CPCCCO2013A Carry out concreting to simple forms

Student Learning Resource

Student Name ______

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Student Information Purpose: The purpose of this learning package is to help you understand the technical and theoretical knowledge and associated skills of your selected trade area. This package contains a number of learning and associated documents for this unit of competency. Please read all parts of this package to ensure that you complete and manage the process correctly. This assessment tools address the mandatory requirements of the unit of competency including, evidence requirements, range statements and the required skills and knowledge to achieve the learning outcomes indicated in the document. Performance criteria are described below. The contents of this unit will contain some or all of the following as required: Unit outlines / Performance Criteria. Self-Checks are self-tests for the student. These have in general been extracted from this learning resource. ELEMENT PERFORMANCE CRITERIA

1. Plan and 1.1. Work instructions and operational details are obtained using relevant information, confirmed and applied for prepare planning and preparation purposes. 1.2. Safety (OHS) requirements are followed in accordance with safety plans and policies. 1.3. Signage and barricade requirements are identified and implemented. 1.4. Plant, tools and equipment are selected to carry out tasks and are consistent with the requirements of the job, checked for serviceability and any faults are rectified or reported prior to commencement. 1.5. Materials quantity requirements are calculated in accordance with plans, specifications and quality requirements. 1.6. Materials appropriate to the work application are identified, obtained, prepared, safely handled and located ready for use. 1.7. Environmental requirements are identified for the project in accordance with environmental plans and regulatory obligations and applied.

2. Erect and strip 2.1. Subgrade is prepared. simple 2.2. Formwork design is identified from drawings. formwork 2.3. Formwork is erected safely on commencement. 2.4. Form release agent is applied to erected formwork where specified. 2.5. Timber components are de-nailed following stripping of formwork. 2.6. Components are cleaned, stacked and stored for reuse or bundled for removal. 2.7. Formwork components are removed from site.

3. Place and tie 3.1. Reinforcing components are handled and positioned safely. reinforcement 3.2. Reinforcing bars and mesh are positioned. 3.3. Bar chairs and spacers are positioned, with minimum edge cover.

4.Place concrete 4.1. Formwork or excavation is cleaned of excess material and debris prior to concrete placement. 4.2. Concrete is safely transported by wheelbarrow. 4.3. Pump line/chute is controlled and concrete placed. 4.4. Concrete is placed in formwork to specified depth. 4.5. Concrete is screeded to the alignment of formwork and project specified datums 4.6. Surface of concrete is finished in accordance with specifications.

5. Clean up 5.1. Work area is cleared and waste materials are disposed of, reused or recycled in accordance with legislation, regulations, codes of practice and job specification. 5.2. Plant, tools and equipment are cleaned, checked, maintained and stored in accordance with manufacturer recommendations and standard work practices.

UNIT DESCRIPTOR CPCCCO2013A Carry out concreting to simple forms This unit of competency specifies the outcomes required to safely install formwork, reinforcement and place and finish concrete for the construction of minor slabs, pathways and other minor works to a specified design finish. The unit includes positioning the truck, placing concrete from truck to work area, spreading concrete and cleaning up site.

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ASSESSMENT Overall Assessment Requirements The instructional outcomes required at the completion of this training are satisfactory for each form of evidence resulting in competent. If you do not achieve the required outcomes of competent, for this assessment you will be required to re sit a supplementary examination within a reasonable time of the original examination date. To achieve successful completion of this unit you should achieve a minimum of 3 forms of assessment. Below are some of the forms of evidence that can be used. 1. Written Assessment 2. Third party reports (usually by your employer or supervisor) 3. Workshop/ On Site Activity (generally referred to as “Practical Assessment”) 4. Logbook Evidence (a record of the tasks you carry out for each unit) Theory Examination During the period of this learning you will be required to complete a written theory examination to establish the level of understanding of technical content. Self Checks Self-checks are to be completed on pages provided when requested by your trainer. These exercises are used mainly as a learning tool; they may form part of your overall assessment if deemed necessary by your Trainer. Verbal Questions Verbal questions may be used and recorded to establish your level of knowledge of the competencies of this learning package. Practical Observation / Assessment Practical may be assessed in either of the following formats: - 1. Practical observations will be undertaken in the workplace. Where the assessor observes the student completing a task in the workplace the observation will be recorded in the observation checklist. 2. Where a student is not able to undertake an activity in the workplace a simulated practical activity will be setup by the assessor. (Refer to the practical exercises outlined in this Student Learning Resource.) The observation checklist will be used to record the student’s performances. Where a student undertakes an activity in the workplace and the trainer is not able to be present the employer / supervisor will confirm the activity on the Third Party Report. The student and employer / supervisor will provide photographic evidence of the activity with an explanation of the task undertaken. The assessor will contact the student by phone or face to face to question the student about the activity to confirm the students understanding and skills. The outcome of this contact will be recorded in the Practical Assessment.

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Log Book or Training Record Book It is the responsibility and requirement for the learner to complete the training record based on the on-the-job and structured training tasks received by the employer or Supervising Registered Training Organisation (SRTO) or as indicated in the training plan, which may be produced to the employer and SRTO at reasonable intervals of not more than 3 months. Log Book evidence from your employer and other forms of evidence relating to this unit of competency will contribute to the outcome of this learning package. If the required activity is not part of your employer’s scope of activity you will be required to complete the skill learning process within a simulated environment. Logbook evidence must reflect the “Elements” shown for this unit. Results A statement of Attainment may be printed for this unit if required, but in general your achievement of this unit will be recorded and presented to you on completion of the entire qualification. Your certificate will record all the units you have completed. RPL and Acceleration Recognition of prior learning is available to all students. This provides an opportunity for being credited for previous learning. Acceleration provides an opportunity to reduce the allocated learning hours for this unit of competency. There is a separate RPL kit for this process. Methodology This unit may be provided as a separate learning instruction or provided with other units of competency in a practical or theoretical learning experience. Due care Every care has been taken to ensure that the information in this learning guide is correct, but trainers are advised to check the currency and the relevance of the content to their own training package. Copyright protects this publication. Except for purpose permitted by the Copyright Act 1968, reproduction, adaptation, electronic storage and communication to the public is prohibited without prior written permission. Pre-requisites Pre-requisite units: CPCCOHS2001A Apply OHS requirements, policies and procedures in the construction industry Feedback to the learner The trainer will provide feedback to the learner on the progress of assessment This learning package is intended for use by those completing the Competency Unit - CPCCCO2013A Carry out concreting to simple forms as part of Basic Stream Skills within the Building Construction Skills Stream of the National Competency Framework.

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History of Cement An early version of cement made with lime, sand, and gravel was used in Mesopotamia in the third millennium B.C. and later in Egypt. It is uncertain where it was first discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture (see also: Pozzolanic reaction), but concrete made from such mixtures was first used by the Ancient Macedonians and three centuries later on a large scale by Roman engineers. They used both natural pozzolans (trass or pumice) and artificial pozzolans (ground brick or pottery) in these concretes. Many excellent examples of structures made from these concretes are still standing, notably the huge dome of the Pantheon in Rome and the massive Baths of Caracalla. The vast system of Roman aqueducts also made extensive use of hydraulic cement. The Romans found that a cement could be made which set under water and this was used for the construction of harbours. The cement was made by adding crushed volcanic ash to lime and was later called a "pozzolanic" cement, named after the village of Pozzuoli near Vesuvius. In places such as Britain, where volcanic ash was scarce, crushed brick or tile was used instead. The Romans were therefore probably the first to manipulate the properties of cementitious materials for specific applications and situations. Although any preservation of this knowledge in literary sources from the Middle Ages is unknown, medieval masons and some military engineers maintained an active tradition of using hydraulic cement in structures such as canals, fortresses, harbors, and shipbuilding facilities. The technical knowledge of making hydraulic cement was later formalized by French and British engineers in the 18th century.

The Pantheon in Rome and the Pont du Gard Aqueduct in France used large amounts of cement Modern Cements Modern hydraulic cements began to be developed from the start of the industrial revolution (around 1800), driven by three main needs: Hydraulic cement render (stucco) for finishing brick buildings in wet climates. Hydraulic mortars for masonry construction of harbor works, etc., in contact with sea water. Development of strong concretes. In Britain particularly, good quality building stone became ever more expensive during a period of rapid growth, and it became a common practice to construct prestige buildings from the new industrial bricks, and to finish them with a stucco to imitate stone. Hydraulic limes were favored for this, but the need for a fast set time encouraged the development of new cements. Most famous was parker's "roman cement". This was developed by James

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Parker in the 1780s, and finally patented in 1796. it was, in fact, nothing like any material used by the romans, but was a "natural cement" made by burning septaria – nodules that are found in certain clay deposits, and that contain both clay minerals and calcium carbonate. The burnt nodules were ground to a fine powder. This product, made into a mortar with sand, set in 5 –15 minutes. The success of "roman cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk. The Renaissance and Age of Enlightenment brought new ways of thinking, which for better or worse, led to the industrial revolution. In eighteenth century Britain, the interests of industry and empire coincided, with the need to build lighthouses on exposed rocks to prevent shipping losses. The constant loss of merchant ships and warships drove cement technology forwards. Smeaton, building the third Eddystone lighthouse (1759) off the coast of Cornwall in Southwestern England, found that a mix of lime, clay and crushed slag from iron-making produced a mortar, which hardened under water. Joseph Aspdin took out a patent in 1824 for "Portland Cement," a material he produced by firing finely-ground clay and limestone until the limestone was calcined. He called it Portland Cement because the concrete made from it looked like Portland stone, a widely used building stone in England. While Aspdin is usually regarded as the inventor of Portland cement, Aspdin's cement was not produced at a high-enough temperature to be the real forerunner of modern Portland Cement. Nevertheless, his was a major innovation and subsequent progress could be viewed as mere development. A ship carrying barrels of Aspdin's cement sank off the Isle of Sheppey in Kent, England, and the barrels of set cement, minus the wooden staves, were later incorporated into a pub in Sheerness and are still there now. A few years later, in 1845, Isaac Johnson made the first modern Portland Cement by firing a mixture of chalk and clay at much higher temperatures, similar to those used today. At these temperatures (1400C-1500C), clinkering occurs and minerals form which are very reactive and more strongly cementitious. While Johnson used the same materials to make Portland cement as we use now, three important developments in the manufacturing process lead to modern Portland cement: - Development of rotary kilns - Addition of gypsum to control setting - Use of ball mills to grind clinker and raw materials Rotary kilns gradually replaced the original vertical shaft kilns used for making lime from the 1890s. Rotary kilns heat the clinker mainly by radiative heat transfer and this is more efficient at higher temperatures, enabling higher burning temperatures to be achieved. Also, because the clinker is constantly moving within the kiln, a fairly uniform clinkering temperature is achieved in the hottest part of the kiln, the burning zone. The two other principal technical developments, gypsum addition to control setting and the use of ball mills to grind the clinker, were also introduced at around the end of the 19th century.

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THE Placement And Finishing Of Concrete Types Of Concrete And Concreting Materials

Concrete is a “stone-like” hardened substance, which is used for footings, pathways, drives, roads, floors and in some cases, whole buildings or other structures such as bridges.

Concrete is a mixture of coarse and fine aggregates (stones and sand), cement and clean drinkable water.

Figure 1: Concrete Raw Materials

It is important that all the materials are free from soil, leaves, lawn cuttings, plastic and paper waste.

In its plastic state, concrete may be moulded into practically any shape required.

When concrete is hard it is capable of carrying heavy loads and withstanding weather, fire and other deteriorating influences.

The term aggregate is given to natural sands, gravel and rocks, (crushed or uncrushed) and these are used in good quality concrete production.

Aggregates compromise approximately 75% of the concrete mix. The water/cement paste, the remaining 25%.

Good quality concrete made with well-graded gravel and sharp sand showing good blending and bonding of the aggregates of various sizes.

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Figure 2: Section Through a Sample of Good Quality Concrete Material Characteristics The first step is to identify the characteristics of all the materials to be used in a concrete mix.

Cement Cement can be purchased by weight or by the bag. It is only necessary to purchase it by the weight when amounts are large.

Figure 3: Portland Cement – Bagged

Types of Cement The commonest type of cement used for most concrete applications is Portland cement. However, there are a number of special types of cement produced for use in special circumstances. • Type B: High early strength or rapid hardening cement. • Type C: Low heat of hydration cement. • Type D: Sulphate resisting cement These special products will be specified by the engineer/architect when they are required.

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Cement must be fresh, dry and free from lumps. Cement bags should be stored off the ground on pallets or undercover in a weatherproof site shed or well inside the factory area.

Figure 4: Cement Should Always Be Kept In A Dry Site Shed Or Well Inside The Factory Area

Course Aggregates • Coarse aggregate, sometimes called gravel, is usually available in aggregate • Sizes of 10mm, 15mm, and 20mm • Crushed rocks have the advantage that they can be produced in any desired • Size and grading by crushing and screening equipment

Figure 5: Coarse Aggregates

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Fine Aggregate Fine aggregate, commonly called sand, consists of sharp sand particles graded up to 5mm

Figure 6: Fine Aggregate

Storage of Aggregates Should be stored on clean, hard, well-drained surfaces. Avoid mixing various sizes and Store separately

Figure 7: Store Aggregates Separately

Sand May contain excessive amounts of dirt, salt or organic impurities, which can seriously weaken concrete and affect the setting time. A simple test would be to half fill a jar with sand from the stockpile and 3/4 fill the jar with clean water. Shake the jar vigorously and allow it to stand for 3 hours. The depth of the clay-silt impurities should not be more than 10% of the total depth of sand.

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Figures 8: Impurities in Sand

Water In general, water used for drinking is suitable for mixing concrete

Figure 9: Use Drinkable Water

Grading Concrete aggregates are generally made up of stones or particles having different sizes, ranging from the maximum permissible to fine sand particles.

The aggregate grading significantly influences the water demand and workability of the concrete. This affects the control of concreting operations on the job.

Ultimately, it may affect the strength and other properties of the hardened concrete. It is extremely important either that aggregate grading be uniform during the currency of a project, or that the concrete mix be adjusted when changes occur in the grading.

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Figure 10: Range of Particle Size in Aggregate

Sieve analysis of coarse aggregate shows good grading of particle sizes. It should produce a workable concrete

Concrete Strength Grade of Concrete Concrete is designated by its grade, e.g. 25 grade concrete means 25 MPa. This is the strength the concrete is expected to reach after 28 days. The grade is what is specified when ordering concrete. Normal concrete generally reaches 70 percent of its grade strength after 7 days. For general information only at this stage: MPa is an abbreviation of the term “megapascal” which is used to describe compressive strength of any material. The term can be broken down into two words: Mega, which means 1,000,000 (one Million), and Pascal, which is one newton of force over an area of one square metre, a newton being 0.1 or 1/10th of a kilogram

The strength and quality of concrete depend on the following: • Water/cement ratio. • Compaction. • Curing. • Batching of materials. • The strength, grading and cleanliness of materials

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Water-Cement Ratio

Figure 11: Comparison of Strengths

Compaction Hand Compaction Ordinary hand tools of compaction consist of rodding, tamping and spading with suitable tools.

Vibration Although hand compaction produce satisfactory results for some purposes, the use of vibration allows the use of drier mixes, resulting in higher strength and reduced shrinkage for given mix proportions.

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Figure 12: Correct Vibration

Curing After placing and compacting the concrete, it is important that the settling and hardening process be controlled as far as possible. This is curing. It is done to reduce cracking and shrinking and to allow the concrete to achieve its designed strength under controlled conditions.

In general, the measures taken to cure concrete are designed to: Prevent it drying out too quickly Control the temperature of the hardening concrete

Common methods of curing include:

1. Keeping concrete damp or wet for two or three days, by: • Spraying with water • Flooding with water

2. Covering with plastic sheet or similar material.

3. Spray on chemicals.

4. Admixtures included in the concrete at the mixing stage.

Keeping concrete wet slows the curing process giving a better finish & reducing the possibility of cracking

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Figure 13: Application of Curing Compound

Protection After concrete is placed and finished it is necessary to ensure that it is protected from damage until it has hardened sufficiently to be walked on or loaded. This will require temporary barriers or signs and strict control on access.

Figure 14: Surface Protection Hot dry conditions including winds can quickly dry out a concrete slab causing it to crack very severely. This can be similar to an outback water hole where the mud dries and cracks after all the water has evaporated. It is your job to prevent this happening by keeping the moisture in.

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Mixing the Concrete All concrete should be mixed thoroughly until it is uniform in appearance and all ingredients are uniformly distributed.

Very small quantities of concrete for patching or small post bases, etc, can be mixed by hand using a shovel. Small quantities of concrete can be mixed on site using a small mixing machine. This would be used where the small quantities make it uneconomical to use truck mixed or ready mixed.

The vast majority of concrete is now provided to the sites as ready mixed or truck mixed concrete discharging directly into the formwork by the truck, or pumped, or wheeled to it’s place.

Figure 15: Discharging Concrete Directly from Transit Mixer Truck & Concrete Bell

Site Batched Concrete Very large sites, e.g. large civil engineering projects have their own batching and mixing plants on the site.

Mixing time will depend on several factors: • The speed of the machine • Size of the batch • The condition of the mixer

Generally, the mixing time should be at least one minute for mixes up to one cubic metre, with an increase of twenty seconds for each half a cubic metre. Mixing time should be measured from the time all materials are in the mixer.

Mixers should not be loaded above their capacity. They should be run at the speed for which they were designed. Mixers coated with hardened concrete or having badly worn blades will not perform as efficiently as they should. These conditions should be corrected.

Generally, about 10 percent of the mixing water is placed in the mixer before the aggregate and cement are added. Water should then be added uniformly along with the dry materials. The last 10 percent of the water is added after all the dry materials are in the mixer.

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Figure 16: Site Mixing Concrete

Ready-Mixed Concrete Ready-mixed concrete is purchased directly from a central plant. It is convenient and usually of high quality. In some ready-mixed operations, the materials are dry batched at the central plant and then mixed en route to the site in truck mixers. Another method is to mix the concrete in a stationary mixer at the central plant just enough to intermingle the ingredients. The mixing is then completed in a truck mixer en route to the job site.

Most truck mixers have a capacity of 1.2 cubic metres to 5.0 cubic metres, and carry their own water supply.

Initial Set Initial set of concrete usually takes place two or three hours after the cement is mixed with water. It then continues to harden for many years to come.

Admixtures for Concrete Admixtures are substances added to concrete during the mixing process. The substances differ according to their purpose.

Some of the purposes for using admixtures are: To slow down the setting process - Retarders. To speed up the process – Accelerator e.g. in hot or cold weather. To reduce water - Add Strength. To expand the product during drying - Ensure a firm fit e.g. underpinning. To thicken or increase the viscosity of the cement paste. To improve resistance to varying temperatures e.g. freezing and thawing - these are called Plasticisers or Anti freeze agents The types of admixtures used will depend on the purpose the concrete is to be used for and the principal desired effect.

There are other advantages to the use of intentionally entrained air in concrete and it is these which have led to its widespread use even in the more temperate regions of Australia. For example, the workability of the fresh concrete is increased, enabling a reduction in the water content of the mix. In addition, the cohesiveness of the concrete is increased.

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Figure 17: Slump Cones - Testing of Concrete

Slump Test Except for drier mixes this test is a measure of workability. It is the simplest method of ensuring that the consistency of the concrete does not alter throughout the job. The equipment required consists of a slump cone, a bullet - pointed 15mm diameter steel rod 600mm in length, a trowel, straight edge and rule. The test is carried out in the following way: • Make sure the cone is clean and stand it on a smooth, hard surface, preferably a sheet of metal. • Stand on the footrests and fill the cone in three layers, rodding each layer as required by the Australian Standard. (Usually 25 times) • Overfill the cone and strike off the surplus. • Clean round the base and lift the cone vertically, placing it upside down beside the resulting mound of concrete. • Place the straight edge across the cone and measure down to the topmost point with the rule

This dimension is termed “the slump” and it should be reasonably constant throughout the job. To measure the slump, the rod is rested on the cone and the distance from the underside of the rod and the top of the concrete is measured. Collapse as shown in the adjacent figure, is caused by excess water in the mixture.

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Figure 18: Measuring the Slump

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Quantities

Volume Volume is important in relation to concrete, as before any quantities of materials can be obtained, the volume (amount) of the required concrete must be known. Volume is the cubic content and is calculated as cubic metres.

Volume = Length x Breadth x Thickness or; the area of the base multiplied by the perpendicular height.

Cubic Measurement

1.0m x 1.0m x 1.0m = 1.0m3

NOTE: All work is to be kept in metres and the decimal point used. This simplifies and minimises mistakes.

Example: Calculate the amount of concrete required for a floor, 5.6m long, 4.5m wide and 150mm thick.

Volume: = Length x Breadth x Thickness = 5.6m x 4.5m x 0.150m = 3.780m3 rounded to the next 0.2 of m3 = 3.8m3

NOTE: Ready mixed concrete is purchased in cubic metres (m3) in increments of 0.2m3. Therefore, concrete calculations are rounded off to the next 0.2m3.

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TYPES AND USES OF REINFORCEMENT IN CONCRETE

Reinforcement is a material used to strengthen the hardened concrete, which is inserted prior to or during concrete placement and is almost always made from steel.

