Ash (HVFA) cement3-5 in concrete. Though the process of corrosion requires oxygen and a moist environment, carbon dioxide, chlorides, acids and sulphates can further add to the destabilizing processes. It needs to be noted that, like oxygen, even acids and chlorides, the well-known agents of corrosion, will be ineffective in causing or augmenting rebar corrosion unless there will be a moist environment. Similarly, other harmful reactions in concrete, viz., alkali-silica reaction, sulphate attack, etc. will fail to take place unless there will be moisture. On the other side of the picture, water alone will not cause any problem unless there will be oxygen. A case in point is a ship under water on the sea bed. In the absence of sufficient oxygen, the rate of corrosion is very slow even when there are chlorides in the water. Thus, though it is essential, for corrosion to take place, that the concrete environment, surrounding rebars and prestressing elements, be moist, submersion in water is likely to inhibit the process of corrosion.

The above suggests that all structures above ground and those portions of structures below ground, which are exposed to the atmosphere (e.g. basements, tunnels, underground water reservoirs, machine pits, lift pits, and so on), will be vulnerable, if left unprotected, whereas rebar corrosion may not be a problem in the case of foundations. In simpler terms, all structures, exposed to air, will be vulnerable. Of these, concrete structures (primarily reinforced concrete structures), constructed during recent decades, have been characterized by early decay and distress. There must be reasons for this development, that goes beyond any possible shortfall in the quality of construction. This has been borne out in a survey6-9 in Calcutta, that was carried out by the writer‘s firm in July 1999.

This writer 3-22 has written extensively on the basic causes of the problem of early distress in concrete structures, constructed during recent decades, and solutions thereto. Of particular interest to the reader will be the articles in Refs. 3, 4, 8 and 9. The writer has shown in Ref. 9 and elsewhere3,4,6,7,16,19-22 that the use of high strength rebars with surface deformations has been primarily responsible for the early decay in concrete structures of recent constructions. The problem has been more acute in India where the HSD bars were of the cold twisted deformed (CTD) type, commonly known as tor bar.

CTD bars are particularly susceptible to early corrosion (Figures 4 and 5) as high post-yield stresses are locked in such rebars from the time of manufacturing, inducing speedy corrosion in keeping with the phenomenon of stress corrosion at high stress levels, even before concrete is cast (Figures 4 and

5). Early corrosion sets in CTD bars also because the protective surface layer of Fe2O3 or Fe3O4 is destroyed during cold twisting of the rebar as a part of the manufacturing process.

Other factors, which can make concrete structures predisposed to early decay and distress, is the lowering of the duration of moist curing of concrete from 28 days of earlier years to 7 days or less and the shift towards the use of fly ash based PPC from OPC that used to be commonly used in construction in earlier days.

The PPC concrete lacks the capacity of OPC (with about a month‘s curing) to produce 15 to 25% (by mass of cement paste) calcium hydroxide Ca(OH)2 and with it to maintain a pore water alkalinity of 12.4 and above for prolonged periods of time, thereby protecting rebars and prestressing elements through the formation and preservation of the Fe2O3 layer of passivation. Furthermore, unlike OPC concrete, PPC concrete lacks the properties of self- healing of pores and cracks. Details can be found in Ref. 5.

In summary, in addition to the absorption of water or moisture, porous concrete permits the diffusion of carbon dioxide and oxygen, all of which are present in the atmosphere. Because of the changes in the properties of materials of construction and because of the shortening in the duration of curing, today‘s concrete structures, compared to structures of earlier decades, are affected more adversely by the atmospheric and other external agents of corrosion, viz., water or moisture, carbon dioxide, oxygen, etc.

The Solution

An obvious solution to the problem of early decay and distress in concrete structures would be to use the appropriate rebar and cement and to cure the concrete over prolonged periods of time. That would mean the use of plain round bars of mild steel and OPC with curing for about a month. But since the construction may not be with plain round bars of mild steel and OPC, coupled with a month‘s curing, the next best option would be to protect the structures, both new and existing. This protection of concrete structures will have to be, as a minimum against water, oxygen and carbon dioxide. It can be said, as an analogy, that concrete structures, similar to steel structures, can benefit from surface protection. Just as in the case of steel structures, the failure to provide surface protection to concrete structures will mean loss of durability and high life-cycle cost of the unprotected structure.

Effective and durable waterproofing treatments will make structures durable. Such treatments will also prevent any architectural nuisance of damp ceilings and walls.

This concept of providing surface treatment to concrete structures for the purposes of making such structures waterproof as well as durable has been stressed by the writer10 since 1987 through numerous publications and lectures. The concept was adopted by Central Public Works Department of the Government of India in 1999 and subsequently in the code IS 456:200024. It is mentioned in clause 8.1.1. of the code that ―One of the main characteristics influencing the durability of concrete is its permeability to the ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious substances.‖ It has further stated in clause 8.2.1 that ―The life of the structure can be lengthened by providing extra cover to steel, by chamfering the corners or by using circular cross-sections or by using surface coatings which prevent or reduce the ingress of water, carbon dioxide or aggressive chemicals.‖

It has been explained in details in Ref. 8 that, of the four alternatives, recommended in IS 456:200024, the provision of surface protection systems is the only logical and practical way of ensuring long life for concrete structures.

Even six years after the publication of the code24, architects and engineers appear to have overlooked the mandatory provisions of the code as they have failed to implement the provisions in clause 8 of the code.

The failure to provide the surface protection will not only condemn the unprotected structures to early decay and distress, the constructed structures will also fail to meet the requirements of the code IS 456:200024. The surface protection system is provided as a waterproofing system on the surface of structures, and not on reinforcing bars25. Though the code has recommended the provision of surface coatings, all concrete surfaces are not necessarily amenable to the application of coating systems. Thus, this writer believes that since the objective is to prevent the ingress of harmful elements, coatings or other waterproofing systems should serve the purpose of lengthening the life of concrete structures.

Effective Waterproofing Treatments

It has already been explained that waterproofing systems or treatments, provided on the surface of structures, can do much more than preventing an inconvenience or architectural nuisance. Such treatments, if effective, can make structures durable. That, however, requires that the treatments are not only effective in preventing the ingress of water into the structure, but that the treatments are also durable. Many different materials and systems have been tried for the waterproofing of structures. Field experience shows that most of the treatments fail to achieve the desired results even in the short term.

The reasons are many, and these include: a) Wrong concept b) Lack of a will to do the work well c) Failure to adopt an appropriate technology d) Failure to improvise

Wrong Concept

Failure of waterproofing treatments due to the application of wrong concepts are all around. A few examples will suffice. Waterproofing treatments are provided on compressible treatments for thermal insulation. The excessive compressibility of the material for thermal insulation leads to large movements in the waterproofing treatments and their consequent failures.

Waterproofing treatments are provided on a course of Plain Cement Concrete (PCC), which fails for the lack of reinforcing elements and a lack of adequate bond at the interface between the substrate and the PCC. A small quantity (0.5% to 2.0%) of a plasticiser or a superplasticiser is admixed with concrete in the name of waterproofing, simply because it meets the requirement of the code IS 2645:2003, which, with its name Integral Waterproofing Compounds for Cement Mortar and Concrete ¾ Specification27, has a misleading title, ignoring the fact that the text of the code reads : ‗The permeability to water of the standard cylindrical specimen prepared with the recommended proportions of waterproofing compound shall be less than half of the permeability of similar specimen prepared without the addition of the compound when tested in accordance with the method given in Annex B‘, thereby qualifying chemicals, without waterproofing properties, as chemicals suitable for successful waterproofing treatments.

Lack of Will to Do The Work Well

It is believed that the manufacturer of chemicals will be particularly keen to see that the waterproofing system, based on his chemicals, will perform well. In the Indian environment, many manufacturers are keen to sell the chemicals to anyone for any purposes and the work of waterproofing is executed by contractors as authorized/ approved applicators.

In this system of work by applicators, the quality of work generally suffers as: a) The manufacturer of chemicals is not aware of the field conditions of individual sites, and the developer of the chemicals and systems, generally chemists, have limited knowledge about construction. b) The applicator is not aware of the limitations of the chemicals. c) The applicator does not use the right quantity of chemicals as he does not have the reputation of chemicals/ systems to uphold.

Failure to Adopt Appropriate Technology

Waterproofing is an activity in the domain of civil engineering, and it involves structures. It can thus be very helpful to have a good knowledge of civil engineering and structures. Thus, when chemists and material scientists develop chemicals and systems of waterproofing , they are likely to overlook fine points in civil-structuralconstruction engineering, and the technology for waterproofing may not be appropriate. This is particularly so as most often technologies are first developed, and avenues are sought to apply the technology. The best results are possible when technologies are developed to solve problems, and not the other way round.

Failure to Improvise

Every work site has a character of its own, requiring improvisation. Though a particular waterproofing chemical and a particular system will be employed as the basic treatment, local conditions frequently require for a successful waterproofing treatment that certain modifications are made to the implementation procedure or that a different chemical and a different system be employed locally as a stand-alone or as an additional treatment. A failure to make necessary improvisation may lead to a failure of the waterproofing treatment.

PERMAKAR Technology

PERMAKAR Technology for waterproofing is free from the shortcomings, commonly found in other technologies. The waterproofing systems for waterproofing under Permakar Technology were developed to solve specific problems after others had failed to solve such problems by the application of different known systems of waterproofing.

It all started in 1983 when Metro Railway in Calcutta requested Engineering Services International (ESI) to arrest running water leakages and make dry the treated areas of the tunnel. Until that time, ESI excelled in providing consultancy services in wide areas of engineering related to nuclear power plants. Also, starting as the first Indian consultant to the Defence Research and Development Organisation of the Ministry of Defence, Government of India, ESI provided consultancy services on different projects of the DRDO. The experiences of ESI in the cutting edges of technologies in wide areas of engineering came in handy and the PERMAKAR surface treatment method of waterproofing for tunnels and other underground/water retaining structures was developed. The hitherto unknown and unthinkable surface treatment method succeeded where grouting or injection of different materials had failed. Here are copies of extracts from documents of Metro Railway, Calcutta on observations on ESI‘s Permakar surface waterproofing treatments (a) inside the tunnels of Metro Rail, and (b) inside Pedestrian Subway at Tollygunge. ―The surface treatments (as opposed to grouting) were found to be fully effective and in excellent conditions even eighteen years (in one case) and six years (in other cases) after the treatment.‖ — certificate.

(b) ―However, temporary bored piles locations (total 8 locations), seepage of the leakage could not be stopped in the main subway with cement pressure grouting or Non-Shrinkable, Pumpable, Groutable (NSPG) due to which ‗Permakar‘ Technology (surface layer) treatment was adopted and seepage/ leakage arrested completely to achieve ‗bone dry‘ condition.‖ — project report.

The continued success of treatments under Permakar Technology and frequent failures of waterproofing treatments by others 12 gradually led to the development of systems of waterproofing for virtually all types of structures. The effectiveness and durability of waterproofing treatments under Permakar Technology have given beneficiaries of the work the confidence to include waterproofing treatments under Permakar Technology in the schedules of rates of work (SOR) of various organizations of the central and state governments. The versatility of waterproofing treatments in the line of Permakar Technology can be found in examples of waterproofing of different types of work.

Tunnels, Below or Underground Structures And Water-Retaining Structures

Figure 6 is a view of the pedestrian subway in front of Sealdah Station at Calcutta. The structure is known as the only zeroleakage tunnel around. A 6 mm thick Permakar 3 plaster type waterproofing treatment (Figure 7) was provided on the entire inner surfaces of ceiling, walls and floor. There is no water leakage.

Prior to the Permakar 3 treatment with an octadecanoic acid compound, waterleakages at construction joints, point leakage locations and honeycomb areas were arrested with cement, admixed with quick setting compounds Permakar 1 and Permakar 4. There were special treatments at ends of H-piles and at expansion joints.

The waterproofing treatment of the Pedestrian Subway at Sealdah is described in Refs. 26. There is virtually no difference in waterproofing treatments for tunnels, basements, machine pits, below ground structures, underground and overhead water reservoirs, swimming pools and other water retaining structures. Countless such structures have been successfully waterproofed with the Permakar 3 surface treatment. As the continuous Permakar 3 treatment is provided on the entire inner surfaces of the Pedestrian Subway at Sealdah, exposed to air, it provides the protection against carbon dioxide, oxygen, etc. as required in IS 456:200024. The unprotected outer surface, in contact with soil, generally does not pose any problem as there is very limited supply of oxygen and carbon dioxide, and water alone cannot cause rebar corrosion. The case is comparable to a concrete foundation of a structure. There is no corrosion, whereas above ground areas, exposed to air, have problems of early corrosion in rebars and prestresssing elements.

Building Structures

Figure 8 shows a typical building with the Permakar 3 (Figure 7) surface protection (5 mm thick on roofs and other locations, except bathrooms, where the treatment thickness is 6-7 mm). Over the years, over a hundred thousand square metre of concrete and old lime terraced roof structures were provided with the Permakar 3 waterproofing treatment. In most of these cases, earlier treatments by other parties had failed.

At the time of writing this paper steps have been taken for the waterproofing of over a thousand square metre of additional Permakar 3 surface treatments for roofs and walls of buildings in the year 2006.

The Permakar 3 waterproofing treatment can be provided virtually on all types of concrete, masonry and lime terraced structures. Unlike in the case of coating type treatments, the Permakar 3 waterproofing treatment can be provided on surfaces with honeycombs and large irregularities. The treatment can be provided on dry as well as wet surfaces. When tested for leakages, under a water head of 40 metres, a 5 mm thick Permakar 3-cement treatment was found to have zero leakage.

The typical building in Figure 8 can be provided with coating type waterproofing treatments with Permarpoof of modified phenolic resins instead of the plaster type treatment with Permakar 3, except in areas with honeycombs and large surface irregularities. Such areas can, however, be repaired and prepared for the Permaproof treatment. The details of the Permaproof treatment are shown in Figure 9. Figure 10 represents an example of total structural protection, provided in 1996. The concept was later adopted by CPWD in 1999 and included in IS 456:200024 in 2000. When tested for leakage under a water head of 40 metres, a two-coat Permaproof treatment was found to have zero leakage.

Being oil based, Permaproof can be applied only when the surface is dry. ESI has also PERMANAR-D (without or admixed with cement) for water-based polymer treatment. The polymer treatment with the organic compound Permaproof needs to be protected against ultraviolet rays. In the case of a roof, this protection is generally provided with a cover plaster which permits the normal use of the roof. In the more demanding case of roof gardens, advantage can be taken of the soil cover to give protection against ultra-violet rays. The cost of the waterproofing treatment for this more demanding case of roof gardens can thus be provided at costs less than the cost of waterproofing of a roof for normal use. It should be noted that, because of the possibility of roof drains getting choked, the material and system of waterproofing for horizontal roofs should be such that the same can be effectively used inside water reservoirs. Permakar 3 and Permaproof satisfy such requirements.

Roof Gardens for Green Buildings

Both the Permakar 3 and Permaproof treatments have been widely used to waterproof roofs for roof gardens. Figure 11 shows the Permaproof waterproofing treatment (2 coats) in progress on the 6000 square metre roof of a water reservoir in Central park, Salt Lake City in the year 1996. Figure 11 shows Permaproof bridging fine cracks. Figure 12 shows the same roof with a green cover ten years later in 2006.

Permaproof, which has been used on roof and all other elements of buildings, superstructure and substructure of bridges and inside water reservoirs, provides resistance against chemicals used in gardening. Figure 13 shows an inclined roof with a green cover. Prior to the preparation of the green top, the roof was provided with the plaster type Permakar 3 waterproofing treatment (Figure 7).

Bridge

Bridges, like building roofs, can benefit from surface protection7,16,18. This writer propagated the idea and need for surface protection of bridges, which are more adversely exposed to the environment than buildings are. The idea is catching in India. Permakar 3, Permaproof, Permacil-GA and Permacil-B have been used to protect quite a few bridges. All areas of the bridge superstructure are given the surface protection with Permaproof, Permacil-GA and Permacil or combinations thereof, except that wet areas, like piers, abutments, etc., are given the Permkar 3 plaster type treatment (Figure 7).

Most often one coat of Permaproof, followed by a coat of Permacil-GA, is provided. Figure 14 shows such protection on the Bankim Setu (Buckland Bridge), a road over-bridge (ROB) at Howrah Station across the river from Calcutta. Figure 15 shows the same treatment on the girders of the Katakhali Bridge over the Goureswar river between Hasnabad and Hingalganj in West Bengal. Figure 16 shows a span of the multi-span bridge over the Ajoy river near Katwa Town connecting Katwa Ketugram Road,

West Bengal. Two coats of Permaproof were provided. In order to provide protection to the polymeric compound Permaproof against ultraviolet rays, sand was bonded to the top coat of Permaproof on the outer faces of the exterior girders. The interior surfaces were not given the sand cover. The piers were given the Permakar 3 surface protection, Figure 7.

Concluding Remarks

Concrete structures, constructed with high strength rebars with surface deformations, are characterized by early distress, brought on by corrosion in the rebars. Prestressed concrete structures also suffer from corrosion in the prestressing elements. The presence of a moist environment inside concrete structures is a prerequisite for corrosion to take place. Since concrete, without any surface protection, absorbs water or moisture from the environment, it will be necessary to provide a surface protection system in the form of a waterproofing treatment to prevent the ingress of moisture/water and other harmful elements, viz., carbon dioxide, oxygen, etc. The provision of waterproofing systems on the surface of concrete structures will make such structures durable by delaying and slowing down the process of corrosion in the ferrous elements inside concrete structures. Any failure to provide surface protection to concrete structures will mean that such structures will not meet the requirements of the code IS 456:2000. Chemicals in the line of Permakar Technology, viz., Permakar 3, Permaproof, Permacil, etc. are very versatile and practically all types of structures, bridges, buildings, tunnels, water reservoirs and other water retaining structures can be protected with waterproofing systems, based on such chemicals. The surface protection systems make the protected structures durable, thereby lowering the life-cycle cost of such structures.

Reference

1. V G Papadakis, M N Fardis and C G Vayenas. ‗Physical and Chemical Characteristics Affecting the Durability of Concrete.‘ ACI Materials Journal, American Concrete Institute, March-April, 1991. 2. Chief Engineer (Designs). ‗Technical Circular 1/99, Memo No. CDO/DE(D)/ G-291/57 dated 18/02/1999.‘ Central Public Works Department, Government of India, Nirman Bhawan, New Delhi - 110 011. 3. A K Kar. ‗Concrete Jungle ¾ Calamity May be Waiting To happen.‘ The Statesman; Calcutta, 4 August, 2000. 4. A K Kar. ‗Concrete Structures ¾ the pH Potential of Cement and Deformed Reinforcing Bars.‘ Journal of The Institution of Engineers (India), Civil Engineering Division, Volume 82, Kolkata, June, 2001. 5. A K Kar. ‗Concrete in the Context of Durability.‘ RITES Journal, RITES Ltd., Vol. 8, Issue 1, April, 2006. 6. A K Kar. ‗Deformed Reinforcing Bars and Early Distress in Concrete Structures.‘ Highway Research Bulletin, Number 65; Highway Research Board, Indian Roads Congress, New Delhi; December, 2001. 7. A K Kar. ‗Durable Concrete Structures for Infrastructure.‘ All India Seminar on Improving Transportation in a Congested Metropolitan City; American Society of Civil Engineers ¾ India Section in association with The Institution of Civil Engineers, UK, Eastern Region, India Chapter, at Calcutta, 13 & 14 December, 2002. 8. A K Kar. ‗IS 456:2000 on durable concrete structures.‘ New Building Materials & Construction World, Vol.9, Issue-6, New Delhi, December, 2003. 9. A K Kar. ‗Reinforcing bars in the context of durability of concrete structures.‘ All India Seminar on Utilisation of Skyways and Subways in the Cities in India, organised by American Society of Civil Engineers ¾ India Section and Institution of Engineers, UK, Eastern Region, India, at Calcutta, 9th and 10th December, 2005. 10. A K Kar. ‗Arresting Water Leakages in Tunnels and Other Underground Structures.‘ All India Seminar on Underground Construction with Particular Reference to Metro Railways, organised by the Institution of Engineers (India), West Bengal State Center, at Calcutta, December, 1987. 11. A K Kar. ‗Waterproofing of Structures.‘ International Symposium on Housing, Energy & Environment, organised by Shelter Promotion Council (India), at New Delhi, 27–29 January, 1996. 12. A K Kar. ‗Protection of Structures as a Means to Durability.‘ All India Workshop on Preventive Measures Maintenance and Life Extension of Civil Engineering Structures, Civil Engineering Division, organised by The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 18 September, 1997. 13. A K Kar. ‗Waterproofing As a Means to a Long Life for Structures.‘ All India Seminar on Construction Chemicals, Present Status and Scope for Improvements, organised by The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 30th & 31st July, 1998. 14. A K Kar. ‗A Long Life for Structures.‘ MDC News, Management Development Centre, National Buildings Construction Corporation Limited (NBCC), New Delhi, September, 1998. 15. A K Kar. ‗Durable Concrete Structures.‘ MDC News, Vol. 8, National Buildings Construction Corporation Ltd., New Delhi, September, 1999. 16. A K Kar. ‗Making Bridges Durable.‘ All India Seminar on Development of Inter-State Highway Corridors, organized by American Society of Civil Engineers ¾ India Section, at Calcutta, September, 1999. 17. A K Kar. ‗Durability of Containment Structures for Water and Hazardous Liquid Wastes.‘ Environcon 99, 15th National Convention of Environmental Engineers, organized by Environmental Engineering Division, The Institution of Engineers (India), West Bengal State Centre, at Calcutta, 26–27 November, 1999. 18. A K Kar. ‗Protection of Structures as a Means to a Long Life for Bridges.‘ Indian Highways, Vol. 28, No. 7, Indian Roads Congress, New Delhi, July, 2000. 19. A K Kar. ‗Concrete Structures in the Twentyfirst Century.‘ All India Seminar on Structures in the 21st Century, organised by American Society of Civil Engineers ¾ India Section, at Calcutta, 8–9 December, 2000. 20. A K Kar. ‗Role of Cement and Steel in Causing Early Distress in Concrete Structures.‘ 1st National Workshop on Ageing and Restoration of Structures, organised by Indian Institute of Technology, at Kharagpur, West Bengal, 11-12 January, 2001. 21. A K Kar. ‗Reinforcing Bars and Early Distress in Concrete Structures.‘ MDC News, No. 13; National Buildings Construction Corporation Limited (NBCC), New Delhi, January 2001. 22. A K Kar. ‗Reinforcing bars ¾ the good and the bad.‘ Steel Scenario Journal, Kolkata, Vol. 14, No. Q1, July- September, 2004. 23. A K Kar. ‗Waterproofing for Green Buildings.‘ Seminar on Elements of Green Buildings in Indian Context, organized jointly by Institute of Public Health Engineers and Central Pollution Control Board, at Agra, 4–5 March. 24. IS 456:2000. ‗Indian Standard Code of Practice for Plain and Reinforced Concrete, Fourth Edition.‘ Bureau of Indian Standard, New Delhi. 25. A K Kar. ‗FBEC Rebars Must Not Be Used.‘ The Indian Concrete Journal, Mumbai, Vol. 78, No. 1, January, 2004. 26. A K Kar. ‗Waterproofing of Tunnels.‘ All India Seminar on Geo-Technical Aspects of Infrastructure and Environment, organised by American Society of Civil Engineers ¾ India Section, and Institution of Civil Engineers, (UK), Eastern Region (India), at Calcutta, 10–11 December, 2004. 27. IS 2645:2003. ‗Indian Standard :Integral Waterproofing Compounds for Cement Mortar and Concrete ¾ Specification (Second Revision).‘ Bureau of Indian Standard, New Delhi.