This unit of learning relates to terms used in reinforcement, sizes, position bar chairs and spacers. The main stresses which occur in concrete are explained to a basic level of understanding.

Concrete when first made is a fluid material and needs to be confined in a mould until it sets. In large works, such as bridges and dams, the mould is a large construction in its own right.

When hardened and cured, concrete has great compressive strength. (This means it has the ability to support great loads placed directly upon it.) However, it has very little strength to resist stresses or forces that tend to bend or pull it apart.

The compressive strength of concrete is about 10 times its tensile strength. Steel reinforcing is used to give concrete tensile strength.

When hardened and cured, concrete is very strong, particularly in compression but has very little strength when under tensile loads.

Figure 19: Concrete Without Reinforcement Under Tensile Stress

A beam when loaded compresses on its top side and the bottom tends to stretch as it is in tension. The concrete beam has an inherent weakness.

Figure 20: Loaded Concrete Beam

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To overcome this, reinforcing steel is used. The hooked ends of the reinforcing steel rod transfer load from the concrete to the reinforcement.

Figure 21: Reinforcing Rod in Concrete As indicated earlier in this unit, concrete when first made is a fluid material, and needs to be confined in a mould until it sets. In large works such as bridges and dams, the mould is a large construction in its own right.

Figure 22: Concrete Mould or Formwork

Concrete Stresses The following types of stress may occur in concrete:

• Tension or Tensile • Compression or Compressive • Shear • Torsion

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The reasons any of these stresses develop are explained in the following diagrams:

Figure 23: Stresses in Concrete

Reinforced Concrete

Reinforced concrete is designed to combine the best characteristics of concrete and steel.

Reinforcing steel has the following characteristics:

Can be formed into different shaped rods and mesh (also called fabric) which can Easily be embedded into concrete. Possesses a high tensile strength. Low resistance to fire It is essential that an effective bond between the concrete and steel is achieved

Bonds are best achieved by using twisted and deformed reinforcing rods rather than plain round sections.

Reinforcing cages can be made up on-the-job to suit a design specification.

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A wide range of welded mesh reinforcements are also manufactured for reinforcing concrete footings, walls and floor slabs.

Figure 24: Making Up A Cage The placement of the steel in a reinforced concrete member is designed to be placed in the concrete where it will effectively resist the tensile and other stresses which occur when loadings are applied to a member.

Figure 25: Tensile Stresses in Concrete Members

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Reinforcing also reduces the shrinkage cracks that occur in concrete during the initial setting and hardening.

Tensile stresses occur in that part of a member subjected to a stretching action as shown on the previous page.

Vertical shear stresses, resulting in diagonal cracking, occur in a structural member near to the support.

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Figure 26: Vertical Shear Stresses When a member is supported at its end-points the tensile stress is greatest at the bottom. Figure 27 shows where the reinforcing should be placed.

Figure 27: Reinforcing Near Bottom of End Supported Beam

A cantilever beam will require reinforcing in the top of the beam to resist the tensile stress as shown in Figure 28.

Figure 28: Reinforcing Near Top of Cantilever Beam

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Handling and Storage of Steel Reinforcement When delivered to site it should be kept clear of dirt and other contaminants and should be placed on suitable timber packers.

When carrying reinforcement the following should be observed: Use of sufficient labour for safe movement of the load. Handle reinforcement so that the ends do not cause damage to structures or injury to people. Always wear protective clothing

All exposed reinforcement already cast into concrete should have safety caps placed on the ends.

Types of Reinforcement Steel is regarded as the best reinforcing material for concrete because it has almost the same contraction and expansion rate due to temperature changes as concrete. It may also be purchased in many sizes and forms.

The two main types of steel reinforcing used in concrete are reinforcing bars and welded wire fabric (or mesh). Bars may be smooth or deformed. Smooth bars are generally smaller in diameter. Deformed bars have ridges along the sides. These improve the bond between the concrete and steel.

Steel reinforcing is used in footings, slabs, columns, beams, walls and other concrete work to add strength and control stresses. Reinforced concrete is a composite material which utilises the concrete in resisting compression forces, and some other material, usually steel bars or wires, to resist the tension forces.

Reinforcing for Footings and Ground Piers Y Bar Deformed bar called Tempcore - High Strength S Bar Deformed bar called Structural GRA08 - Mild Steel R Round Bar Mild Steel Rod F Fabric Mesh Is made from Hard Drawn Wire - High Strength

The two most common types of steel reinforcement used in strip footings are: Welded fabric, called trench mesh; and Individual bars

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Figure 29: Trench Mesh, Individual Bars and Ligatures

Cutting Fabric and Rod Reinforcing Sheets are cut to size using either abrasive cut-off wheels or bolt cutters. Large bolt cutters can cut up to 19mm diameter mild steel reinforcing rods

Figure 30: Cutting Fabric and Rods

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Positioning Steel Reinforcement in Beam Footings The following points must be observed when placing reinforcement in position:

Place the cage in the trench clear of the trench sides. Support the bottom bars on chairs or hung from a timber support across the top of the trench. See Figure 31 Ensure the laps at change in direction are properly made and the cages are located firmly in position. Steel must be lapped at the corners for the full width of the cage and at joins in the length a minimum of 500 mm or as specified.

Figure 31: Supporting Reinforcement in Footing Excavations In some States, wider rather than deep beam footings are used as shown in Figure 32. In these situations the lower steel/trench mesh would be supported as described above on trench mesh supports or bar chairs.

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Figure 32: Broad Independent Footing

Reinforcement in Slab-on-Ground A slab-on-ground has thickened edges, which are called edge-beams. Sometimes slabs also have internal beams, which act as stiffening beams or wall supports. All these beams need steel reinforcement fixed near the bottom - this is called bottom-steel.

Bottom-steel must be placed on bar chairs or trench mesh spacers.

Trench mesh is the usual type of bottom-steel - a single layer or a double layer (one directly on top of the other separated by a fitment or ligature) as required by the building plans. 40mm minimum concrete cover to the reinforcement is required (up to 75 mm may be specified if soil has aggressive ground water). In some areas greater depth and heavier reinforcement is required.

Top-steel is needed over the whole area of a slab-on-ground. The main reason for this top- steel is to control the cracking, which inevitably occurs as the concrete dries out.

Fabric sheets (6 x 2.4m standard size) are usually used as top-steel and are set on bar chairs and bases prior to placing the concrete so as to leave the specified concrete cover above the steel reinforcement.

Trench mesh should have a half-a-metre minimum overlap. Full-width overlap at corners. (It is a sound precaution to wire the mesh together at these overlaps).

Slab fabric should be lapped by one full panel of fabric so that the two outermost transverse wires of one sheet overlap the two outermost transverse wires of the sheet being lapped. Placing Fabric Fabric is usually placed towards the top surface of ground floor slabs, about mid thickness In reinforced paving and towards the bottom of suspended slabs. Joints should be lapped at intersection as specified in the reinforcement schedule. Laps can be made less congested by turning over the joining sheet. When the bottom reinforcement is tied together the supporting bar chairs can be spaced out and wired to the reinforcing bars at 500mm centres. Supporting the Reinforcement There is a wide range of bar chairs for on-ground or in formwork application which can support the reinforcing steel at the height specified in the reinforcing schedule.

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Reinforcing must be held firmly enough to support the weight of workers during the placement of concrete. Bar chairs are spaced in accordance with details given on drawings, but should be greater than 1 metre for large diameter wire but closer for small diameter wires.

Figure 33: Positioning and Lapping of Fabric Reinforcement The most common type used for fabric consists of a wire chair which clips into a plastic base. The base provides support, and prevents damage to the plastic moisture barrier, if used in a ground slab.

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Figure 34: Bar Chairs Edge Cover of Reinforcement Standard cover of reinforcement by concrete is specified in the AS concrete code or on engineering drawings.

Figure 35: Edge Cover of Reinforcement

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Fixing Steel Bar Reinforcement In Columns, Suspended Beams, Slabs And Specialist Structures Steel reinforcement for commercial and industrial, high-rise buildings and specialist structures, e.g. industrial applications, is invariably specially designed by an engineer and has its own set of drawings.

The reinforcement is then codified onto “Bending Schedules” which detail each bar, ligature and stirrup separately.

The steel is usually delivered to the site already cut and bent in accordance with these bending schedules. Columns After sorting on site, the reinforcing steel for columns is usually pre-assembled into cages on site, lifted into position by crane, and fixed to the starter bars that have already been cast into the lower floor or edge beam. The formwork for the column is then erected around the reinforcing cage. Suspended Beams The steel for these beams is often pre-assembled on-site into cages and placed into the formwork by crane. Depending on the complexity, weight, and design of the reinforcement, it may be necessary to assemble the reinforcing in position AFTER the formwork has been erected. Suspended Slabs, Walls and Specialist Structures The steel reinforcement is almost always assembled and fixed in place in accordance with the drawings and specifications bonding schedule, after the formwork (or one side of the formwork has been erected).

Fixing of this type of reinforcing steel requires the ability to read and interpret drawings and bending schedule, and is a recognised trade or skill.

The above information dealing with the handling and fixing of reinforcing steel in columns, suspended beams, and slabs, and retaining walls is general information for all participants.

However, the practical application of handling, placing and fixing reinforcement in these situations is to be carried out only by trainees of the structures and civil operations streams.

Many offsite construction trades use concrete and reinforced concrete to place their work on or fix it to. In most cases the concrete will already be in position but in some cases you will be required to set up, pour and finish the concrete.

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ERECTION, DISMANTLING AND MAINTENANCE OF FORMWORK

This unit refers to the basic work practice of selecting, erecting and dismantling formwork.

Erection, dismantling and maintenance refers to the “putting together” (assembly), taking down and taking care of the formwork used on a construction site, which is used to form a mould for the concrete to be placed into.

Assessment of this unit is carried out in practical tasks involving the erection of formwork for slab-on-ground and pavement concrete work.

These tasks must involve a demonstration of the skills required in stripping, cleaning and storage of formwork.

Formwork can best be described as a mould that shapes concrete, and is used extensively in the building industry. Some typical applications of formwork are: Footings Columns Slab-on-Ground Suspended Slabs Suspended Beams Walls

Figure 36: Applications For Use of Formwork

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Slab-on-Ground Formwork for slab-on-ground construction usually consists of one of the following:

Timber or metal forms to the edges of the slab Brickwork Concrete blockwork

Suspended Concrete Slabs Formwork for suspended slabs usually consists of form ply or special metal sheeting supported and braced above ground level.

Figure 37: Supporting Suspended Slab

Beams

Figure 38: Beam Formwork

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Formwork Formwork is the temporary construction that gives form to and supports the freshly placed concrete. The loads carried by the formwork are considerable and it must be strong enough to support workers, materials and equipment as well as the concrete without movement or fear of collapse. It is often specially designed and supervised by an engineer.

There are three main principles that must be observed in the design and construction of formwork. They are: • Quality • Safety • Economy Quality The forms which shape the freshly placed concrete will imprint in the surface of the concrete any defect present on the face of the form. Forms must be true to size, plumb, square and correctly aligned in accordance with acceptable tolerances as stated in the specification. Four factors are important to good craftsmanship. • Accuracy • Rigidity • Tightness of joints • Finish Accuracy The plasticity of fresh concrete allows it to be moulded into any desired structural or architectural shape. The moulds or forms are equivalent to a photographic negative of the concrete construction, any inaccuracy or blemish in the formwork being reproduced identically in the structure. It is therefore essential that forms be designed and constructed accurately, so that the desired size, shape, position and finish of the cast concrete structure are obtained. Wherever possible, forms should be set level with the finished top of the proposed concrete so that they can be used as a screed.

Rigidity Formwork should be of substantial construction to prevent distortion when supporting wet concrete. It should be sufficiently rigid to prevent: • Bulging • Sagging • Movement

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Figure 39: Insufficient Support Allows Bulging of Form Bulging can be prevented by ensuring that the supporting members are strong enough to support all of the loads and are spaced in accordance with the specified centre-to-centre dimension.

Formwork must be braced to prevent movement in any direction. For suspended beams and slabs, lateral ties prevent the vertical supports from being displaced by knocking or from bending while under load.

Collapsed formwork, a result of shoddy workmanship causing a massive clean-up operation

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Figure 40: Brace Formwork Support Thoroughly

Tightness of Joints Joints between intersecting members in direct contact with the concrete during placement, must be tight enough to prevent leakage of the cement paste.

Leakage of cement paste will form unsightly fins and result in a honeycomb surface to the concrete.

Any flaws in the concrete will require a considerable amount of work to restore the surface finish.

Planed timber or formply will provide a neater finish and is much easier to clean for re-use than sawn timber.

Figure 41: Examples of Open Joint Flaws

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Both of these concrete-honeycombing problems are a direct result of incorrect or insufficient concrete compaction and vibration. They could have ben avoided with correct workmanship. The one on the left can be repaired at a cost whilst the structural beams load properties have been compromised and it is possible crusher material.

Finish There are several surface finishes which can be obtained by treating the surface of the form. Industrial buildings generally require a smooth finish; however, simulated wood grain finishes can be produced by exposing the grain of timber forms by sand blasting. Special plywood sheets can also be made for this purpose. Joints, nails, screws, and tie wire leave unsightly imprints on the concrete surface. Always ensure that you provide a clear and even surface to the face of the forms.

Stripping When formwork is stripped, ensure that safe and damage limiting procedures are used, for example, supporting components during the process.

Figure 42: Off-Forms Face Finish

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Figure 43: Causes of Defects in Concrete Face Finish

Safety There are two aspects of safety which must be observed: Strength, design and construction of formwork and supporting components. Work procedures Strength - Design & Construction

The “dead load” of the fresh concrete and reinforcing steel is approximately 2500kg (per cubic metre). It is essential that the formwork and formwork components are strong enough to support the concrete and all other imposed loads.

While the design and the supervision is the work of a specialist, you can contribute to the safety of the job by ensuring that directions and specifications are strictly observed.

Work Procedures The safety of yourself and other workers on-the-job can be ensured if safe working procedures are practised at all times. The following safety factors must be observed:

Keep the work area clear of off-cuts and loose materials. Make sure that all structural components are firmly fixed before leaving the job; even for a few minutes. When you have finished using a particular tool, put it in your tool box. This practice will prevent it form being lost or from falling on a work mate. Ensure electric leads and air hoses do not create tripping hazards. Always report unsafe equipment or structural components to your supervisor immediately they are noticed and warn your fellow workers. Ensure that handrails and kickboards are in place and securely fixed. Observe safety signs and wear your safety clothing and equipment at all times while on the job.

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Figure 44: Wear Personal Safety Gear

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Observe Safety Signs Formwork can collapse as a result of faulty design or careless workmanship. A collapse may result in costly structural damage or, more seriously, injury or even loss of life.

Safety is of particular importance to workers involved in the construction and removal of formwork. Always ensure that you pay attention to constructional details and observe correct working practices.

Economy Formwork components and forms are usually designed for re-use, either on the same project or on others. You can contribute to the economic operation of the job by observing the following procedures: • Timber and plywood form panels are expensive. Never cut these materials without checking your measurements. • Never cut from a large piece of material when a smaller piece will produce less waste. • When stripping the forms take care not to damage the ends or edges with your hammer or pinch bar. • Remove nails and other fixings with care. • Always store and stack materials and equipment in the designated storage area when not in use.

Figure 45: Safely Store All Equipment

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Preparation of Forms for Concreting Cleaning All dirt, mortar, wood chips, sawdust, etc must be removed from inside the forms before concreting can commence. If the bottom of the form cannot be reached, then clean out holes should be provided at suitable points to permit the removal of foreign matter. A jet of air or water can often be used effectively to remove debris. All clean out holes must be carefully closed after cleaning out the forms. Release Agents (Form Oils) Most form materials require the application of a release agent to the surfaces which will make contact with concrete. The following are the requirements for release agents: To act as a parting compound to facilitate the easy release of forms without concrete sticking to their surfaces. To act as a sealer to prevent the forms absorbing water from the concrete. Not to stain or disfigure the concrete surface. Not to leave a surface deposit which will prevent adhesion of a subsequently applied render, paint or other material

Figure 46: Applying Release Agent

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Types of Release Agents Release agents (also known as form oils) are generally one of six types: 1. Neat oil 2. Mould cream (water emulsified into oil vehicle). 3. Water soluble emulsion (oil emulsified into water vehicle). 4. Neat oil with additives (surfacing or wetting agents). 5. Chemically reactive agents. 6. Barrier paints and coatings. Application of Coatings Surface coating should be applied to smooth, clean surfaces by roller, brush, spray, wiping, etc, depending on the type of coating. Coverage must be complete and uniform for good stripping and appearance. There should be no excess coating to stain the concrete. Cleaning of Formwork Any concrete adhering to the forms must be removed before re-use of the forms. The sooner it is removed the easier it will be and less sustained by the forms. Different means are used on the various materials: Steel Forms: - metal scraper Plywood Forms: - stiff brush Sawn Timber: - metal scraper Glass Reinforced Plastic: - brass brush

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Installation of Formwork for Slab-On-Ground

Formwork for slab-on-ground construction usually consists of one of the following:

(a) Timber or metal forms to the edges of the slab;

(b) Brickwork in place and used to contain the concrete, or

(c) Blockwork in a similar situation.

Figure 47: Formwork Construction Types Procedure for Installing Formwork for a small Slab-on-Ground

Excavate if necessary, a level area free of vegetation. Drive pegs securely into the ground in the required positions. (Remember to allow for the thickness of the form boards). Mark the form height onto the pegs.

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Figure 48: Prepare Area for Fixing Form boards

Nail form boards onto the pegs at the required height, (support should be placed directly behind where nail is being driven so as not to loosen peg)

Figure 49: Fixing Form Boards To Pegs

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Where necessary bracing should be installed

Figure 50: Bracing Wide Formwork All pegs protruding above formwork should be trimmed to provide a uniform flat surface for screeding

Figure 51: Trim Off Projecting Pegs

In some situations it may be necessary to construct and assemble formwork first, then position and secure. Fill and level inside forms with sand or coarse gravel as necessary to required level. Compact filling to ensure a solid base for concrete.

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Figure 52: Fill and Consolidate Sub-Grade

Figure 53: Place and Support Reinforcement

Install vapour barrier (if required) and cut, place and tie reinforcing. Support reinforcement on approved bar chairs at the specified cover position Install Blockouts When the formwork is in place and prior to the placement of the concrete, all services to be built-in must be accurately placed according to the drawings and firmly fixed in position so as not to move during the concreting procedure.

Blockouts or core holes for service penetrations or other structural elements must be accurately positioned and firmly fastened to the formwork or reinforcing steel, if applicable. Polystyrene foam, shaped to the required size and detail, is often used for small and sometimes large blockouts. At other times timber formwork, capable of being easily dismantled at removal, is fabricated and installed prior to the placement of the concrete.

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Remove and Reclaim Formwork Removal of formwork for suspended concrete slabs should not be undertaken by inexperienced persons. Removal of formwork before concrete has gained sufficient strength to support itself and the loads placed upon it will result in failure of the concrete. In many cases the engineer will require back propping for continued support after the formwork has been stripped.

Ideally formwork should be left in place as long as possible to provide protection for the corners of edges and to assist with curing.

Stripping formwork requires considerable care on the part of workers to avoid damage to the green concrete. Concrete can easily be damaged by scratching and shipping, even though it may have developed sufficient strength to support itself.

Care must be taken to protect the concrete and to extend the useful life of the forms by careful handling. Not only must the forms hold together, but they must remain dimensionally accurate and stay in good condition to make accurate alignment and clean joints possible. Form panels and column, wall and floor components should not be dropped. All Nails Should be Removed from Formwork Preparation for Storage To prevent steel forms rusting during prolonged storage it is advisable to coat them with a thin film of oil, of a type, which will not damage the concrete. If sump oil is used, it will need to be removed before the forms are re-used for columns, which are to be cement rendered.

Storage If the forms are to be re-used at a later time it is important that they are: • Stacked to prevent distortion • Stacked to prevent rising dampness • Protected from heat/wind/rain • Protected from contact surfaces

The above information dealing with the removal and reclaiming of formwork, preparation for storage and storage is general information for all participants.

The practical application in respect to all footing and slab-on-ground formwork is also applicable to all participants.

However, the practical application of assisting with the team of formworkers in the erection and stripping of formwork for structural columns, suspended floors and retaining walls is applicable only to trainees of the structures and civil operations streams.

Assist with Placement of Concrete Placing concrete refers to the action of placing the concrete, either manually or mechanically into it’s required construction position.

This unit deals with the work involved before and during the placement of concrete.

Preparation Before concrete is placed it is essential that all formwork, damp-proof membranes, and reinforcement should be checked. Formwork Needs to be secure and cleaned of any debris and waste

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Screeding Points Need to be checked and in the right place

Damp-Proof Membrane Should be checked for damage, and in compliance with the specification

Reinforcement Must be in the correct position and securely tied and supported

Figure 54: Materials Required for 1 Cubic Metre of Concrete Mixing of Concrete Site Mixing When mixing concrete on site by hand or in a mixer the person mixing material is responsible for proportioning by volume.

Proportioning of Materials Course aggregate contains approximately 50% of voids (spaces). Fine aggregate is used to fill these voids, therefore, fine aggregate required equals half of the course aggregate. Fine aggregate contains approximately 30% voids and cement is used to fill these voids. Therefore, cement content equals 30% of the fine aggregate quantity.

Experiments show, however, that in order to coat all surfaces with cement a further 20% is required, thus making 50% of cement to fine aggregate.

From the figures above we obtain a mix of 4:2:1 or 4 parts course, 2 parts fine and 1 part cement or 4:2:1 is considered a good general mix. See Figure 55.

Water required is approximately 20 litres for every bag of cement, depending on the moisture content of the aggregate. Accurate proportioning is a major factor in concrete strength. Figure 55 shows the sand occupying the voids (spaces) formed by the gravel. It also shows the voids between the sand grains filled with cement.

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Figure55: Proportioning of Aggregates and Cement Pre-mixed Concrete Concrete must be placed quickly and simply.

Direct from a transit mixer truck is easiest and best.

The most convenient and least labour intensive of concreting is to use ready mixed concrete. A phone call to a ready mix plant will confirm your order. Details given when ordering must include: The volume in m3. The slump required. The strength of concrete stated in MPa. The nominal mix of aggregates Concrete Mix The concrete mix should be such that there is just sufficient fines (cement and sand) to allow a mortar to be worked to the surface with vibration and a little tooling effort. Too many fines will make finishing easier but will probably lead to surface crazing, as well as being more expensive than a well proportioned mix. Too much water in the mix (high slump) will create delays in finishing, as well as producing a weak surface layer of mortar, resulting in a dusty and crazed surface with low resistance to wear and abrasion. A satisfactory uniformed concrete surface requires: • A properly proportioned concrete • Adequate mixing, handling and placing methods which will minimise segregation • Adequate compaction • Controlled finishing techniques • Adequate curing

Placing and Compacting the Concrete Order concrete by strength-grade and slump, as required by the project specification.

As soon as the concrete is properly mixed, it is delivered to site. Placing should begin without delay and should be completed within half an hour. If a long time is allowed to elapse, the concrete will begin to stiffen and become difficult to place and compact.

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If water is added the mix will become sloppy and easier to work into place - but the concrete will be weaker, crack more and have a poor surface finish. For this reason no water would be added to concrete during the placement and finishing operations. Place each load of concrete next to the previous load. Start at one end and work along the slab or beam making sure that each new load is well mixed into the load before.

As far as possible concrete should be placed in one operation, and succeeding batches placed one against the other before initial set has commenced. Each batch of concrete should be well rodded to compact it and to weld it with the preceding batch.

Figure 56: Placing Concrete Directly From Chute

Handling and Transporting Concrete to Avoid Segregation Do not let concrete free-fall more than one metre from a chute, pipe or bucket when it is being placed. Level the surface of the concrete with a screeding board. It is important to move the screeding board with a sawing and chopping motion as this helps to compact the concrete.

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Figure 57: Discharging from Chutes and Conveyors Use of Vibrator A mechanical vibrator should be used to compact the concrete. Poke the vibrator into the concrete every half metre over the length of the beam and slab and hold it in place until the concrete settles and bubbles stop rising to the surface.

Hold the vibrator straight up and be careful not to move the steel reinforcement, or damage the formwork.

Care must be taken not to over-vibrate concrete or segregation may occur.

Figure 58: Using a Vibrator

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Once placed, concrete should be as near as possible to its intended location. For example, it should not be placed in large quantities in one place and allowed to run or be worked over a long distance in the form. Segregation (separating) of ingredients results from this practice. It should be avoided. Generally, concrete should be placed in horizontal layers having uniform thickness. Concrete should be distributed by shovel NOT with the vibrator. The vibrator separates the components if used too much. Initial Finishing Immediately after placing and vibration a screed board (straight edge) is used to quickly level the concrete. The screed board is moved along with a sawing motion and in such a manner that a small amount of concrete is always pushed ahead of the screed. Concrete is shovelled up to or away from the front of the screed as is necessary. Finishing Irrespective of the type of surface finish required the essential requirements are: Initial finishing should be completed as soon as possible after placing and vibration. Final finishing, floating and trowelling should be delayed until the surface is ready - the final work should also be kept to the minimum necessary to produce the required surface NO finishing operations should be performed in any areas where there is free surface water.

Figure 59: Levelling and Screeding with a Straight Edge

Precautions Precautions must be taken when placing concrete to ensure that: Formwork and reinforcement are not damaged or dislodged. The concrete does not segregate The placing of concrete should start from the corners of formwork and from the lowest level if the surface is sloping.

Each load of concrete should be placed into the face of the previously deposited concrete, not away from it.

Where a layer of concrete cannot be placed before the previous layer hardens, as on the morning after an overnight stop, a construction joint should be formed.

Concrete should not be placed in heavy rain without overhead shelter, otherwise the rain may wash cement from the surface.

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Use and Maintenance of Concreting Tools You will have observed and identified most of the basic tools and equipment used by concreting operators in the Learning Resource Package for NBC1005 Basic Plant, Equipment and Tools.

In this unit the care, maintenance and special uses of each tool or piece of equipment will be described.

The tools are to be used in accordance with accepted industry practice, and this will be explained in the following unit of work.

The application of selected pieces of equipment and the tools will be demonstrated and applied in the Practical Activities included at the end of this Learning Resource Package.

Care of Concreting Tools and Equipment All tools and equipment must be cleaned of any concrete or concrete residue immediately their use has finished. Failure to do so will make the tools and equipment difficult to use and inefficient to operate, and could mark or damage the finished work.

They should be scraped and washed clean, oiled or greased as required and stored in a dry secure place.

During storage, handling and use, finishing tools should be stored in such a way that the surface in contact with the concrete is not accidentally damaged or bent.

If storage is to be for a considerable period of time, then tools can be coated with a light application of form oil to prevent corrosion.

Types of Tools and Equipment There are two main types of tools and equipment used in concreting:

• Powered • Hand

Powered Tools and Equipment This equipment is commonly powered by petrol engines, electric motors, or compressed air. The items are usually small enough to be moved around by one or two workers.

Common items of powered equipment includes: Small mixers ...... petrol or electric Screeds ...... petrol Vibrators ...... petrol, electric or compressed air Floats (trowelling Machine) ...... petrol Concrete pumps ...... Specialised equipment usually truck mounted

Small Mixers These are now used only for the smallest jobs, or in country areas where ready-mixed concrete is either not available or very uneconomic to use.

It is essential that the agitators inside the drum should frequently be cleaned of any concrete residue. On completion the mixers should be thoroughly cleaned and washed out with water.

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on

Figure 60: Concrete Mixers Screeds These consist of a large plank with double handles at each end and a small petrol engine centrally mounted on the beam. They are used on very large slab pours with substantial side forms. Two operators, one at each end, use these screeds to spread and compact the concrete in one operation to a finish as soon as it is placed. Special care is needed when storing these to prevent warping, bending or damage to the beam.

Figure 61: Vibrating Screeds Vibrators These are used to compact the concrete after laying and before screeding off and finishing. There are two main types: • Internal, eg. Poker vibrators. • External - applied through the forms or at the surface of the concrete (external types are relatively rare and specialised) Internal Vibrators These are usually poker types that are placed in the concrete being poured at about half metre intervals, and held until the concrete has settled and all the air bubbles have been removed. The vibrating pokers are made in a range of sizes. Selection will depend on: (i) Size of pour (placement). (ii) Spacing of reinforcing (the poker has to pass between the bars). (iii) Output and number of vibrators required and power source limits.

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Figure 62: Internal Vibrators in Use Floats (Trowelling Machines) Mechanical floats or trowelling machines commonly called helicopters are used for trowelling the concrete to a satisfactory finish. By altering the speed of rotation and the angle of the “floats” a good finish suitable for carpet or vinyl, can be achieved.

Figure 63: Trowelling Machines

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Hand tools and Equipment The following is a list of hand tools commonly used in concreting: • Wheelbarrows • Planks • Shovels • Straight edges and screeds • Floats • Steel trowels • Edging and jointing tools • Brooms Again, it is very important that these tools are kept clean of hardened concrete and concrete residue. Wheelbarrows Used to transport concrete from the delivery point (usually the mixer truck) to the final place in the forms.

Planks Used to make a smooth path across ground, over formwork and across reinforcement for the wheelbarrow to be wheeled along and reduce the effort required by the concrete worker.

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Shovels Used for mixing, moving concrete around in the forms, initial placing and tamping, and cleaning up.

Screeds and Straight Edges These are used to compact concrete by tamping and to screed off to the required levels. Special care must be taken when storing, handling or using straight edges to ensure that they do not bend and are protected from damage.

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Floats There are several types of floats, each designed to produce a different finish.

Bull Floats

Figure 64: Using a Bull Float A back and labour saving tool used for large surface areas. Made from magnesium alloy and designed to have a long handle, it aids surface finishing to concrete surfaces and is used immediately after screeding off. Wood Floats The wood float is used to level out any slight imperfection left after screeding off with the straight edge or bull float. It can also be used to provide a textured finish to the surface of concrete.

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Plastic Floats Has a similar use to the wood float but produces a finer finish.

Steel Trowels The steel trowel is used after wood floating or bull floating to provide a dense smooth surface to concrete.

Figure 65: Using a Steel Trowel Edging Tools When the concrete has been poured and has stiffened, it is often required that the edges be worked to a neat rounded finish. A bricklayer’s large laying trowel is used to develop a clear line between the existing formwork and concrete edge. The edging tool is then used to form a neat rounded finished edge to the work.

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Figure 66: Using a Edging Tool

Jointing Tools

Figure 67: Using a Jointing Tool Used for putting smooth edges on construction joints or induced cracking joints, after the joint has been formed or cut, or just in the surface of thin slabs.

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Figure 68: Brooming Surfaces Brooms Used for producing a non-slip finish on concrete (Brooming or Broom Finish). Also used for general clean up.

Assist with Finishing Concrete Finishing Concrete Slabs Finishing concrete refers to the final top finish process which is completed in various ways according to the specified use of the concrete or the appearance required. This unit will introduce you to the techniques of surface finishing and you will be given the opportunity to apply the knowledge and skills gained in this and previous units of this section, by completing Practical Activities incorporating all aspects of preparing for, placing and finishing concrete. Concrete slabs may be finished several ways. It depends on the effect desired and the use of the product. Some surfaces may be left rough, others broomed, floated or trowelled, and other surfaces may be textured, coloured or have exposed aggregate.

Screeding Screeding is usually the first finishing operation after the concrete is placed in the forms. It is performed with a screed.

Screeding is the process of striking off the excess concrete to bring the top surface to the proper grade or elevation.

The edge of the screed may be straight or curved depending on the surface requirements. The screed rests on the top of the forms and is moved across the concrete with a sawing motion. It is drawn backwards slightly.

An excess of concrete should be carried along in front of the screed to fill low places as the tool is moved forward. But if too much concrete is allowed to build up in front of the screed, it may tend to leave hollows behind it. In normal concrete the dry materials used are heavier than water. They will begin to sink or settle to the bottom of a plastic concrete mixture shortly after placement. This settling action causes excess water to rise to the surface.

This condition is called bleeding. Bleeding does not usually occur with air-entrained concrete. It is very important that the first operations of placing, screeding and wood floating be performed before any bleeding takes place.

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Figure 69: Using a Screed If any finishing operation is performed on the surface while the bleed water is present serious scaling, dusting or crazing can result. The high and low spots may be eliminated and large aggregate embedded using a bullfloat. The operation should follow immediately after screeding to prevent bleeding.

Figure 70: Eliminating High and Low Spots with a Bull Float

Some surface finishes may not need any further finishing, but most will require one or more of the following operations. Edging and Jointing If edging is necessary, this could be the next operation.

Edging provides a rounded edge or radius to prevent chipping or damage to the edge. The edger is run back and forth until the desired finish is obtained.

Care should be taken to cover all coarse aggregate and not to leave too deep a depression on the top of the slab. This indentation could be difficult to remove during subsequent finishing operations. Edging produces a radius on the edge of the slab which prevents chipping. In step one, above, trowel is inserted between form and concrete, to provide track of an edging operation shown in step two below.

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Figure 71: Using an Edging Tool As soon as edging has been completed, the slab is jointed or grooved. The bit (cutting edge) of the jointing tool cuts a groove in the slab which is called a control or contraction joint.

Any cracking due to shrinkage caused by drying out or temperature change will occur at the joint. These cracks are not noticeable when controlled. The joint weakens the slab and induces cracking at that location rather than some other place.

In sidewalk and driveway construction, the tooled joints are generally spaced at intervals equal to the width of the slab, but not more than 5m. They should be at right angles to the edge of the slab.

Use a straight edge as a guide when making a groove. A 25 x 200 or 25 x 250 board will be ideal. Be sure the board is straight.

Figure72: The Jointing Operation Large concrete surfaces may be jointed by cutting with a power saw using an abrasive or diamond blade. When grooves are cut rather than jointed the operation should be performed 4 to 12 hours after the slab has been finished. The cutting must be done before random shrinkage cracks develop, but after the concrete is hard enough not to be torn or damaged by the blade.

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Figure 73: Sawed Control Joint Floating After concrete has been edged or jointed, it should be allowed to harden enough to support a person and leave only a slight foot imprint. Floating should not begin until the water sheen has disappeared.

When all bleed water and water sheen has left the surface, the concrete has started to stiffen.

The surface is floated with wood or metal floats or with a finishing machine using float blades. Aluminium or magnesium floats work better especially on air-entrained concrete.

Metal floats reduce the amount of work required by the finisher. Drag is reduced and the float slides more readily over the surface.

It provides a dense smooth surface that could be slippery when wet.

A wood float tends to stick to the surface and produces a tearing action. It provides a rougher texture that is not as slippery in wet conditions.

The light metal float also forms a smoother surface texture than the wood float.

Figure 74: Floating or Surfacing the Concrete with a Wooden or Metal Float

Generally, finishing begins when the sheen has left the surface (in the case of air- entrained concrete there may be little bleed water and no visible sheen and it may be possible to finish this type of concrete after a short delay). Normally when the sheen has left the surface, the concrete will support your weight. This may cause indentation of 5mm or more so finishers must use foot and knee pads to distribute their weight. As shown above (Figure 75).

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NOTE 1: Finishing should NOT be attempted in any area where there is free surface water.

Where power equipment is used the delay period can be increased so that the concrete can support the weight of a person with little marking.

NOTE 2: Cement should NOT be used to dry up surface moisture as this will cause cracking later on.

Brooming A broomed finish is very popular. It provides a non-slip surface which is particularly useful for paths and driveways.

This finish is achieved by pulling a damp broom across freshly floated surfaces. Coarse textures, suitable for steep slopes or heavily trafficked areas are produced by stiff-bristled brooms. Medium to fine textures are obtained with a soft-bristled broom. The broom should be kept damp during the work.

Broomed textures can be applied in straight lines, curved line or wavy lines. It is advisable when applying the curved or wavy lines to take care to keep the lines regular in curve and pitch - and not to be too flamboyant with this finish.

On paths and driveways the broomed lines should be at right angles to the direction of the traffic. For long paths or areas with many panels it may be useful to broom diagonally - changing direction for each adjoining panel.

As with the floated finishes, after brooming it will be necessary to clean up the grooves and edged with another pass of the grooving and edging tools.

Figure 75: Applying a Broomed Finish

Exposed Aggregate Exposed aggregate offers a simple way of obtaining decorative finishes which are textured, colourful and highly immune to wear and weather. Various sizes and colours of gravel are available - but it is advisable to use aggregate 5 to 20mm diameter which is smooth - not crushed rock with abrasive sharp edges.

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While the correct delay before removing the surface cement to expose the aggregate is most important to the production of a quality finish, it is difficult to nominate the specific time as it depends on many variables. Some of these are concrete temperature and age, type of cement, admixture type and the quantities of water, cement and admixtures used. The delay also depends on weather conditions, depth of pour, type of aggregate, type of sub-grade, etc.

Curing Curing is the drying out of concrete under conditions of humidity and temperature, which help in the proper setting of the concrete. The properties of concrete such as strength, watertightness, wear resistance and stability; improve with age as long as conditions are favourable. The improvement in the properties is rapid at first and continues at a diminishing rate for an indefinite period as long as moisture is present and the temperature is favourable. Evaporation of water from newly placed concrete can cause the cement hydration process to stop at an early age. Loss of water also causes the concrete to shrink thus creating tensile stresses at the drying surface. If these stresses develop before the concrete has attained adequate strength, surface cracking will result.It follows that concrete should be protected so that the moisture is not lost during the early hardening period. Concrete should also be kept at a favourable temperature.

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Curing Methods Concrete can be kept moist by a number of curing methods. The one used should be the one that will be the most effective and economical for the particular conditions under which the concrete is to be placed.Most curing methods have advantages and disadvantages as shown in the following table.

Method Advantage Disadvantage

Sprinkling with water or Excellent results if Likelihood of drying covering with wet hessian. constantly kept wet. between sprinklings. Difficult on vertical walls.

Moist sand Good results, if Can dry out, messy and constantly kept wet. removal problems.

Waterproof paper Excellent protection, Cost can be excessive. prevents drying. Must be kept in rolls, storage and handling problems.

Plastic film Absolutely water tight, Should be pigmented for excellent protection. heat protection. Requires Light and easy to handle. reasonable care and tears must be patched, must be weighed down to prevent blowing away.

Curing compounds Easy to apply. Sprayer needed - Reasonably inexpensive. inadequate coverage Requires little allows drying out; film can maintenance after be broken or tracked off application. before curing is completed; careful consideration of future finishes required, before selection of type.

Length of Curing Period The length of time that concrete should be protected against loss of moisture is dependent upon the type of cement, mix proportions, required strength, size and shape of the concrete mass, weather and future exposure conditions. For most structural uses, the curing period for cast-in-place concrete is usually three days to two weeks, depending on conditions. A commonly specified period is seven days. At this stage, it would be to your advantage to visit a building site, with your instructor, to observe: Excavated footings, trimmed and with reinforcing steel in place, tied and supported An area prepared for a basic slab-on-ground, pathway or vehicular drive. This area should have formwork and reinforcing steel in place and it would be an advantage if placing and finishing of the concrete was in progress. If you work in an offsite workplace making stairs, stone monuments or signs your instructor will show you some examples of excavated footings and areas prepared for basic slab work.

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Attachment 1 - Housing Industry Concrete Handbook

1 CONCRETE PROPERTIES Concrete is a versatile material with many uses. Good concrete, that which achieves its specified properties, depends first of all on the careful selection and proportioning of its constituent materials, and on effective methods for handling, placing, compacting, finishing and curing.

In its basic form, it is a mixture of cement, water, fine and coarse aggregates, which is plastic (can be worked and moulded) when first mixed, and hardens to a solid mass. The properties of concrete, in its plastic and hardened states, are affected by the physical characteristics, the chemical composition, and the proportions of the ingredients in the mix- ture. In its hardened state concrete must be strong enough to carry the loads imposed on it, and durable enough to resist wear, weather and chemical attack. In its plastic state it must suit the methods of handling, placing, compacting and finishing.

The cement paste (cement and water) in the mixture lubricates the aggregates and allow them to move freely while the concrete is placed and compacted. Generally, the more cement paste in the mixture, the more workable the concrete. It is important that concrete delivered to site is sufficiently workable for it to be placed and compacted by the means available. If it is not properly placed and compacted, concrete will not achieve its potential strength and durability.

Addition of water increases the workability, but dilutes and weakens the cement paste. In this respect, cement paste is like any other glue: dilution will weaken it. It is the aim of concrete mix design, or proportioning, to strike a balance between the need for workability, so that concrete can be placed and finished, and the need for it to be strong and durable. Workability can also be improved by the use of chemical admixtures such as plasticisers.

Many of the characteristics of concrete, particularly its strength and durability, depend on the development of chemical and physical bonds: of the cement paste itself as it hydrates (see glossary), and between the cement paste and the aggregate particles as the concrete hardens. The chemical reaction between cement and water (hydration) takes time. Concrete must therefore be kept moist (cured) for a time to ensure that hydration continues and that the concrete achieves its potential strength and durability.

Technologists use a range of materials other than cement, water and aggregates to modify the properties of concrete. These include pozzolanic and other cementitious materials, chemical admixtures, and special aggregates.

2 CONCRETE MATERIALS 2.1 Cements and supplementary cementitious materials

The term ‘cement’ covers a wide variety of organic and inorganic binding agents. By far the most widely used are those known as Portland cements – finely ground inorganic materials that have a strong hydraulic binding action. These binders, when mixed with water, will harden in the absence of air to produce a stable, durable product.

Hydraulic cements manufactured in Australia fall broadly into two classes, namely Portland cements and blended cements, both produced to AS 3792.

Type GP – General purpose Portland cement Type GP cement is used as a general-purpose cement suited to all types of construction, including major construction projects and in precast concrete product applications. Type GP cement may contain up to 5% of approved mineral additions. Mineral additions include limestone, fly ash and blast-furnace slag.

Type GB – General purpose blended cement Type GB cement incorporates supplementary cementitious materials (such as fly ash) used at rates greater than 5% and typically 10 – 40%. Due to the blending of ingredients, type GB cement has a wide range of construction applications for residential construction in concrete, grouts, mortars and

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renders. GB cements gain strength at a lower rate than type GP cements but 28-day strengths are similar.