Knowledge and Technology Management for Waterproofing Using Construction Chemicals

Er. P. Srinivasa Reddy, Chief Executive Officer, Rehab Technologies & E. Jagannadha Rao, Consultant, Rehab Technologies, Hyderabad.

“Great leaders do not do great things, but execute simple things brilliantly”- Peter Drucker

Management Guru What we build brick-by-brick, may get destroyed by drop-by-drop seepage of water. To avoid premature deterioration of the buildings and other concrete infrastructure facilities, a scientific approach towards waterproofing is essential to avoid leakages and seepages. This calls for knowledge and technology management for designing efficient waterproofing treatments, selection of site-specific materials and methodologies for execution. This paper presents context pertinent conceptual and procedural guidance in the field of usage of construction chemicals for post construction activities such as maintenance, waterproofing, repair, rehabilitation, retrofitting, and so on, on large-scale implementation. This paper deals with vital topics like technology issues, ideas and initiatives pertaining to this field.

Civil engineering is known as mother of all engineering branches. Construction practices and building material sciences is a highly matured technology, world over. Hence, even a layman is able to understand and execute complex construction projects. However, the other side of civil engineering that is post construction activities, which is commonly referred as maintenance and repairs, is a field where continuously incremental improvements are happening. Yet times even radical and breakthrough technologies are been adopted successfully. Hence, knowledge and technology is highly dynamic and volatile in this field.

Knowledge and Technology Management (KTM) is a concept highly useful for forward-looking concrete professionals who increasingly need more specialized knowledge and stateof- the-art technologies in the core and wider concrete maintenance and repair process:

 To raise confidence in waterproofing technology.  To avoid hit-or-miss methods (often used in repair projects).  To avoid premature failure of maintenance and repair schemes.  To achieve longevity of concrete structures.  To assess the suitability of materials and methods for a given situation.

Setting up standards through benchmarking high quality precision for repairing, protecting concrete in industrial and infrastructure projects, with knowledge and technology management as key driver and enablers. Any deficiency and distress caused due to deterioration, corrosion, leakages, seepages, cracks, and so on, leads to the serious malfunctioning in terms of capacity and health of the structures. Thus, the strength and condition of the industrial, institutional, and national vital infrastructure concrete facilities are to be safe guarded. Deteriorated buildings can effectively be repaired and rehabilitated to enhance their performance by usage of modern materials, broadly known as construction chemicals. Annually, lot of money is spent right across the globe on protecting and maintaining new as well as existing concrete structures to enhance the durable life by appropriate treatments and modern methods.

Holistic approach consists of tasks like inspection, assessment, condition survey, residual life analysis followed by the implementation of the best possible treatment. Concrete maintenance and repair, as a specialized field is gaining more and more significance, than never before. This is even relevance, in present scenario, due to the consequences of the aging of the housing, institutional, and infrastructure related to concrete structures.

A Strategic Need

Concrete maintenance and repair is a relatively young and fast growing field with dynamic advancements of knowledge and technology. It is necessary for the engineers involved in the maintenance and repair works to become aware of the various intricacy issues involved in this multi- disciplinary engineering, which is interlinked to the nation‘s progress. This is very critical, due to the newness of the technologies, creates interest for the adoption and diffusion and eliminates the confusion prevailing among the decision-makers.

―How are we going to prepare the nation to meet the challenges of the next century, to meet the challenges of the latest technology, as it comes?....Development has to mean absorption of the most modern techniques at the most basic levels in our society….‖-Shri Rajiv Gandhi Former Prime Minister

Indian Industry Scenario

In the wake of policy of liberalization, privatization and globalization, there has been a tremendous influx and exchange of knowledge and technology in several fields of civil engineering. Technology is the most non-linear tool that can affect the most fundamental changes. The proper exploitation of technology strongly influences economic competitiveness. Thus, usage of new methods and materials is no longer a matter of choice, but a matter of necessity.

Significance of Waterproofing

Waterproofing is a major challenge to the civil engineers in several situations. Poor waterproofing causes inconvenience to the occupants. Ineffective / absence of waterproofing reduces the durability of structures by way of corrosion of reinforcement.

Waterproofing or Damp proofing?

Many a times, we come across the dilemma whether damp proofing to be adopted or waterproofing materials to be used or both to be implemented or both these are one and the same. Here comes the knowledge of the specifications data mine.

As per ASTM D 1079, Waterproofing is defined as ―Treatment of surface or structure to prevent the passage of water under hydrostatic pressure.‖ Whereas, Damp proofing is defined as ―Treatment of surface or structure to resist the passage of water in the absence of the hydrostatic pressure.‖ Hence, these are not only two different words with two different meanings, but altogether two different technologies for similar purpose.

Current Scenario

The waterproofing industry in India has undergone a sea change in the past decade. Several players entered the market with both imported and indigenous technologies. Unfortunately some offer a ―quick fix‖ low quality solutions with tall claims, which will not perform as estimated. But in reality, quality conscious customers are on a lookout for a ―Total Solution Provider‖ for long lasting results. Hence, many waterproofing manufacturers and service players are intending to serve these quality clients, which necessary needs knowledge and technology to match the explicit and implicit needs related to waterproofing of concrete structures, such as buildings.

Quality Conscious or Knowledge?

Typically as the waterproofing and construction chemical industry in India is upgrading rapidly in a very relatively short period from no treatment to mortars using sand and cement, to bituminous coatings, felts and to innovative coatings and membranes as knowledge has grown. Traditionally, specifications for waterproofing central around waterproofing systems such as brickbat coba, bituminous coatings, felts etc. The conventional waterproofing systems are slowly becoming outdated due to their inherent disadvantages and membrane waterproofing coatings, are gaining popularity. In the recent times, waterproofing specifications are being reworked and modifications are being incorporated to replace the old systems with the modern materials, broadly known as construction chemicals.

Materials/ Systems for Waterproofing

Waterproofing of roof slabs, basements, floors, terrace gardens, sunken slabs etc. needs different materials and systems. Waterproofing like any other aspect of the construction engineering need to be understood, analyzed and designed for a suitable system on a case to case basis, before implementation through experienced professional applicators.

Presently, wide range of waterproofing technologies available, such as:

 Lime terrace  Brick bar coba / Surkey  Cement sand screeds  Cement paints  Tar based cold and hot applied coatings  Tar felts  Polyurethane coatings  Multilayer membranes  Silane Siloxane based sealers  Silicon based water repellents  Neoprene based coatings  Polymer modified cementitious coatings  Spray applied membranes  Foam waterproofing  E l a s t o m e r i c membranes  Polymer modified cementitious systems  Bitumen / Neoprene / Polyurethane systems

Application Techniques

The waterproofing materials and systems are expected to be installed or applied by using one of these methods:

 Brush applied  Roller applied  Spray applied  Impregnation  Spreading, laying, and bonding

Performance Selection

Each of these systems and materials, when applied by employing one of the above techniques, the performance of the waterproofing is expected to be one or combination of these, depending on the requirements.

Protects concrete from the intrusion of liquids thru‘ cracks / joints

 Excellent adhesion and water resistance  High flexibility and elongation – crack arresting  Minimizes liquid absorption by concrete  Typical applications – Below and above grade waterproofing, traffic decks…

Many times due to lack of awareness of knowledge and technological advances and choices around us, will end up using inferior methods and materials, leading to premature failure of the treatments.

Selection of right technology is essential to avoid this. Hence, knowledge plays a key role while making decisions about waterproofing in mega projects, by either over or under specifying than the necessary and wasting the valuable resources of the nation.

Value System in Waterproofing

Stake holders in construction industry consists, end user of the facilities, owner / operator of the asset, designer – consultant / engineer, major civil contractor, subcontractor – labour / materials / tools, product distributor, and building materials manufacturer.

Building materials manufacturers, especially construction chemical manufacturers, in the case of waterproofing and repairs are the torch bearers of the technology in construction industry.

They exist at the very bottom of the value chain, contributing significantly converting knowledge in to commercially viable technology to suit the industry need. Yet times they drive the industry. Thus, enabling the growth of the industry. Is it in the right direction, is a mystery.

Role of Knowledge and Technology Management

In recent years, there has been a surge of interest in managing knowledge, created by people to address a specific given problem. Usage of appropriate chemical based treatment for waterproofing in a multi-million projects, do need knowledge management initiatives. In critical and highly complex situations project authorities, need more than technology experts. Essentially, Six forms of Knowledge, enables to take the most logically correct decision.

1. Context Knowledge—Stems from understanding the circumstances and underlying Systems.

2. Experience—having tacit information about how things are done around here.

3. Content Knowledge—having deep level understanding about processes and subject.

4. Applied Skill—being able to do things to a high level of quality.

5. Insight—being able to use creative imagination and reason to make connections, create ideas and suggest new ways forward.

6. People Knowledge—an awareness of who can do what, and how well they can do it.

A critical and challenging engineering project such as waterproofing using construction chemicals must state its strategies and objectives. The knowledge requirements have to be identified to meet these goals. The difference between the requirements and what current levels are referred to knowledge gap. If properly done, has potential to form tie-up for complementary capabilities.

Waterproofing Technology is continuously progressing. In this context several important concepts are illustrated which are of use to technology planners and forecasters in this filed. Waterproofing Technology, per say is all the knowledge, products, tools, methods and systems employed in the Creating of a leak proof structure. Sustaining success depends on the skill in choosing technology based engineering decisions. Technologies are of several types, such as: New technology, Emerging technology, High technology, Low technology, Medium technology, Appropriate technology, creative technology, breakthrough technology, and so on.

Strategic Directions to Waterproofing Technology

The performance of a technology has a recognized pattern over time that if properly understood, can be of great use in planning. Technology requires deep understanding of the life cycle of the technology, products, process, and system. A technology‘s improvement of performance follows the S– curve. When a technology performance parameter (on y axis) is plotted against time (on x axis), the resultant resembles an S – shaped diagram, called S- curve. Any technology progresses through a three stage technology life cycle (TLC). The first stage is the new invention period, also known as embryonic stage. The second stage is technology improvement period, also known as the growth period. The third stage is mature – technology period. The technology becomes vulnerable to substitution or obsolescence when new or better – performing technology emerges. S-cure of technology is a powerful model in technology forecasting.

Technology Push Vs. Market Pull

Technology opens new vistas. Technology is also often developed to meet a market need or demand. Technology push leads to scientific discoveries, applied knowledge, recognized needs, intellectual capital. On the other hand market pull creates market demand, proliferation of application areas, recognized needs, opportunities for increased quality, productivity, and so on. Ideally integrating technology push and market pull to stimulate innovation.

Conclusion

In recent past, usage of construction chemicals for waterproofing had increased, as the construction industry had grown on a sustainable basis. There is a sudden shift from conventional rigid waterproofing technologies, which predominantly consists of a single material viz. bituminous coatings and felts to elastomeric waterproofing, and so on, coatings which are a combination of several materials to achieve major performance advantages on a long term basis. Now its time to develop indigenous skills, knowledge, processes, rather than inviting and importing the low technologies. Construction chemical manufacturers should promote technologies suitable to our national economy i.e affordability and environment i.e weather and climatic conditions. Non Invented Here (NIH) technologies unfortunately are highly appreciated, encouraged, recommended, and implemented by waterproofing industry stake holders.

“It is the knowledge society that will transform India into a developed nation.” - Dr. A P J Abdul Kalam President of India

Here an attempt is made to introduce the knowledge and technology management concepts to bring out the intricacies associated with contemporary waterproofing systems using construction chemicals. Hope the mind set will change where new dynamic ideas are encouraged and implemented.

Authors Profiles Er. P Srinivasa Reddy is a civil engineering graduate, associated with the Construction Industry for more than fifteen years, and is Chief Executive Officer of Rehab Technologies, currently consultant in the area of civil engineering materials & its applications, repair and rehabilitation of concrete structures.

E Jagannadha Rao is a graduate in Applied Sciences from Andhra University, Post-Graduate Diploma in Systems Management, trained in Six Sigma and a Certified Software quality professional. He possesses about 18 years of International and National level IT industry experience in the United States and Saudi Arabia. Currently, associated as Consultant with Rehab Technologies for conceptualizing and implementation of highly knowledge and technology intensive consulting assignments in the field of civil engineering.

Acknowledgment

Our sincere acknowledgments are due to Dr. Atul Sen, Head, Knowledge Management Center, Defense Research and Development Laboratory, Hyderabad. Dr. Sen had trained, encouraged and supported us to learn and understand KTM concepts and permitted to use some of his presentation material in this paper. We also acknowledge all our clients and business associates, who had provided opportunity to offer our consulting services in the area of implementing new technologies to enhance performance of their concrete structures.

Waterproofing An Overview

Gopal Krishna & P.T.Thomas, Chembond Chemicals Ltd, Navi Mumbai.

Concrete, a composite, construction material made with cement, aggregate, water and admixture, comprise the largest of all man made construction material of our time. Its plasticity, workability, ease to place, to cast and compact while wet and strong and durable when hardened, make it one of the unique material. Generally strength of concrete is considered as the most important criteria among the properties of concrete.

But when taking the account of durability of the structure, resistance to water permeability is also considered as an essential requirement of the structure for which it is designed to withstand the environmental condition for over period of time without any deterioration. Being a water based product, and due to its composition of cement-aggregate-water is often susceptible to damage and deterioration from water and chemical penetration. Although it appears to be solid material, it is porous and permeable. Normally to make concrete workable and easy to place and consolidate more water than necessary is added. This extra water will bleed out of concrete leaving behind pores and capillary tracts. Another drawback is shrinkage cracks, shrinkage is a common phenomenon generally encountered in cement based products due to contraction of total mass upon loss of moisture.

Although concrete is designed to be durable, normally it is observed that inadequate mix proportion, use of substandard material, improper compaction and placing makes the structure vulnerable to ingress of water chemicals resulting reinforcement corrosion and further deterioration of structure.

To overcome all these, to a very good extent, and make concrete reasonably impermeable, precautionary steps like, good mix design, usage of standard materials, proper supervising while placing and compacting, giving enough coverage to reinforcement, proper curing, use of flyash and other pozzolona blended cements, using permeability reducing admixtures etc are to be considered seriously. Permeability retards the durability and reduces the life span of the structure, waterproofing or damp–proofing is carried out to prevent or to seal unwanted water containing deleterious salts and chemicals to enter in the structure, resulting reinforcement corrosion and other destructive activities. The activity of waterproofing of the structure/building, which is practiced in one form or other ever since the construction started in our history. The methodology has gone through various changes, by design of the structure, availability & application of different construction materials.

There are lots of conventional and unconventional methods practiced for waterproofing in construction field. Old methods like brick bat–cobba, cement–lime based treatments, bituminous coatings are still practiced successfully. But the development of modern construction material and technology, the concept of waterproofing has changed tremendously. Nowadays integral waterproofing compounds are admixed into the plastic concrete.

These materials impart water repelling (damp-proofing) to concrete, may reduce moisture migration through capillary reaction. Surface coating application is another known method generally followed. But most of these are found to be ineffective in reducing the water passage under a positive hydrostatic pressure. Treating the concrete to retard the absorption of water or water vapor by concrete or to retard their transmission through concrete is considered as Damp-proofing.

Treatment of a structure or asurface to prevent the passage of liquid water under hydrostatic pressure is called is Waterproofing. This positive prevention of the ingress and movements of water under hydrostatic pressure distinguished waterproofing from damp-proofing. Further there are positive and negative side waterproofing. Positive side waterproofing is applied on the same side as the applied hydrostatic pressure. Negative side waterproofing is applied on the side opposite to that applied hydrostatic pressure. Due to the unavailability of access to the positive side, negative side waterproofing are also practiced.

The most common waterproofing methods:

 Brickbat coba method: This system involved in laying clay bricks with light weight lime mortar on the roof and spreading it for easy draining away of rain water. This system is popular not because of the waterproofing, but the weather proofing capabilities.  But it adds weight to the structure and once water starts entering, the porous clay brick pieces absorbs large quantity of water, resulting continuous leakage of roof.  Cement/lime based treatments: Coating the surface with cement lime mortar is a time proven and economical method with good insulation properties. But it is non-flexible and also increases the load of the structure. 3 Mineral slurry with polymer component is an easy method to apply. It retains the breathing capacity of concrete but with moderate flexibility. 4 Epoxy & polyurethane coating is highly abrasion resistant and resistant to UV radiation and does not add weight to the structure. But this has limited pot–life, not very flexible and stops breathing capacity of concrete.  Elastomeric membrane forming products: It forms seamless membrane, highly flexible, UV resistant, retains breathing capacity of concrete with indirect insulation, but with low abrasion value.  Silicon based impregnators as water repellent, easy to apply and economical, but it has no crack bridging capacity, and does not withstand pressure.  Bituminous based products and modified bitumen are very economical, flexible, with good crack bridging capacity. But it softens under heat and brittle when cold, limited life upon solvent evaporation and other limitation due to its unpleasant black colour.

Crystalline water proofing system: In this system water bearing capillaries are blocked with insoluble crystals, the saturated surface is applied one or two coatings with crystalline waterproofing slurry.

In modern construction technology developments a single product or technique is not usually enough, involvement of various bodies and techniques in co–ordination is essential for making the structure waterproof. Structure should have sufficient and efficient various control joints like expansion joints, contraction joints, etc. if proper control joints are not provided in large slabs, no waterproofing system will be successful.

Among the various methods mentioned above, two are proven successful and effective, they are: Crystalline waterproofing system Flexible membrane waterproofing system.

Crystalline waterproofing provides a quick, cost saving alternate to the traditional flexible membrane waterproofing system. In some cases, external waterproofing application requires enough space to make application outside of a structure. This can cause problems as there is not enough space for membrane application because of adjacent structures. Crystalline waterproofing can solve this problem to some extent; by negative side application as the unavailability of access to the positive side. Crystalline water proofing when applied to a surface either as a coating or dry shake application to a freshly placed concrete slab a process called chemical diffusion takes place.

Crystalline water proofing compound reacts with various chemicals and moisture in the concrete to form insoluble crystals which seal the capillaries and shrinkage cracks. Its action as by filling and plugging pores, capillaries, micro-cracks and other voids with a non-soluble/insoluble highly resistant crystalline formation makes waterproofing more effective. As the crystalline waterproofing chemicals continue to migrate through water, a crystalline structure is formed. This reaction will continue until the crystalline chemicals are either depleted or run out of water. Some manufacturers are claiming that this chemical diffusion takes place about 12 inches into the concrete.

If water has soaked only 2 inches and stop but, they have the potential to travel 10 inches further, if water re-enter the concrete at some point in future and reactivate the chemicals. Thus the crystalline formation engages the material filling and plug the voids in the concrete to became an integral and permenant part of the structure. Because this crystalline formation are within the concrete and are not exposed at the surface, they cannot be punctured or damaged like membrane or surface coatings.

Crystalline waterproofing system can be executed in three different ways as per the requirement and the situation demands. Surface coating is most common, other are dry shake powder application and as an admixture added at the time of batching. In dry shake powder application for horizontal set concrete and structural slabs, the Crystalline waterproofing compound is spread across uniformily to fresh concrete after initial set and power trowelled. Unset concrete matrix contains an abundance of moisture for optimal penetration of crystalline waterproofing compounds. As an admixture, when added at the time of batching, crystalline waterproofing compounds reacts with moisture in fresh concrete and the bi-products of cement hydration to cause catalytic reaction, which generates a nonsoluble crystalline formation through the pores and capillary tracts of the concrete.

Advantages

This integral CWP system has so many advantages compared to other waterproofing systems. When used as a negative side waterproofing application, which is as effective as positive side waterproofing, allow to expedite the construction schedules by back filling sooner. It is highly resistant to abrasion, wear and tear, no risk of tearing or puncturing. Cost of material and labor are lower. As there is no problem like insufficient seam coverage, poor surface preparation and inadequate adhesion as there in the membrane system. The integral crystalline waterproofing system become a part of concrete matrix, are permanent can self seal hair line cracks, resistant to hydrostatic pressure, allows concrete to breath, protect for a life time.

Waterproofing by Surface Applied Membranes

Surface applied membrane type waterproofing system currently accepted worldwide. The recent progress in polymer technology with the development of polymer modified bitumen like ATACTIC POLYPROPYLENE (APP) modified bitumen improves the physical property of bitumen. This modified bitumen coating has overcome to a very good extent, to remove the drawback of conventional bitumen membrane of its undesirable temp; related variations like to become brittle at freezing temps and soft at high temps.

Since waterproofing connot be carried out using a single material, i.e. suitable for one structure, may not apt for another. The use of various materials in combination and methodologies are vital for effective waterproofing to meet the specified design and durability requirements has significantly revolutionized waterproofing as waterproofing system. This system includes combination of materials, application techniques, specified requirements like providing efficient drainage system, using various construction joints, water stops etc. To demonstrate waterproofing as system one of the very recent example is construction of Delhi metro, underground structure. Here the various material in combination to meet or to conform, international & Indian standards, techniques, test methods for performance guarantee etc made this particular project a typical example to describe waterproofing as a system.

Application of APP Membrane for Base Slab

The underground structure of Metro rail project has proven with this APP bituminous modified membrane system without any water leakage. These underground structures are designed for a life span of 120 years and 50 years for over ground structures. To meet the design stipulation of life span of 120 years, a well designed and nearly effective waterproofing system is utmost essential, here the structures are provided with a fully covered waterproofing membrane protection to all the external faces of the structure.

Base slabs are constructed over leveling concrete which is applied with waterproofing membrane. External walls and roofs are covered with waterproofing membrane, which is bonded with parent concrete, and these membranes are further protected with concrete blocks protection layers coverage for any possible tearing or puncturing from external sources. Besides there are provided construction joints and water-stops and other drainage systems as per the design requirements.