Masonry cement Masonry cement is a finely ground mixture of Portland cement clinker, gypsum and suitable inorganic materials such as hydrated lime, limestone and pozzolans. It is characterised by producing mortars of high workability and high water retentivity, but which have a lower rate of strength development than those made from Portland cement. These characteristics make masonry cement especially suitable for masonry work but unsuitable for any form of structural concrete.

Off-white and white Portland cements The grey colour of Portland cement is due mainly to the presence of iron in the cement. By lowering the iron content, light coloured cements can be produced. Off-white and white cements are used principally for architectural applications. Australian-made off-white cements are produced to meet general requirements for type GP cement. Currently all white cements are imported. Generally, these would comply with AS 3972.

Supplementary cementitious materials (SCMs) SCMs are defined as fly ash, blast-furnace slag and silica fume, which are added to concrete to improve its characteristics & properties. These additives are sourced from industry by-products.

Fly Ash is the fine residue extracted from the flue gases at coal-fired power stations. These particles are of spherical shape with a glassy appearance and are processed to meet the requirements of AS 3582.1.

Blast-furnace slag is a non-metallic material produced simultaneously with iron in a blast furnace and which is then granulated by the rapid quenching process. It possesses some latent hydraulicity but behaves as a cement in the presence of activators.

How do SCMs work in concrete? When Portland cement reacts with water, calcium hydroxide is produced. This material is soluble and adds little to the strength of concrete. Fly ash, however, reacts with the calcium hydroxide to form insoluble cementitious compounds similar to Portland cement. Slag is also activated by calcium hydroxide and reacts with it. Potential benefits of SCMs • Improved workability • Lower water demand for constant workability • Reduction in bleeding • Durable concrete • More cohesive mix • Longer setting period • Higher ultimate strengths • Reduced heat of hydration.

2.2 Admixtures Admixtures are classified by the characteristic, or principal, effect on the concrete. Most concrete is described by the supplier as either a ‘summer-mix’ or a ‘winter-mix’, and will include admixtures that affect setting times to suit the prevailing conditions.

Air-entraining admixtures are added to general purpose concrete to improve its workability and cohesiveness and to reduce the water demand, thereby reducing bleeding and material segregation. Excessive amounts will reduce potential strengths. Set-retarding admixtures slow the setting of concrete. They are useful during warm to hot weather, and when a concrete mix must be transported long distances.

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Set-accelerating admixtures reduce the setting times of concrete. They are often used during cool weather.

Water-reducing admixtures disperse the cement particles and improve the workability of the concrete without the addition of water.

Superplasticisers increase fluidity of concrete; improving the workability for easier placement where, for example, reinforcement is congested or the formwork makes placement difficult. Working time depends on the type and dosage. Using superplasticisers does not remove the need for proper compaction.

2.3 Water

Most concrete specifications simply require that mixing water shall be potable, ie fit for drinking; or that it be clean and free from impurities harmful to concrete. Generally, water drawn from reticulated town-water supplies is suitable for making concrete. 3 SPECIFYING, ORDERING AND TESTING

3.1 Specifying

3.1.1 General

Australian Standard AS 1379 sets down a number of ways of specifying and ordering concrete to promote uniformity, efficiency and economy in production and delivery.

It refers to two classes of concrete– • Normal-class, which is intended to cover most of the concrete delivered to building sites. Its specification and ordering has been simplified as far as practicable. • Special-class, which allows for the purchaser to incorporate into the project specification any special requirements for the project.

3.1.2 Normal-class concrete

Normal-class concrete is specified by reference to basic parameters which describe the characteristics of concrete suitable for most purposes– • The strength grade (N20, N25, N32, N40, or N50), or the corresponding characteristic strength (20, 25, 32, 40, or 50 MPa at 28 days) • The slump required at the point of delivery (20 –120 mm) • The nominal maximum size of the coarse aggregate (10, 14 or 20 mm) • The level of entrained air (if required)

In addition, the order for concrete should specify– • The intended method of placement • If the project assessment is to be carried out by the supplier

3.1.3 Special-class concrete

In general terms, special-class is concrete specified other than normal-class. It will be specified where the concrete will be used in harsh environments, particularly where corrosive elements are present (such as air-borne pollution or corrosive ground waters) or where the concrete will be used in the construction of liquid-retaining structures designed for holding substances that require a special, resistant concrete.

3.2 Ordering For most housing projects, ordering normal-class concrete is simple. A typical specification is–

Strength 20 MPa Aggregate size 20 mm Slump 80mm

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The purchaser can ask for a higher slump to make the concrete easier to place. This will help when manual placement is necessary because of restricted access to parts of a project; or when an 80-mm slump might prove difficult to work, for example around congested reinforcement.

To produce a suitable mix, the supplier should always be advised of the task being undertaken, eg footings, floor slabs or driveways. For example it would be essential to order a ‘block-fill’ mix (high slump and suitable aggregate sizes) in the case of a project that entails core-filling blockwork. The timing of deliveries should be carefully planned. Traffic or site delays can result in several trucks waiting to discharge loads if successive deliveries are too close together. It may be 3.3 Testing

3.3.1 General

Builders will find it beneficial to have an understanding of the reasons and procedures for testing concrete. We explain here why and when tests are done. Concrete supplied for floor slabs and driveways in particular, should be subject to slump and compression tests in accordance with Australian Standard AS 1379-1997 The specification and supply of concrete. A slump test is carried out on plastic (freshly mixed) concrete, whereas a compression test is carried out on hardened concrete, usually at 28 days after placement. The slump test measures the mix consistency and workability, and gives an indication of the amount of water in the mix, which will affect the eventual strength of the concrete (see p1 Concrete Properties). The compression test measures the compressive strength of hardened concrete. The testing is done in a laboratory using a concrete sample made on site from a cylinder mould. Testing is a specialised procedure and should be carried out by experienced qualified people.

Builders have the choice of taking responsibility for testing or they can order pre-mixed concrete from a manufacturer that undertakes testing. Many suppliers of pre-mixed concrete have quality assurance systems that, among other checks, make periodical tests of the grades of the concrete they commonly supply. If builders order from a pre-mixed concrete manufacturer that undertakes testing it is important that they examine the delivery docket (referred to as an Identification Certificate in AS 1379 ) to ensure it matches their specifications. They should be sure that the docket indicates the four main attributes of a specification, namely class, strength, aggregate size and slump. They should retain this documentation for their records.

Builders taking responsibility for testing are advised to engage a testing laboratory accredited by the National Association of Testing Authorities, Australia (NATA).

We summarise, below, the testing procedures for the two tests should the builder want to undertake their own testing or witness the procedure and be sure that it has been done properly.

3.3.2 The slump test

Pre-mixed concrete manufacturers generally proportion the concrete mix with consideration to the travel time and ambient temperature so that the concrete meets the specification at the time of delivery. They are not required by AS 1379-1997 to carry out a slump test on site, unless water is added to the mix during the discharge of the concrete, in which case the concrete must be thoroughly re-mixed in accordance with the Standard and a slump test carried out on the remainder of the batch to ensure it remains within the tolerances of the specified slump. The tolerances of an 80-mm slump are plus/minus 15 mm. The amount of water added to the mix should be recorded on the delivery docket.

If a builder has serious concerns that the concrete mix is not the specified slump they should request an on-site slump test. If the builder undertakes the responsibility for slump testing, samples should be taken on site from concrete discharged directly from the agitator truck.

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Figure 3.1: Typical mould for slump test

The slump test is covered by AS 1012.3

The tools used are–

• Standard slump cone (see fig. 3.1) • Small scoop/shovel • Bullet-nosed rod (600 mm long x 16 mm diameter) • Rule • Steel float • Slump plate (500 mm x 500 mm).

The method (see fig. 3.2) is as follows– 1 The clean slump cone should be dampened with water and placed on the slump plate. The slump plate should be clean, firm, level and non-absorbent. 2 Collect a sample from the batch of concrete. This should be done within 20 minutes of the concrete arriving on site and after the first 0.2 m2 of the load has been discharged. 3 Stand firmly on the foot plates of the cone and fill 1/3 the volume of the cone from the sample. Compact the concrete by ‘rodding’ 25 times. Rodding is to push a steel rod in and out of the concrete to compact it into the slump cone or cylinder mould. Always rod in a definite pattern, working from outside into the middle. 4 Now fill to ⅔ and again rod 25 times, just into the top of the first layer. 5 Fill to overflowing, rodding again, this time just into the top of the second layer. Top up the cone until it overflows. 6 Level off the surface with the steel float. Clean any concrete from around the base and top of the cone; push down on the handles and step off the footplates. 7 Very slowly lift the cone straight up, making sure not to move the sample. 8 Turn the cone upside down and place the rod across the upturned cone. 9 Measure the average distance to the top of the sample. 10 If the sample is outside the tolerance (i.e. the slump is too high or too low), another must be taken. If this also fails, the batch should be rejected.

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The making of compression-test cylinders is covered by AS 1012.9.

The tools used are– • Cylinders (See fig. 3.4: 100-mm diameter x 200-mm high or 150-mm diameter x 300-mm high. The smaller cylinders are used for most testing because they are lighter). • Small scoop • Bullet-nosed rod (600 mm long x 16 mm diameter) • Steel float • Steel plate

Figure 3.2: Slump test

ACCEPTABLE Figure 3.4: Cylinder-moulds for the two sizes Typical slump and high slump respectively for compression tests

NON-ACCEPTABLE – REPEAT TEST Shear failures (lateral collapse)

Figure 3.3: Examples of slump

3.3.3 The compression test

Compression testing may be a part of either production assessment or project assessment as described in AS 1379- 1997. Production assessment requires the pre-mixed concrete supplier to take samples for testing at a designated frequency, and that records and reports of test results for each grade manufactured are retained by the testing organisation for at least 12 months.The supplier must make available certified copies for examination by the customer, namely the builder.

AS 1379-1997 also provides for builders who want to receive production assessment information from their supplier. Their project is registered with the supplier and reports relating to the concrete supplied during a particular production interval are sent to the builder or their nominee.

In the case of project assessment the builder takes responsi- bility for testing and reporting, and makes reports available to the supplier. Samples are taken from each 50 m3 of concrete at the project site before handling. Figure 3.5: Compression testing

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The method– 4 FROM BATCHING PLANT TO FINISHED 1 Clean the cylinder mould and coat the inside lightly CONCRETE with form oil and place on a clean, level and firm 4.1 Transporting surface, ie the steel plate. 2 Collect a sample from the batch of concrete. 4.1.1 General 3 Fill the volume of the mould with concrete then compact by rodding 25 times. When water is added to cement it triggers hydration, setting 4 Fill the cylinder to overflowing and rod 25 times first begins and the concrete mix begins losing workability. Plan to into the top of the first layer, then top up the mould until avoid delays in deliveries from the batching plant, on the road overflowing. and on the site. Delays reduce the amount of time to place 5 Level off the top with the steel float and clean concrete while it is still workable. Additional mixing of the con- any concrete from around the mould. crete may be necessary on site, further delaying placement. 6 Place cap on cylinder, clearly tag the cylinder and put The setting process is also accelerated in high temperatures. it in a cool, dry place to set for at least 24 hours. 7 After the mould is removed, the cylinder is sent to To avoid premature setting and difficult placement, adopt the the laboratory where it is cured and crushed to test following procedures– compressive strength (see fig 3.5). • Select a pre-mix supplier close to the site to reduce travelling time. • Provide good access for trucks to enter, and clear space for turning and manoeuvring, to allow for the quick discharge of the load. • Ensure that adequate labour is on hand to reduce the unloading time for the concrete. • Always try to finish the placement of all reinforcement, erection of formwork and site inspections at least 24 hours beforehand. • Check that all mechanical appliances are in working order the day before placement to allow time for replacement or repair if needed. • When pumping concrete, plan delivery schedules with enough time between loads to avoid delaying trucks. • Consider using a pump if the weather is unpredictable. Overnight rain can limit access to the site and reduce the amount of time for placement. • When access through a neighbouring property is necessary, ensure authorised passage beforehand to prevent delays arising from misunderstandings. • Check that all underground services have adequate load bearing cover to prevent damage and rectification work. • Where trucks must be driven over trenches, provide strong bridging to carry a fully laden vehicle. A loaded concrete truck bogged in a trench will cause long delays. • If the soil-bearing capacity is in doubt, do not bring trucks in – pump only. • Have all tools, equipment and materials at hand to avoid disruption.

4.1.2 The addition of water

Concrete will lose many essential properties if water is added to it on site. The addition of water will alter the water-cement ratio (see glossary), diluting and weakening the cement-paste, which is the essential ingredient that binds the mass.

Many concreting contractors mistakenly assume it is accept- able to add water on site to improve workability. The need to add water is often due to incorrect specification of the con- crete mix or ordering details.

Adding unspecified amounts of water on site should be avoided. The correct way to adjust this is to add water and cement at rates that maintain the specified water-cement ratio. Always discuss these matters with the plant manager or batcher. In certain situations, the addition of polypropylene fibres will reduce both the slump and workability of the concrete.

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The table below summarises the properties affected by the addition of water.

Property/performance Effect CORRECT INCORRECT Slump Increased Commence placing at one corner Random placing can result in of the formwork. segregation and makes it more Workability Increased difficult to achieve correct levels. Compressive strength Decreased

Incidence of shrinkage cracks Increased

Chance of dusting surfaces Increased

Chance of segregation Increased

Volume of bleedwater Increased

Value of compaction Decreased

Value of curing Decreased CORRECT INCORRECT Durability Decreased If either the final surface or the Placing commenced from the soffit is sloping, commence highest point makes it more Permeability/absorption Increased placing at the lowest point difficult to achieve correct levels and can lead to segregation as the concrete tends to settle down the slope 4.2 Placing

4.2.1 General

Common placement methods, other than chute placement and pumping, require barrowing the concrete to position or Baffle and drop manual shovelling; usually in successive placements. Barrowing concrete over reinforcement is often necessary. Prevent displacement of the reinforcement by supporting running boards above the reinforcement on blocks.

It is important not to over-handle the concrete as this can lead to segregation of materials (see glossary) and result in poor CORRECT INCORRECT finishes. If placing on a sloping surface The velocity from the free-end with a chute, always use a baffle chute tends to carry the concrete The most important rule is to avoid segregation during place- and drop at the end of the chute. down the slope, separating the ment. Concrete should be placed vertically and as near as aggregate, which goes to the possible to its final position. When it must be moved, it should bottom of the slope. be shovelled into position and not forced to flow into position.

Other techniques for avoiding segregation during placement depend on the type of element being constructed and on the type of distribution equipment being used.

For flatwork and slabs incorporating ribs and beams (shallow forms) the techniques shown in figure 4.1 should be adopted. For walls and columns (deep, narrow forms), problems occur when the concrete is dropped from too great a height and CORRECT INCORRECT Regardless of the distribution Depositing concrete away method, always deposit from the face of that already concrete into the face of that placed can cause poor already placed. intermixing and segregation

CORRECT CORRECT CORRECT INCORRECT When placing from When placing with When placing Long uncontrolled chutes and crane and bucket, from a concrete drops cause segregation barrows, discharge use a flexible drop pump, extend the as concrete hose to the concrete strikes CORRECT INCORRECT into a hopper leading chute connected the bottom of against the forms and the Use a drop chute if concrete has Allowing concrete to free-fall more to a light, to a collector cone form and withdraw aggregates to fall more than two metres. than two metres can displace flexible drop which is permanently as the form is filled. richochet off reinforcement, damage formwork chute. attached to the reinforcement. and cause concrete to bucket frame. Mortar is also left on the form faces and segregate. reinforcement.

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ricochets off the reinforcement and form-faces, resulting in 4.3.2 Methods segregation. The means of avoiding this vary with the type of distribution equipment being used (see fig. 4.2). The use of a tremmie could prove the most practical solution.

4.2.2 Placing in layers

To improve compaction of the concrete, place concrete in layers of a suitable depth for the compaction equipment. Layers that are too deep make it virtually impossible to adequately compact the concrete (see fig. 4.3), leaving entrapped air, which will create voids and blowholes in the surface of the concrete, and prevent it achieving its potential durability and strength.

4.2.3 Cold joints

Placing concrete in a continuous pour, if practicable, avoids the formation of cold joints. Cold joints are formed when fresh concrete is placed against the face of concrete that is about to set. The cracks resulting from cold joints will pass through Figure 4.4: Use of poker vibrator the full depth of the slab.

Cold joints can be avoided by working ‘hot-on-hot’, which Poker vibrators (see fig. 4.4) are good for expelling skilled paviours can do with enough labour at hand. When entrapped air in deep forms: beams, columns and walls. The cold joints could occur – due to hot or windy weather, or poker will allow easy placement of what appears to be stiff delays for example – it is good practice to blend the faces by concrete. Vibration will liquefy the mix and reduce demands revibrating the concrete or to compact the joint with a shovel for extra water.

in a tossing motion to re-blend the faces. They have an effective radius of between 100 mm and 600

Cold joints often occur when temporary internal formwork must mm depending upon the casing diameter and the specific be removed, which is common practice for internal step-downs amplitude of the device. They should be inserted quickly and and set downs. Good planning of formwork will avoid this. removed slowly. They should not be dragged over the rein- forcement but inserted vertically. Adequate compaction is sig- nalled when the surface bubbling subsides.

4.3 Compaction and vibration Vibrating screeds (see fig. 4.5) are the preferred method

4.3.1 General for vibrating and compacting concrete flatwork for slabs up to Compaction of concrete is undertaken to improve its overall 180 mm thick. Lower-slump concrete can be used if com- performance. The most common form of compaction is pacting this way. This method is often the most effective and vibration, undertaken with a poker or needle vibrator, but economical option for long, continuous pours. this is not the only method. Tamping with the screed board on thin ground slabs is an Proper compaction and expelling of entrapped air can greatly effective method of compaction. In certain situations, reduce the incidence of plastic settlement cracking over deep tamping with wood floats and surface working closes up beams and fabric/bar reinforcement or restraints. some types of cracking.

Properties improved by compaction – Rodding with a purpose-made rodding tool or equivalent, is • Strength and density effective for compacting piers or where pokers cannot be • Bond to fabric reinforcement and inserted inserted; especially where fabric reinforcement is congested structural anchors and hold-downs and space is limited. Shovels can be used for rodding at • Hardness of wearing surface beam edges, around pipes and penetrations and at placement • Reduced risk of plastic settlement cracking joints to re-work the old and new pours to prevent cold joints. • Off-the-form finishes. External vibration can be done simply (where other methods cannot be used) by using a hammer to tap the form or boxing. The concrete in contact with the form is vibrated and com- pacts, improving the surface finish.

Vibrators should extend 150 mm into the lower layer. 4.3.3 Vibration hints

Under-vibration will cause serious defects in concrete and is the most common failing. Under-vibration will adversely affect structural properties, lower strength, increase permeability,

150 lower durability and increase susceptibility to corrosive ele- ments: both air-borne and contained in ground water.

150 Over-vibration, with grossly oversized equipment, may cause problems but ‘well-proportioned’ mixes are not likely to suffer any detrimental effects. Adding water to the mix can cause a Concrete to be placed in uniform layers and of a thickness to match problem with vibration, possibly leading to material segrega- the ‘power’ of the vibrator (usually between 250 and 400 mm) tion and poor surface finishes, such as those prone to dusting and flaking.

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Re-vibration is used to blend cold joints, to close plastic shrinkage and plastic settlement cracking; to increase the potential strength of previously vibrated concrete; and to improve bonding to reinforcement when concrete is placed in layers (for example structural elements or deep beam sections).

4.4 Finishing

4.4.1 Screeding

Screeding is the operation of levelling the concrete after it is placed in the forms and roughly distributed with shovels. It is done by hand, or by means of vibrating-beam screeds, which work off the forms or guide rails. It should be done before bleedwater rises to the surface. Figure 4.5: Use of a vibrating screed Hand screeding off edge forms involves the use of a screed board (or beam) to strike off the concrete to the required height. The striking surface of a screed board should always be straight and true. The surface is struck off by pulling the screed board forward, while moving it back and forth in a sawing-like motion across the top of the edge forms. A small roll or surcharge of concrete should always be kept ahead of the screed. Surface hollows created by aggregate ‘roll out’ or insufficient surcharge in front of the screed should always be filled immediately to prevent variations in floor levels.

4.4.2 Floating

The purpose of floating is to make the surface even and open in texture, ready for finishing. Figure 4.6: Bullfloating

Floating is working the surface of concrete with hand floats, bullfloats or with rotary finishing machines fitted with suitable floats or shoes. Generally, it should not begin until all bleed- water has evaporated from the surface, or has been carefully removed with a hessian drag or garden hose; and the con- crete is hard enough to withstand foot traffic with only minor indentations in the surface. These indentations are removed by the floating operation.

Floating– • embeds large aggregate particles beneath the surface; • removes slight imperfections and produces a surface closer to the true plane; • compacts the concrete and consolidates mortar at the surface, preparing it for finishing; and • closes minor surface cracks, which might appear as Figure 4.7: Hand floating with wooden floats the surface dries.