Following is a brief description of the materials used application techniques executed on the waterproofing treatment of under ground structures like base slab; walls and roof of all under ground structures built with cut and cover method of Delhi metro projects. Here all the cut and cover underground structures are provided with a fully tanked waterproofing membrane fully bonded with external faces of structure.

Vertical Application of APP Membrane

On sufficiently hardened, surface leaned, blinding concrete a bituminous primer is applied. A waterproofing membrane–4mm thick homogeneous thermoplasticblend of Atatic polypropylene (APP) distilled between with a reinforcement of 160 gm per square meter of non-woven polyester, top surface is covered with mineral protection with silica and the bottom surface is covered with a flamable polyethylene film, is then thermo fused by flame torching of inside face of membrane, which is embossed and protected by a seven micron thick polyethylene film. On this membrane applied surface a high abrasion resistant polymeric mortar is laid up to 3 mm thickness. At least three days curing is provided to this mortar layer before laying reinforcement.

For walls, on a clean and dry surface a primer is applied. When it is touch dry, the similar APP membrane is thermo fused by flame torching. To protect this membrane system from any further damage during other external activities a 75mm thick concrete block work is provided. For roof structures the similar methods followed for membrane application and protection layer of concrete is provided.

The recent economic boom in India generated the upcoming of lot of mega projects, like, metro rail projects, express high ways, multi-storied building complexes with large capacity underground facility for vehicle parking and other utilities. Unavailability of surface land at crowded cities, shortening of distance of rail and roads, maximal utilization of available space etc are forced construction agencies to consider seriously for underground projects.

Metro rail projects, tunnels through mountains and under the bed of water, and deep basements are typical examples. For all these projects waterproofing has a vital role for the designed durability especially surface applied membrane system to prevent passage of water under hydrostatic pressure to form a continuous impermeable membrane barrier to prevent leakage into usable space or to prevent loss of water from a retaining structure. So waterproofing nowadays revolutionized as a major preventive measure than a cosmetic treatment.

Why Waterproofing is Essential

Dr. Surendra P. Bhatnagar, CMD, Tech-Dry (India) Pvt. Ltd. and Mr. R. N. Kaura, CEO, BPS Building Protection Systems Pvt. Ltd. Bangalore.

Waterproofing is one of the most critical, yet neglected subjects because the common man is not exposed to the concrete technology. He just wonders and is shocked when he sees leakage in his building, but most of the time he considers it as inconvenience rather than a serious matter.

Water infiltration causes major problems to a structure. Water damages a building first cosmetically then structurally. It is important to realize that by the time a stain shows up on the interior of your building most likely irreversible damage has been caused to the exterior. Water soaked roof insulation will never dry out.

Trapped moisture in insulation can also decay a roof deck and will cause roofs to fail prematurely. Water entering walls will rust steel relieving angles and carrying beams, which support the structure. Moisture penetrating reinforced concrete structures carry chloride ions, which will rust reinforcing bars causing them to expand in size resulting in spalling of concrete. As one begins to understand the mechanics of water infiltration one begins to understand the importance of keeping a building watertight.

Water enters the building and can have immediate and long term undesired effects. Apart from damage to the building contents, structural damage is unavoidable if the problem persists. Water damage can be compared to fire as a cause of building decay and deterioration. Water is hydrophilic and to convert it into hydrophobic is the definition of waterproofing.

Concrete is Hydrophilic But What Makes it Absorb Water?

Concrete, bricks, stones and mortars are composed of crystals of carbonate, silicate, aluminates or oxides, whose surfaces are rich in oxygen atoms, which carry negative electrical charge of hydroxyl groups, which carry both negative and positive charges. Such surfaces are polar and are also called hydrophilic. When water comes into contact with these surfaces, hydrogen bonds are formed between the surface and the water molecules. Once the buildingmaterials come in contact with water, they absorb water through their pores by the capillary action.

Concrete, which is prepared by mixing of cement, sand, aggregate and water, is the most successful building material of the modern world. Portland cement is made from clay and limestone. Once the cement has been mixed with water, a reaction commences. The chemical reactions are complex but the hydration reaction of cement with water produces insoluble silicate compounds and calcium hydroxide (Scheme 1.1 and 1.2).

Carbonation starts simultaneously with hydration (Scheme 1.3). Carbonation hardens the concrete and helps reduce the permeability of the concrete. However, carbonation reduces the alkalinity of the concrete and it is the alkalinity of the concrete which protects the reinforcing steel in a steel-reinforced concrete structure.

Strength of Concrete The strength of concrete is very much dependent upon the hydration reaction as discussed above. Water plays a critical role, particularly the amount used. The strength of concrete increases when less water is used to make concrete. The hydration reaction itself consumes a specific amount of water. Concrete is actually mixed with more water than is needed for the hydration reactions. This extra water is added to give concrete sufficient workability.

Flowing concrete is desired to achieve proper filling and composition of the forms. The water not consumed in the hydration reaction will remain in the microstructure pore space. These pores make the concrete weaker due to the lack of strengthforming calcium silicate hydrate bonds. Some pores will remain no matter how well the concrete has been compacted. The relationship between the water/cement ratio and porosity is illustrated in the figure give below.

During hydration calcium hydroxide is produced which protects the reinforcement from corrosion since the steel cannot corrode in highly alkaline condition. Normally, concrete exhibits a pH above 12 because of the presence of calcium hydroxide-the term pH is a measure of the alkalinity or acidity, ranging from highly alkaline at 14 to highly acidic at zero, with neutrality at 7.

Although the precise nature of this passive film is unknown, it isolates the steel from the environment and slows further corrosion as long as the film is intact. The effect of the environment on mineral building materials is a natural process, which has not attracted significant scientific interest until recently. The initial work in Germany around 1900 investigated the weathering of natural stones. The problem, which has now attracted is the entry of water containing dissolved toxic substances to the inner parts of the concrete by capillary action.

This statement may be extended to the entry of deteriorating agents as a gas or in solution. Later a problem associated with modern concrete construction emerged-that of steel corrosion in steel- reinforced structures causing spalling. Unless this phenomenon of degeneration of reinforcement is not slowed or stopped, buildings will not be durable and can lead to problems of safety. Infact depending on the chemistry of the environment the malignancy can set-in as early as 3 months of the substrates exposure to the strong environment. Rain with dissolved materials from atmosphere, CO2, SO2, SO3, Nitrogenoxides present in the atmosphere around and water penetration by rising damp influence the building structures and cause deterioration. Macing spray + salt water, Gases, deicing salts and rain with dissolved chemicals from atmosphere influence the bridge structures.

How Water Enters?

Normally we would be expecting a building to be watertight but there are always ingress points on the concrete, in other parts of the building because of variety of reasons and water can enter through these points to cause the following damages

 Corrosion of metals such as steel reinforcement in concrete structures causing malignancy.

 Swelling of plasterboards and subsequent debonding of ceramic tiles.  Possible short circuit of lighting and power points.  Blistering of Paint.  Damage to structures and finishes such as floor joints, beams, floors, studs, skirting, and frames.  Health problems due to dampness, which may lead to respiratory problems, growth of micro- organisms and exposure to gas like radon.

Water in the building can also be a big threat to health and happiness, it contributes to environmental pollution especially in big cities where very large population concentrated in a small space, creates carbon dioxide, sew ge, smoke from motorized vehicles, etc. This is a very complicated problem with no single solution.

The environment is polluted with chloride, carbon dioxide and other gases like sulphure dioxide, oxides of Nitrogen, sometimes known as acid rains and these pollutants dissolve in water, enter into the building and damage the reinforcement.

In some states, in India, there is a report that because of high uranium in stone the presence of highly dangerous and killer gas radon to be checked. Concrete building contributes significantly to the environmental pollution more so when we use products like bitumen and asbestos.

A dark roof coated by bitumen can attain a very high surface temperature and in addition the reflected radiation from adjacent surface can raise the surface temperature much above than attained by direct radiation. The composition of the Asphalt will vary based on the origin of crude oil.

Saturated felts consist primarily of organic or inorganic fibres (asbestos) which are interlocked to form a continuous sheet, then saturated with asphalt or coal tar pitch (organic felts only) and perforated for use in roofing. The coal tar is known to contain chemicals, which can be classified as polycyclic aromatic hydrocarbons, a class of chemical with harmful properties. Polycyclic aromatic hydrocarbons in high concentrations are harmful not only to wild life, but to humans as well.

Inspite of these problems, we would atleast want to live in a house which is comfortable and secured. Unfortunately, indoor pollution is quite prevalent and equally damaging. Important sources of chemical indoor pollutants include outdoor air, the human body and human activities, emissions from building materials, furnishings and appliances and use of consumer products. Microbial contamination is mostly related to the presence of humidity.

The heating, ventilating and air conditioning system can also act as a pollutant source, especially when it is not properly maintained. Two essential components of a healthier home are moisture control and air infiltration. Excess moisture and/or high humidity can contribute to the growth and dispersion of biological contaminants like mold and dust mites. Excess air infiltration resulting from warm and cold air meeting within wall cavities can cause condensation and contribute to mold growth which can cause upper respiratory irritation and infections and a myriad of other health effects, including allergic reactions, hypersensitivity pneumonitis (like bacterial pneumonia), eye irritation, ear infections, skin rashes and various immunologic symptoms.

The typical components of building a healthy home include foundation waterproofing and slab moisture control; advanced framing techniques; air sealing and advanced insulation techniques; energy efficient, high performance windows; energy efficient and sealed combustion appliances; high efficiency air filtration and ventilation; humidity control; and carefully selected interior finishings.

Biological pollutants, which are living organisms, can cause serious problems like fungus growth in the house causing allergies, infections etc. Two conditions are essential to support biological growth; nutrients and moisture. These conditions can be found in many locations, such as bathrooms, damp or flooded basements, wet appliances, rooms with seepage and leakage.

Some diseases or illness have been linked with biological pollutants in the indoor environment. Moisture control and waterproofing of the house is one of the solutions to avoid biological pollutants inside the house. Therefore, it is essential to fix leaks and seepages and it is equally important to ensure that mold surfaces are clean and after waterproofing, there is no further mold growth throughout the house, including attics, basements and crawlspaces, and around the foundation. See if there are many plants close to house, particularly if they are damp and rotting. They are a potential source of biological pollutants.

In view of the fact that water does not only damage the building but also causes health hazards and it is therefore essential to give top priority to waterproofing.

Approaches to Building Protection

Approach 1

Change the environment—To reduce the level of damage the level of pollutants at particular situations could be reduced, for instance, by the careful siting of industrial areas and by reduction of motor vehicle emissions and other emissions.

Approach 2

Reduce the water ingress—The ingress of water could be reduced by design and by intervention. For instance flashings can be used to run water off buildings and monuments. Rising damp may be stopped by intervention so arresting decay due to salts. Drainage may be improved.

Approach 3

Protect the building material by impregnation—The building material may be impregnated with a material which will reduce liquid water ingress. At the present state of knowledge it is not possible to impregnate the building material and effectively stop damaging gas diffusion.

Approach 4

Protect the building material by surface coating–The surface of the building may be coated with a specialist surface coating to interrupt the diffusion of damaging gases and liquid water. Alternatively, this coating may be a thicker protective coating such as a render. This coating should allow the transmission of water vapour.

Conclusion Question to be calibrated is whether we are living in a safe and durable structure? Inspite of the best technologies available today we find that the buildings start showing stress within a very short period. As soon as monsoon arrives, leakage and seepage problems especially for roof and terraces are at the forefront, besides the heavy expenditure, which is incurred on repair and rehabilitation is swelling and would cripple our economy one day. A wide range of products for waterproofing have been offered under brand protecta.

Concrete Waterproofing with Crystalline Technology

Stanley Stark, FAIA, XYPEX , USA

From foundations, floor slabs and exterior precast panels, to water treatment facilities and under ground urban infrastructure, concrete is one of the most commonly used building and construction materials. However, due to its composition, a mixture of rock, sand, cement, and water, concrete is often susceptible to damage and deterioration from water and chemical penetration.

These deleterious effects can be avoided through the use of crystalline waterproofing technology, which effectively improves the durability and life span of concrete structures, there by reducing long- term maintenance costs. This article explore & show crystalline technology provides a high level of performance to Concrete mixtures, materials, and structures, and what design professionals need to know in order to specify and understand how this chemical technology will enhance building projects.

The Nature of Concrete

The aggregate base of a concrete mixture is formed by rock and sand. This cement and water mixture creates a paste that binds the aggregates together. As the cement particles hydrate, or combine with water, they form calcium silicate hydrates. The mixture then hardens into a solid, rock-like mass.

Concrete is also a water-based product. To make this mixture workable, easy to place, and consolidate, more water than is necessary for the hydration of the cement is used. This extra water, known as the water of convenience, will bleed out of the concrete, leaving behind pores and capillary tracts. Although concrete appears to be a solid material, it is both porous and permeable.

Water reducers and super plasticizers are used to reduce the amount of water in the concrete mix, and maintain its workability. However, pores, voids, and capillary paths will remain in cured concrete and can carry water and aggressive chemicals into structural elements that will corrode steel reinforcement and deteriorate concrete, thus jeopardizing the structure‘s integrity.

The Porous and Permeable Nature of Concrete Concrete is best described as a porous and permeable material. Porosity refers to the amount of holes or voids left in concrete, is expressed as a percentage of the total volume of a material. Permeability is an expression of how well the voids are connected. Together, these qualities allow pathways to form that allow the movement of water into, and through, along with the cracking that occurs due to shrink–age. Permeability, a broader term than porosity, is the ability of liquid water under pressure to flow through porous material.

Permeability is described by a quantity known as the permeability coefficient, commonly referred to as D‘Arcy‘s Coefficient. The water permeability of a concrete mix is a good indicator of the quality of the concrete for durability reasons. The lower D‘Arcy‘s Coefficient, that is, the more impervious, the higher the quality of the material. Never–theless, a concrete with low permeability may be relatively durable but may still need a waterproofing agent to prevent leakage through cracks.

Despite its apparent density, concrete remains a porous and permeable material that can leak and deteriorate rapidly when in contact with water or the intrusion of aggressive chemicals, such as carbon dioxide, carbon monoxide, chlorides, sulfates or other substances. But there are other ways in which water can be transported through concrete.

Vapor Flow and Relative Humidity

Water also migrates in the form of water vapor as relative humidity. Relative humidity is water held in air as a dissolved gas. As water vapor heats up, it contains more water and exerts vapor pressure. Water can also be transported through concrete as vapor. The direction of flow travels from high vapor pressure, generally the source, to low vapor pressure, by a process of diffusion.

The direction of flow could vary base on environmental conditions. The direction of vapor flow is critical when applying water proofing treatment in situations where an unbalanced vapor pressure gradient exists. Typical examples include:

 Applying a low vapor permeable membrane, such as a traffic deck coating over a damp concrete surface (even if the very top surface is dry) on a warm day will result in pressure vapor pressure build-up and pin-holing or blistering.  Applying a coating or sealant to the outside of a building wall may trap moisture into the wall if the sealant is not sufficiently vapor permeable.  Applying low vapor permeable flooring over a slab-on-grade where there is high sub surface moisture content may resulting delamination of the flooring. Generally, a low vapor permeable sealant or coating should not be placed on the down stream face of a building or structure. Either the vapor pressure or water pressure will act to damage and blister the membrane. Some types of coatings and water permeability reducing admixtures in the concrete accommodate considerable vapor movement, thus allowing them to be placed successfully on the down stream side. Primary examples are cement- based waterproof coatings and water permeability reducing admixtures.

How Crystalline Waterproofing Technology Works

Crystalline technology improves the durability and performance of concrete structures, lowering their maintenance cost and extending their lifespan by protecting them against the effect of aggressive chemicals. These high performance qualities result from the ways in which the crystalline technology works, when used with concrete.

Crystalline water proofing technology improves the water proofness and durability of concrete by filling and plugging pores, capillaries, micro-cracks, and other voids with a nonsoluble, highly resistant crystalline formation. The water proofing effect is based on two simple reactions, one chemical and one physical. Concrete is chemical in nature. When a cement particle hydrates, the action between waterand the cement that causes it to be come a hard, solid mass. The reaction also generates chemical by products that lie dormant in the concrete.

Crystalline waterproofing adds another set of chemicals to the mixture. When these two chemical groups, the byproducts of cement hydration and the crystalline chemicals, are brought together in the presence of moisture, a chemical reaction occurs. The end product of this reaction is a non soluble crystalline structure.

This crystalline structure can only occur where moisture is present, and thus will form in the pores, capillary tracts, and shrinkage cracks in concrete. Wherever water goes, crystalline water proofing will form filling the pore, voids and cracks. When crystalline water proofing is applied to the surface, either as a coating or as a dry shake application to a fresh concrete slab, a process called chemical diffusion takes place. The theory behind diffusion is that a solution of high density will migrate through a solution of lower density until the two equalize.

Thus, when concrete is saturated with water prior to applying crystalline water proofing, a solution of low chemical density is also being applied. When crystalline waterproofing is applied to the concrete, a solution of high chemical density is created at the surface, triggering the process of chemical diffusion.The crystalline waterproofing chemicals must migrate through the water (the solution of low density) until the two solutions equalize.

The crystalline waterproofing chemicals spread through the concrete and become available to the byproducts of cement hydration, allowing the chemical reaction to take place. A crystalline structure is formed, and as the chemicals continue to migrate through the water, this crystalline growth will form behind this advancing front of chemicals.

The reaction will continue until the crystalline chemicals are either deplete do run out of water. Chemical diffusion will take these chemicals about 12 inches into the concrete. If water has only soaked two inches into the surface, then the crystalline chemicals will only travel two inches and stop but, they still have the potential totravel 10 inches further, if water reenters the concrete at some point in the future and reactivates the chemicals.

Instead of reducing the porosity of concrete, like water reducers, plasticizers, and super plasticizers, the crystalline formation engages the material filling and plugs the voids in concrete to become an integral and permanent part of the structure.

Because these crystalline formations are within the concrete and are not exposed at the surface, they cannot be punctured or otherwise damaged like membranes or surface coatings. Crystalline waterproofing is highly resistant to chemicals where the pH range is between three and 11 under constant contact, and two to 12 under periodic contact.Crystalline waterproofing will tolerate temperatures between-25 degrees Fahrenheit (-32degrees Centigrade) and 265 degrees Fahrenheit (130 degrees Centigrade) in a constant state. Humidity, ultraviolet light, and oxygen levels have no impact on the products ability to perform.

Crystalline waterproofing offers protection against the following agents and phenomena:  Inhibits the effects of CO, CO2 , SO2 and NO2 , the gasses responsible for the corrosive phenomenon known as ‗carbonation.‘ Carbonation is the process where exterior gasses create a corrosive phenomenon that‘ softens the surface layers of the concrete. Carbonation testing shows that the multiplicative crystalline formations also reduce the flow of gases into concrete, thus significantly retarding the carbonation at the surface in which the alkalinity is reduced and the surface layer is softened.  Protects concrete against alkali aggregate reactions (AAR) by denying water to those processes affecting reactive aggregates.  Extensive chloride-ion diffusion testing shows that concrete structures protected with a crystalline waterproofing treatment prevent the diffusion of chlorides. This protects reinforcing steel and prevents deterioration that could occur from oxidation and expansion of steel reinforcement.

The more traditional methods of protecting concrete, such as membranes and other coatings, may still leave it susceptible to water and chemical damage. Only with the addition of crystalline technology the pores and micro cracks that normally result from the process of setting and curing, allow concrete to be sealed.

Negative Side Waterproofing

Existing basements that are subject to water seepage or vapor transmission through foundation walls and floors can be treated by the application of crystalline waterproofing and protection on the negative side, or the inside, of the structure. Surface coatings will blister and peel when moisture seeping through the concrete dissolves soluble minerals and deposits them on the surface, under the coating, in the form of efflorescence, a white powdery substance that forms on the wall surface. Because crystalline waterproofing penetrates into the concrete, plugging the pores beneath the surface, it does not depend on surface adhesion and will not blister and peel off, like surface barriers. ―I specify crystalline waterproofing on virtually every one of my projects as an admixture for the retaining side of walls where applied membranes cannot be used,‖ says Mel Cole, FCSI, an architectural specifier in Soquel, California. Vapor transmission through basement floors and walls is a common problem that may lead to damp, musty odors. Testing has shown that the application of multiplicative crystalline technology under these conditions will reduce vapor flows as much as 50 percent, which in most cases, will result in a drier environment.

Conclusion

Although concrete may appear to be a simple product to put together, it requires a highly engineered approach. In an increasingly competitive design and construction environment, where high performance requirements, such as longer life cycles, more durable concrete, and value engineering are expected, careful consideration must be paid to basic requirements, such as the concrete, water, and cement ratio; cementing materials, and more sophisticated chemical admixtures. Effective use of crystalline waterproofing technology will reduce the porosity and permeability of conventional concrete, and provide the high performance advantages and benefits that building owners and design professionals have come to rely upon in design and construction projects.

Waterproofing with Cementitious Slurries

Water is a vital resource, but also a construction material‘s greatest enemy, since rain, ground water and surface water can cause rapid and extensive damage to buildings. The solution lies in water- repellent construction materials with sealing properties such as cementitious slurries modified with dispersible polymer powders.

Water, in liquid or in vapor form, is the most destructive weathering element for buildings constructed of materials such as concrete, masonry, and natural stone. Waterproofing techniques therefore must preserve a structure‘s integrity, functionality and usefulness for the whole of its life. Due to the harsh conditions of the monsoon, there‘s a special challenge for waterproofing systems in India. To eliminate all possible causes of water intrusion, the exterior walls, the roof and the basement of a building must be completely covered with waterproof material. All waterproof measures must be part of a whole system and must interact totally to be completely effective in preventing the ingress of water.

Should one component of the system fail or not interact fully with all other parts, leakage can occur. Possible damage, deterioration and unnecessary repairs to building facades can be avoided by controlling groundwater, rainwater and surface water, as well as the transport of humidity in the form of water vapor.

Traditional sealing and waterproofing systems include bituminous materials, plastic waterproofing foils and metal tapes for interior and exterior applications. In addition to these systems, products based on reactive resins, purely dispersionbound, pasty products and cementitious waterproofing membranes are now widely used to seal and protect the outer surfaces of buildings and structural components against the action of water and moisture.

Cementitious waterproofing membranes have been used successfully to protect a wide range of buildings and structural components exposed to either periodic or long-term wetting, low hydrostatic pressure or, in combination with appropriate engineering, even high hydrostatic pressure. Cementitious membranes are used for waterproofing wet rooms and water tanks and, due to their excellent weathering resistance, also for exterior surface protection. Typical applications are the sealing and waterproofing of e.g., terraces, basement walls, water tanks, swimming pools, walls and floors in wet-rooms such as toilets and bathrooms. In addition, flexible cementitious waterproofing membranes are often used as protective surface-coating systems for structural concrete or to protect building constructions against aggressive chemicals.

The advantages of cementbased waterproofing membranes are their excellent resistance to water, even if exposed permanently, their outstanding resistance to long-term weathering, good scratch resistance, good load-bearing capacity and much higher water vapor permeability compared to most other systems (consequently no danger of blistering when water vapor permeates through the waterproofing membrane).

Cement-based waterproofing slurries are easy to use, non-toxic, provide a monolithic, fully bound, joint-free surface and can easily be applied to substrates with complex surface shapes. In contrast to other systems, cementitious waterproofing slurries can be applied even to wet or damp mineral surfaces, and their physical properties are less temperature-dependent than bitumen based materials.

Simple cement-based slurries are still used for protection against surface water, but they are not suitable to seal against water under hydrostatic pressure. In order to improve the poor adhesion, the poor water impermeability and the extremely low deformability and flexibility, a polymer must be added to the system. The use of special additives such as water retaining agents, thickeners and rheological additives, combined with a polymeric binder, confers excellent workability and ensures that wetcuring of the applied slurry is unnecessary.

As polymeric binder, dispersible polymer powders have proved their value. Dispersible polymer powders are thermoplastic, plasticizer-free polymers derived primarily from vinyl acetate and ethylene. When water is added, these spray-dried dispersions ―redisperse,‖ while retaining all the properties and functions typical of a liquid polymer dispersion. As the mortar sets, flexible polymer bridges are formed between the brittle mineral constituents of the mortar, producing a polymer film that acts as an organic binder. This greatly improves the mortar‘s adhesion to a wide range of substrates and increases the system‘s flexibility.

Today, several different systems of cementitious waterproofing membranes or slurries are available.

Standard or Rigid Mineral Waterproofing Slurries

Standard, rigid mineral waterproofing slurries are polymer-modified, prepacked, drymix mortars which are gauged with water before being applied as a slurry by brush, roller or airless spraying, or, if less gauging water is used, by trowel. Standard or rigid waterproofing slurries can only be used for mineral substrates which are stable, sound and solid, and if there is no risk of crack formation, movement or dimensional change (e.g., shrinkage). Dispersible polymer powder is used as a polymeric binder to improve the adhesion of the waterproofing membrane to different substrates, to improve its cohesive strength, its flexibility, its abrasion resistance and toughness and, last but not least, the water impermeability and density of the membrane. Such polymer modified cementitious waterproofing membranes can withstand water pressure, not only from the positive side, but also, to a limited extent, due to their excellent adhesion and cohesion, from the negative side, if this is necessary for a special application. A dispersible polymer powder which confers a hydrophobic effect is the preferred type of polymer which should be incorporated in the drymix mortar.

Flexible Cementitious Waterproofing Membranes (Two-component Systems)

Flexible waterproofing membranes are capable of bridging over small cracks in the substrate. The flexibility of such products depends strongly on the polymer/cement ratio and, to a lesser extent, on the flexibility of the polymer itself.

In addition, the flexibility of a cementitious waterproofing membrane depends on the environmental conditions to which it is exposed. Flexible, cementitious waterproofing membranes are applied to substrates expected to be subject to shrinkage, vibration, movement, stress and crack formation and to substrates which are difficult to stick to, such as wood, steel, aerated light weight blocks and gypsum. Due to their high polymer content, these coatings have a low coefficient of diffusion and are resistant to chemicals such as chloride ions, sulphate ions, carbon dioxide and other aggressive products.

One-component Flexible Cementitious Slurries

In practice, a major disadvantage of two-component systems is the possibility of mixing errors due to the lack of knowledge, experience and education of the workers concerning the appropriate dosage of the liquid component. Wrong doses may be used by chance or even intentionally in order to save money in the short term. If the dosage of the liquid dispersion is too low, the resulting membrane may not be waterproof if exposed to hydrostatic pressure or will, at the very least, have a reduced flexibility with a consequent failure of the system. Other reasons for not using two-pack systems are the difficult and risky handling, the expense and logistics difficulties and more time consuming and harder work on the job-site when handling two-pack systems.

Because of the many disadvantages of modifying a mortar with a liquid dispersion as mentioned above, the so-called one-component flexible cementitious slurry in the form of a premixed dry-mix mortar is increasingly being used.

Dispersible polymer powders are employed, with very low glass transition temperatures, low water absorption and high water resistance in order to be able to formulate one-component, flexible, cementitious waterproofing slurries.

Dispersible polymer powders have been invented exactly 50 years ago in Germany. In 1957, the German chemical Group WACKER succeeded in industrially manufacturing the first powder binder as an additive for construction mortars, marketed worldwide under the VINNAPAS® brand. This invention revolutionized the entire construction sector, because it finally made possible the production of one- part, premixed dry mortars that merely needed reconstituting with water at the building site. To this very day, polymer powders give the construction industry key benefits, such as major cost savings, not to mention greatly simplified mortar production and handling. In cementitious sealing slurries, they not only protect buildings against damage from water penetration, but also against CO2, chlorides, sulfates and acid rain.

The higher cost of such products, due to the high dosage of the dispersible polymer powder, is compensated by the advantages of having a one-component, polymer-modified, dry-mix mortar, e.g., low-cost logistics and packaging, safety and reliability for the application by excluding mixing errors, and higher productivity on the job-site.

Wacker Polymers

Wacker Polymers is a leading producer of state-of-the-art binders and polymer additives in the form of dispersible polymer powders and dispersions, polyvinyl acetates, surface coating resins, polyvinyl butyrals and polyvinyl alcohol solutions. These products are used by companies in the construction, automotive, paper and adhesives sectors, as well as by manufacturers of printing inks and surface coatings. Wacker Polymers has production sites in Germany, China and the USA, as well as a global sales network and technology centers in all major regions

Selection of Suitable Types of Waterproofing Systems

Pramod Pathak, Director, Multichem Group, Mumbai.

Durability and Impermeability

Concrete is the most widely used building material which is versatile,and has desirable engineering properties, it can be molded intomany shapes, and more importantly, it is produced with cost-effective materials. In recent years, the use of concrete has increased phenomenally, specially in infrastructure and highrise buildings worldwide.

These days, concrete is beingused for wide varieties of applications to make it suitable for different conditions. In these conditions, normal concrete may fail to exhibit the required quality performance and durability. In practice one of the most important requirements of concrete is that it must be impervious to water under two conditions: firstly, when subjected to pressure water on one side, secondly to the absorption of surface water by capillary action.

Concrete possesses a pore structure which distinguishes concrete from metals and makes it airtight and watertight. The capillary pore structure of concrete allows the permeation of gas or liquid, especially under pressure. The macrostructure of concrete reveals that it consists of

(a) coarse and fine aggregates

(b) hydrated cement paste, and

(c) entrapped air voids.

The macrostructure also reveals visible cracks in the hydrated cement paste and aggregates, mainly due to the volume change caused by shrinkage, settlement, and expansion/ contraction of temperature. The permeability of concrete depends on these pore structures. Even the best of the concrete is not gastight or watertight unless the pores are closed. The low durability that we witness in many concrete structures, which gets manifested in the form of cracking, and spalling due to poor quality of materials or workmanship and corrosion of steel, is principally due to inferior design, specification or construction. Certain parts of a concrete structure may also be subjected to physical wear and tear. Parking garages, concrete roads, and breakwater wall are examples of structures subjected to repeated wear. The factors governing the permeability of concrete can be summarized as follows:

 The quality of materials, e.g., Cement, sand and aggregates  The quality of pore structure, based on w/c ratio, the admixtures used and the degree of hydration  The quality of interfacial transition zone  The degree of compaction  The cracking arising because of structural loading  The adequacy of curing It is also true that all concretes produced for different application may not be designed to be completely impermeable.

Products Selection and System

Hence it is very important that the selection of any construction product must be done with care and this is especially the case with waterproofing of concrete structures. Failure here has been the subject of numerous claims and litigation, something that no professional person wants to be the subject of. The problem is neatly summed up in a quote by John Ruskin (1819–1900): ―There is hardly anything in the world that some man can‘t make just a little worse and sell just a little cheaper, and the people who buy on price alone are this man‘s lawful prey‖ Multichem manufactures wide range of waterproofing systems which are classified into (a) Membrane Waterproofing (b) Waterproofing by crystallization. Under membrane waterproofing, an external layer is formed by way of application and water is not allowed to enter the structure. Multiguard A (Figure 2) is a two component, thixotropic, cementitious modified polymer coating with high adhesion to both steel and concrete, which falls into this category. It has high level of impermeability of more than 6.00 X 10–16 m/sec. Multiguard A forms a hard, highly alkaline coating with a degree of elasticity which not only protects the concrete, or other substrates, from the effects of aggressive acidic gases, moisture and chlorides, but also has greatly enhanced chemical resistance. There include: Rigid waterproofing of water tanks, sealing internal basement and cellar walls against dampness, protection of concrete structures in marine environment, external tanking of substructure concrete such as foundations and basement walls in new buildings.

Under Waterproofing by Crystallization, structure is waterproofed in-depth. The active ingredients create catalytic reaction generating billions of crystals to block cracks and capillaries in the concrete. Multichem manufactures (a) Multiguard In-depth TA/TB for surface application (b) Multiguard In-depth Premix, additive to be added to the concrete. Multiguard In-Depth (Figure 3) contains active waterproofing chemicals which create catalytic reaction when in contact with moisture, and cementitious products in the concrete, generating insoluble crystalline complexes which seal the capillaries tracks, pores and minor shrinkage cracks. They penetrate even against strong hydrostatic pressure, becoming an integral part of the concrete. As the reaction is catalytic in nature the waterproofing chemicals remain active for the life of the structure, permanently sealing it from water and waterborne chemicals penetration. The crystals continue to grow as long as moisture is present, often reaching several feet in length. Once moisture is removed, the chemicals remain dormant in the concrete, ready to be reactivated by water even years later if new non-structural cracks (which are <0.4mm) develop through natural settling or other factors.

Multiguard In-Depth Premix (MIP) (Figure 1) is designed to enhance by effectively waterproofing the concrete and reducing the shrinkage cracks. This provides a cost effective solution to membrane systems while increasing concrete‘s durability. Multiguard In-Depth Premix is added to fresh concrete easily at the batch plant or directly into ready mix trucks. It works to continuously prevent moisture from penetrating through the Concrete by creating a chemical reaction within the pores and capillaries to enhance the hydration process of the cement component within the concrete. As an additive for concrete, the Multiguard In-Depth Premix (MIP) will promote additional CSH crystals to grow within the concrete utilizing the concretes own natural hydration process to reduce the permeability of the concrete. The increased hydration process also allows for an increased ability for the concrete to self- heal micro cracking upon the presence of moisture. Multiguard In-depth systems are recommended for the following:

 Swimming pools  Tunnels and subway systems  Parking garages  All below grade concrete foundations  Rooftops  Dry vaults  Water towers and water reservoirs  Marine structures  Pipes  Bridge decks  Concrete walls and floor  Sewage and water treatment plants

Conclusion

It is important to choose right products and system to achieve a durable and impermeable concrete structure which can last more than its anticipated life. It is important to consider that all products are not the same although most of the datasheets look alike. In a market where the offer often creates confusion about the real quality of the products, it is important to remember that waterproofing accounts for less than 1% of the total budget foreseen for the building, but 75% of possible damages to the same building could be caused by incorrect waterproofing products and their short term durability.

Sealants In Concrete Pavements, Roads, Highways, Airfields and Building Construction

Mr. Dinesh Chavan, Sr. Manager-R&D, Choksey Chemicals P. Ltd, Mumbai.

A sealant is a viscous material that changes state to become rubber like compound, once applied, and is used to prevent the penetration of air, gas, noise, dust or liquid from one location through a barrier into another. Typically, sealants are used to close small openings that are difficult to seal with other materials, such as concrete, drywall, etc. Desirable properties of sealants include insolubility, corrosion resistance, and adhesion. Uses of sealants vary widely and sealants are used in many industries, such as construction, automotive and aerospace.

As we know that concrete structures are provided with joints and these joints are to be sealed with an Elastomeric Sealant according to its durability.

The sealants should be in either Thermoplastic or Thermosetting in nature depending upon the specification provided.

Polysulphide sealants are the best sealants to be used for joint sealing. Moreover the performance and durability of sealant always depend on the quality of sealants or some times on the design of the joint. Proper joint design and best quality sealant are needed for obtaining longer durability.

Why Joints are Required or Needed?

Concrete is a rigid material in nature with low flexural strength made up of inorganic binder cement, sand, gravel and water.

Concrete always changes its plane due to atmospheric conditions. Carbonation may take place and the overall effect may be contraction because of its drying and shrinkage. Expansion and contraction may occur due to change in cyclic effects or change in environmental conditions like humidity and temperature or the extra load on to cracking.

Joints are provided in the concrete to prevent development of extra stresses in the concrete structures which lead to expansion and contraction due to moisture changes, temperature variation, etc or loads and vibrations.

If the contraction movements, both permanent and transient of concrete units are more than it leads to cracking. Sealant accommodates these movements in concrete without loss of integrity in concrete structure.

Why Joint Sealing is Needed?

Considering the possibility of expansion and contraction & construction joints in the concrete structure, gap (expansion joints), which is usually to be sealed in order to prevent passage of gases, liquids, solids or other undesired substances in to the gap or through them.

In building structures, to protect a gap is very important to prevent the entry of wind and rainwater in to the gaps or openings. In case of water retaining structures, e.g. tanks, dams, canals, pipes, etc. joints are required to be sealed to prevent the loss of water due to leakage.

In case of roads or bridges, which are exposed to extreme weather, the concrete itself must be protected against the damage from all the possibilities of water at the joints openings. The solid material must be prevented from falling and collecting in the open joints if so the joints cannot contract freely later. If it occurs then high stress may be generated and can damage the concrete structure.

In case of highways the joints are needed to be strengthened and sealed to prevent the damage from Heavy traffic. Hence, the function of a sealant is to restrict the entry of water, solids, gases and to protect the concrete structure from them.

The main function of sealant is to improve thermal, absorption of the vibrations and prevent unwanted matter collected in the joints. The sealant must work as its prime function when it is subjected to repeated contraction and expansions as the joint opens and closes constantly while exposed to the weather conditions.

How to Design the Joint and the Types of Joints?

The working of the joint sealants depends on the movement to be accommodated at the joint, on the shape of the joint and the physical properties of the sealant. The location and the width of the joints that requires the sealing can only be specified when a sealant is available which will take the required movements and joint shape, or the concrete structure must be redesigned to reduce the movements at the joints.

The type of sealant available must meet the requirement of joint design and shape.

Design should be as per the appropriate standards like ASTM, BS and IS.

The source of the movements and the nature of movements for both long and short duration must be considered. The experience and the judgment play an important role in designing the joints which functions satisfactory.

Factors to be considered while Designing Joints

1. The joints between two concrete units may take the total movements of both units. 2. The movement of the end of a unit depends on its effective length 3. The actual service temperature of the material being joined. 4. When different types of material are joined together and having different surface temperature then the appropriate Linear coefficient thermal expansion of each material must be considered while calculating the joint movements. 5. In case of butt joints the movements to which sealant can properly respond is at correct angle to the joint faces. The joint must be taken into account where such comparisons and deflection occurring is very large. 6. The movement capability factor of a particular sealant must be taken for calculation. The sealant manufacturer can provide the movement capability factor for a particular sealant.

Movement Calculation

Calculation of section and spacing of joints

The calculation of section and spacing joints is complex, because there are many factors. There are several standard methods of calculation to simplify the procedures, which appears in publications such as those of the Building Research Establishments and the British Cement Associations. The methods differs basically in the compromises or assumptions made. Summary of the Joint Design Procedure

1. Calculate the Maximum potential movement in the structure from all causes. 2. Decide the location of the movement joint. 3. Calculate the maximum movement at each joint. 4. Select a possible sealant, and, from its MAF, calculate minimum theoretical joint width. 5. Increase the value obtained in step 4 by applying manufacturing and erection deviation and arrive thereby at the minimum design joint width. Allow for an appropriate depth of sealant, and for back up material. 6. If the result of step 5 gives a joint width which is too wide for aesthetic, economic or technical reasons, go back to step 4 and recalculate with an alternative sealant of higher MAF. 7. If the problem still appears insoluble, go back to step 2 and recalculate on the basis of installing more joints at smaller intervals. 8. Ensure the final result is consistent with nature and quality of the joint surface likely to be produced in the given building materials.

Movement Accommodation Factor (MAF)

Most of the sealant manufactures assign a movement accommodation factor (MAF) to each of their products to provide a value for the calculation of joint dimensions. But so far there is no universal definition for this factor.

The movement accommodation factor means the total movement range between the maximum compression and the maximum extension that a sealant can accommodate. It is expressed as a % of the minimum design joint width.

All construction materials changes in size as temperature changes. The amounts by which the dimensions of materials will change are calculated by using their linear coefficient of expansion in the expression.

Change = Length of span X Linear coefficient of expansion X temperature differential.

The Minimum Joint Width is then calculated by,

Wt = M X 100 MAF Where M= total expected movement

For Example (Figure 1)

M = 4mm

MAF = 25% then

Wt = 4 X 100 = 16 mm

25 Thus on the basis of this calculation, the sealant appears to be working to its maximum rated capacity of 25% if the joint is 16mm wide.

However, in practice, while the joint may have appeared on the drawing at 16mm, the joint may be sealed when thermal expansion has given rise to, for example, 2.5mm. of movement resulting in a reduction of the actual joint width from 16mm to 13.5mm. This joint could then cool and be subjected to the full 4mm movement used as a design base. Thus the joint could open from 13.5 to 17.5mm.

But the joint was sealed at a width of 13.5mm.Thus the extension to which the sealant has been subjected is not 25%

but

4 X 100 =29.6 %

13.5

On the original basis of 25% MAF, the sealant in this example has been over extended by

29.6-25/= 14.8%

25

This problem may be overcome by always calculating the joint width from the worst-case configuration, which assumes that the joint is at its minimum width. This is achieved by a modification to the equation used above. Using the same example as for Figure 1, the modification is illustrated in Figure 2

Wt = 4 X 100 + 4 = 20 mm

25

Thus if joint closes by 2.5mm before sealing and is then subjected to the full 4mm movement, the values become

Joint sealed at 17.5mm

Joint sealed at 21.5mm

Total Movement = 4 mm

The sealant has been subjected to 4mm extension on an initial sealed width of 17.5mm,therefore the % movement is calculated as

4 X 100 = 22.8%

17.5

Thus the sealant is operating within its rated MAF.

Joint Depth Considerations

For most applications of sealants in butt movement joints, 5mm is considered to be the practical minimum sealant depth. For Elastomeric sealants the depth should be approximately half the joint width. This ratio is a rectangular section, and it represents apractical compromise between sealant depth and adequate bond area to the substrate to give minimum stress to the sealant resulting from the movement.

For Elastomeric sealants, a sealant depth equal to the joint width is usual to ensure an adequate volume of sealant for optimum service life.

W= Width of Joint

M = Total Expected Movement

Figure 3 Width- to-depth ratio of a sealant

These typical width:depth ratios may be modified by manufactures for their sealants in particular applications, such as in trafficked joints or those subjected to sustained loading.

In such cases, sealant depth may be increased to provide a greater bonding with concrete surface. Reference should made to individual manufacturers literature in such cases,

The use of circular section (see Figure 4) back-up strips can modify the sealant profile from square or rectangular to one with a concave shape at the backup interface. The depth of the sealant in such a case should be considered to be that at the center of the curved face where sealant depth is least.

Joint depth should also be considered, from the point of view of sealant selection and the curing characteristics, as well as the requirements of the preferred joint profile. The suggested width to depth ratios of sealants in roads, bridges and airfields.

Selection of a Proper Sealant

If the sealants are to be performed well in the joints then it should have the following properties:

1. It must be an impermeable material. 2. It must accommodate the movement and the degree of movements occurring at the joint by deformation. 3. It should be capable of accommodating the movement for cyclic changes like temperature, moisture, vibrations etc. 4. It should have strong adhesion with the joint faces and there should not be any peeling at the corners when there is a deflection of joints. 5. Should have a good impact without cohesion failure, must resist the load, stress due to compression, tension and impact. 6. Must resist flow due to gravity.

7. Should have a good flexibility at all service temperatures. 8. It should be durable. It should not adversely affected by aging, weathering, freezing of water, light, water vapor, growth of the fungus and human damage. 9. It should have good fire resistance and fuel resistance. 10. Should have a partial reparability. 11. Low maintenance cost.

Types of Sealants

1) Butyl Sealants

These are the materials which form a surface skin after application, thereby protecting the main body of material underneath. They are commonly referred as mastics.

These are useful in the joints where very little movements are expected.

2) Bitumen and Rubber/Bitumen-based Sealants

These are Thermoplastic in nature and retain the degree of flexibility. Typical application are in roofing, water-retaining structures, and areas where compatibility with bitumen materials are desirable. 3) Acrylic Sealants

Basically two types of acrylic resin sealants are in common usage. Solvent base and water base. Solvent-based material is thermoplastic in nature. They are used externally. Water based sealants are widely used on corners of windows, doors, internally.

4) Flexible Epoxide Sealants

They are based on Epoxy resins, and varying degrees of flexibility are available by addition of other polymers or extenders.

These are normally available in multi-component products, when mixed together, it cures at ambient temperature though they have good degree of flexibility, becomes rigid at low temperature.

5) Polysulphide Sealants

These are available in one or two component systems.

The single part materials cure on exposure to moisture. Slow cure is generally expected for these sealants. They are elastic-plastic in nature‘s BS 5215 refers to these materials.

Two part Polysulphide requires on site mixing and cures chemically. These are available in Gun grade BS 4254 and pouring grade BS5212. Polysulphide are widely used in construction/expansion joints of pavements and buildings.

6) Polyurethane Sealants

This is also available in one or two component system. Available in both Gun and Pouring grade.

One part is moisture curing and used in building constructions. Two part sealants are chemically cured and can be used in trafficked joints (BS5212). Pitch or tar modified polyurethane sealants are also available.

7) Silicone Sealants

Available in one-component system follows BS5889.Can be used for interior purpose.

Two component silicone sealants are used for glass insulation.

8) Hot-poured Sealants

These comprise bitumen, rubber/bitumen and pitch/polymer combinations. They are primarily used in road pavement joints, subways and water retaining structures.

Requirements to Seal the Joints

For effective sealants field performance, the following points are very important.

1. Selection of correct sealant 2. Calculation of correct width to depth ratio. 3. Proper cleaning of the joint faces. 4. Through details on the joints. 5. Suitable primer depending upon the surface. 6. Use of non-impregnated backup material. 7. Provision of Bond breaker 8. Suitable application equipment and techniques. 9. Qualified applicator 10. Adequate field inspection.

Specification of Sealants

A quality sealant must comply with international standards. Only British STDs are mentioned.