Bullfloating The bullfloat (see fig. 4.6) is a large float on a long handle, which is worked back and forth on the concrete in a direction parallel to the ridges formed by screeding. Bullfloating is useful as an initial floating operation to smooth the concrete surface immediately after screeding, and should be completed before bleedwater appears on the surface. A second use of the bullfloat may be required but care must be taken not to overwork the surface.

Floating by hand Three types of hand float are in common use: wooden, magnesium and composition.

The hand float is held flat on the surface and moved in a sweeping arc to embed the aggregate, compact the concrete, and remove minor imperfections and cracks (see fig. 4.7).

The surface may sometimes be floated a second time – after some hardening has taken place – to impart the final texture to the concrete.

Floating by machine (see fig.4.8) Float blades are wider than trowel blades and are turned up along the edges to prevent Figure 4.8: Floating by machine them digging into the surfaces in the flat position. For this rea- son, floating with a trowelling machine equipped with normal

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trowel blades should not be attempted. The power-float 4.5.2 Curing methods should be operated over the concrete in a regular pattern, Curing methods include– leaving a matt finish. Surfaces near to obstructions, or in slab corners, that cannot be reached with a power-float should be • Curing compounds applied by spray or roller. • Polythene sheeting placed and secured over the concrete manually floated before power floating. to prevent evaporation. 4.4.3 Trowelling • Formwork for edge beams and face panels left in place. • Ponding water on the concrete surface where practicable. Trowelling is carried out some time after floating. The delay is to allow some stiffening to take place so aggregate particles The practice of intermittent wetting down morning and night is are not torn out of the surface. not curing and can cause greater harm to the concrete by causing expansion and contraction, increasing the incidence Trowelling by hand A trowel for hand finishing has a flat, of shrinkage cracking – or craze-cracking. broad steel blade and is used in a sweeping arc motion with each pass overlapping the previous one. For trowelling to be most effective, the timing of the operation calls for some 4.5.3 Curing compounds experience and judgement, but in general terms, when the trowel is moved across the surface it should give a ringing Curing compounds are liquids that can be sprayed, brushed, sound. or squeegeed (usually sprayed, see fig. 4.9) directly onto concrete surface, which dry to form a relatively impermeable For the first trowelling (often referred to as ‘breaking’), the membrane that limits the loss of moisture from the concrete. trowel blade should be kept as flat against the surface as Their properties and use are described in AS 3799. possible because tilting, or pitching, the trowel at too great an angle can create ripples on the surface. More trowelling Use of curing compounds increases the smoothness, density, and wear resistance of • Easy to apply with either spray or roller the surface. Successive trowelling operations should be made • Allow construction to continue unhindered with smaller trowels at increasing pitches. This increases the • Applied immediately after finishing pressure at the bottom of the blade and compacts the surface. • Fugitive dyes assist in assessing coverage • Rate of coverage is affected by the actual surface Later trowelling, after further hardening, will increase the finishes, eg rough or broomed surfaces will require more density of the surface concrete, making it harder wearing. as there is greater surface area Successive trowelling operations should be at right • Compatibility of compounds with intended adhesives angles to each other for best results. should be checked as some compounds may require Trowelling by machine The trowelling machine (power removal for glued-down floor coverings. trow- el or ‘helicopter’) is a common tool in Australia for all 4.5.4 Plastic sheeting classes of work and consists of several (generally four) steel trowel blades rotated by a motor and guided by a handle. Plastic sheets, or similar materials, are effective in limiting water loss, provided they are kept securely in place and pro- Trowelling by machine should be carried out systematically tected from damage. Their effectiveness is reduced if they over the concrete in a regular pattern. Corner areas, areas are not secure and wind can enter underneath. closest to obstructions and small irregularities should then be ‘touched-up’ with a hand trowel. Use of plastic sheeting for curing • Plastic must be placed over the concrete and sealed Edging Edging provides a quarter-round arris along the and secured at the edges as soon as possible after edges of footpaths, patios, curbs and steps. It is achieved by finishing. running an edging trowel along the perimeter of the concrete. • Plastic must be lapped and sealed to prevent exposure Edging trowels are steel and incorporate a quarter-round to the drying effects of heat, wind or low humidity. forming edge. They are available in a variety of widths and • Lightly coloured plastic sheeting will reflect the sun’s rays with various diameter quadrants. Edging improves the appear- ance of many types of paving and makes the edges less vul- in hot weather and keep the concrete cooler during the summer. nerable to chipping. • Black plastic, however, absorbs the heat but could be used in cooler regions, or in the winter months, to accelerate strength gain by raising the concrete 4.5 Curing temperature. 4.5.1 General • The sheeting should not be lifted to add water to the surface. Additional water is not required. Curing is the procedure for retaining moisture in concrete for several days. It prolongs the chemical reaction of hydration (see glossary), which occurs when water and cement are combined to form cement paste.

Curing will– • improve compressive strength • reduce the incidence of drying shrinkage cracking • reduce surface dusting • improve protection of reinforcement • increase the hardness of surfaces, and consequently their resistance to abrasion.

Curing should be maintained for a minimum period of 3 days for all types of housing concreting. It should begin no more than 3 hours after finishing, or the benefits will be markedly reduced.

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4.6 Effects of weather conditions 4.6.3 Cold-weather concreting

4.6.1 General In cold conditions prolonged setting times can be shortened by adding a set-accelerating admixture. In exceptionally cold Experienced paviours are always aware of the effects that conditions, concrete can crack when the water in the con- weather can have on concrete. Low workability, early setting crete mass freezes and expands. In these conditions freshly times or plastic shrinkage cracking are not symptomatic of hot placed concrete must be protected to prevent freezing. weather alone but can occur at all times of the year. Water is Formwork and sub-bases should be protected from frost, and the catalyst for hydration of cement. Maintaining the water concrete should never be laid on frozen ground. All materials balance is important for full hydration, and to yield, ultimately, should be kept warm, and while curing, the concrete should the properties of good concrete. be kept warm where this is practicable. When the final finish does not meet expectations, the product is often wrongly blamed; when the most likely cause is a failure to adopt concreting practices suitable to the conditions.

In hot (above 300C) and windy conditions concrete must be cured by covering with plastic sheeting, spraying with a liquid membrane curing compound or ponding of water on the top surface. (Building Code of Australia Volume 2 Housing Provisions: Clause 3.2.3.1d).

Weather factors to consider– • Air temperature • Relative humidity • Prevailing winds and wind intensity

Effect of weather conditions on concrete properties

Property Hot Cool Dry/Windy Slump Decreased Nil Decreased Setting time Reduced Increased Nil Strength gain – short term Increased Decreased Nil – long term Decreased Increased Nil Workability Reduced Increased Nil Incidence of Increased Reduced Increased plastic shrinkage cracking Incidence of Increased Nil Increased drying shrinkage cracking Incidence of Increased Decreased Increased cold joints Period required Reduced Increased Nil prior to removal of formwork

4.6.2 Hot-weather concreting

Hot weather increases the possibility of cracking. Temperature is not the only problem. Low humidity and high winds cause moisture loss and, in turn, shrinkage cracks.

Special attention to the following details will reduce the risk of poor quality work– • Plan the job to avoid delays once the concrete pour has started. • Provide shade and wind-breaks to work areas. • Dampen the sub-base before placement of concrete (but do not leave surface water). • Use a set-retarding admixture. • Spray concrete with an aliphatic alcohol (see glossary) to reduce the rate of evaporation. • Cure the concrete for a minimum of 3 days; 7 days is better. (If plastic sheeting is used, it should not be black.)

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5 FORMWORK AND REINFORCEMENT

5.1 Formwork

5.1.1 General

Accurate formwork construction is necessary to ensure correct levels and dimensions. Formwork joints should be tight to prevent cement paste leaks, which cause poor off- form finishes. Formwork should be coated with form oils to improve concrete finishes and aid the removal of the form- work.

Formwork is left in place, primarily, to protect the edges of the pre-hardened slab from mechanical damage during site works, and to avoid damage during the premature removal itself. Formwork is also an effective means of curing when it is left in place. If the formwork is stripped before 3 days have elapsed it is advisable to continue curing exposed surfaces with one of the methods described in 4.5 Curing.

Figure 5.3: Solutions to common problems with deep edge forms

Figure 5.1: Basic ground forms 5.1.4 Edge forms with rebates

5.1.2 Basic ground forms Many house slabs have rebates at the slab edge to allow an external skin of brickwork to sit on a damp-proof course Basic ground forms are suitable for paths and driveways on (DPC) below the floor level. Figure 5.4 shows a typical con- firm ground, up to 150-mm thick. The correct method of fixing struction method with timber formwork for raft slab construc- forms to pegs is shown in figure 5.1. tion; and figure 5.5 shows the method used for footing-slab 5.1.3 Deep edge forms construction. Edge forms are secured to greased 25 mm steel dowels placed into footing beams and removed after the In varying ground conditions formwork is often required for slab has set. slabs up to 300 mm. Where the height of formwork exceeds Alternatively, the method depicted in figure 5.5 can be used 150 mm, it should be braced as shown in figure 5.2. Deep without a rebated edge, with the brick veneer carried down to edge forms can be constructed from clean-faced ply with top sit on the footing beam, leaving a 30-mm cavity between the and bottom walers. If solid timber forms (minimum 38 mm) veneer and slab.

are used, the bracing and formwork will be different. When 5.1.5 Cantilevered formwork depths exceed 200 mm, solid timber forms should be a minimum of 50 mm thick. A wider step-down is sometimes required, for example to accommodate steps at the slab edges. These are best Illustrated in figure 5.3 are simple solutions to common prob- constructed as shown in figure 5.6. lems when using deep edge forms.

Figure 5.2: Braced formwork for slabs more than 150mm thick Figure 5.4: Formwork for raft slab with rebate

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FULL BRICK BRICK VENEER outer and inner courses are aligned

Figure 5.5: Formwork for footing slab with rebate

5.1.6 Other types of ground forms

Fabricated metal forms speed up ground slab construction and can be re-used. Several telescopic metal form systems are available and can be effective for highly repetitive construction. Ply and metal composite forms are suitable for applications with repetition and heavy working loads (deep SINGLE-LEAF MASONRY beams). Figure 5.7: Masonry formwork

Figure 5.8: Two-piece forms to provide reinforcement continuity

Figure 5.6: Cantilevered formwork

5.1.7 Masonry formwork

Masonry formwork (brick or block) maintains the same face material below natural ground. It removes the need for a formworker but requires a two-part slab construction (see fig. 5.7).

5.1.8 Construction joints

At construction joints, where continuity of reinforcement is required, two-piece formwork is suitable for both fabric and bars as shown in figure 5.8.

Proprietary metal key-forms or timber forms are suitable for Figure 5.9: Construction-joint formwork use as construction joint formwork to allow for the engaging of adjacent slab panels (see fig. 5.9).

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5.2 Purpose of reinforcement 5.3 Types of reinforcement

It is important to understand that incorrectly positioned Reinforcement is usually provided by steel bars or by steel reinforcement can reduce both the strength and durability wires welded together to form a mesh or fabric. Bars are of reinforced concrete, and greatly reduce the ability of normally associated with beams and columns, and fabric with reinforcement to control shrinkage cracking. We recommend floors and walls. a structural engineer be engaged for the design of reinforce- Concrete may also be reinforced with fibres, the main type ment. being steel. Polypropylene fibres are also available but do not Concrete has high compressive strength but low tensile increase the tensile strength of a concrete member in the strength. Steel, on the other hand, has a very high tensile same way as steel bars fabric or steel fibres. strength (and a high compressive strength) but is much more expensive than concrete. By combining steel and concrete, we are able to make use of both the high tensile strength of 5.4 Fixing reinforcement steel and the relatively low-cost compressive strength of concrete. 5.4.1 General

Fixing is more than just tying bars together. It should ensure Characteristics Characteristics that once the reinforcement has been placed in its correct of concrete of steel position, it cannot be displaced during placing and compact- ing of the concrete and will remain in place until the concrete High compressive strength High compressive strength has fully hardened. A number of methods are used to locate reinforcement correctly. Low tensile strength High tensile strength 5.4.2 Bar chairs and spacers High fire resistance Low fire resistance Bar chairs and spacers support bar or fabric reinforcement Plastic and mouldable Difficult to mould and shape above horizontal surfaces, and provide adequate when fresh except at high clearances temperatures to vertical formwork and/or excavation facings. They are avail- Relatively inexpensive Relatively expensive able in a variety of shapes and may be made from wire, plas- tic or concrete (see fig. 5.11). They are also manufactured in a range of sizes, each of which provides a specific thickness The combination of concrete and steel in reinforced concrete of concrete cover. is mutually beneficial– • Upon hardening, concrete bonds firmly to steel rods, Factors to consider in the suitability of a chair or space– bars and wires so that, when loads are applied, the two • Cover A bar chair or spacer should be selected to act as though they are one. Any tendency for the concrete provide the correct cover, not one ‘close to’ that required. to stretch or crack in a zone of tension is counteracted by • Membrane damage Bar chairs which could puncture the steel embedded in that zone. • When subjected to changes in temperature, concrete dampproof membranes during placing operations should be avoided, or supported on purpose-made and steel expand or contract by similar amounts, and ‘saucers’. therefore remain firmly bonded. • Stability Some types of bar chairs and spacers are • Concrete, having a relatively high resistance to fire, and a easily displaced or knocked over during concrete-placing relatively low thermal conductivity, protects steel embedded operations. in it. • Spacing of bar chairs The spacing of chairs must • Concrete provides an alkaline environment to steel embedded in it, thus protecting the steel from rusting. ensure that the reinforcement is adequately supported in the required position. Bar chairs for mesh are spaced at The principal types of stresses (see fig. 5.10) which develop in 0.9-m to 1.0-m intervals, or at an average of three chairs concrete elements are– per metre square. • Compressive stresses – those which tend to cause concrete to compact and crush. • Tensile stresses – those which tend to cause concrete to stretch and crack. • Shear stresses – those which tend to cause adjacent portions of concrete to slide across each other.

COMPRESSION

TENSION Figure 5.11: Typical bar chairs

5.4.3 Tying

Reinforcing bars may be tied together, or to stirrups (liga- SHEAR tures), to form a ‘cage’ that helps maintain the bars in position during the subsequent concreting operations. The cage must be strong enough to achieve this and sufficient ties used for the purpose.

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5.4.4 Splicing (joining) the middle third of the beam depth. Localised deepening to the beam section and additional reinforcement may be Lengths of reinforcing bar or fabric may be joined or ‘spliced’ needed. together in a variety of ways. The most common method is simply to lap the bars or mesh. The lapped portion of the With any reinforced concrete projects– bars or mesh must always be in contact and tied unless • Do not hook mesh into position (use bar chairs). otherwise indicated on the drawings. • Place bar chairs for general work at a maximum 900-mm spacing. The requirements in Section 5.3 in AS 2870 Requirements for • Do not ‘walk’ the mesh into the pour during placement. Lapping of Reinforcement are summarised– • Prevent mud being walked onto reinforcement. • Fabric mesh should be lapped a minimum of two cross Stack materials on skids off the ground. wires to both side and end laps. • Do not allow trucks to drive over reinforcement. • Trench mesh should overlap a minimum of 500 mm • Adequately splice and secure reinforcement. For and be tied and secured. fabric, a good standard is to secure each third wire lap • Trench mesh at T and L-intersections should and stagger tying off line. For bar splicing and overlaps, be overlapped by the full width of the mesh. double splice along the length of the lap and secure all • Bars used in reinforced footing cages should be lapped a overlapping bars. minimum of 500 mm at T and L-intersections (see fig. 5.12). 5.6 Inspections

Items to be inspected and checked where applicable–

• Number, size and spacing of bars, or the sizes of fabric. Refer to specifications and project drawings. • Number, size and spacing of fitments (in beams). • Height and distribution of chairs to maintain required bottom and side covers. • Distance of cut-off ends of bars from support faces. • Extension length of bars and fabric past support faces. • Location and lengths of lap splices. Separate L-bar One outer bar • Location of service pipes, conduits, openings and lapped on each leg bent and lapped outlets with respect to conflict with bar on fitment locations. • Trimming of bars around openings in slabs at re-entrant corners. Figure 5.12: Lapping of reinforcement at corners • Effectiveness of tying (bars to bars, bars to fitments,

lap splices, chairs to bars or fabrics). • Remove tie wire offcuts, particuarly where 5.5 Cover to reinforcement slabs/beams soffits will be exposed. The cover to reinforcement (the minimum thickness of con- Supports and ties are intended to support only the weight of crete between the outside of reinforcement and the nearest the reinforcement and the concrete over them and, together concrete surface) is provided basically to give protection with tie-downs, to prevent the reinforcement being accidentally against corrosion (rusting). displaced during concrete placement. They are not intended Section 5.3 in AS 2870 gives the minimum cover to reinforce- to support general construction traffic. It is therefore important ment in house construction. that, once the reinforcement has been placed, fixed and checked, independently supported plank runs are provided to keep personnel and equipment off the reinforcement. If this is Situation Cover not done, all the previous good work and effort in correctly (mm) positioning the reinforcement will have been wasted.

Top cover to fabric for shrinkage 20 control internal surfaces

Top cover to all reinforcement in slabs 40 or paths members exposed to weather

Bottom cover to all reinforcement in beams 30 and slabs protected by vapour barrier

Bottom cover to all reinforcement in members 40 cast directly against non-aggressive ground

Important considerations for reinforcement

Where penetrations occur, cut away the fabric to prevent fouling the penetration and interfering with the penetration alignment. Check with the engineer that extra reinforcement is not required to maintain structural strength.

Horizontal penetrations to footings and beams are permitted in

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6 CRACKS AND CRACK CONTROL

6.1 General

Cracks can occur in concrete construction for a variety of reasons. Some cracking is inevitable because concrete, like most other building materials, moves with changes in tempera- ture and its moisture content. Specifically, it shrinks as it loses moisture. Cracking can be controlled, but not entirely prevented.

Cracking in concrete falls into two categories– • Cracking prior to set • Cracking after set

6.2 Cracks prior to set

6.2.1 General

Cracks in concrete prior to final setting are not always recog- nised since they can be temporarily closed up by bullfloating or may be hidden by surface bleedwater. The two common forms of pre-setting cracking are plastic shrinkage cracking and plastic settlement cracking.

6.2.2 Plastic shrinkage cracking

Plastic shrinkage cracking is caused by rapid drying of the surface in dry, windy conditions or in cooler, low-humidity weather conditions. It can occur at any time of the year. It occurs after placement, compaction and screeding as the bleedwater evaporates, exposing the fresh concrete to the elements and causing the surface to shrink before it has any strength. Concrete cracks in much the same way as clay soils.

Polypropylene fibres can be added to the concrete mix to reduce the incidence of plastic shrinkage cracking. Figure 6.1: Settlement cracking

Prevention– • Erect wind breaks to direct drying winds away from 6.3 Cracks after set the surface. 6.3.1 General • Dampen the ground to reduce absorption (or if suitable to conditions, place a vapour barrier). Cracking in concrete after setting also occurs for a variety of • Use a continous fine mist spray to fog the surface of reasons. The two most common forms of after-set cracking the concrete. are crazing and drying-shrinkage cracking. • Spray evaporation retardants such as Antivap, Eucovap or Confilm over the freshly screeded concrete surface. 6.3.2 Crazing

The addition of a fugitive dye will show the evenness of This is best described as a network of very fine cobweb-like the coverage. In extreme conditions, re-application of or alligator-skin cracks, which are usually evident when the retardants may be necessary after trowelling. concrete has been subjected to periods of wetting and drying • Use physical remedies such as revibrating the concrete, while it is still ‘green’. They are, however, more common in vigorous wood floating over cracks or extended use of surfaces with a highly polished, steel-trowelled finish. power trowelling to close up the cracks to the full depth. The main causes of this form of cracking are– 6.2.3 Plastic settlement cracking • Trowelling bleedwater into the surface of the concrete.

This is caused when concrete settles under its own weight, • Steel trowelling the concrete before the water sheen has often because of inadequate compaction. gone. • Using cement as a drier to remove excess water. It occurs over reinforcement, in deep section beams, and • Overworking the surface and bringing excess mortar steps in formwork such as in a waffle floor (see fig. 6.1). to the surface. • Adding extra water to the mix. Cracking in the hardening mass occurs over restraints, and • Inadequate or inconsistent curing. may leave voids under reinforcing bars. Crazing is not detrimental to anything other than the appearance. Prevention– • Fill any deep beam sections to the level of the bottom of Prevention– the slab before placing the concrete in the slab. • Do not work the bleedwater into the surface. • Always ensure adequate compaction. • Drag excess bleedwater off with a hose. • Revibrate surface where there is more than a 300-mm • Do not repeat power trowelling unnecessarily. depth of concrete below top bars. • Avoid excessive ‘wet wiping’ of the surface. • Ensure all formwork can withstand expected working • Do not use cement, oxides or colour hardeners to mop up loads and that the formwork stays in place to support the bleedwater. concrete until it is self-supporting.

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6.3.3 Drying shrinkage cracks

These are caused by concrete shrinking; the result of moisture loss. This is not a major problem if the concrete is free to move, but, if restrained, tensile stresses can develop in the concrete and cause it to crack. The water content of the mix is the major factor influencing drying shrinkage. Shrinkage, however is not the only cause. Restraints, detailing CORRECT geometry and construction practices may also affect the probability of cracking in hardened concrete.