Concrete Road/Highways, BS 5212 (1990) Bridges, BS 4254 (1983) Airfields, BS 5212 (1990)

Normal Civil construction, BS 4254 (BS1983)

Back up Materials

Back up materials shall be compatible with sealants. It must be resilient in nature. Materials impregnated with oil or bitumen shall not be used.

Polyethylene-closed cell foam, polyurethane-closed cellfoam, sponge rubber-closed cell, neoprene foamed rod, pre-formed gasket. The back up material shall be used in the joints to adjust width to depth ratio as recommended.

Bond Breaker

Bond breaker can be a polyethylene tape. The bond breaker tape shall be placed over the back up material. It is to avoid third surface bonding of the sealants.

Primer

The primer to be used as per the manufacturers recommendations. Primer for porous and Non-porous substrate should be separate. It is to be applied in two coats.

Masking Tape

It should be self-adhesive polyethylene. Tape is to be applied on the joint surfaces to protect joint edges from being spoilt by sealants material while application. Tape must be removed after application of sealant.

Solvents

Solvents are used for equipment cleaning. Generally Xylene, toluene are used for cleaning immediately after the use.

Storage of Material

Store the material as per the supplier‘s recommendations. Methods of Applications of Sealants

Hand Mixed Sealants

Machine Mixed sealants

Hand Mixed Sealant Mixing

Hands mixed sealants are supplied in two parts that consist of base component and another is hardener that is curing agent.

Supplied in Part I and Part II. Each pack is packed in proportionate ratio of mixing.

Mixing should be done as per the ratio suggested by the manufacturer. Mixing can be done by spatula/ rod/ wooden bat. For proper and homogeneous mixing efficient mixing can be accomplished by means of hand held power drill motor at RPM around 150 to provide adequate shearing action.

Mechanised Sealant Mixing

It is an automatic machine used for application of high volume. The equipment is designed to deliver the two fluid component materials in proportionate a portable mixer head through suitable flexible hoses by means of a positive displacement. The mixed material flows at a fixed pressure into the joints and self levels itself.

Application- sealing of the joints

1. Examination of the Joints The contractor should examine the joint size and condition of all joints and should reports all technical/practical difficulties which are not acceptable to the main contractors. The joints shall not be wet. 2. Cleaning of Joints Faces The joint faces should be cleaned by wire brush and dust to be removed thoroughly. If there is oil then it has to be cleaned by xylene or toluene. 3. Installation of Back Up Material and Bond Breaker The back up material and bond breaker shall be placed in the joints to allow the placement of the sealant to the desired depth, the surface of which should be recessed by not less than 3mm below the pavement surface. 4. Priming Apply primer in two coats as recommended by the manufacturers. Avoid brushing on the bond breaker tape. Allow the primer to dry as per the specification. 5. Apply the masking tape on the edges of the both the joint faces. Tape shall be removed immediately after the tooling. 6. Sealant Pouring Fill the sealant in the ready joint by hand or machine. Use spatula for filling in to joints Fill some extra material and then do the tooling by a knife blade and pull down the level of sealant surface. After tooling remove the masking tape. The material will self leveled. 7. Curing of Sealant Allow the sealant to cure as per the manufacturers recommended specification before starting the any other operation. 8. Cleaning of Tools Clean the tools and equipment immediately after the application by solvents such as xylene or toluene.

ERO-leakage Concrete Tunnels for Durability

Dr Anil K Kar, Chairman, Engineering Services International, Salt Lake City, Kolkata

Introduction

Conventional concrete, which can be considered to be an artificial rock, is not intrinsically waterproof. It absorbs water. The rate of absorption depends upon many factors, including the porosity of concrete. In addition, excessive contents of water-soluble alkalis in cement (as in the case of Indian cements of recent periods) can make concrete highly absorbent1-4. Today‘s concrete structures, compared to concrete structures of earlier decades, also suffer from higher thermal and shrinkagestresses and the resulting cracks1-5. The result: water retaining structures, e.g., tunnels, subways, basements, etc. are characterized by water seepage and leakage unless such structures will be effectively waterproofed.

In the case of tunnels and other water retaining structures, in addition to the seepage of water due to the development of thermal and shrinkage cracks or due to porosity in concrete, waterleakages may also occur at expansion joints, construction joints, honeycomb areas, and isolated locations of defects and discontinuities as at locations of inserts and embedments. In addition to running water leakages through these locations of defects or planned structural separations, there can be minor sweating or dampness of the surface. This sweating or dampness is generally influenced by the general porosity or perviousness of concrete.

Besides general porousness or permeability, local defects or discontinuities, and besides the existence of planned structural gaps (expansion joints), the waterhead outside the structure greatly influences the rate of water leakage into underground structures. Thus, there will be many tunnels which may exhibit little or no water leakages during the dry season whereas the same tunnels may show profuse water leakages during the wet season of the year or when there will be flooding of grounds surrounding the tunnels.

Water leakages or seepages through a structure can go much beyond being an architectural nuisance or an operational inconvenience. The leakages may prevent the use of the facility. The leakages may also damage equipment and systems inside tunnels and other underground facilities.

In addition to ungainly sights, operational difficulties and damages to contents, etc., waterleakages, seepages and dampness adversely affect the durability of tunnels and other concrete structures, as even minor dampness can lead to an early ruination of the structure by accelerating the process of corrosion in rebars and thereby inviting conditions of distress in the structure.

The Essence of Surface Protection

Kar1-14highlighted the problem of early decay and distress in concrete structures that could be encouraged by the dampness in concrete or even by the exposure of the concrete structure to the general environment. In most cases of concrete structures, it is corrosion in reinforcing bars and prestressing elements, that leads to conditions of distress in such structures.

The Indian standard IS 456:200015 recognizes the problem of early distress in concrete structures as well as the causes for such early distress when it states in its Clause 8, Durability of Concrete: ―One of the main characteristics influencing the durability of concrete is its permeability to the ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious substances.‖ The interior surfaces of tunnels are generally exposed to air and thus these surfaces, if not protected, will permit the ingress of oxygen and carbon dioxide. While the diffusion of carbon dioxide may lead to depassivation of reinforcing bars, making corrosion in such bars possible, the diffusion of oxygen into the structures will lead to corrosion in the rebars in the presence of the moist environment inside the structure.

As a solution to the problem of early distress, Kar1-14recommended the prevention of the ingress of water into or flow of water through structural elements and the protection of all structural surfaces, exposed to either air or intermittently to water and air. The dual goal was to be achieved by the provision of waterproofing treatments on all exposed surfaces of structures. The Indian Standard15followed suit when it wrote in its Clause 8: ―The life of the structure can be lengthened by providing extra cover to steel, by chamfering the corners or by using circular cross-section or by using surface coatings which prevent or reduce the ingress of water, carbon dioxide or aggressive chemicals.‖

Kar12,13 explained why, among the four options recommended in IS 456:200015, the provision of surface coatings or other surface treatments to prevent the ingress or passage of water, and to prevent or reduce the diffusion of carbon dioxide and oxygen or permeation of aggressive chemicals, was the only viable

option.

Thus, a concrete structure needs to be waterproof and damp-proof. The mere arresting of running water leakages through isolated spots, like construction joints, as is the case when grouting methods are employed, may not make water retaining structures of concrete sufficiently durable. In other words, in order that a concrete structure may be durable, it, like a steel structure, needs to have surface protection. Dense concrete will help, but it may not be sufficient to make today‘s concrete structures reasonably durable.

In order to make concrete structures durable, the exposed surfaces (i.e. all of inside surfaces of the tunnel) should be given a post-construction surface treatment to create an impermeable surface region that would, besides preventing water leakages and seepages, prevent the easy ingress of air (moisture, carbon dioxide, oxygen) into the structure. This is the essence of surface protection of concrete tunnels and other structures, and the surface protection is best achieved through the provision of waterproofing treatments on the surface of concrete structures. Though the most important objective of the provision of surface protection systems is to prevent or inhibit corrosion in rebars and prestressing elements of steel, it is not the recommendation of the writer to provide any surface treatment to such rebars or prestressing elements.

It need be emphasized in the context of durability of concrete structures that the mere absence of any visible sign of water leakage through a structure is not a proof of its being a waterproof structure. The development of conditions of distress in the columns in the middle of the tunnel (away from the leaking walls) of Metro Railway, Kolkata is an example.

A false impression of water tightness of a water retaining structure can also be created when the rate of evaporation of water from the structure is greater than the rate of ingress of water into the structure.

It must be recognized that most of the damages due to corrosion in rebars and prestressing elements inside concrete structures, adversely affecting the durability of such structures, will take place if there will be a moist environment inside the structure and air will enter into the structures15. in the absence of air even a lot of water inside a concrete structure may not cause much damage. This is exemplified in the virtual absence of any condition of distress in foundation structures of concrete, unless the ground water will be patently harmful for concrete.

Thus, whereas the absence of a surface protection system on the visible surfaces of a concrete tunnel is likely to invite conditions of distress early, the absence of any waterproofing system on the outer faces of the tunnel is not likely to cause any such problem in most of the cases.

It has thus become essential, specially in the case of today‘s concrete structures, which are built with cement, with very high C3S/C2S ratios and excessive amounts of water soluble alkalis1,2, and with today‘s high strength rebars with surface deformations1-5,11,16,17, that such structures be given surface protection (on faces exposed to the atmosphere) in the form of waterproofing treatments1-14. The provision of such a surface protection system will arrest the leakage of water on a long term basis. It will also help fulfill the second objective of the prevention of water seepage at the post-construction stage. Furthermore, it will prevent or inhibit the ingress of carbon dioxide and oxygen. It may also prevent the ingress of chlorides and other aggressive chemicals. The process of corrosion in rebars and prestressing elements will thus be arrested or slowed down, leading to a lengthening of the life span of the tunnel structure and prevention of damages to other systems housed inside the tunnel.

Surface Protection for Tunnels and Other Water Retaining Structures

Against the prevailing practice of grouting for the purpose of arresting water leakages in underground concrete structures, Engineering Services International of Salt Lake City, Kolkata–700 064 pioneered in 1983 the concept and technique of waterproofing of tunnels and other underground structures with surface treatment (Figures. 1 and 2). According to this technique, no grouting or injection is strictly necessary for arresting running water leakages and for making the treated surface bone dry.

In this scheme of surface treatment for underground structures, local treatments, instead of grouting, are provided on the surface to arrest running water leakages at construction joints honeycomb areas and at isolated locations. This is followed by the provision of a continuous waterproofing treatment on the entire surface in the interior of the tunnel. In the case of tunnels and other underground structures, the surface treatment for waterproofing is effectively provided in the form of a two-layer plaster.

It was observed in the case of the tunnels of Metro Railway in Kolkata, the Pedestrian Subway at Tollygunge, Kolkata and at many other sites with structures beneath the ground that when grouting or other methods of waterproofing had failed to prevent water leakages and seepages fully, the method of surface treatment with cementitious waterproofing compounds succeeded in making the concrete surface bone dry; thereby making the structures more durable.

A write-up on this technique of post-construction waterproofing treatment, with special reference to the surface protection to some difficult areas of the tunnel of Metro Rail

in Kolkata can be found in Ref. 6. This paper describes the technique of waterproofing treatment for the prevention of water leakage through reinforced concrete tunnels, similar to those of the tunnels of Metro Railway, Kolkata, the Pedestrian Subways at Tollygunge Station for Metro Rail, at Sealdah Station for Eastern Railway, at Kolkata Station for Eastern Railway, etc. The unique technique of surface treatment method, employed in the years 2000–01, to make the Pedestrian Subway at Sealdah, Kolkata, completely watertight (except at the expansion joints) and to simultaneously add years to the life of the structure, was developed and applied for the first time in 1983 to arrest water leakage through certain locations of the Metro Railway tunnels in Kolkata. The waterproofing treatments, provided on selected areas of the Metro Rail tunnels in 1983 and later in other areas in 1995, remain effective till date as a testimony to the long term effectiveness and durability of the particular cement-based surface protection system for underground structures.

In its coverage, this paper goes beyond the traditional concept of controlling or containing large volume seepage of water. It covers surface protection of concrete to create a bone dry condition inside tunnels. The surface protection, as opposed to grouting, helps to make concrete structures durable.

The transformation of leaky tunnels into zero-leakage structures is described in this paper with special reference to the Pedestrian Subway at Sealdah Rail Station, Kolkata.

The contents of this paper, though specially related to tunnels, are equally applicable to water reservoirs and underground facilities, like basements, machine pits, etc. The treated tunnels may be used as conduits for liquid, or these may carry people, traffic, materials or other systems.

Concept of Surface Treatment to Under–ground Structures

The transformation of a pervious underground structure into an impervious water retaining structure requires that a continuum with waterproofing materials be provided to the entire inner or outer surface of the structure. It is explained why it is so.

Grouting No Help

Grouting or injection of chemicals, commonly adopted techniques for arresting water leakages in underground structures, can help arrest localized running water leakages, termed as point leaks. It can minimize, but generally not fully control, water leakages at construction joints and at honeycombs, unless these joints and honeycomb areas will also be provided with surface treatment in one form or another.

It is recognized that particulate materials cannot be injected into a mass of concrete unless pores inside the concrete would be continuous and the size of the pores would be at least three times the size of the particles in the injection material. Cement cannot thus be injected into a concrete structure except at discontinuities, e.g., at cracks, defective construction joints, honeycombs, etc. As a result, grouting of cement, with or without admixtures, can at best seal cracks and honeycombs. It cannot generally arrest water leakages at all the locations of a large concrete structure, as in the case of a tunnel. It cannot prevent general seepage. It cannot prevent dampness and it cannot provide protection against the elements in the atmosphere.

Grouting can at best help to arrest water leakages at isolated locations. In the absence of a blanket coverage of the entire surface (either outer or inner) of the tunnel with an effective waterproof system, leakages will keep sprouting at new locations in a concrete structure as existing leakages will be arrested.

Grouting is not thus the surest way to make concrete tunnels waterproof.

Justification for a Surface Treatment

When the hull of a boat or a ship springs a leak, nobody injects any material into the leakage area. Instead, it is plugged or a piece of a plate is attached to the hull, covering the leakage area or the tear.

The hull of a boat or that of a ship is a water retaining structure. So is a tunnel.

The concept of arresting water leakages through a boat hull or a ship hull can be applied in the case of a concrete tunnel with water leakages.

Furthermore, common sense would suggest that the isolated treatment through grouting cannot provide a continuous waterproofing barrier, let alone a barrier to the ingress of carbon dioxide and oxygen into a concrete structure. A continuum with such properties is necessary1-16to make the surface of a tunnel impervious and the structure durable.

Justification for Providing Treatment on Interior Surfaces of Tunnels

As the waterproofing treatment must be in the form of a continuum, as it is generally not practical to provide the continuous treatment on the outer surfaces of tunnels and other underground structures, and as it is generally not practical to attend to any damages to any waterproofing treatment on the outer surfaces of underground structures, the only option is to provide the waterproofing treatment to the

interior surfaces of tunnels and other underground structures in the form of a continuum. The waterproofing treatment on the interior surfaces would provide the additional protection against the ingress of atmospheric oxygen and carbon dioxide, and possible carbonation and depletion of the pH level in the pore water of concrete. It will be so because the waterproofing system, with a continuous medium on the exposed (inner) surfaces of underground structures, will be relatively impervious to the entry of carbon dioxide and oxygen into the structure.

The provision of a waterproofing treatment on the interior surfaces of a concrete tunnel structure will thus prevent not only water leakages and the wash-out of the products of cement hydration and other components of concrete but also early corrosion in reinforcing bars. The treatment will consequently enhance the durability of tunnel structures of concrete.

Effectiveness of Surface Treatment The Pedestrian Subway at Sealdah, Kolkata, following the provision of the surface waterproofing treatment on the inside of the tunnel in 2000–01, is recognized as a zero-leakage tunnel. The tunnel is still bone dry after eight monsoons, except at an expansion joint, which, this writer believes, should not have been provided. Surface treatment has provided the tunnel at Kolkata Station too with a zero leakage surface during the 2007 and 2008 monsoons. The surface treatments, which were developed by Engineering Services International in 1983 as a part of its PERMAKAR Technology, and which was provided at select areas of the Metro Rail tunnel in Kolkata in 1983 and in 1995, still remain effective as before, whereas the same tunnel, after extensive and expensive grouting with cement as well as cement, admixed with chemicals, or isocyanate chemicals, over the last two and a half decades, still suffer from a lot of water leakage at many locations. In the absence of a surface protection system in most of its areas, the tunnel (20–30 years old) required repairs, even in structural elements/surfaces which had no visible signs of water leakage.

The fact that grouting methods of waterproofing, without the aid of surface treatments, may not be fully successful even in the stated task of waterproofing, is exemplified in the case of the Metro Rail tunnel in Kolkata and in the cases of innumerable other tunnels and other underground structures all over the country. It is recorded in the project report on Construction of Pedestrian Subway Opposite

Tollygunge Metro Rly Stn. in Kolkata : ―However, at temporary bored pile locations (total 8 locations), seepage of the leakage could not be stopped in the main subway with cement pressure grouting or Non-Shrinkable, Pumpable, Groutable (NSPG) chemicals due to which ‗PERMAKAR‘ Technology (surface layer) treatment was adopted and seepage/leakage was arrested completely to achieve ‗bone dry‘ condition.‖

The consistently successful performance of PERMAKAR Technology in the task of arresting water leakages through the tunnels of Metro Rail and Eastern Rail at different stations and through innumerable basements, machine pits, lift pits and underground water reservoirs stand testimony to the effectiveness of the surface treatment method in the task of waterproofing of concrete tunnels. As explained earlier, the surface protection system has also the advantage of making concrete tunnels and other structures durable, whereas waterproofing by grouting fails to satisfy the requirements set for Durability of Concrete in Clause 8 of IS 456:200015.

Durability of Surface Treatment

Surface waterproofing treatments (Figures 1 and 2) provide a continuous barrier, which is essential for making underground structures waterproof and durable. The concept was pioneered by Engineering Services International in 1983. It has been observed in the case of the Metro Railway tunnels in Kolkata that surface waterproofing treatments, provided by the said firm twenty–five years ago in 1983 and in later years, are still fully effective. Similar observations were made on treatments provided at countless other establishments. Basic reasons for the durability of the PERMAKAR surface waterproofing system are : (1) the PERMAKAR waterproofing system is cement based and thus compatible with the basic material of construction of concrete tunnels and other underground structures, (2) cement is generally durable in water, and (3) the surface treatment itself adds years to the life of the structure by preventing the ingress of carbon dioxide and oxygen, the facilitator and the agent of corrosion. All of these add up to make PERMAKAR 3 surface waterproofing treatment durable. Specifications

As mentioned earlier, there are a few typical treatments for the waterproofing of tunnels and other water retaining structures. A set of standard specifications, the implementation of which led to the successful protection of tunnels, water reservoirs, basements, machine pits and other underground structures, can be found in Appendix-I to this paper.

Pedestrian Subway at Sealdah

The Pedestrian Subway at Sealdah Station (Figure 3) is constructed of reinforced concrete. It has seven pieces of concrete boxes along the length of the tunnel. There is an additional exit structure (taxiway), in the transverse direction. Each of the five intermediate tunnel segments (16.4 metres wide) has three bays. The two side bays are separated from the 6.0 metre wide central bay by rows of circular columns. Besides the columns between the central bay and the two side bays, there are the exterior walls which support the floor slab and the roof slab.

The base and roof slabs were designed as flat slabs even though the slabs, with just four columns in each box, did not quite qualify as flat slabs. The columns were away from the ends of the boxes, i.e. away from the expansion joints.The cantilevered slabs yielded appreciably at the column strips, leading to the development of visible cracks along the long axis of the tunnel at the cantilever regions as the reinforcement became inadequate.

The surface treatment was found to be sufficient in preventing any water leakage along the cracks.

Figure 3 is a view of the central bay with shop fronts at the two side bays. The entry and exit segments (3 numbers, including the one at the taxiway) of the tunnel are single bay structures with wide stairs.

The length of the seven-segment subway, excepting the taxiway structure, is about 138.0 metres, and the height from the floor to the ceiling is 3.0 metres.

The interior of the subway, with its long and wide body, finished with plaster (as a part of the basic waterproofing system), and punctuated by circular columns, with tapered and circular renderings at the top, has an aesthetic appeal (Figure 3).

The tunnel was constructed according to the cut-and-cover method. A steel framework, covering the entire extent of the trench, was used to facilitate construction of the concrete structure. The steel framework was dismantled and removed following the construction of the tunnel structure. stubs of steel wide flange sections (H-sections), as remnants of this temporary framework, were, however, left embedded in concrete slabs at the floor and at the roof. The locations of these steel elements, wherever these penetrated the floor slab and the roof slab, became additional sources of troublesome water leakage. Similarly, steel rods, used to support stays/struts for the formwork for concreting the two walls, were left protruding from the floor. The penetration points (in concrete) of these steel rods led to water leakage (until these were treated as a part of the waterproofing treatment) from the floor. Initial Observations

Initially, the elements of the Pedestrian Subway at Sealdah, as in most other cases of underground structures in environment with high water tables, had water leakages along the horizontal construction joints between different pours of concrete (e.g., at the interface of floor and side walls, different pours/levels of the walls, and at the interface of walls and the top slab), at isolated locations (point leaks) on the floor, walls and the ceiling, at a few honeycomb areas, along innumerable steel bar inserts (used to support formwork for the construction of walls) in the floor slab, at the locations of ends of steel H- sections (temporarily used to support side shorings, floor and ceiling) at the floor and the ceiling, and at the expansion joints between different segments of the tunnel structure.

Waterproofing

The initial tender requirements had called for the post-construction treatment for arresting water leakages at isolated points (point leaks) (Figures 1 and 2) and along horizontal construction joints (Figure 2). It was also required to provide a waterproofing treatment (two layer plaster system in Figure 1) on the entire interior surface of the tunnel, i.e. on the floor, at walls and at the ceiling. The waterproofing treatment would thus be provided from inside the tunnel. The objective was to provide a continuum with waterproofing materials to prevent the flow of ground water into the interior of the tunnel.This waterproof surface would additionally prevent or minimize the entry of atmospheric carbon dioxide and oxygen into the structural elements of the tunnel.

There was no provision for the treatment of expansion joints as here were provisions for the provision of plastic water bars at such joints by the contractor who was engaged for the construction of the tunnel.

Subsequent to the appointment of the writer‘s firm for the task of waterproofing treatment, steps were taken also to provide special treatments at (a) ends of H-sections at the floor and at the ceiling, (b) at base of the protruding steel rods at the floor, (c) at honeycomb areas and (d) at expansion joints such that the tunnel structure would be fully water-tight and dry.