Prevention– • Do not add any water to concrete on site. • Provide adequate reinforcement and ensure correct placement. • Place joints in correct location and ensure proper construction. INCORRECT • Place concrete correctly. • Compact the concrete adequately. • Start curing promptly and correctly. Figure 6.2: Construction joint in slab

6.4 Joints

6.4.1 General

Joints serve a number of purposes, but they fall into two broad categories– • Those that allow no relative movement of the concrete on either side of the joint. • Those that do allow such movement.

The first, referred to as construction joints, make a monolithic bond between the sections of concrete either side of the joint.

The second, referred to as control joints, allow for lateral movement of the concrete. In some cases dowels, isolated from the concrete, are embedded in the concrete to maintain vertical alignment of adjoining sections of concrete.

Because house slabs are comparatively small in area, joints are not commonly needed in their construction. However where they are needed, their location and detailing should be in accordance with the design and instructions of the geo- technical or structural engineer. Joints are not suitable for some slab types – this is often not understood. Providing joints Figure 6.3: Isolation joint between slab and wall in a house slab without expert advice can cause structural problems that may be expensive to fix. the concrete’s moisture content. • Isolation joints: allow concrete sections to move A house slab is often placed directly on the ground and is independently of walls, columns, posts and therefore subject to ground movement. Without careful con- penetrations. sideration and construction, joints can become a hinge in the slab and exaggerate ground movement, sometimes resulting Contraction joints allow two concrete panels to move apart in damage. as a result of shrinkage, or temperature changes. The joint is a line of least restraint and induces a controlled crack under 6.4.2 Construction joints tension, relieving tensile stresses across the surface of the Construction joints (see fig. 6.2) are concrete-to-concrete concrete, and minimising the incidence of uncontrolled cracking. joints that prevent any relative movement across the joint. Contraction joints are essential in both reinforced and unrein- They are commonly used when there is discontinuous forced concrete flatwork. place- Fabric reinforcement is placed in the top 1/3 of the concrete ment of concrete and successive pours are allowed to harden to control and reduce shrinkage cracking. In unreinforced beyond the initial set; or at the end of the working day. They concrete, extra contraction joints are provided to control may also be necessary if unforseen events (for example cracking. delays in delivery or bad weather) interrupt a pour. Keyed joints allow horizontal movement and restrain vertical Most house slabs are placed and finished in the course of a displacement of adjoining slabs. A series of steel dowels with day obviating need for construction joints. one end fixed in the concrete and the other isolated do the 6.4.3 Control joints same.

Types of control joints– Expansion joints allow concrete elements to expand and push against each other (without damage), with changes in • Contraction joints: allow shrinkage movement at designated temperature or moisture content. There is some argument locations. about the need for expansion joints in concrete structures • Expansion joints: allow the concrete to expand (and because shrinkage is usually greater than thermal expansion. contract) with changes in temperature, and changes However, there is no argument about their value in exposed in

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concrete flatwork, particularly in large and long sections. 6.4.7 Slab proportions

Expansion joints, with flexible sealants, prevent edge Where it is possible, concrete slab sections are best formed, approximately, as squares. For rectangular slabs, the longer spalling, side should be no more than 11/2 times the shorter side. slabs riding up and joint peaking, all of which are detrimental to slab performance and appearance. This rule, in addition to the joint spacings recommended above, ensures correct spacing of joints to minimise cracking. Isolation joints allow for the independent movement of slabs between walls, around columns, posts or ground fixtures such 6.4.8 Joint maintenance as kerbing or access holes. They allow free movement, and The long-term performance of joints is crucial to long - life are often used in combination with other types of joints to pavements. Dirt must be kept out of the joint’s groove – by allow maximum panel movement caused by shrinkage, sealing with a flexible sealant – because a build-up can result temperature changes and seasonal variations. in joint peaking, edge spalling and edge rupturing. Joint spacers Compressible, cellular materials are commonly used to fill should be stopped about 10 mm below the surface to allow these joints (see fig. 6.3). for sealing.

Figure 6.4: Sawn joint in concrete pavement

6.4.4 Forming control joints

Control joints can be made at any of three stages during construction– • During placement, a pre-moulded strip is embedded into the concrete to create a line of weakness. Examples include preformed plastic strips and metal strips in terrazzo. • During finishing, a groove can be formed in the surface with a suitable jointing or grooving tool, which creates a line of weakness that induces a crack as the concrete hardens. • Soon after the concrete has hardened, a joint can be sawn in the surface (see fig. 6.4). It should be made just before drying shrinkage occurs–when the surface is hard enough it will not chip, spall and collapse on the cutting blade (sometimes referred to as ravelling). If it is deferred, drying shrinkage could cause random cracking. The sawn joint is filled with a flexible sealant to keep out dirt. Unsealed joints fill with dirt and do not function effectively (see clause 6.4.8).

6.4.5 Joint locations

In concrete flatwork the layout of joints is very important. Joints, of various details, can be transverse and longitudinal, but are predominantly transverse in residential work, such as paths and driveways.

6.4.6 Joint spacing

Joints are generally not needed in floor slabs because of the amount and layout of reinforcement.

In unreinforced slabs – perhaps a path – transverse joints are usually placed at intervals of 2.5 – 3.0 m. When a slab is reinforced this distance can be increased, depending on the type and amount of reinforcement.

Longitudinal joints are generally provided when the slab is wider than 4 metres, for example driveways or terrace pavements.

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7 FOOTING TYPES 7.4 Stiffened slab with deep edge beam (see fig. 7.3)

7.1 General This is suitable for sloping sites where cut and fill

A variety of standard designs for footing systems are provided excavation in Section 3 of AS 2870. The choice of footing system can be is not practicable. The system uses deep perimeter beams for one of preference based on local experience, or it may be stiffness. These beams can incorporate reinforced masonry. based on particular site conditions. Geotechnical or structural engineers undertake an increasing number of designs.

The term ‘slab-on-ground’ is adopted in AS 2870 (and in this handbook) and refers to concrete slabs supported by the ground and incorporating integral edge beams. ‘Stiffened raft’, ‘waffle raft’ and ‘stiffened slab with deep edge beam’ are all types of slab-on-ground.

7.2 Stiffened raft (see fig. 7.1)

A stiffened-raft floor slab is placed at the same time as the external and internal beams, all of which are reinforced. Internal beams are not necessary on stable sites, however for reactive soil conditions the beam sizes and quantity of rein- forcement are varied accordingly.

A stiffened raft is often placed in one pour. They are cost- Figure 7.3: Stiffened slab with deep edge beam effective, and provide a strong footing that can be supported on bulk concrete piers if placed on uncontrolled fill. 7.5 Footing slab (see fig. 7.4)

The footing slab is cast on ground in two stages: the edge footings first, followed by the slab. This method reduces the length of time excavations are open and does not require extensive formwork. The footing-slab system can be adapted well to sloping-site applications.

Figure 7.1: Stiffened raft

7.3 Waffle raft (see fig. 7.2)

Waffle rafts are constructed on level sites using cardboard or polystyrene void formers to produce a closely-spaced grid of Figure 7.4: Footing slab reinforced concrete ribs. Site preparation is minimised because the concrete is placed on surface forms rather than in excavated trenches. This system avoids occasional, unin- 7.6 Strip/Pad footings (see fig. 7.5)

tended, over-excavation when trenching, allowing more accu- Strip footings are rectangular in section and are used for rate measurement of the quantities of concrete and reinforce- continuous support of walls. Pad footings are used to support ment. Waffle rafts can be designed for support with piers. piers, columns or stumps. Strip and pad footings can be used together to support a range of suspended flooring systems for sloping sites. Floor slabs between walls – on strip footings – can be supported on controlled fill.

Figure 7.2: Waffle raft

Figure 7.5: Strip/pad footings

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concrete is transported, placed, compacted, finished and Note that polypropylene fibres are no substitute for steel rein- cured in accordance with the good work practices outlined in forcement, which is also used to counteract drying shrinkage this handbook. in addition to its structural purpose. If steel reinforcement is omitted, then the spacing of joints should be the same as for 8.4.2 Soils unreinforced concrete. Subgrades for slabs must have adequate strength after com- 8.4.7 Skid resistance paction with a plate compactor or a vibrating-drum roller. When deciding the surface finish consider if a non-slip Prepare the subgrade by first removing topsoil containing surface would be advisable given the use of the pavement, roots and grass, and levelling the subgrade. Backfill over ser- its steepness, and the effectiveness of its surface vice trenches and fill isolated hollows or soft spots, then com- drainage. pact to the level of natural ground. Skid resistance can be improved with simple techniques. Note Clay soils need to be moist for optimum compaction. For example, textures can be made with a broom, wood float, 8.4.3 Sub-base stipple roller or a hessian drag, or by exposing aggregates with a wash-off finish (see clause 8.7.3). Incorporating silica A sub-base is required to build up areas or adjust falls or lev- dust or carborundum dust in an applied sealer is another els. Sub-base materials should be free-draining, and capable technique. of being compacted in layers of no more than 100-mm deep. 8.4.8 Protection against staining Correct sub-base and subgrade preparation ensures the con- crete pavement alone does not carry the service loads. Sealers, clear and tinted, prevent most stains penetrating Unstable, or filled sites with inadequate compaction, should the concrete surface. Coloured paints, suitable for the be thoroughly investigated by a geotechnical or structural concrete and the conditions, can also be applied to the engineer before design and construction. surface.

8.4.4 Formwork Concrete surfaces, however, are often subject to the abrasion of tyres and foot traffic. Sealers or paint coatings may need to Formwork should be strong and true to line. The accuracy of be applied repeatedly for continuing surface protection, and the formwork will be reflected in the finished line of the hard- to keep them looking good. ened concrete. By placing the top edge of the form boards at the finished level of the pavement surface, screeding can be efficiently done using the form edge as a guide. Form boards 8.5 Coloured concrete should be thick enough and securely fixed so they do not bend or move when placing concrete. Formwork should be 8.5.1 Introduction constructed with care so it is easily removed when the con- Colours can be readily applied to concrete. crete has hardened. A light coating of form oil before pouring will make removal easier. Durable colour is achieved when mineral oxide pigments are

It is good practice to leave formwork in place for a minimum added to concrete while it is in a plastic state: that is at the time of placement. They can be added to the mix to produce of 3 days – depending on weather conditions – to allow integrally-coloured concrete and coloured toppings, or broad- concrete to harden and become self-supporting. cast onto the surface of pre-hardened concrete as a dry- 8.4.5 Reinforcement shake topping.

Reinforcement should be located in the top half of the slab as Hardened concrete pavements– new and old – can be close as possible to the surface but keeping a minimum cover enhanced with purpose-made paints and coatings, however of 30 mm. This is done by supporting the reinforcement on they may need to be reapplied some time later to keep them bar chairs or concrete blocks arranged in a 500-mm square looking good. grid. The colours of aggregates–sand and stones–can provide When two or more sheets of reinforcing fabric are necessary permanent colour in exposed-aggregate finishes, but the the sheets are lapped so that the two outermost transverse range of colours will be limited by the available aggregates. wires of one sheet overlap the two outermost wires of the Exposed aggregate finishes are discussed in part 8.7. other. They are tied together (spliced) with wire. See clause 5.4.4. 8.5.2 Integral colouring (with mineral oxide pigments)

8.4.6 Polypropylene fibres Mineral oxides occur naturally in soil and rock.

Polypropylene fibres are used, primarily, to reduce the inci- Synthetically dence of plastic shrinkage cracking. They also reduce bleed- produced oxides, however, are more pure, uniform and ing of water in the mix. stronger colouring agents. They are suitable for concrete because of their resistance to the alkalies in cement, their They resist shrinkage of the surface (in its plastic state) under chemical inertness, and their resistance to fading under conditions that cause rapid evaporation, notably hot, dry and exposure to weather and UV light. They are produced as a windy weather. Plastic shrinkage cracks can impair freshly fine powder, a tiny fraction of the size of cement particles. placed concrete, are unsightly and difficult to fix (especially in Unlike a dye, which colours by staining, mineral oxide coloured work), and induce larger uncontrolled cracks as the powders are insoluble in water, and colour by masking the concrete dries. cement matrix. They are produced in a range of colours: blues, greens, red and yellow ochres, grey and black. In drying conditions, the use of polypropylene fibres, together with evaporation retardants (aliphatic alcohols) and effective Integrally-coloured, or colour-through, concrete refers to curing methods reduce the incidence of plastic shrinkage colouring of the entire mass of the concrete. Mineral oxide cracking, and the likelihood of repairs. powders or liquids are added at the batching stage, and thoroughly dispersed through the concrete mix. In correct proportions, oxides do not have a significant affect on the strength of concrete. The amount of oxide powder required

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7.7 Pier/Pile and slab (see fig. 7.6) 8 PATHS AND DRIVEWAYS

On highly reactive sites, and areas of collapsing or uncon- 8.1 General trolled fill, piers or piles can be used to support a concrete The primary function of concrete paths and driveways is to slab-and-beam floor system. provide trafficable access to a property, however they are also Piers are poured, after excavation, whereas concrete piles are important to the general appearance of the property, and for driven into the ground to a specified depth or until reaching a control of surface rainwater. specified level of resistance. The piles are cut off at the Prior to undertaking construction, a number of aspects need required level to suit the floor system. to be considered – • The type of subgrade (soil) the pavement is to be constructed on. • The loads/traffic the pavement will be expected to carry • The area of pavement to be concreted. • The finished levels of the work. • The level of the damp proof course in adjoining buildings. • Termite control. • Drainage requirements. • The type of surface finish required. • Reinforcement requirements and the spacing/location of joints. • Method of curing. • Safety.

8.2 Grade and thickness of concrete

Figure 7.6: Pier/pile and slab The loads that the pavement can be expected to carry determine the correct concrete grade and thickness. In typical domestic situations, the following are recommended –

Table 8.1 Concrete thickness/grade

Application Concrete Strength thickness grade (mm) Footpaths 75 20 Patios/Garden-shed floors 100 20 Cars and other small-vehicle 100 20/25 traffic (less than 2t) Light trucks 150 32

8.3 Selecting reinforcement

Selecting reinforcing fabric depends on the thickness of the concrete. The type and extent of reinforcement also has a bearing on the spacing of joints.

Polypropylene fibres can be added to the concrete mix to control plastic shrinkage cracking.

In typical domestic situations, reinforcement as shown in Table 8.2 is suitable.

Table 8.2 Reinforcement and joint requirements

Concrete Reinforcement Max. joint Thickness (mm) fabric spacing (mm) 75 RF52 2000 100 RF62 3000 150 RF82 4500

8.4 Construction

8.4.1 Planning for concreting

Before ordering concrete, careful planning will ensure the

will generally be 5–8% of the weight of the cement in the mix. For best results, follow the recommendations of oxide suppliers.

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24 Figure 8.1 Dry-shake topping being applied After placing, the concrete surface is struck, floated and fin- ished in the same way as ordinary concrete, and particular care should be taken with curing to produce the best finish.

For uniform colour, a consistent mixing procedure is crucial, whether it is done at the batching plant or in the barrel of a pre-mix truck. Results are improved if the concrete mix design, the proportions of water and oxide powder, and the method of mixing do not vary. Sample panels are useful to find the right mix, and provide the basis for quality control. Borders, of different colours or concrete pavers, can be used to divide large areas into smaller sections–which can be placed in a single pour–making less obvious the colour variations of different sections that might result with different batches.

8.5.3 Dry-shake toppings

Dry-shake toppings are commercially available products con-

taining cement, sand, and mineral colour oxides, and in some cases, special hardeners to increase the strength of the sur- face of finished concrete. They are sometimes referred to as ‘coloured surface hardeners’ because of this. They come in a range of colours: blues, greens, red and yellow ochres, grey and black, and are often used in conjunction with stencilled and stamped pattern finishes (described below).

Dry-shake toppings can also be made on site from similar materials. The usual blend is 1 part cement: 2 parts clean sand; and mineral oxide pigment measured by weight in the ratio of 1 part pigment to 10 parts cement. The powdered pigment is first blended with dry cement before combining with the sand.

The dry powder is cast by hand over the surface (hence the term ‘dry-shake’ see fig.8.1) of fresh concrete and worked into the surface by trowelling. All traces of bleedwater must be allowed to evaporate before applying the powder. Using the powder to soak up bleedwater is bad practice, and invari- ably results in a much weaker surface, which will wear quickly, and may delaminate or chip. The rate of application of a dry- shake topping for flatwork will typically be a minimum of 2 kg per square metre.

The manufacturers of coloured surface hardeners state that correct use of coloured surface hardeners produces 40 to 60-MPa surface strengths. They are cement-based products and must be finished and cured like any concrete work to achieve the strengths advertised by manufacturers.

When using dry-shake toppings it is important to protect adjacent surfaces, with plastic sheeting for example, because splashes are difficult to remove.

Figure 8.1 Dry-shake topping being applied After placing, the concrete surface is struck, floated and fin- ished in the same way as ordinary concrete, and particular 25 care should be taken with curing to produce the best finish. Type Title Standard Issue Version Ref Release date Kit CPCCCO2013A NVR Standard 15.5 1 004 Carry out concreting to simple forms 09/08/2017 Page 93 of 120 For uniform colour, a consistent mixing procedure is crucial, whether it is done at the batching plant or in the barrel of a 19/082013 pre-mix truck. Results are improved if the concrete mix design, the proportions of water and oxide powder, and the method of mixing do not vary. Sample panels are useful to find the right mix, and provide the basis for quality control. Borders, of different colours or concrete pavers, can be used to divide large areas into smaller sections–which can be placed in a single pour–making less obvious the colour variations of different sections that might result with different batches.

8.5.3 Dry-shake toppings

Dry-shake toppings are commercially available products con- taining cement, sand, and mineral colour oxides, and in some cases, special hardeners to increase the strength of the sur- face of finished concrete. They are sometimes referred to as ‘coloured surface hardeners’ because of this. They come in a range of colours: blues, greens, red and yellow ochres, grey and black, and are often used in conjunction with stencilled and stamped pattern finishes (described below).

Dry-shake toppings can also be made on site from similar materials. The usual blend is 1 part cement: 2 parts clean sand; and mineral oxide pigment measured by weight in the ratio of 1 part pigment to 10 parts cement. The powdered pigment is first blended with dry cement before combining with the sand.

The dry powder is cast by hand over the surface (hence the term ‘dry-shake’ see fig.8.1) of fresh concrete and worked into the surface by trowelling. All traces of bleedwater must be allowed to evaporate before applying the powder. Using the powder to soak up bleedwater is bad practice, and invari- ably results in a much weaker surface, which will wear quickly, and may delaminate or chip. The rate of application of a dry- shake topping for flatwork will typically be a minimum of 2 kg per square metre.

The manufacturers of coloured surface hardeners state that correct use of coloured surface hardeners produces 40 to 60-MPa surface strengths. They are cement-based products and must be finished and cured like any concrete work to achieve the strengths advertised by manufacturers.

When using dry-shake toppings it is important to protect adjacent surfaces, with plastic sheeting for example, because splashes are difficult to remove.

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The procedure for stencilling –

Place the concrete slab Place, screed, bullfloat and trowel the concrete to its finished level.