The Treatment

Seven types of special treatments were provided from inside the box structure of the Pedestrian Subway at Sealdah to make it waterproof and thereby add years to the life of the structure a) by preventing the flow of water through concrete

(b) by preventing the ingress of carbon dioxide and oxygen into the structure.

The seven treatments were:

1) arresting running water leakages as in point leaks (Figure 2A)

2) treating full lengths of all the construction joints (Figure 2B) as much of the construction joints had running water leakages

3) treatment to honeycomb areas (Figure 2C)

4) bar insert locations on the floor

5) interfaces of steel H-sections and concrete at the floor and at the ceiling

6) surface treatment (Figure 1) to the entire interior surface of the tunnel

7) expansion joints between segments of the tunnel.

In the case of treatment at bases of protruding steel rods in the floor, the protruding rods were sawed off and the base locations were treated in the same way with quick-setting cementing compounds as the area of a point leak is treated. The honeycomb areas also were treated in the same manner, except that no groove was made by chipping off concrete at the affected area. The details of treatments for point leaks, construction joints, honeycombs and surface treatments are given in Figures. 1 and 2.

Portland slag cement was used in providing the waterproofing treatment to all interior surfaces of the pedestrian Subway of Sealdah even though ordinary portland cement (OPC) was used equally effectively by the writer‘s firm in many other projects.

Point Leak

The areas of point leak (Figure 2A) were plugged with cement, admixed with a quick-setting cementitious waterproofing compound and a liquid silica compound that hastens the setting of cement. A small groove was cut at the location of each point leak. A cementitious chemical (a powder chemical) was mixed with cement in given proportions. A quick-setting paste was made by adding water, and the liquid silica compound was mixed with the paste. This resulted in a quicker-setting cementing compound with improved properties for plugging concrete holes. The resulting material was used to plug the grooves at the locations of the point leaks.

Construction Joint

The construction joints at bases and at tops of the walls (Figure 2B) and at junctions between different pours of concrete were treated to arrest running water leakage in the same way as it was done in the case of the point leakages, except that grooves were cut and plugged along the length of the construction joints. Waterproofing chemicals were similar to those which were used to arrest running water at areas of point leakages.

Honeycomb Areas

Prior to the provision of surface treatments, the honeycomb areas (Figure 2C), highly prone to water leakages, as are point leakage areas and construction joints, were provided with special treatments to arrest running or probable water leakages following techniques similar to those which were adopted in arresting water leakages at locations of point leaks and at construction joints, except that the surface concrete was not chiselled out as deep as in the case of areas at point leaks and at construction joints.

Bar Insert Locations

The bars, which were used only as an aid to facilitate construction and which had no place in the constructed tunnel, had their protruding portions sawed off and the surrounding areas were sealed as in the case of treating areas with point leakages.

Ends of Steel H-section

The ends of steel H-sections, or of other metal elements, as remnants of temporary work (or even if those would be permanent features at the faces of the structure), created special difficulties in arresting water leakages, for the reason that concrete, used in the construction of the tunnel did not bond strongly to steel. The situation called for special formulations. The treatment, provided at the locations of the H- sections of steel, was a combination of several treatments. The treatment was provided at the interface of concrete and steel. Finally, the surface was provided with the two layer surface treatment with cement and an octadecanoic acid based cementitious water– proofing compound, preceded by the application of a cement slurry, enriched with a co-polymer of acrylic-styrene as a means to improve the bond between the exposed surface of steel and the surface treatment.

Surface Treatment

The surface treatment (Figures 1 and 2) was provided in the form of a two-layer plaster. The first layer was a 6.0 mm thick plaster of a combination of an octadecanoic acid based cementitious waterproofing compound and cement in the weight ratio of 3:50. The 8.0 mm or 12.0 mm thick cover plaster was of cement: sand (1:2 to 1:3). Point leakages and other running water leakages at construction joints, honeycomb areas, inserts and expansion joints having been arrested, the purpose of the surface treatment was to ward off any future leakages of water and to provide a completely dry environment inside the tunnel. The provision of the surface treatment served the other purpose of preventing the ingress of carbon dioxide and oxygen into the structure.

Normally, the thickness of the cover plaster at ceilings and at walls is 8.0 mm whereas it is 12.0 mm on the floor. Similarly, the cement-sand ratio for the cover plaster and thickness of the first layer of octadecanoic acid based cementitious waterproofing compound and cement can be varied to meet specific requirements of individual cases of water retaining structures.

Tests at National Test House, Kolkata, according to the provisions of IS 2645:1975 and IS 2645:200318, have consistently shown that the surface treatment (even with smaller thicknesses of 4 or 5mm) for waterproofing with the octadecanoic acid based cementitious water– proofing compound of proprietary formulation is impermeable under a waterhead of 20.0 metres. The 5 mm thick waterproofing treatment with octadecanoic acid based cementitious waterproofing comp– ound, when tested also under a waterhead of 40.0 metres for 8.0 hours at National Test House, Kolkata, was found to be impermeable.

The provision of the cement-based surface treatment requires a good bond with the existing concrete surface.

Several options could be considered for an improved bond. These include (a) chiselling the entire surface (as opposed to the conventional practice of making occasional pock marks), (b) roughening by etching with acid, (c) roughening with water jets, and (d) the use of polymers. The second option was selected in the case of the work at the Pedestrian Subway at Sealdah. It is explained later in the paper. In the case of the subway at Kolkata Station, the surface was roughened by etching with acid in some areas whereas polymer was used to improve the bond between the structure and the waterproofing plaster in other areas. Expansion Joint

Expansion joints were provided in the construction of the tunnels of Metro Rail, Kolkata. After decades of trying, various techniques and material the leakages at the expansion joints are yet to be prevented totally. As a copy of the scheme, it was planned to provide similar expansion joints in constructing the tunnels of the Pedestrian Subway at Sealdah.

This writer has maintained that a) it is unnecessary to provide any expansion joints in concrete tunnels on consideration of the length of tunnels; any thermal or shrinkage strain or stress is independent of the length. b) the provision of expansion joints is tantamount to an admission of foundation sliding failure of tunnels c) the provision of expansion joints in concrete tunnels invites unnecessary (in view of item (a) above) problems of water leakages which may be difficult to arrest fully

The performance of the expansion joints in the tunnels of the Pedestrian Subway at Sealdah at different stages of treatment confirms the non-essentiality of the provision of any expansion joints in tunnels.

According to the original scheme of construction, the contractor, engaged for the construction of the tunnel, had provided rubber water bars at the expansion joints as it was used in the case of the tunnels of Metro Rail, Kolkata. It could be seen that there were gaps (even large pockets, between the water bars and the concrete underneath. The water bars, put in position at the time of concreting, could not prevent the leakage of water at the joints as, besides the large gaps between the water bars and the concrete, there could be no bond between concrete and the plastic elements of water bars.

The expansion joints, provided in the case of the pedestrian Subway at Sealdah, had variable widths up to 100mm. Even if expansion joints were required, no computation could have shown the need for such wide joints. The same mistake was committed in the case of the tunnel at Kolkata Station and the contractor, engaged for the treatment of the expansion joints, struggled for over a year without total success.

The expansion joints at the Pedestrian Subway at Sealdah called for various types of treatments.

The expansion joints at Sealdah were re-treated by caulking of leadwool at fine openings, preceded by the application of quick setting cementing compounds and epoxies (insensitive to water) at wide openings. As the contractor, engaged for the construction of the tunnel, had provided boards in the joints, the quick-setting cementing compounds were provided for a depth of about 50mm. Minor leakages persisted in three of the six joints. This leakage at the three joints was finally arrested by injecting cement- based non-shrinking crack sealing compound, admixed with a bonding agent of an acrylic-styrene based copolymer deeper into the joint. In effect, the joints were jammed with cementing materials. This made the expansion joints completely dry. As an additional level of protection, the three troublesome expansion joints were finally provided with a polysulphide sealant.

]The expansion joints in the tunnels of the Pedestrian Subway at Sealdah Station, Kolkata were essentially sealed with cementing compounds and there has not been any water leakage during the last eight monsoons, except minor leakages at one of the joints which was neither grouted nor provided with the polysulphide sealant, thereby confirming the reasonableness of the assumption that there is hardly any relative movement between neighbouring segments of tunnels that would require the provision of an expansion joint.

In another case, expansion Joints were provided at different locations on the Intake water tunnel for Unit I of the Singrauli Super Thermal Power Project of NTPC at Shaktinagar in UP, leading to profuse water leakages at the expansion joints. In the absence of any expansion joint, the Intake water tunnel for Unit II of SSTP did not suffer from similar problems.

Results of the Waterproofing Treatment

The Pedestrian Subway in front of the Sealdah Railway Station in Kolkata was waterproofed partly in the year 2000 and the rest during early 2001 in keeping with the progress of the construction of the tunnel. At the time of writing this paper, a part of the treatment has provided protection for nine monsoons. The remaining part of the treatment has given the protection through eight rainy seasons. Observations have revealed that similar waterproofing treatments, which were provided by the writer‘s firm in select locations inside the Metro Railway tunnels in Kolkata twentyfive years ago, remain effective even after these many years.

The tunnel structure of the Pedestrian Subway at Sealdah, unlike most tunnels where grouting techniques are employed for the purpose of waterproofing, has zero leakage following the surface waterproofing treatment, except minor leakages at one of the expansion joints, which was unnecessarily provided, and which had rubber water bars but which was neither grouted nor sealed with a sealant.

As the basic waterproofing treatment in the form of a surface plaster is impermeable to water, the treatment, besides preventing any water leakage through the tunnel structure, provides protection against the ingress of carbon dioxide and oxygen into the structure. The surface treatment in the form of a waterproofing system, with an octadecanoic acid based cementitious waterproofing compound, will thus make the tunnel structure durable. This is in stark contrast to the case of tunnels, where grouting, but not surface protection, is resorted to for the purpose of waterproofing. The seeping and damp surfaces of tunnels, lacking surface treatments, are without the benefits of surface protection and without any mechanism to prevent the ingress of carbon dioxide and oxygen. It is easier for reinforcing bars to corrode early inside such structures. The corrosion of reinforcing bars ultimately leads to the development of cracks in concrete structures and spalling of concrete therefrom.

The Metro Rail tunnels in Kolkata, which lack the presence of surface protection systems in most of its areas inside the tunnels, have already undergone repairs.

The Lessons

Several lessons can be drawn from the work of waterproofing of the Pedestrian Subway Box at Sealdah, Kolkata and similar other tunnels and underground structures. These are recorded in the following.

Expansion Joints

The maintenance of expansion joints in water retaining structures is a tough proposition. With proper detailing of the work of treatment, it is, however, possible to stop all leakages at expansion joints in underground structures. The writer‘s team waterproofed an expansion joint in the Metro Rail tunnel in the 1980‘s and all the joints in the Sealdah Subway on the assumption that there would not be any relative movement between neighbouring segments of the tunnels. It generally worked.

Towards the end of construction of the Subway at Kolkata Station, the project owners agreed with the writer and they did not provide expansion joints at certain locations where they had earlier planned to provide expansion joints. The absence of expansion joints did not cause any problem in the structure. As mentioned earlier, the total absence of expansion joints in the Intake Water Tunnel at Singrauli Super Thermal Power Project too did not lead to any problems.

A consideration of several factors suggests that it is not essential to provide expansion joints in underground structures. In fact, there is nothing that would suggest that an expansion joint must be provided if the length of a tunnel would exceed a certain limit. The lessons which can be drawn are:

1. It will be generally unnecessary to provide expansion joints in structures which are fully underground.

2. Expansion joints, provided in underground structures and requiring post-construction treatment, should best be treated as long after the construction as it will be practical so that the structure will have the time to experience as much of the initial shrinkage, if any, as will be possible before the application of the treatment at the joint; in effect, the expansion joint will act as one wide construction joint (of course, without the benefit of interconnecting rebars) and it will generally be sufficient to treat it as one. Of course, it would be desirable not to leave any segment unreinforced.

Ends of Steel H-sections

The ends of steel H-sections in the floor and roof slabs are not necessary elements of the structure. The steel sections are occasionally provided to facilitate construction. In the bargain, the interface of these steel sections and concrete provides vulnerable passages for the entry of water into the tunnel structure. Furthermore, corrosion in the exposed steel sections would lead to cracks in the surrounding concrete, which too would increase the possibility of water leakage. The interfaces between the foreign elements and concrete as well as the exposed surface of steel require innovative treatments, added time and cost for the provision of such treatments.

The lessons to be drawn are:

1. Non essential steel inserts through the floor and roof slabs or through any other part of the structure should be avoided, if possible.

2. Before concreting, reinforcing bars in slabs should be welded to steel sections, if such foreign elements will be provided.

3. As in the case of the expansion joints, the work of waterproofing of the ends of H-sections or other inserts should be done as late as possible so that concrete will have sufficient time for most of the final shrinkage, if any, to take place before the start of the work of waterproofing.

Protruding Steel Rods

The interface between concrete and protruding steel rods on the floors, used to provide support to the formwork for the construction of the walls, provide passages for water leakage. Steel inserts tend to create difficulties in the prevention of water leakage. This is due to the fact that cement/concrete does not bond well to steel. In the event such rods should still be provided, the rods should preferably be plain round bars instead of deformed bars, along the surface of which water flows more easily.

The lesson is

Steel rods, which are not essential elements of the structure, should best be avoided; if need be, the objective of preventing the slippage of stays for supporting wall shutterings can be met by providing small recesses in the floor slab.

Oil on Formwork

The use of inappropriate oil on formwork creates another problem if such oil will leave marks on the concrete. It is not only that the oil marks may stand in the way of proper wet curing of concrete, the oil marks, if not removed, will stand in the way of waterproofing or in the way of any further work of plastering, painting, fixing marble or tiles on the concrete surface. The lessons, which can be drawn, are:

1. Formwork with non-drying oil should not be permitted for concrete work.

2. Should any oil mark be visible on concrete on removal of formwork, it should be promptly removed by chiselling or with appropriate chemicals

Plastic Sheets

The greatest problem, faced during the work of waterproofing the Pedestrian Subway at Sealdah, was caused by thin plastic sheets of poor quality, which were used on the shuttering in the construction of the roof slab.

1. In many areas, the plastic sheets at the ceiling became invisible, being covered with a hardened paste of cement or cement and sand.

2. The plastic sheets were fused with the concrete; at numerous locations, the plastic sheets became deeply embedded inside concrete; it was not possible to remove such pieces of plastic, which were embedded inside the concrete.

3. The plastic sheets left behind a sheen (on the entire surface of the ceiling) of the same color as that of the plastic sheets; the sheen would prevent any bond between the waterproofing material and the ceiling; it would thus stand in the way of waterproofing or any other work at the ceiling unless the sheen would be removed.

The bright sheen of plastic stood in the way of speedy work. It required inordinately extra efforts to clean the surface of the ceiling. In spite of all efforts, plastic stood in the way of quality work as wherever plastic remained in position, embedded into concrete, the waterproofing plaster or any plaster would not bond well with the ceiling. Chiselling of the complete ceiling (not small isolated areas) was attempted but it was found to be not practical under the tight time schedule.High pressure water jet could be used to remove the plastic sheen and plastic which was not embedded into the concrete.

In the case of the Pedestrian Subway at Sealdah, muriatic acid was applied repeatedly and the ceiling was rubbed and washed with water between successive applications of acid.

The lesson that must be drawn is:

Under no circumstances thin plastic sheets should be permitted in the casting of concrete slabs; thicker plastic sheets will have a smaller chance of getting fused to concrete; the plastic should be fixed taut on the shuttering boards; better still, no plastic sheet should be used; instead only the joints between shuttering boards should be sealed. Experience shows that it is not at all difficult to make plywood boards non-sticking, as the senior writer‘s team has done on umpteen number of projects.

Etching of Surface for Improved Bond

For an improved bond with the substrate, the cement based waterproofing system or any other plaster work will require the substrate to have a rough surface, unless polymers would be used.

The conventional practice of roughening the surface is chiselling at isolated spots. This does not lead to much of an improvement in the surface texture as the improved area does not cover more than three to five per cent of the surface area.

Etching with muriatic acid provides an easy technique for improving the bond as it can help roughen the entire surface. This technique of etching the concrete surface with acid was resorted to in the case of the Pedestrian Subway at Sealdah. Several applications of muriatic acid, followed by scrubbing and washing after each application, made the surface of the concrete ceiling suitably rough. The vertical surfaces of the walls too required several applications of muriatic acid, whereas a single application of muriatic acid was sufficient in etching the floor.

The writer‘s team has successfully roughened several hundred thousand square metre of concrete surface with muriatic acid for waterproofing treatment with cement based materials.

The lessons learnt from the operations to roughen the surface with acid are:

1. unlike the floor, the ceiling and vertical surfaces of walls, etc. require repeated applications of muriatic acid and brushing/cleaning with water following each application of acid.

2. Due to acid fume, other operations on the leeward side inside the tunnel have to be suspended at the time of etching with muriatic acid; this may require time adjustments by workers of different trades.

Other Elements and Other Considerations

Following the waterproofing treatment, light fixtures were attached to the ceiling (near the column tops in Figure 3). this had the potential for puncturing the waterproofing treatment and inviting water leakage. However, because of large irregularities in the level of the ceiling, the cover plaster, as a part of the waterproofing treatment to the ceiling, was much thicker than the specified 8 mm (see item 8 in APPENDIX-I). As a result, there was no instance of water leakage through the ceiling of the Pedestrian Subway at Sealdah Station.

It is suggested that when the cover plaster (and also the waterproofing treatment in some cases) will be punctured, the hole be filled up with appropriate waterproofing materials before inserting the bolts.

There will be instances of anchor/embedment plates for attaching/supporting heavier items. In such cases, concrete at the edges of anchor/embedment plates can be treated as in the case of treatment to Ends of Steel H-Sections, which has been described earlier in this paper. The treatment can be improved, if desired, by pre-treating the anchor/embedment plates for better bond between metal and concrete.

Conclusion

Concrete tunnels can be made to be appealing aesthetically. The Pedestrian Subway at Sealdah, with good proportioning and waterproofing treatment in the form of surface plasters, is an example (Figure 3).

Unless given special protection, it will be natural for concrete tunnels to have water leakage and/or seepage. With the provision of appropriate surface protection systems, concrete tunnels can be made to be water-tight and damp-proof. These structures can also be made to be durable with the prevention of atmospheric carbon dioxide and oxygen from entering into the body of concrete.

Continuous surface treatment on the interior surfaces can make underground structures waterproof and dry, which may not be achieved by injection or grouting. The surface treatment can be in the form of waterproofing plasters or in other forms. The surface treatment is provided after arresting water leakages at point leaks, construction joints, honeycomb areas and at structural discontinuities, as at locations of inserts.

Should the waterproofing treatment be in the form of plasters, it should be ensured that the water-cement ratio for the waterproofing plaster is as low as possible, preferably not greater than 0.35, and certainly not above 0.4. Should ordinary portland cement be used, the curing should be for a minimum period of seven days. Should slag portland cement be used, the curing should be for a minimum period of fourteen days. Recent experiences with the performance of cement and concrete suggest the need for carefulness in the selection of any particular cement, whether ordinary Portland cement orPortland slag cement.

Should the surface treatment for waterproofing be punctured for the fixing of electrical, air-conditioning or any other fixtures, such locations of discontinuities in the waterproofing continuum should be provided with special treatments to restore continuity in the water-tight treatment to prevent leakage of water.

The method of sealing one expansion joint at the tunnels of Metro Railway in Kolkata and several expansion joints in the tunnels of Pedestrian Subway at Sealdah, and the performance of the sealed joints confirm that the provision of expansion joints is unnecessary and such joints should best be avoided in tunnels.

Suitable form release chemicals should be used on formwork for concrete work. Chemicals should not leave any oil mark on the concrete surface.

The use of plastic sheets on formwork should best be avoided. In the event such sheets will be used, great care should be taken in the use of such materials such that plastic sheets will not get fused to concrete or those will not leave any mark on concrete.

References

 Kar, A. K., ―Concrete Structures We Make Today,‖ New Building Materials & Construction World, Vol. 12, Issue 8, February 2007.

 Kar, A. K., ―The Ills of Today‘s Cement and Concrete Structures,‖ Journal of The Indian Roads Congress, Vol. 68, Part 2, 2007.

 Kar, A. K., ―Woe betide today‘s concrete structures‖, New Building Materials & Construction World, Vol. 13, Issue-8, February, 2008, also Vol. 13, Issue-9, March, 2008.

 Kar, Anil K, ―Concrete Structures: A Tale of Reverse Technology,‖ RITES Journal, RITES Ltd., Vol. 10, Issue 2, July, 2008.

 Kar, A. K., ―Concrete Structures— the pH Potential of Cement and Deformed Reinforcing Bars,‖ Journal of The Institution of Engineers (India), Civil Engineering Division, Volume 82, Kolkata, June, 2001.

 Kar, A. K., ―Arresting Water Leakages in Tunnels and Other Underground Structures,‖ All India Seminar on Underground Construction with Particular Reference to Metro Railways, The Institution of Engineers (India), Calcutta, December, 1987.

 Kar, A. K., ―Protection of Structures against Water,‖ Workshop on Structural Waterproofing, Road and Building Research Institute, Govt. of West Bengal, 16 July, 1997.

 Kar, A. K., ―Protection of Structures as a Means to Durability,‖ All India Workshop on Preventive Measures Maintenance and Life Extension of Civil Engineering Structures, Civil Engineering Division, The Institution of Engineers (India), West Bengal State Centre, Calcutta, 18 September, 1997.

 Kar, A. K., ―Durability of Containment Structures for Water and Hazardous Liquid Wastes,‖ ENVIROCON 99, 15th National Convention of Environment Engineers, Environmental Engineering Division, Institution of Engineers (India), W.B. State Centre, Calcutta, 26-27 November, 1999.

 Kar, A. K., ―Protection of Structures as a Means to a Long Life for Bridges,‖ Indian Highways; Vol. 28, No. 7, The Indian Roads Congress (IRC), New Delhi, July, 2000.  Kar, A. K., ―Concrete Jungle — Calamity May Be Waiting To Happen,‖ The Statesman,Calcutta, 4 August, 2000.

 Kar, A. K., ―Durability of Concrete Structures with Special Reference to IS 456:2000,‖ presented at Kolkata Metropolitan Development Authority, Kolkata, 1 November, 2002.

 Kar. A. K., ―IS 456:2000 On Durable Concrete Structures,‘ New Building Materials & Construction World, New Delhi, Vol. 9, Issue-6, December, 2003.

 Kar, A. K., ―Waterproofing of Structures: Challenges and Solutions‖, New Building Materials & Construction World, Vol. II, Issue-10, April 2006.

 IS 456:2000. Indian Standard, .Plain and Reinforced Concrete —Code of Practice (Fourth Revision), July 2000.