Embed the stencils Points to note– • Where applicable, stencils are placed in the following sequence: features such as rosettes or motifs, borders and finally the main (general area) stencil are cut in. • Carefully work the stencil into the surface with a roller or a trowel. • Stencils can become deeply embedded in concrete that is too wet. They will be difficult to remove and will result in varying ‘joint’ depths. • If the concrete has become too stiff, the stencils may not be fully embedded or in full contact with the Figure 8.3: Stamping concrete concrete. The coloured topping will stick to the edges of the stencils causing ragged lines; or if the coloured topping The dies are usually a metal ‘grid’ with an attached shaft. gets under the stencil it will stain the ‘joints’. • When placing and aligning stencils it is good practice to The procedure for a stamped finish – lift them, rather than drag them into position. • Drying-shrinkage control (contraction) joints in stencilled Place the concrete slab concrete are ‘wet-formed’ such as inducement-strips and Place, screed, bullfloat and trowel the concrete to its final level. key joints, or sawn joints (see clause 6.4.4). Wet-formed joints are placed under the stencil and aligned with a ‘joint’ Note the thickness of a stamped concrete slab is determined so they are not repeatedly trowelled over. as the thickness from the bottom of the impression to the

Apply coloured surface hardener underside of the slab. In driveways for example, if the See 8.5.3: Dry-shake toppings thickness needs to be 100 mm, and a 15-mm deep stamp is used, the formwork will need to be set at 115 mm, to ensure Apply surface texture the mini- mum thickness is achieved. Surface textures, if specified, are made while the surface is still plastic. Common finishes include steel-trowel, broomed, Apply coloured surface hardener wood-float, sponge, and hessian-drag. See 8.5.3: Dry-shake toppings The use of integrally-coloured concrete as the base colour Remove the stencils may give the paviour more time to apply highlight colours, and Lift the stencil when the surface has stiffened and remove stamp the surface, which is helpful in drying conditions. residue with a leaf blower, not a high-pressure hose. At this stage avoid walking on the concrete with heavy, Apply surface release agent patterned-soled boots. If necessary the leaf blower can be After working in the coloured surface hardener, a release attached to a long pole for greater reach. agent is applied. The reason for the release agent is twofold. Firstly, it prevents concrete sticking to the stamping mould Cure the concrete and spoiling the appearance. Secondly, it can be a highlight A sealer (see below) is often used to slow evaporation colour, creating a variety of two-tone effects. Release agents because conventional curing methods are unsuitable for this come in a range of colours to complement coloured surface type of finish. hardeners. Stamping with sufficient pressure will ensure good bonding of the release agent to the surface, which is Do not confuse curing with drying. See section 4.5: Curing. why the highlight effect generally occurs in deeper joints and Seal the surface depres- sions. The surface release agent is not a curing Sealers are applied to protect the surface from stains (for agent. example oil) because they are difficult to remove using A thin film (about 1.0mm) of clear polythene plastic can be cleaners or solvents without affecting the colour. used as an alternative bond breaker. It is placed over the pre- Most sealers cannot be applied to moist concrete without pared concrete before stamping, preventing the concrete problems–usually the sealer turns a milky-white. Special sticking to the moulds. same-day sealers are available which can be applied to the Stamp pattern ‘set’ surface of the concrete while, underneath, the concrete Before stamping, plan the layout of the pattern to finish mass is still ‘moist’. They are generally not as effective as nor- against walls and around fixtures. In many cases it will be mal sealers or curing compounds for retaining moisture in the necessary to use hand tools (jointing/ironing tools) or small slab, but are a satisfactory alternative. moulds to complete the pattern up to the edge. The use of same-day sealers should be followed with an Cure the concrete application of the final sealer when the surface has dried to The surface release agent does not allow the use of curing its final set. Although this is not the best curing regime, it compounds. minimises initial moisture loss and surface strength loss. Cover the surface with plastic (polythene) sheeting but make 8.6.3 Stamped concrete sure it is in complete contact with the surface of the concrete, Purpose-made metal moulds (dies), rollers, or rubber mats, or colour variations may occur. Polythene sheeting may pro- are pressed into the surface of the wet concrete (see fig. duce some dark or mottled areas because of condensation 8.3). The patterns produced are not unlike – and often under the plastic, which will become less noticeable as the simulate – brick paving, cobblestones, setts, slate or natural concrete dries. stone.

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Remove the release agent together with a continuous water spray, to wash away When the concrete has hardened (so it will not be damaged), the cement paste. Do not broom the surface repeatedly. remove the release agent using high-pressure water, or by This will weaken the paste and dislodge aggregates. scrubbing with a detergent-based wash. The use of water-based surface set-retarders should be considered. Those that are developed especially for this Seal the surface technique slow the setting time of the surface of the A same-day sealer (see 8.6.2) can be used after the release slab to a predetermined depth without affecting the set agent is removed. The final sealer is applied when the surface of the mass of the concrete. This ensures consistent is dry. Apply it evenly with a broom or brush in accordance depth of exposure. They are very useful when drying with the manufacturer’s instructions. weather conditions would otherwise limit the time Concrete may have set and appear hard but it may not yet be available for aggregate exposure. dry and ready for sealing. The premature application of • After exposure, cure the surface by covering it with sealers can trap moisture causing surface imperfections. plastic sheeting for a minimum of 3 days (7 days is preferable). Glass grit (silica chip), or carborundum dust can be sprinkled • An acid-wash treatment is usually necessary to brighten over the final coat to increase skid resistance for a non-slip up the stones by removing the fine cement film from the finish. On steep grades, the sealer may need to be thinned surface. Thoroughly rinse the surface with clean water to down so it can soak into and key with the concrete, rather remove all residues and apply a surface sealer if desired. than remain as a thick layer on the surface, which will become slippery when wet. 8.7.3 Wash-off finish

Joints The procedure– Points to note – • Order the special mix of concrete from the concrete (Refer also to section 6.4: Joints) supplier, containing specified aggregate sizes and • Plan the layout of control and construction joints so they types, and colour pigments. correlate with the grooves in the pattern. • Place the concrete, screed and bullfloat the surface to • Wet-formed contraction joints can be tooled after the finished level, ensuring even paste coverage over the stamping is finished, while the surface is still plastic; aggregate on the surface. although this is difficult if the stamping makes deep • Follow the steps for exposing the aggregate and curing in impressions. clause 8.7.2. • Form key joints before placement. Key joints may 8.7.4 Bonded topping interfere with stamping of deeper patterns. • Install isolation joints against abutting structures before Bonded toppings are placed on the structural slab while it is placement. Installing them after will probably damage the in a plastic state. The slab and topping harden together, mak- finish. ing a monolithic bond. (An unbonded topping is placed on a • Sawn joints should be cut no later than 24 hours after hardened slab with a bond-breaker between the two). finishing. The procedure– • Place the base slab and screed it to a level 25–40mm 8.7 Exposed-aggregate finishes below the finished level. • Prepare a topping mix in the proportions 1 part sand: 11/2 8.7.1 Introduction parts cement: 3 parts aggregate (and colouring pigments Exposed-aggregate finishes can be produced by ‘seeding’ the if required) and just enough water for workability–or order surface of the concrete with selected stones; or by ordering a a special pre-mixed concrete mix. special mix (for the full depth of the slab or for a topping) • Use a surface set retarder on large jobs (or in drying which contains selected stones. They are exposed when the conditions) to allow more time to place and finish thin layer of cement paste on the surface is washed away toppings. soon after the concrete stiffens. Aggregates are available in a • Wait until the surface bleedwater has evaporated from the range of colours including white, black and green quartz, dark base slab before placing the topping. grey basalt, brown and red gravels. The concrete can be • Screed and float to ensure consolidated and coloured (see section 8.5) to complement or contrast with the complete bonding. selected stones. • Follow the steps for exposing the aggregate and curing in clause 8.7.2. Sample panels are recommended to assess techniques, surface finish, distribution of stones and, if applicable, 8.7.5 Stamped exposed-aggregate consistency of colour. Aggregate exposure (by either the seeding or wash-off These finishes should be done under the supervision of a method) and the stamping technique described in paviour experienced in these techniques. clause 8.6.3 can be combined to produce other finishes. 8.7.2 Seeded aggregate 8.7.6 Environmental considerations The procedure– • Place the concrete, screed and bullfloat the surface to the Environmental issues, particularly water run-off, must be finished level. con- sidered with coloured and exposed-aggregate finishes. • After the bleedwater has dissipated, sprinkle the selected Flushing cement paste, coloured surface hardeners, oxides aggregate over the surface. An aggregate size of 8–12 mm and release agents into stormwater drains affects the water is recommended for ease of placement although sizes up quality in natural water systems and may be prohibited by to 20 mm can be used. local authorities. • The selected aggregates are fully embedded by tamping To prevent this– and by repeatedly working the surface with wood floats. • Provide filters at strategic points using sand as • Aggregate exposure begins when the surface can bear a sediment-control barrier and remove from site. the weight of the paviour without making surface impress- • Use hessian wraps to divert run-off to surface ions deeper than 2 mm. Use a medium-bristle broom, catchment or into excavated silt traps. Overflow from silt

traps can 28 be diverted to a surface catchment with excavated channels. • Temporarily cap all drainage inlets.

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29 random cracking by inducing an acceptable crack at • Use raised formwork to control sediment run-off. the joint itself, which relieves the stresses resulting • Where practicable, wash off the residue from one section from drying shrink- of a pavement onto the bare earth to be subsequently covered by an adjoining section.

8.8 Topping existing pavements

8.8.1 General

Existing slabs can be sprayed with coloured and textured finishes (varying in thickness from 3 – 5 mm), however, the success of any topping depends on the bond to the substrate.

8.8.2 Materials Spray-on toppings are available as cementitious or acrylic- based materials. They can look similar but their life expectan- cy may vary. Consult the supplier about suitability and perfor- mance of materials.

8.8.3 Preparation

Clean the existing pavement to remove grit, paint, oil, and other substances that will affect the bond and finish. Use high-pressure water cleaning, acid etching (a mild solution of 1:25 ) and – where severe surface deterioration has occurred – the use of concrete grinding or dustless shot blast- ing to produce a clean, even and sound substrate.

8.8.4 Repairs to substrate

Cracks can be filled with a cementitious or epoxy grout, how- ever, this will not prevent continued cracking due to thermal or ground movements. These cracks will again appear in any new topping or coating, though narrower and less noticeable.

Different levels of adjoining slabs (caused by tree roots, expansive soils, moisture problems and subsidence) can be made flush with a topping or purpose-made levelling compound. Prepare and apply strictly in accordance with the manufacturer’s specifications. The cost of levelling compounds may be prohibitive. Moreover they are not recommended externally because of the possibility of warping and delamina- tion. Where there is a serious case of subsidence, and the slab has lost support, an alternative to replacement is the injection of grout under the slab (‘slab jacking’). This is expensive but may be necessary in some cases.

Broken corners can be repaired by fixing a new section of concrete to the existing. The fixing may be a reinforcing bar (or a stainless steel pin if enough concrete cover is not possible) epoxied into the existing concrete.

Joints are difficult to repair because movement may cause failure of the repair.

Spalling is usually caused by rusting reinforcement. Exposed bars are cut back to give the required cover, before patching with a repair mortar. Before proceeding, a structural engineer should be consulted to determine the structural implications of removing reinforcement.

Surface defects that are shallow can be filled with a spray-on topping material. A purpose-made repair mortar can be used for deeper depressions.

Note repairs should be carried out by specialists.

If extensive repairs are necessary, consider replacing with a new slab. The total cost of repairs and a sprayed finish may be greater than the removal and replacement.

8.8.5 Joints

Contraction joints fall under the general heading of control joints. They control (do not resist) movement and minimise random cracking by inducing an acceptable crack at • Use raised formwork to control sediment run-off. the joint itself, which relieves the stresses resulting • Where practicable, wash off the residue from one section 30 from drying shrink- of a pavement onto the bare earth to be subsequently covered by an adjoining section.

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Existing slabs can be sprayed with coloured and textured finishes (varying in thickness from 3 – 5 mm), however, the success of any topping depends on the bond to the substrate.

8.8.2 Materials Spray-on toppings are available as cementitious or acrylic- based materials. They can look similar but their life expectan- cy may vary. Consult the supplier about suitability and perfor- mance of materials.

8.8.3 Preparation

Clean the existing pavement to remove grit, paint, oil, and other substances that will affect the bond and finish. Use high-pressure water cleaning, acid etching (a mild solution of 1:25 ) and – where severe surface deterioration has occurred – the use of concrete grinding or dustless shot blast- ing to produce a clean, even and sound substrate.

8.8.4 Repairs to substrate

Cracks can be filled with a cementitious or epoxy grout, how- ever, this will not prevent continued cracking due to thermal or ground movements. These cracks will again appear in any new topping or coating, though narrower and less noticeable.

Different levels of adjoining slabs (caused by tree roots, expansive soils, moisture problems and subsidence) can be made flush with a topping or purpose-made levelling compound. Prepare and apply strictly in accordance with the manufacturer’s specifications. The cost of levelling compounds may be prohibitive. Moreover they are not recommended externally because of the possibility of warping and delamina- tion. Where there is a serious case of subsidence, and the slab has lost support, an alternative to replacement is the injection of grout under the slab (‘slab jacking’). This is expensive but may be necessary in some cases.

Broken corners can be repaired by fixing a new section of concrete to the existing. The fixing may be a reinforcing bar (or a stainless steel pin if enough concrete cover is not possible) epoxied into the existing concrete.

Joints are difficult to repair because movement may cause failure of the repair.

Spalling is usually caused by rusting reinforcement. Exposed bars are cut back to give the required cover, before patching with a repair mortar. Before proceeding, a structural engineer should be consulted to determine the structural implications of removing reinforcement.

Surface defects that are shallow can be filled with a spray-on topping material. A purpose-made repair mortar can be used for deeper depressions.

Note repairs should be carried out by specialists.

If extensive repairs are necessary, consider replacing with a new slab. The total cost of repairs and a sprayed finish may be greater than the removal and replacement.

8.8.5 Joints

Contraction joints fall under the general heading of control joints. They control (do not resist) movement and minimise

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9 MORTARS, RENDERS AND ROOF-TILE BEDDING conditions and location (see Table 9.1). Mix proportions are expressed as ratios, eg 1:1:6, 1 part cement to 1 part lime to 9.1 Mortars for masonry 6 parts sand by volume. 9.1.1 General 9.1.4 Site-mixed mortar Mortars for concrete, clay or calcium silicate masonry perform When site-mixing, it is important to carefully measure the similar functions, whether veneer, double, or single-leaf con- material by volume in a suitable container, not by the struction. shovelful. The design of masonry including the requirements for mortars Mechanical mixing is usually done in a concrete mixer. A small are covered by Australian Standard AS3700. amount of mixing water is placed in the mixer followed by the Mortar– sand, cement and lime. Water is slowly added to create a thick • Provides an even bedding for masonry units, and takes creamy mixture. Each batch should be thoroughly mixed for up the dimensional variation of units. two to three minutes for uniform consistency. • Transmits compression loads. Hand Mixing should be done in a clean wheelbarrow or on a • Bonds the units together so they resist tensile and mixing board to avoid contamination. The dry materials should shear forces. be combined and mixed to an even colour before slowly • Seals the joints from the weather. adding water as the mix is constantly turned until a thick • Holds damp proofing and flashings in place. creamy mortar is made. • Is essential to optimum acoustic performance and fire resistance of masonry units. Mortar should be used within half an hour of mixing. Mortar that has stiffened should not be retempered by the addition of 9.1.2 Materials water. Cement 9.1.5 Pre-mixed mortar For normal brick and blockwork general-purpose cement Factory-blended, ready-to-use, general-purpose mortars (Type GP or Type GB) or masonry cement are suitable. The are available in bags from most cement retail outlets. They proportioning of the mortar, however, varies with the type of only need the careful addition of water (and colour additives cement, see Table 9.1. To avoid on-site confusion, it is prefer- if required) for mixing. able if only one type of cement is used on a project. 9.1.6 Mortar mixes for particular environments Cement has a limited shelf life and should be stored off the See Table 9.1 ground in a dry environment. M2 applications– Lime • Above DPC in interior environments not subject to Hydrated lime suitable for hard plastering should be used. wetting and drying. Lime is added to make the mortar creamier or more workable. • Above DPC in other than marine environments. It also helps to minimise cracking as the mix dries out. It is • Above DPC and protected by a waterproof coating, good practice to soak the lime in an equal volume of water for flashed junctions and top covering. 24 hours prior to use to improve its performance in the mix. • Below DPC or in contact with ground but protected from water ingress by waterproof coating. Sand (fine aggregate) • In domestic barbeques and incinerators.

Sand is the fine aggregate in mortar. Fine sands are preferred. M3 applications– Sands with high clay content should not be used, nor should • Above DPC in interior environments but subject ‘fire clay’ or ‘brickies’ loam’ be added to the mortar. (Loam is to non-saline wetting and drying. commonly referred to as ‘fatty’ sand.) • Above DPC in marine environments (100 m –1km

Sand with a high clay content degrades the mortar, markedly of non-surf coast or 1 km–10 km of surf coast). reducing bond strength and lowering durability. • Below DPC or in contact with non-aggressive soils • In fresh water. Water M4 applications– Should be clean, fresh and free of impurities. Mains water or • Above DPC in interior environment but subject to saline water suitable for drinking is usually satisfactory. wetting and drying. • Above DPC in severe marine environments (within 100 Admixtures m of non-surf coast or 1 km of surf coast). Chemical additives should not be used to replace lime. Use • Below DPC or in contact with aggressive soils. in strict accordance with the manufacturer’s instructions. • In saline or contaminated water, including tidal and splash zones. Powdered pigments – or oxides – for colouring, should not exceed 10% of the weight of cement in the mix and should be thoroughly mixed with the other materials prior to the addition of water.

Liquid colour additives should be measured and used in accordance with the manufacturer’s instructions.

A sample of coloured mortar should be made and allowed to dry before starting work, to ensure the right colour is achieved.

9.1.3 Mixes and applications

Mixes should be varied to suit the particular exposure

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Table 9.1 Mortar mixes for masonry Water (based on Tables 5.1 and 10.1 in AS 3700) Should be clean, fresh and free from impurities. Mains water Mix proportions (parts by volume) or water that is suitable for drinking is usually satisfactory. Use just enough water to make the mix workable.

Mortar Type Type Building Masonry Sand Admixtures GP GB Lime Cement Cement Cement Generally, admixtures are not required in render. However, if they are added they should be used strictly in accordance M2 1 2 9 with the manufacturer’s instructions.

1 2 8 Pigments, added to colour the render, should not exceed 8% of the weight of cement in the mix and should be thoroughly M3 1 1 6 mixed with the other materials prior to the addition of water. 1 1 5 Liquid pigments should be measured consistently and added in accordance with manufacturer’s instructions. 1+ water thickener 5 A sample of coloured render should be made and allowed to dry before starting work, to ensure the right colour is 1 4 achieved. 1 M4 1 0– /4 3 9.2.3 Mixes and applications 1 1 1 /2 4 /2 A variety of render mixes can be used, and depend on the 1 0–1/4 21/2 background surface and the conditions the rendered surface is exposed to. 1+ water 4 thickener Table 9.2 Render mixes

1 3 Mix Internal/ Application (cement:lime:sand) External Note these mortars are not suitable for autoclave aerated concrete (AAC) units. For calcium silicate units use only the 1:1/4:3 Internal Single coat mixes with added water thickener. Undercoat work (two part)

1:1/4:5 Internal Finish coat work

9.2 Renders (two part)

9.2.1 General 1:1/2:41/2 External Strong mix for

Cement-based renders, on internal and external walls strong improve: waterproofing, fire rating and the appearance background s with the use of coloured or textured renders.

To get the best results from a render– 1:1:6 External Moderate strength • The mix should be suited to the background surface. mix for porous and • It should be properly applied in the correct number of weaker backgrounds coats, and to correct thicknesses. • It should be properly cured. 1:2:8 External Final coat for weak

9.2.2 Materials backgrounds in sheltered Cement conditions

General Purpose (Type GP or Type GB) cement is normally used, but where a light or coloured finish is required an off- Site-mixed renders white cement may be used.

Lime When site-mixing, it is important to carefully measure the material by volume in a suitable container, not by the Hydrated lime suitable for hard plastering should be used. shovelful. Lime is added to make the render creamier or more workable. It also helps to minimise cracking as the mix dries out. Mechanical mixing A small amount of mixing water is placed in a concrete mixer followed by the sand, cement and lime. It is good practice to allow the lime to soak in an equal volume of water for 24 hours prior to use. This will improve its perfor- Water is slowly added until a stiff mix that will ‘sit up’ on the mance in the mix. trowel is made. Each batch should be thoroughly mixed for two to three minutes to ensure uniform consistency. Sand Hand mixing is done in a clean wheelbarrow or on a mixing Sand is the major ingredient of the mix and should be of board to avoid contamination. good quality. Plastering sands and finer washed concrete sands – commonly referred to as ‘sharp’ sand – are available The dry materials should be combined and mixed to an even from builders’ suppliers. In general, coarsely graded sands colour before the addition of water, which is slowly added and mixed in until a stiff creamy mix ‘sits up’ in the barrow. are more suitable for undercoats, and a finer grading is more suitable for finishing coats. Renders should be applied within half an hour of mixing. Render mix, which has stiffened, making it difficult to apply, should be discarded and not retempered by the addition of water.

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9.3.2 Pointing 10 TROUBLESHOOTING AND REPAIRS

Pointing cappings provide a weather seal. The use of wet 10.1 Defects–Prevention and repair mixes prone to excessive shrinkage cracking should be 10.1.1 Dusting avoided. Dusting is a condition where a fine powder comes off the sur- Pointing of the joints between ridge and hip cappings, should face of the concrete. be done using a 3:1, sand:cement mortar. Cause: Concrete with high water content (often the case Where tiles converge at a valley (or steep roof pitches), it is when water has been added on site) will bleed more easily often essential to point under the cut tiles in the valley line to and bring fines to the surface. When the surface is worked prevent the up-wash of roof water under the opposing tile prematurely, these fines become dominant and the cement edge. paste is diluted. With little cement binder available, the sur- Pigments are usually added to pointing-mortars to match the face dusts. Another cause is rain on fresh concrete surfaces colour of roof tiles. Some trials will be required to achieve a before the concrete has set. A deluge of rain will flood the good match. In all cases, the pigment used should be no surface and wash out or dilute the cement binder. The failure more than 10% by weight of the cement in the mix. Pigments to undertake proper curing may also cause dusting. should be used strictly in accordance with the Prevention: Do not work the surface too early while bleedwa- manufacturer’s recommendations. ter is present. Avoid adding water to concrete. Do not over- When pointing, the mortar should be lightly brushed or wiped work the concrete because this will also bring fine material to after the initial set to remove loose particles. All tiles adjacent the surface. When rain threatens, take decisive action to pro- to the ridge tiles should also be cleaned and brushed free of tect the surface. Do not attempt to broom the surface when loose mortar particles. wet because this will drag away the cement paste and create rutting in the surface. Always adopt a good curing procedure as early as possible.