 Kar, A. K., ―Deformed reinforcing bars and early distress in concrete structures,‖ Highway Research Bulletin, Highway Research Board, Indian Roads Congress, Number 65, December 2001, pp. 103-114.

 Kar, A. K., ―Deformed Rebars in Concrete Construction,‖ New Building Materials & Construction World, New Delhi, Vol. 12, Issue 6, December 2006.

 IS 2645:1975 and IS 2645:2003. ‗Indian Standard: Integral Waterproofing Compounds for Cement Mortar and Concrete,‘ Bureau of Indian Standard, New Delhi.

Appendix-I

The implementation of work according to the following specifications proved effective in making tunnels, basements, machine pits, underground structures, swimming pools and water reservoirs waterproof.

A.Local treatment as in Point Leaks, Construction Joints, etc.

Arresting water leakages at isolated locations (point leakage) and at construction joints with a putty of cement (OPC or slag), modified with a cementitious quick setting compound (bulk density 0.80 to 0.85 gm/cc and a pH of 7.5–8.0 for a 20% aqueous solution at 350C), e.g., PERMAKAR 4, in a weight ratio of 1:10 (1 part of the compound and 10 parts of cement), further modified with a silica waterproofing compound (density not less than 1.53 and a pH of 10.0–10.5 for a 5% aqueous solution at 350C), e.g., PERMAKAR 1 having the properties of making cement quick setting and non-shrinking in quantities to suit the water pressure conditions at the site.

B.Surface treatment to protect entire exposed surface

Cleaning the surface; preparing the surface by acid etching or with water jets; treating the surface with a two layer plaster; the first layer shall be 7 mm thick in case of inside walls and floors of water reservoirs and swimming pools, 6 mm thick for sunken slabs/toilet floors and inside of tunnels, basements, etc. with octadecanoic acid based cementitious waterproofing compound (bulk density not greater than 0.5 gm/cc, moisture content not greater than 2.0% and a free fatty acid not greater than 0.2%), e.g., PERMAKAR 3, and cement in the weight ratio of 3:50 for waterproofing compound and cement; cement-sand (1:2 on floors of basements and tunnels; 1:3 elsewhere) plaster (12 mm thick on floor; 8 mm thick on vertical surfaces and at ceiling) and curing the plastered surface; the treatment shall be impermeable under a waterhead of 20.0 metres.

Besides these basic specifications, specially tailored specification, are followed for the treatment of honeycomb, inserts, embedments and expansion joints, where such features may be present. Waterproofing of Bridge Decks The Latest Technique and Material

Pratap Singh Rautela, Nile Waterproofing Materials, Co. S.A.E. company Noida.

Bridges are important infrastructure facilities connecting different areas and allowing smooth movement of men, material and machinery from one place to another. Roads have no purpose unless bridges are provided for crossing rivers. Railway lines (ROB), highways (Flyovers) etc.

Early deterioration of cement concrete bridge structures resulting into weakness or even part collapses disturb the movement of traffic and has serious impact over social and financial status of the local society. Minor causes like leakage and seepage of water or deicing salt solution into even the slightly permeable deck concrete surface result into corrosion of reinforcing steel which result into spalling, cracking and loss of section of structure.

The problem can be solved to a great extent if concrete surface is protected against ingress of moisture and salts. In other words, if a protection layer is introduced over the bridge deck concrete surface in form of a dependable water proofing system.

Bridge Decks: Waterproofing Choice

The waterproofing of bridge decks is recognized in many European countries as a vital and necessary operation to enhance the durability and longevity of the life of bridge.

It represents the first line of defense and prevents the ingress of water, road de-icing salts, and aggressive chemicals which would corrode the steel reinforcing bars in the concrete causing severe structural damages.

Some countries with mainly warm weather and dry climates choose not to waterproof their bridge decks but, a recent analysis in the USA showed that 200,000 Bridge decks are seriously suffering from corrosion resulting in direct cost of $2 billion for replacement and refurbishment . Concrete will always have some degree of porosity and allied with surface wear and hair line cracking, will allow water and corrosive materials to penetrate and attack the steel reinforcement. The primary defense against such destructive agents is good dense concrete, along with a proven waterproofing system installed by a qualified contractor.

Bridge Deck Waterproofing Systems

Two types of Bridge deck waterproofing systems are available for use: 1-Sheet Systems

These are Polymer Modified Bituminous sheets bonded to the bridge deck, using torch application, hot mopping asphalt, or through self-adhesion. Manufacturers have developed various systems that would satisfy the enhanced requirements of the bridge deck waterproofing market.

2-Liquid (Sprayed) Systems

These systems largely fall into acrylics and Polyurethanes and normally consist of three elements. Primer, Membrane applied in one or two coats and tack coat specially developed to enhance the bond of the membrane to the surfacing mix.

Performance Requirements for the System

Independent of the bridge deck waterproofing system choice, certain performance criteria has to be met in order to avoid potential concerns regarding leakage, poor bonding, embitterment or softening of the membrane in service.

Such performance criteria are:

 Impermeability to water under all conditions  Good adhesion to deck  Good adhesion to surfacing.  Capable of bridging shrinkage cracks n concrete  High mechanical properties to handle traffic loads including shear forces in curves and during braking and accelerating  Tolerant of deck texture and details  Tough to withstand site damage and operations  Safe to apply  Able to withstand elevated surface temperatures  Can be applied over a wide range of ambient conditions  Nonegradable

Proper Site Practice

The key Success

The success of bridge deck waterproofing operation is often reliant on site procedures, workmanship and weather conditions.

Professional preparation is as important as the properties of material or system to be used. Before the work commences at site the following major issues need be addressed:

 Availability of properly trained workforce and qualified supervisors  Site engineer must have design detailing and construction records accessible  Provision of adequate strong area for material to be used  A Safe access to bridge deck must be secured for personnel, equipment and materials  Established method of statement, and execution program discussed and approved by all parties  Review of weather conditions likely to affect the waterproofing operation  Preparation of concrete deck to meet strict surface finish requirements (Sound, even, uncontaminated, dry, dust free). Thereby offering optimum opportunity for a strong bond to waterproofing membrane.  Use of an appropriate primer  Choice and application of a waterproofing system approved and in compliance with Highway Agency Standards  Adequate protection of the waterproofing membrane prior to the application of the asphalt road  Surfacing  Use of approved asphalt road surfacing with low void content mix design

Bitunil Bridge Deck Waterproofing System

BITUNIL Bridge Deck Waterproofing System consists of two layers of fully torch welded heavy duty APP modified bitumen membranes with composite polyester reinforcement, applied on a primed substrate.

System Application:

 Concrete surface must have a minimum acceptable gradient to ensure water drainage on the surface of the asphalt pavement.  A primer coat must be applied to concrete deck to seal the voids, promote W.P. adhesion, and assure against blister formation.  Prior to membrane application, a reinforcing MBM strip shall be applied to cover all intersections with edge beams.  Waterproofing Membrane shall be applied fully bonded to bridge deck, parallel to down slope direction. Side laps and end laps shall be 8-12 cm, and 12-15 cm respectively.  Second waterproofing layer shall be applied fully bonded onto the first layer, at the same direction of rolls length, with shifting the side laps 0.5 meter in order to secure the membrane waterproofing system with maximum overlaps.  Flashings must extend min. of 10 cm up against the edge beams.  Waterproofing must be protected against sunlight until asphalt layers, of drainage, protective and wear courses are applied. It is recommended to apply the asphalt layers as soon as possible.  Thickness and mix design of asphalt courses are as per consultant and project specifications.  Bridge deck joints must be filled up (Grouted) and covered with 200 mm  MBM cover strip prior to membrane application.  Bitunil System recommendation is for two layers of MBM fully torch welded onto deck surface however, for bridges with low daily traffic (ADT<2000), without significant importance to local and regional traffic, and without frequent breaking and turning traffic, a single layer system is adequately sufficient.

The wonder product from the Nile Waterproofing Materials Company S.A.E., BITUNIL, is the product of experience, prudence and knowledge. The Bitunil plant is built over an area of 20,000 square meters in Al Max Alexandria Port. The production plant is state- ofthe- art for manufacturing of modified bitumen membranes, and is fully equipped to manufacture quality products that comply with most of the internationally recognized standards.

Bitunil manufactures and market large types of waterproofing systems to suit different requirements of Engineering industry to mention few of those are BITUBOND–4, BITUBOND 4/ E, NILOBIT-PM, NILOBIT-PM-MINERAL NILOBIT-F, BITY FLEX 4 & 4E, BITUPLAST 4 & 4/E, BITUGARDEN 4- 4E & M BITUTER 4 & 4E, BITUGUM MINERAL, NILOBIT-PN, NILOBIT-PM.

The company has achieved great reputation for its products and services it offers to its clients. The products are being used in almost all corners of the world due to their high quality, reliability, uniformity in Quality and successful performance. Bridge Joints: Selection and Water Management

Based on the predicted movement related to imposed design loads, and temperature variation ranges, the bridge designer specifies the appropriate bridge joints. Selection can vary from a wide range of pre-fabricated expansion joints, to cast in place Asphaltic plug joints. The drainage system for the joint should ideally overlap the deck waterproofing system used. Combined subsurface drainage outlets serve to discharge water and prevent build-up behind the joint. Regular inspection of surfacing and joints is necessary to maintain satisfactory performance throughout bridge service life. Early fault detection, such as blocked drainage or damaged surfacing, is necessary to avoid major remedial work. Inspection and maintenance should be scheduled to coincide with other bridge maintenance work to reduce disruption and consequential costs.

New Generation Bentonite Geotextile Waterproofing Solution

D P Gohil, Sr. Sales Manager, Ashapura Volclay Ltd – CETCO BMG

Ashapura group of Industries are India‘s largest and one of the top five players in Bentonite globally. The Company has extensive reserves of high quality Sodium and Calcium Bentonite which are mined and processed carefully into several grades.

CETCO USA – Colloid Environmental Technologies Company provides products and services worldwide, extending to customers in a diverse range of industries including, Basement waterproofing for underground structures and Tunnels application. CETCO is a wholly owned subsidiary of AMCOL International with more than 81 years of Bentonite mining and manufacturing experience.

Ashapura Volclay Ltd & CETCO a joint venture company, has set up India‘s first Bentonite base Geotextile waterproofing membrane plant in Bhuj in district of Gujarat under technological collaboration with Colloid Environmental Technologies Company (CETCO).

CETCO has ten manufacturing facilities located in America, UK, Spain, Poland, Korea, China, Brazil, Russia and India are supported by a global sales and distribution network.

Waterproofing Property of Bentonite

Bentonite is hydrophilic in nature (it has a strong attraction to water) and upon coming into contact with water will swell in size. When Bentonite is confined under pressure and hydrated, rather than swelling in size, it forms a dense, impermeable hydraulic barrier. This unique hydrophilic property of Bentonite gives it an ―active‖ quality, meaning it can swell to seal punctures within itself and also small voids and cracks that develop within concrete over the life-cycle of the building.

Voltex and Voltex DS - Bentonite Geotextile waterproofing membrane.

Voltex is a highly effective waterproofing membrane ideal for below-grade vertical and horizontal foundation surfaces. Voltex uses the high swelling and self-healing properties of sodium Bentonite to form a monolithic, low permeable membrane to protect the structure from water. Installation is fast and easy, requiring no primers or protection courses.

Voltex is composite comprised of two high strength Geotextile and 4.8 kg of sodium Bentonite per square metre. The two Geotextile are interlocked by a patented needle punching process which encapsulates the Bentonite and keeps it uniformly distributed.

Voltex DS is comprised with an integrated HDPE liner on Voltex.

Typical applications include backfilled concrete walls, under structural rafts/slabs, tunnels and property line construction.

The superior performance of Voltex is based on the remarkable properties of sodium Bentonite and the high strength of the interlocked Geotextile. When hydrated, the polymer enhanced Bentonite expands under confinement, forming an impervious membrane that will be maintained for the life of the structures.

Over 200 million square metre of Voltex has been successfully installed on prestigious projects worldwide. In India, Reliance Hyper Market New Delhi, Hafeez Contractor House Mumbai, Kalpataru Mumbai, Novatel Hotel Bangalore, Chalet Hotel Powai – K.Raheja Group Mumbai, ING Vysya Bank Mumbai, Orbit World Trade Centre–Mumbai, Panchshil Group Pune, Lunkad Realty Pune, Pride Group Pune, Mani Group Kolkata, and SKF Technology Ahmedabad.

Waterstop RX-101 Waterstop-RX 101 is a flexible strip concrete construction joint Waterstop that provides a positive seal by expanding upon contact with water. Waterstop-RX 101 is an active Waterstop that functionally replaces conventional passive PVC dumbbell Waterstop. Waterstop-RX101 is designed for both continuous and intermittent hydrostatic conditions and has been successfully tested to resist 70 m (231 feet) of hydrostatic pressure.

The key to the effectiveness of Waterstop-RX 101 is its 75% sodium Bentonite content which provides superior expansion to seal cracks and fill small voids. Waterstop-RX is a reliable and cost-effective solution to preventing water infiltration through construction joints and penetrations.

Waterproofing Treatment

Hasan Rizvi, CICO Technologies Limited, New Delhi.

Waterproofing is considered to be an important part in modern construction. The word Waterproofing‘ may be a misnomer as it is virtually impossible to provide absolute exclusion of water or moisture from a masonry/concrete structure. The process is basically an attempt to exclude maximum amount of water or moisture from a structure.

Waterproofing is essentially required where there is hydrostatic head of water to be resisted or where unusually dry conditions must be maintained. On the other hand damp proofing maybe defined as the treatment to retard the passage of water with application of suitable treatment methodology coating or integral waterproofing compounds.

The basic causes of defects in buildings are due to usage of excess water (high w/c/ ratio), by excess water we mean that, adding more water than required for hydration. This leads to formation of capillaries, pores, gel pores through which water can penetrate into the structure thus endangering the durability of the structure.

Concrete possesses a pores and capillaries and in this respect, it is fundamentally different from metal. The capillary and pore structure allows water under pressure to pass slowly through the material. Concrete subject to chemically polluted environment also gets deteriorated and damaged. It is here where polymer technology can be advantageously utilized to provide protection against the attack by water under pressure, acid and alkalis and chemically polluted environment.

Usually water intrusion in concrete structures is through the following areas: a. Basement b. Bathroom/ Kitchen sunken portion c. Roof

There are various systems tried and tested by CICO Technologies Limited over a span of 75 years for various sectors of the building. These tested systems are described here.

Basement (System of waterproofing treatment to the underground/ basement structures.)

Raft Portion a. The sub-base concrete (lean concrete) should be rendered smooth with ‗Cement: Sand‘ mortar in the ratio of 1:3 by weight of cement while sub-base concrete is still green. b. Then apply two coats of Tapecrete P-151, acrylic polymer modified cementitious slurry coating in a ratio of 1:2 i.e. 1 kg Tapecrete P-151 mixed in 2 Kg cement. This slurry should be applied by brush. c. Over the Tapecrete P-151 topping one should provide a protective plaster of 12 mm thickness. This is done to protect the Tapecrete applied surface against probable mechanical damage due to dragging of reinforcement while placing it.

d. Cast the RCC slab admixed with a superplasticizer like CICO Plast SUPER. e. This should be followed by injection grouting by placing 12 mm NBMS threaded nozzles of 75 mm length placed in a grid pattern. The spacing should not exceed 1.5 m c/c in the slab. f. Then inject the cement slurry admixed with CICO non-shrink polymeric waterproof grouting compound through the nozzles. g. Finally the nozzles should be sealed by CICO quick setting compound.

Retaining Wall a. Cast the RCC walls admixed with a superplasticizer.

b. Place and fix 12 mm NBMS threaded nozzles of 75 mm length by drilling in a grid pattern (from inside) with maximum spacing of 1.5 m c/c. c. Then inject grout with cement slurry admixed with CICO non-shrink polymeric waterproofing grouting compound d. This should be followed by application of two coats of Tapecrete P-151 acrylic modified cementitious slurry coating over the properly rendered external face of the retaining wall. e. Provide 12 mm thick cement plaster on the external face of the retaining wall.

Roof (System of roof waterproofing treatment.) a. The roof should be cleaned of all loose mortar, laitance and existing treatment so as to expose the mother R.C.C. roof surface. b. Then cut grooves at a height of 200 mm from roof slab all along the parapet walls if there is no spring of the parapet wall. c. Moisten the surface with water. Then apply one coat of Tapecrete P-151 acrylic modified cementitious slurry coating (this slurry coating consists of 1 kg Tapecrete P-151 mixed with 2 Kg cement.) d. Place the fiberglass cloth over the slurry coat and follow by Tapecrete P-151 brush topping. The brush topping slurry consists of Tapecrete P-151 mixed with cement and silica quartz (1:2:2) by weight. e. A protective screeding should be provided over this treatment.

Refer Figure 2 for details.

Bathroom/Kitchen (System of waterproofing treatment for Toilet / Kitchen sunken areas.) a. Clean the RCC sunken slab and vertical portion of all dirt and loose material etc. with a wire brush. b. Make corner fillets with polymer mortar of 25 X 25 mm size at all joints. Seal all pipe joint with polymer mortar. Then apply Tapecrete P-151 slurry coat on these pipe joints followed by wrapping it with fiberglass cloth again apply a second coat of Tapecrete slurry.

c. Moisten the RCC sunken slab and apply one coat of Tapecrete P –151 slurry coating. d. Lay fiberglass cloth over the slurry coated surface. e. Apply a second coat of Tapecrete P-151 slurry over the fiberglass laid surface. f. Apply one coat of brush topping over the second coat of acrylic polymer modified cementitious slurry coating. g. Provide a protective plaster over the treated surface as a protective layer, Figure 3.

The above systems of waterproofing has worked perfectly well in thousands of buildings and even various government agencies are considering to change their specification of conventional box type system for basements to chemical injection and acrylic polymer modified cementitious coating system.

Roof Waterproofing Demands Reliability...

Pramod V. Patil, Product Manager [Waterproofing Systems], BASF Construction Chemicals (India) Pvt. Ltd. Mumbai

Preface

Waterproofing of Roof be it concrete, metal decks, timber, etc. has always been a challenge job to the construction industry. With the increased complexity of structures and the complex nature of utilization of this roofs, terraces or podiums and with possibility of structural movements and growing concern on leakages in the structures has created a need for a simple reliable roof waterproofing system.

This article provides an insight to single ply synthetic waterproofing membranes and high performance liquid applied waterproofing membranes for roof which have global reputation and have gain quick acceptance in recent times in India.

Roof Waterproofing Demands  A system which can allow to take the movements in structure  A system that can allow itself to carry heavy intense built-ups such as - landscaping or gardens or ballast / pavers etc.  A system robust enough to take pedestrian / vehicular traffic  A system that can be used to refurbish roofs without disturbing or breaking off the existing substrate  A system that can be left exposed to atmosphere  A UV stable system  A system with reliability and aesthetics.  A system that demands to be laid loose or unbonded to the substrate  Long-life expectancy and maintenance free or minimal maintenance  A complete water-tightness

Prevailing Roof Waterproofing Practices & Viewpoint

Rigid waterproofing barriers A conventional practice of rigid waterproofing such as brick-bat koba and crystalline waterproofing has limitation if structure is designed to undergo movementsduring life span.

Flexible & elastomeric waterproofing membranes This type of waterproofing forms a membranous barrier against water leakage. They are as follows:

They come in form of liquids, either single component or multi-component, applied with hand or spray. They could be cementitious polymer modified or acrylic or P.U. based or bituminous or epoxy based.

They come in form of preformed membranes, either made up of modified bituminous membranes (APP, SBS), PVC, TPO, HDPE, EPDMs etc. they are either torch applied, stuck with adhesive, mechanically fixed.

Rigid waterproofing barriers have shown limitation or failure when subjected to certain aggressive conditions or structural movements during its life span. Bituminous / cementitious polymer modified / EPDM membranes / HDPE based systems do enable elongations but have limiting success, application difficulties and deteriorate with time in limited life span of application.

The reasons of failure of systems are many, it could be wrong system application or the behaviour & limitations of the material itself in terms of adhesion or UV stability etc. Over a period of time excellent development for different types of waterproofing materials and system have been taking place, keeping in mind the criteria or requirements for a good engineered & reliable Roof Waterproofing System.

This article provides insight to the success stories in India & some glimpse of international reference, where a well engineered and reliable Roof Waterproofing Systems has been implemented in various situational demands:

TPO Membranes System: a single ply waterproofing membranes

Coniroof Waterproofing System: Spray or hand applied cold liquid PU roof waterproofing system

Single Ply Synthetic Waterproofing Membranes

Single-ply synthetic waterproofing membranes are widely used in Europe and North America for the past 40 years and have proven performances. The concept is to provide a watertight liner all around the susceptible building element and to ensure the right technique to install the membrane. There are various synthetic liners available for the purpose and the selection is based on the expected performance out of them in the specific situations. The single-ply synthetic liners are designed and build to the various situational needs and normally consisting of synthetic roll of fixed thickness and width and are available in reinforced with glass or polyester fibres options. Today, PVC and TPO are the most popular choice of materials for the application in the civil industry. The synthetic liners have life expectancy of 25 to 50 years v/s 10 to 15 years as offered by bituminous membranes, a single factor which made synthetic liner the popular choice in the construction sector over the years. PVC membranes are manufactured by adding plasticiser in the PVC and this limits their life expectancy in the case of direct exposure to UV and required to be protected, as plasticizers may migrate out of the membrane making the membrane brittle. Thus, PVC membranes have become chosen material for underground and buried situations while TPO, which expensive in comparison to PVC has excellent stability in UV and available in range of colors, has become the choice for exposed roofing situations, ideally suitable for Tropical conditions as in india.

MASTERPREN TPO Liners

MASTERPREN TPO is a new generation synthetic liner made using an innovative formulation: EPR (ethylene propylene rubber) modified polyolefin. MASTERPREN TPO development has been based on experience, synergy, co-operation and manufacturing technologies:

Experience gained by Flag who, since 1963, have developed and manufactured synthetic waterproofing liners for use in the roofing, civil engineering, and hydraulic sectors.

Synergy with industry-leading manufacturers of polyolefins, who have developed and introduced these new materials to the field of waterproofing.

Co-operation with the most qualified designers, general contractors, and installation companies.

Innovative manufacturing technologies for synthetic waterproofing materials.

Main Characteristics of MASTERPREN TPO Liners

The exclusive manufacturing system designed for this type of liner and its unique formulation have resulted in:

 Excellent weldability  Softness and flexibility  Excellent dimensional stability  High weather and UV rays resistance.  Non-toxicity  Resistance to a wide range of chemical attacks  Compatibility with most insulation panels, including expanded/extruded polystyrene  Compatibility with oxidised bitumen  High resistance to puncturing  Resistance to roots and micro-organisms  Adaptability to structural movements  Environment and user–friendly  Life expectancy in excess of 25 years  Proven installation history

MASTERPREN TPO waterproofing membranes can be used for both newly built roof systems and for renovating existing roofs. MASTERPREN TPO membranes have been designed both for ballasted roof systems (protected) and for exposed roof systems (unprotected).

MASTERPREN TPO for more effective light reflecting surface, is manufactured from modified polyolefin with an in ice white finish as standard (with any RAL color available to order) providing very high resistance to weathering and ultraviolet rays. In the research phase, the color of the side exposed to the aggressive action of atmospheric agents was improved so not only did the lighter color reduce the heat within the roof build up, but it produced a more efficient light reflecting surface.

The inherent anti-oxidising and UV-absorber properties of MASTERPREN TPO enabled Flag‘s research team to improve the membrane‘s resistance of the thermo-plastic polymer to light and atmospheric agents by as much as 30% in the development of TPO.

Environmental Impact

MASTERPREN TPO Plus membranes have a positive environmental impact which starts during production and ends with a recyclable product with a 25 year life expectancy. MASTERPREN TPO Plus membranes do not contain harmful chlorines, bromide or halogens.

The development has not been limited to the mere theoretical assessment. Technical tests have been carried out relating to the re-use and recovery wastes from the production process and from end of life products.

The TPO Plus has an FAA fire rating from Warrington Fire Research Centre.

TPO Plus is manufactured to UNI EN ISO 9001 and UNI EN ISO 14001 certified plant standards

Extensive tests were performed in the Xenotest and the QVU Weathering Tester.

Typical Applications

MASTERPREN TPO membranes can be applied in the following circumstances:

 Exposed roofing laid loose  Exposed roofing mechanically fixed  Exposed roofing fully bonded (requiring a fleece backing)  Landscaped areas  Roof gardens  Old Roofs for Refurbishment, without disturbing the existing substrate.  May be used in underground structures and water storage structures etc.

Manufacturing Process for MASTERPREN TPO Membranes

MASTERPREN TGE, MASTERPREN TPE liners are manufactured in UNI EN ISO 9001 certified plants and fully comply with the performance standards CEN European Standard, UNI 8629/6 – SIA 280 – DIN 16726. The raw material used to produce MASTERPREN TPO membranes is created by blending a mix of synthetic polyolefins and softening agents (EPR) with various additives that, through a catalloy procedure, are transformed into a moulded mass and then into granules. This combines:

 Resistance to ageing, weathering and micro-biological attack  The EPR compound gives softness and flexibility with a high resistance to mechanical and chemical influences in conjunction with the strong welding capacity of polypropylene

The unique manufacturing process designed and developed by Flag combines a tri-extrusion process in a single pass encapsulating a reinforcement mesh that produces a complete homogeneous product with stability and high tensile strength and an effective dual light/dark colour signal layer. The particular property of MASTERPREN TPO synthetic liners is the reinforcement insert embedded in the body of the liner. This reinforcement may be a non-woven glass mesh or polyester mesh, according to application needs, ensuring an efficient and aesthetically flawless end result. MASTERPREN TPO liners are produced by co-extrusion in two-colours, known as a ―signal layer‖ system. The upper sand-grey colour, which provides lower heat absorption, increased longevity and aesthetic qualities, represents 10-15% of the membrane thickness and the black underside, which protects against UV damage, 85- 90%. The major benefit of the system becomes apparent during installation; should the membrane become damaged, the black underside is immediately detected by the contractor and simply repaired.

Situation– Roof Waterproofing Over Precast Segment

Application Case Study- MASTERPREN TPO Membrane at Bangalore International Airport

Project: Bangalore International Airport

Client: BIAL, Bangalore

Scope of Project: Roof waterproofing of terminal building

Design & Construction: Larsen & Toubro Limited, ECC Construction group

Year of execution: 2006 to 2008, Completed

Systems used: MASTERPREN TPE

Project Description

The roof of terminal building is made up of large precast segment, each of having 24 metre span and 10m length. Total there are more then 200 segments in the terminal building. The curve shape and complex detailing made client to choose most reliable waterproofing membrane which can be quickly installed and can last for the design period of the structure.

The Solution offered

Considering the complexity of the job and life expectancy, 1.2mm thick MASTERPREN TPE was selected. MASTERPREN TPE is polyester reinforced TPO membrane, manufactured by latest tri- extrusion process. Considering the wind loading on the structure the fasteners are designed. On the diaphragm walls the membrane is fully adhered to the substrate using special MASTERPREN adhesive glue.

Situation:– Refurbishment & Waterproofing of Old Roof Without Disturbing the Existing Substrate

Application Case Study- MASTERPREN TPO Membrane at IIT- Mumbai Convocation Hall

Project: IIT Mumbai, Convocational Hall Roof

CIient: IIT- Indian Institute of Technology, Mumbai.

Scope of Project: Roof Refurbishment with Waterproofing of old RCC Folded roof of convocation hall.

Year Completed: 2008

System Used: MASTERPREN TPE

Project Description

The convocation hall at IIT-Mumbai is about 35years old structure. The Roof of this hall is RCC roof about three inches thick RCC folded panels. Over the period of time various waterproofing systems have been tried to make the roof waterproof. The system used were from conventional IPS to brush applied polymer coating to Bituminous felts. The water-tightness of the roof could not be achieved to it satisfaction and with time and exposure to the elements has failed to give water-tightness to the roof, resulting in leakages and seepage of water into the RCC roof slab. This seepage of water has added to the corrosion into the slab and the concrete is spalling and has become week. IIT was thus looking for a system that could assure water-tightness to the roof and also one does not have to disturb the existing surface of the slab, to prevent damage to the structure.

Solution Offered

Considering the complexity of the job with earlier done various layers of existing on substrate cannot be removed and life expectancy, 1.2mm thick MASTERPREN TPE was selected. MASTERPREN TPE is polyester reinforced TPO membrane, manufactured by latest tri-extrusion process. Considering the situation of doing the treatment over the prevailing surface the MASTERPREN TPE was loosely laid over the roof with mechanical fixing at the end terminations using fasteners with certain customized detailing.

Liquid Cold Applied PU Coating Membrane System Coniroof Waterproofing System

CONIROOF is based upon the use of epoxy resin/polyurethane preparation coatings. Combined with polyurethane based waterproofing membrane and surface coating.

CONIROOF has been designed to provide a minimum of 25 year performance expectancy in severe climate conditions as a fully bonded waterproofing solutions for:

 Built-up roofing systems  Overlay systems  Podium decks  Inverted roofing  Can be applied on Concrete, Timber, Clay tiles, Metal Decks, Precast etc

CONIROOF membrane can be sprayed or hand applied onto different types of substrate by using polyurethane or epoxy resin preparation coats and primers.

Features

Fast Installation: New spray technology applies up to 700 m² / day of the waterproofing membrane including detailing

Monolithic: No laps welds or seams, the inherent weakness of sheeted systems – makes for reliable detailing

Fast-setting: 30 seconds after application

Cold applied: Requiring no hot works and presents no fire risk

Fire retardant: Meets DIN 4102: Part 7, BS 476: Part 3

Lightweight: Less dead load on existing structures / substrates

Solvent-free: No-odour

Robust: Designed to take vehicular traffic without damage

Ideal for Landscaping works: Roof garden and decking

Seamless Detailing: No laps, welds or seams to seal providing simple effective waterproofing of difficult detailing situations

Elastomeric: Will stretch and contract with the movement of the roof

Application:

 SPRAY APPLIED: Fast track seamless solution for complex or larger areas  HAND APPLIED: Perfect for Confined and Restricted spaces Certification: BBA (British Board of Agreements) Approved membrane systems for flat or pitched roofs that are exposed to UV or light traffic (pedestrian and maintenance). Suitable for mixed roof situations where sections are exposed and there are roof gardens or landscaping.

Coniroof Built-up

CONIROOF is a Seamless, monolithic robust waterproofing system obtained from several application stages:

 Cleaning and Surface Preparation.  Selection and application of preparation coats/primers.  Sand board-casting on the primer to have mechanical keys for anchoring.  Spray or Hand Application of the waterproofing Membrane, as per requirement.  Application of Top Coat for Exposed surface: The final stage of Coniroof system is the use of a single component, moisture curing, UV resistant protective coating.

Situation– Roof Waterproofing of Roof with Clay Tiles of A Heritage Structure

Application Case Study- coniroof spray applied waterproof system on pitched roof with Clay tiles

Project Name: St Mary‘s Church Hongkong, Pitched roof waterproofing

CIient: St Mary‘s Church, Hongkong

Scope of Project: Waterproofing of Pitched roof with Clay tiles and to retain the heritage look.

System Used: Coniroof 2111–Roof deck crack-bridging P.U. Waterproofing system (spray applied membrane)

Project Description

A heritage structure with pitched roof covered with clay tiles and in colored pattern. Clients want to retain the same look and do not want to remove the tiles to avoid any damage to the heritage structure.

System Solution

Considering the requirement Coniroof spray applied system was suggested. Coniroof waterproofing system offered a reliable roof waterproofing and helped in maintaining the heritage look of the structure.

Situation– Complex Roof Waterproofing of Mosque in Kuala Lumpur Malaysia

Application Case Study- coniroof spray applied waterproof system on the complex details on the roof.

Project Name: Mosque Kaula Lumpur, Malaysia

Scope of Project: The Roof Waterproofing of Mosque

System Used: Coniroof 2111–Roof deck crack-bridging P.U. Waterproofing system (spray applied membrane)

Project Description

The concrete roof of the mosque is of complex nature with small domes and ventilators spread across the roof. This small domes are covered with tile bits. The entire roof is to be waterproofed without disturbing the substrate.

System Solution

Considering the requirement Coniroof spray applied system was suggested. Which gave a good waterproofing system and helped in covering the most complex details on the roof and making it watertight..

Conclusion

Finally local availability of single-ply synthetic waterproofing membrane and Coniroof system, an engineered watertight system shall enable building owners and structural designers to have choice of dependable waterproofing material. The experienced application team and easy access to global experts shall enable BASF to serve the construction industry better.

Building Waterproofing an Important Aspect

Bijnan Parai, GM-R&D, CICO Technologies Limited, Kolkata

Concrete is one of the major and most economical building products for its long life span and versatility. But concrete, more precisely, cement -concrete is porous in nature. The long life or durability of concrete is greatly dependent on water permeability and ingress of chemicals. In most of the cases, water acts as carriers for harmful chemicals like salts of chlorides, sulphates, alkalis, acids, etc. and these may corrode concrete and/or reinforced steel. Water may also come out from the concrete/ plaster and evaporates from the surface leaving salts and alkalis, which react with paint, and/or making patches. Therefore, waterproofing of concrete is an integral part for construction of a building.

Sometimes it is claimed by some that concrete admixtures are not necessary and are certainly no substitute for sound concrete mix design. But others argue that the addition of admixtures often offset errors at the practical stages of making concrete, so increasing the chance of producing concrete up to the specification. These statements have some justification for that group of admixtures known as integral waterproofers. However, waterproofing of concrete or cementitious substrates does not mean cent percent protection from water, rather some portion of water in liquid or vapour form is beneficial to continue hydration reaction of cement.

Theoretically, 22-25% (by weight of cement) water is needed to complete the hydration reaction of cement. But in normal conditions, concrete is prepared with extra amount (as much as 45-60% by weight of cement) of water to get desired workability. Any extra mixing water over the minimum requirement of hydration reaction is evaporated from the concrete mass leading to an increase of voids or creating more capillary pores. This is a common factor in all concretes allowing the passage of water and/or water vapour is the presence of inter-connected capillary pores without such voids and their inter connections water or vapour transfer can not take place.

Let us consider for a moment how voidage in concrete can be altered.

1. The gel pores that are formed due to hydration reaction of cement. These pores are very minute and have diameter of approx. 2 nano-meters and independent of water-cement ratio. 2. Capillary pores (0.05 to 1 micron diameter) that result from excess water being present and therefore depend upon water-cement ratio. 3. Entrapped voidage reflecting the concrete mixing, laying and finishing method.

Since the diameter of gel pores (approx. 2 nano-meters) are so small that water cannot go through it.

Categories 2 and 3 are relevant to problems of concrete waterproofing.

In category 2, capillary pores (approx. diameter 0.05-1.0 micron) are larger in diameter as compared to gel pores and water can travel through it. Controlling the w/c ratio using water-reducing admixture can reduce these capillary pores. During the hydration of cement some of the capillary pathways become progressively blocked by reaction products of calcium silicate hydrates gel. This gel has a very low hydraulic permeability, if water-cement ratio is low enough (less than 0.4), the volume of gel will be sufficient to completely block the inter connecting capillary within the cement paste. But in case of water– cement ratio is more than 0.40 the capillary pores generated in OPC, there will not be sufficient gel to block the capillary pores so resulting in inter connections. Curing of concrete is also an important factor to continue cement hydration reaction resulting reduction of capillary pores.

In category 3, entrapped voids are created due to following reasons:

1. Poor mix design. 2. Faulty aggregates gradation. 3. Inadequate compaction. 4. Excessive bleeding and segregation. 5. Very high or very low workability than the requirement. 6. Poor workmanship.

Sometimes cracks are developed in the plaster or concrete and water may travel through those cracks. There are so many factors for development of cracks through which water can travel and damage the embedded reinforced steel and/or paints.

Therefore, waterproofing or damp proofing is an essential and integral part of building construction and by doing so one can get following benefits:

1. Life span of the building will be increased remarkably. 2. Frequent repair or maintenance of building shall be eliminated completely or reduced to a greater extent. 3. Life of paint in interior or exterior shall be extended remarkably. 4. Aesthetic look of the building shall remain for much longer duration. 5. Minimises health hazards.

If we consider the cost of effective waterproofing, it is only 0.5 to 2% of the total cost of building, which is really negligible!

Waterproofing or damp proofing of concrete or masonry is carried out in two stages. One is during construction and another is post construction.

Most effective and economical waterproofing or damp proofing treatment is carried out during construction of a building whereas post construction treatment is very expensive, more time consuming and to some extent less effective.

Materials

There are so many waterproofing materials available in the market one may confuse to choose the right material for the right propose. However, for simplicity, we can categorise these materials as per their time of usage. Firstly, some materials are used for waterproofing treatment as a preventive measures and secondly some materials are used when seepage, leakage or dampness are found. Since the space is limited, we will discuss those products, which are used at the time of construction for waterproofing purpose to protect the building.

Integral Cement Waterproofers

These products are incorporated in concrete or plaster during mixing with water for lowering water permeability. In normal condition, it may provide 25 to 90% water tightness of the structures.

There are several types of integral cement waterproofers available in the market. But most common varieties are:

Water reducing admixtures- It reduces the w/c ratio without altering the workability of a particular concrete mix resulting less permeable, denser concrete/masonry structures.

Very fine particulate materials- Very fine particulate materials are of real benefit if the concrete mix is low in cement and in deficient in fines. However, in concrete rich mixes the effect could be the reserve since the addition of fine particles could increase the water requirement leading to a less dense and lower strength concrete. These fine particles block the capillary pores during hardening of cement mass.

Hydrophobic/ water repellent agents- Materials in this group reduce the passage of water through dry concrete, which would normally occur as a result of capillary action and not as a result of an external pressure of water. In principle it is thought that all these materials impart a water repellent property to the concrete surface as well as lining and, in some cases, blocking the pores.

Air-entraining agents (AEA)- Air-entraining agents act in a similar manner to water reducing agents by imparting improved workability to the mix and thus allowing less water to be used. The micro air bubbles entrained into the cement mass shall block the capillary pores. But care shall be taken to minimise the use of over dose. Over dosing of AEA shall lead considerable amount of strength loss of concrete.

Selections and Applications

In view of the large number of possible applications and the variety of waterproofing admixtures available, the choice of a particular waterproofer to perform a given task requires careful consideration.

Many concrete structures are built for water storage or maintain dry conditions within the structure when it is subject to water conditions on the outside. Since concrete is not always completely impermeable to water in spite of the use of integral waterproof compounds and concrete may develops cracks after placement, it is sometimes necessary to use a barrier material to cover the concrete surface to resist water penetration under hydrostatic pressure and/or capillary rise. There are various types of barrier materials available in the market but most common and popular products are cited below:

Coal-Tar / Bitumen Based Coating

This is one of the oldest and cheapest methods for waterproofing of concrete structures. Unmodified hot melt coal tar or pitch is used as waterproofing coating. But hessian cloth impregnated with hot melt tar (popularly known as Tar felt) was massively used to protect concrete from water. This type of waterproofing is not lasted for longer time. There are many drawbacks of unmodified coal tar waterproofing system. One of most important drawback is the coating gradually become brittle and erodes if it is exposed to environmental conditions. Some times coal tar is blended with one or more polymers to modify its performance.

Stone Waterproofing

Natural stone (known as KOTA STONE in Delhi) slab is used for waterproofing of basement of a building. Though, this type of stone is cheap and good water-resistant, there are many joints between stone slabs from where water may percolate to the main concrete. Another major disadvantage is very difficult to rectify the post construction defects.

Membranes

Now a days factory made polymer modified bituminous membrane (APP) sandwiched with synthetic fibre cloth, polymer modified PVC membrane, neoprene rubber membrane, etc. are available in the market for barrier waterproofing. These felts are elastomeric and very good water resistant and long lasting. These felts are available in roll form with different thickness (1.5mm to 5 mm) and may be fully bonded to the substrate or laid loose according to the manufacturer‘s instructions. The main drawback is very poor vapour breathability. Therefore, one should ensure that the structure should be free from moisture as much as possible inside the structure before laying the membrane.

Chemical Impregnations

There are some polymers with very low viscosity used to waterproof of the concrete structures. Most common chemicals are silicone compounds, which are water repellent in nature. Some silicone compounds are water soluble, highly alkaline and very cheap. Basically, these are sodium or potassium siliconate salts solutions. This type of material may generate white patches on the substrate surfaces without hampering the water repellent property. Another version is solvent based silicone compound which is purely organic in nature will not give such type of white patches.

Sometimes, outer surfaces of buildings are kept unpainted or decorated with stones, bricks or brick tiles etc. Most of these materials are porous, therefore, rainwater will be absorbed and that water may travel to the interior surfaces and create dampness and destroy the paint film. Water is retained for longer time within the porous substrate. This facilitates algae/fungi/mildew growth on the surface of exposed wall and aesthetic beauty will be lost within a year. Growth of algae can be prohibited if the surface is kept dry by providing a water repellent coat of silicone, which will not change the surface texture in an economical means.

Non-Shrink Grouts And Grouting Admixtures

In this category, ready – mixed cement grout is used to consolidate honeycombed concrete. This type of materials are mixed with water and injected through a nozzle into the defective concrete. Before hardening this admixed cement slurry will expand and fill the voids. But most of the cases non-shrink grouting admixtures are available which are to be mixed with cement at the time of mixing with water. This slurry is also injected as above for the same purpose.

Cementitious Polymer Coating

These products are available in three varieties. First and most common variety is a single component polymer emulsion, which is to be mixed with cement at site to a brushable consistency. Second variety is a two-component system, one pack is in liquid form and other pack is in cement based powder form. When these two components are mixed together a slurry mix is obtained. Third variety is single component cement based products blended with various types of chemicals and fillers. This type of material shall be mixed with water to a brushable consistency. All these slurry are mainly applied by brush on the substrate surface at the positive side of the water pressure. These products are very good water resistant and flexible in nature which will not crack due to thermal movement of the structure.

Polymeric cement based waterproofing system has special advantages over all other system considering their versatile properties, low maintenance cost, ease of applications, moisture vapour breathability, UV rays resistance, economy and many more.

Polyurethane (PU) Coating

In recent time, various types of polyurethane coating systems are available in the market for waterproofing purposes. One is solvent free or solvent based two packs, chemically cured system and another is tar modified single pack, moisture cures system. The major advantages of PU systems are better adhesion, elasticity, seamless application and resistance to various harmful chemicals. Recently, polyurethane dispersions (PUD) in water are developed for waterproofing which is eco- friendly, but their costs are comparatively high. Occasionally, cast-in-situ polyurethane foam (PUF) is used for roof waterproofing as well as thermal insulation. This system is used for special purposes. Most of the polyurethane coatings are not UV (ultra-violet) rays resistant.

Execution of Waterproofing

Frequently complaints are raised about the failure of waterproofing and blamed the quality of waterproofing materials. If we look into this matter wisely, in major cases, it is seen that waterproofing materials pass all the quality requirements. Most of the failures are due to faulty specification, human error, and poor workmanship.

Therefore, it is very important that full care should be taken at the initial stage, i.e., at the time of making specification of waterproofing. During selection of waterproofing system, the specifier should use his experience and judgment considering severity of water conditions, type of construction and the conditions under which the materials will be applied. Manufacturer should also be consulted concerning selection of materials, method of application, surface conditions, number of coats/ dosage, crack repair, protective covering etc. and that will assure satisfactory performance of waterproofing.

During making the specification following points shall be kept in mind: Type of material, durability or service life, effectiveness of intended purposes, ease of application, ease of repair in future, compatibility with other building materials, cost and effect to the environment.

The waterproofing system should also be designed in due consideration of the present condition of building as well as the worst conditions that may arise in future. The system should not ignore the basics of structural and civil engineering and material science.

Quality Assurance

Normally, waterproofing treatment is carried out with job guarantee given by the applicators. But very few are turned back when problems come. Therefore, one should ensure that the work should be carried out by a well-experienced, trust-worthy applicator who is well versed with products and systems. Now many construction chemicals manufacturers are keeping technical team who can review the system, select right materials and suggest good, company authorised applicator. Normally, company authorized applicators are easily traceable in future if, any problem comes. The common tendency is to spend a little amount of money on waterproofing leads dilution of specification by the applicators or contractors to grab the work. This type of approach spoils the genuine waterproofing system.

A good waterproofing system is a collective and wise effort of the applicator/contractor, homeowner, architect / specifier and the inspecting authority.

Waterproofing system should be checked during execution or immediately after installation by several methods to ascertain the quality of work. This will minimise future rectification or damage of the building. Normally, surface preparation and surface conditions, weather conditions such as humidity, temperature etc are checked prior to application waterproofing treatment. Flood testing with water is carried out during or immediately after completion treatment for horizontal surfaces or liquid storage tanks. Visual inspection is carried out where flooding is not possible. In this case, thorough inspection is necessary. All laps, joints, terminations, must be carefully checked for any evidence of ―fish mouth,‖ inadequate adhesion, etc. that may detrimental to the water tightness of the system.

Conclusion

Waterproofing system is a minor part of a building from economic point of view but a great importance as durability of building is concerned. Since this system is dependent on so many factors it requires sound knowledge of engineering, material science, skilled and experience workforce and good co- ordination between house owner, material suppliers, specifier, applicator and inspector to fulfill the aim of waterproofing.