Repair: Dusting can be rectified in the majority of cases by the application of a sealer that penetrates the concrete (and reacts with the lime in the concrete, effectively case harden- ing the surface). It also bonds the thin, weak layer on the sur- face to the base concrete below. More-severe cases will require the complete removal of the weak top layer with a concrete grinder.

10.1.2 Crazing

A crazed concrete surface is a network of very shallow fine cracks across the surface. They are obvious when the concrete is damp.

Cause: Crazing is caused by minor surface shrinkage in rapid drying conditions (ie low humidity and high temperatures), or alternating wetting and drying. Other contributing factors include having the mix too wet and the lack of adequate curing. Crazing also results when driers such as neat cement are used to soak up excess water and are trowelled into the surface.

Prevention: Adopt a good curing regime and start it early. Do not use cement (or coloured surface hardeners) to soak up water, and limit the trowelling of the concrete. Avoid the addition of water to the concrete. Do not work the surface too early when bleedwater is present.

Repair: Repair may not be necessary because crazing usually will not weaken concrete. If it is visually unacceptable, then a surface coating of paint or other overlay sealer can be applied to cover and/or conceal the cracks.

10.1.3 Blistering

Blisters are hollow, low-profile bumps on the concrete surface filled with either air or bleedwater. Under traffic (both vehicle and foot traffic) these blisters crack and the surface mortar breaks away, exposing the concrete underneath.

Cause: The concrete surface was sealed too early by trow- elling, trapping water, which continued to rise, causing the blistering under the surface during finishing. This can occur particularly in thick slabs or on hot, windy days when the surface is prone to premature drying.

Prevention: The use of an evaporation retardant in hot, dry or windy weather will reduce this problem. Other means of reducing rapid drying include windbreaks and sunshades, and placing at cooler times of the day. If blisters are forming,

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Pre-mixed renders Factory-blended, ready-to-use, general- Decorative finishes purpose and special-purpose renders requiring only the addi- A variety of decorative effects can be achieved using different tion of water are available in bags from most cement retail finishing techniques on the final coat. outlets and decorative-coating manufacturers.

9.2.4 Applying render The application of decorative render finishes can be difficult and application by a competent tradesman is Surface preparation recommended.

The background surface should be free from paint, oil, dust Trowelled finish can be achieved by skimming the final coat and any dirt or other loose material that may prevent a good with a wood float to produce a smooth, dense surface or bond. Purpose-made bonding agents, applied in strict accor- using notched trowels to produce a variety of finishes. dance with the manufacturer’s instructions, can also be used to improve adhesion. Bagged or patterned finish can be obtained by rubbing a ball of damp hessian into the surface with different patterns being Table 9.3 indicates the preparation treatment necessary for a produced depending on the action used. number of background surfaces prior to rendering. Sponge finish can be achieved by mopping or sponging the Table 9.3 Background Preparation unhardened surface with a damp sponge. Water should not be allowed to run down the wall. Background Building material Treatment Roughcast The final coat is thrown and flicked onto the sur- face and no retouching is done. Smooth, strong High-strength Scabble surface concrete and apply dash Textured surfaces can be achieved through the use of coarser coat or fix aggregate in the final coat. metal lath clear of 9.2.5 Control joints surface Cement-based renders can crack as a result of shrinkage as Fibre-cement Fix metal lath they dry, or because of movement in the background material. sheet clear of surface With the careful placement of control joints, this cracking can Strong/porous Standard bricks, Rake joints be minimised. blocks, concrete and apply Control joints should be formed in the render to coincide with dash coat all joints in the background and locations in the structure Weak/porous Lightweight Dampen surface where movement is likely to occur. concrete, 9.2.6 Curing and protection Render undercoat

All render coats, including undercoats and dash coats, should be kept damp for 3 days or until the next coat is applied. Surface dampening Render should not be allowed to dry out quickly and should After initial preparation, the background surface should be be protected from hot weather, drying winds and rain. dampened and allowed to dry back to a surface-dry condition Rendering in direct sunlight or exposed windy areas should immediately prior to rendering. This reduces suction but still be avoided. enables a bond to be achieved. Plastic sheeting should be used to protect fresh render for Dash coat the first 3 days after application. (The plastic sheet should not be allowed to touch the finished surface or it will lead to dis- Dash coats are used to provide a high-strength bond between colouration.) the background and the subsequent render coat. Site-mixed dash coats have the proportions of 1 part cement: 1–2 parts Protection is not normally necessary for internal renders if sand. The dash coat is flicked and splattered over the back- the building provides protection from drying weather ground to produce a rough finish. This open-textured layer is conditions. not trowelled level or smoothed out, but left rough to ‘key’ with the render. 9.3 Roof-tile bedding Number of coats 9.3.1 General This will depend on the condition and the uniformity of the background, the conditions it is exposed to, and the type of Ridge and hip cappings should be laid on a mortar bed. finish required. Usually, one or two coats are all that is required for most work. Single coats should never exceed Mixes recommended by AS 2050– 15 mm in thickness. • Composition mortar 1 cement:1 lime: 6 sand • Cement mortar 1 cement:4 sand A minimum of three days should be allowed between coats. Measurement of the ingredients should be made using a Undercoats are normally applied by trowel to a minimum gauge box or bucket not a shovel. A good bricklayers’-sand thickness of 10 mm and a maximum of 15 mm. When the should be used. The lime in the composition mortar will pro- render is firm, it should be raked or scratched to provide a duce a more workable mix. key for the next coat.

Final coats are normally applied by trowel to a maximum thickness of 10 mm over the undercoat.

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delay trowelling as long as possible and take steps to reduce Causes: One or more factors including incorrect placement evaporation. of the concrete, delays between placement of concrete lay- ers, inadequate vibration, and the loss of cement paste Repair: Grind off the weakened layer to an even finish. Place through unsealed formwork joints. Surface voids may also a topping layer to remedy badly damaged surfaces. indicate a mix that has segregated because of the addition of 10.1.4 Uneven colour of plain concrete water, or concrete that has been dropped into place from a height greater than one metre. Poor surface formwork, poorly There is sometimes colour variation in adjoining sections oiled forms, or damaged form faces restrict the movement of of concrete, and sometimes in the slab itself. the concrete during placement.

Causes: The amount of water in concrete affects its colour. Prevention: Compact and vibrate as close as possible to The more water (and therefore bleeding), the lighter will be formwork and, if necessary allow for external vibration of the concrete. Changing the supplier of the concrete or forms. Vibrate more frequently. Use good formwork that has changing the cement brand may also affect colour. Finishing not been damaged. Do not add water to the concrete. Do not practices such as early trowelling of wet surfaces will lighten drop the concrete into forms from excessive heights. Ensure the concrete and extended hard trowelling will darken the that all formwork joints are tight (tape joints if necessary) to concrete. A steel trowelled surface will be lighter in appear- avoid mortar leakage. Place all concrete continuously and ance than a broomed finish. Curing will darken the concrete ensure that when placed in layers, concrete in one layer is and inadequate or inconsistent curing methods can result in vibrated to blend with the lower layer. mottled surfaces. Curing compounds that are not evenly applied, and plastic sheeting that is not fully in contact with Repair: Honeycombed surfaces can be rendered. If honey- the surface will result in lighter patches. combing is much deeper than the surface layer, it may need to be removed and replaced with a repair mortar. Prevention: Adopt a standard and consistent procedure for ordering, placing and finishing. Do not add water, use the one 10.1.8 Blowholes supplier, trowel after bleedwater has dissipated, trowel the Blowholes are individual, spherical voids in the surface, surface evenly and implement good curing techniques. usually less than 10 mm. Repair: The application of a stain available from concrete Cause: Air-voids are trapped against the form face, usually chemical supply companies may lessen the colour variations. because insufficient vibration (compaction) has not brought A trial, on a concealed section of the slab, is advisable. them to the surface. Blowholes often occur with impermeable 10.1.5 Rain damage forms.

Causes: Heavy rain while concrete is setting, or rainwater Prevention: Ensure forms are rigid, with a thin, even coat of being allowed to run across the concrete surface. form oil (referred to as ‘pickling’). The workability of the mix should be suitable for the application. Ensure careful and Prevention: Prevention is far better than any cure in this case. thorough internal vibration. If caught out, cover the concrete and channel run-off away from freshly laid concrete. Repair: Use repair mortars.

Repair: If concrete has not hardened and damage is only 10.1.9 Wavy or uneven surfaces slight, the surface can be refloated and re-trowelled, taking Causes: Common causes include– care not to overwork excess water into the surface. If con- • Poorly built formwork that has uneven guide rails for crete has hardened, it may be possible to grind or scrape screeding away the surface and place a topping layer of new concrete, • Improper methods of screeding and trowelling or repair compound, over the top. This may not always be • Loading a pre-hardened slab with workers’ foot-traffic possible and should be done only with expert advice. and power trowelling machines, resulting in humps and 10.1.6 Efflorescence hollows in the concrete. Paviours–intent on finishing the surface–can be deceived about the hardness of the slab Efflorescence is a white crystalline deposit sometimes found when hot weather conditions dry out the surface prema- on the surface of concrete soon after it is finished. turely, while the concrete mass underneath is still plastic

Causes: Mineral salts are sometimes present in the water and can be deformed.

used to make the concrete. These salts collect on the con- Prevention: Always keep a uniform surge of concrete ahead crete surface as water evaporates. Excess bleeding can also of the screed board and take accurate levels. To avoid the result in efflorescence. premature set of the surface, use evaporation retardants to

Prevention: Use clean, salt-free water and washed sands. control rapid drying. Maintain a constant slump; do not add Prevent excessive bleeding by avoiding the addition of water water, which will vary the set of different concrete loads.

to the mix on site. Use a vapour barrier to seperate ground- Repair: Use self-levelling floor compounds or repair mortars. slabs from rising ground water, which would otherwise soak Alternatively, grind the surface evenly. into the concrete and possibly brings salts to the surface. 10.1.10 Spalling Repair: Remove salt deposits with a stiff-bristle broom. If the result is not satisfactory, scrub with clean water then lightly Spalling is when fragments of concrete are detached from the rinse the surface. To remove any remaining deposits, the concrete surface.

con- crete can be treated by acid etching and flushing. Causes: Heavy loads or blows from a hammer. Corrosion of Efflorescence is not a permanent discolouration and without reinforcement, which forces off the surface concrete. Entry of treatment will eventually fade away. hard objects – such as stones – into joints, can cause spalling 10.1.7 Honeycombing when a slab expands and pushes against the object. Poor compaction of concrete at joints is another cause. Commonly occurring on vertical faces of edge beams, stair- case and verandah soffits, it appears on the surface as a Prevention: Ensure sufficient cover of reinforcement. coarse texture of interconnecting voids and stones. Remove formwork carefully, to avoid hammer blows or point loads to

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new concrete. Design joints carefully. Keep joints free of 10.2 Crack Repair debris. Keep heavy loads away from the joints and edges until 10.2.1 General they have properly hardened. Ensure proper compaction. The following factors should be taken into account– Repair: Scrape, chip or grind away the weak areas until • Before any repair is undertaken the cause of the cracking sound concrete is reached. Then refill area with new concrete must be ascertained. This may require the services of a or repair mortar. Make sure the old concrete is brushed clean suitable expert or consultant. of any loose material. Compact, finish and cure the new patch carefully. For larger areas, seek expert advice. • Whether the crack is live or dormant. Will it continue to move–open or close–or has it stabilised? 10.1.11 Coloured decorative concrete defects • The width and depth of the crack. • Whether or not appearance is a factor. Stamped concrete Dormant cracks are usually repaired by cutting a groove over • Colour appears to be lifting, exposing a pale, tinged them and filling with a cement grout or mortar. Other materials concrete base. This is caused by the incomplete removal are also available for crack repair. of the release coat. Live cracks are filled with a flexible sealant to allow move- • The depth of the stamped impression tapers down to ment. A wide variety of purpose-made materials are a minimal imprint. This is the result of undertaking the available. stamping when the concrete has hardened too much. There is a large range of repair products. It is not possible, in • The surface has small craters over much of the pattern. the scope of this handbook, to give detailed instructions about Often the concrete has been too wet when stamping their use. The following is only a guide–detail information begins, or the concrete was re-wetted (or ‘wet wiped’) to should be sought from the manufacturers of particular products. make imprinting easier, and the excess surface water has created suction on the stamping mould. 10.2.2 Live cracks

• The colour is fading, although it is not in a high-traffic Live cracks should be sealed with a flexible material area. The colour applied was not sufficient, or only one that allows movement, particularly in seasonal cycles. coat of base colour was applied and the release coat was applied at the same time as the second colour. This will Flexible epoxy resins allow a small amount of movement but mastic sealants, such as silicone and polyurethane, are more also indicate that the sealer is allowing the weather to commonly specified. Cracks are repaired by cutting a groove break down the pigments. Colour may have been poorly (or chase) over them and filling with the sealant. worked into the concrete. 10.2.3 Dormant cracks • The colour surface has crusted and begun to delaminate and flake off. Causes include the use of cement or a dry- Dormant cracks range in width from 0.05 mm (crazing) to shake topping to mop up bleedwater, or the application of more than 5 mm. The materials and methods for repair the colour topping after the concrete has set, resulting in depend on the width of the crack. a poor bond with the base slab. Very fine cracks, for example crazing, are very difficult to Stencilled concrete repair effectively. In many cases it is best to do nothing.

• The edges of the ‘joints’ of the pattern are rough and If the problem is one of appearance (dirt collecting in very fine cracks accentuates them), a solution may be to rub down the variable. The stencil was not fully embedded in the concrete, consequently the colour topping has stuck to surface with a carborundum stone before sealing with a water-repellent material, such as sodium silicate. the stencil and been torn away when the stencil was removed. Fine cracks (up to about 1 mm in width) can often be sealed • The joints are stained with colour. The colour has bled against water penetration by simply rubbing in a cement grout under the stencil due to poor adhesion with the surface. or slurry. Injecting an epoxy-resin into them can also seal The stencil was not sufficiently worked into the surface, them. or the concrete had begun to dry when the stencil was placed, resulting in a weak bond. Repairing fine cracks is often unecessary and can sometimes • The depth of the joints varies. The stencil was placed too detract from the general appearance of the surface finish.

early, when the concrete was too wet, and was embedded Epoxy grouts are widely used because– too deeply into the soft surface. • they adhere strongly to both fresh and • The pattern is out of alignment. The alignment of stencils hardened concrete; was unplanned or the project was comprised of separate • formulations are available which will adhere to pours and care was not taken to align stencils. most surfaces and harden even under wet • The pattern is distorted. This is often caused by dragging conditions; the stencil into alignment across the surface. When aligning • they have good mechanical strength and low shrinkage; and stencils, always hold them off the surface and lay down • they are resistant to a wide range of chemicals, into position. including the alkalies in concrete.

For cracks wider than 2 mm, a cement grout may be the most satisfactory, and is often preferred because of its total compatibility with the parent material, and its ability to main- tain an alkaline environment around reinforcement.

Other materials, such as polyester resins and synthetic latex- es, have also been used satisfactorily to seal fine cracks. They can have lower viscosities than epoxies and hence can penetrate more easily. However, they may not achieve the same bond strengths and may be less reliable in damp or wet conditions.

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10.2.4 Wet-crack repair concrete toppings (which may be either bonded to the exist- ing concrete or unbonded), to the application of pre-pack- In some situations, a crack in a concrete slab can allow mois- aged proprietary levelling compounds. The alternatives have ture to rise through to the surface, possibly due to hydrostatic different advantages and applications for different pressure. Often, moisture is present from seepage or a bro- situations. ken or damaged water pipe under a slab. As the concrete may be very dry, the slab acts as a wick and can draw up any It is crucial to consider the locations of joints in a topping to moisture present. Products are available which react with the avoid cracking. Generally, the area should be limited to 15-m2 moisture present to seal cracks in a moist environment. sections and control joints formed to align with existing joints. The thickness of a topping will depend on the product, and 10.3 General repairs intended use of the floor, including abrasion requirements, 10.3.1 General service and dead loads and exposure to corrosive substances or environments. Concrete needs minimal maintenance if correctly placed. However, minor repairs may be necessary in some instances Cracks in the existing concrete should be repaired, because to improve its appearance and performance. Serious defects it is likely they would appear in the topping, especially in thin may require a complete topping over the whole concrete sur- bonded toppings. face. Some of the simpler repairs are outlined below. New concrete toppings show fine surface cracks because of A variety of purpose-made products are available for repair drying at the surface of the topping, and the bond of the top- and treatment of concrete. It is essential to obtain the manu- ping to the existing base. facturer’s advice and instructions on the product’s application. After curing, the topping can be used by foot traffic, heavier 10.3.2 Mortars loads, however, should be deferred for 28 days.

The filling of chips or gouges is best done with a repair mortar Bonded toppings available from concrete chemical supply companies. A variety Bonded topping slabs are between 20 and 50 mm thick and of products are available and the product selected should suit consist of 1 part cement: 11/2 parts clean sharp sand: 2 parts the particular application. The manufacturer’s instructions of 7 to 10-mm aggregate mixed with a minimal quantity of should be followed carefully. water necessary for workability. 10.3.3 Acid etching/cleaning Toppings are placed on a rough surface, which is clean and Acid etching is an effective method in some instances sound. Old concrete surfaces, which are disintegrating, ie to clean or lightly texture concrete surfaces. dusting or spalling, should be chipped until a sound surface is obtained. Smooth concrete should be chipped or scabbled to Extreme care is required when handling acids. When diluting provide a key for the new topping. Water blasting or captive hydrochloric acid always add the acid to the water, never the shot blasting is preferable, because chipping tends to pro- reverse. Ensure good ventilation and avoid contact between duce a weak base layer. On a prepared surface the coarse the acid and the reinforcement. aggregate should be showing.

Use only diluted acid to clean or etch the concrete surface. Hose and scrub with a stiff broom to remove all dust and The recommended proportions are 1 part hydrochloric acid to foreign matter before placing the new concrete. A suitable 20 parts water. Always saturate the surface with water before bonding compound should be used. applying the dilute acid solution. When applying the solution, ensure that the surface is moist but without any free water Generally, reinforcement is not used when the topping thick- being present. ness does not exceed 50 mm.

The applied solution should be allowed to react on the con- F42 fabric can be positioned 20 mm from the top of the slab crete surface for 10 to 15 minutes. The surface should then and supported on bar chairs will help control shrinkage cracking. be thoroughly rinsed and scrubbed with lots of clean water. Polypropylene or steel fibre reinforcement may also be used. Repeat rinsing at least twice or until all traces of the acid All joints in the original slab should be duplicated in the top- solution has been removed. ping slab to maintain movement control. The process may be repeated if necessary to produce the The topping should be cured for a minimum of 3 days, prefer- required surface finish. ably 7 days. 10.3.4 Slippery concrete surfaces Unbonded toppings Smooth concrete surfaces that have become slippery may be If the topping slab is 50 –75 mm thick, a separate unbonded made coarse by using a high-pressure water blaster or by reinforced topping should be considered with a plastic mem- acid etching the surface. brane separating the old concrete from the new. Toppings If a high-pressure water blaster is used, it should be capable that exceed 75 mm in thickness should be regarded as new of delivering pressure between 6.9 and 8.3 MPa (1000 and concrete slabs and designed and reinforced accordingly. 1200 psi). The use of such equipment to achieve surface N32 grade concrete with a maximum slump of 80 mm should tex- turing can be difficult and specialised use by a be specified. F52 reinforcing fabric is positioned 20 mm from competent tradesman is recommended. If the clean concrete the top of the slab and supported on bar chairs to help surface is sealed (once dry), it will resist dirt and grime. control shrinkage cracking. 10.3.5 Topping existing concrete The topping should be cured for a minimum of 3 days, General preferably 7 days.

A damaged or worn concrete surface can be revitalised by Levelling compounds the application of a topping. Proprietary levelling compounds and toppings are typically A variety of applications are available, ranging from new less than 10 mm thick. They are mixed with water and screeded onto the concrete surface. Levelling compounds

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can be applied in thicknesses as thin as 1 mm. Some self- APPENDIX levelling products require little finishing. It is essential to follow Relevant standards the manufacturer’s advice and instructions about the product’s application. AS 1379 Specification and Supply of Concrete AS 2050 Installation of Roof Tiles AS 2870 Residential Slabs and Footings –Construction AS 3582 Supplementary Cementitious Materials for use with Portland Cement 3582.1 Fly Ash 3582.2 Slag – Ground Granulated Iron Blast-furnace AS 3727 Guide to Residential Pavements AS 3799 Liquid Membrane-forming Curing Compounds for Concrete AS 3972 Portland and Blended Cements

Compression testing

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Self-Check Questions

Question 1 List the 4 basic ingredients that make up concrete? (1)______(2)______(3)______(4)______

Question 2 Explain in your own words the term “Hydration”.

______

Question 3 “Properties of Concrete” - There are 2 x basic requirements of concrete, name them.

1. ______

2. ______

Question 4 Describe in your own words the term “Compressive Strength” in relation to concrete and explain how this is measured

______

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Question 5 List the 4 x factors that influence “Compressive strength” in a concrete mix. (1)______(2)______(3)______(4)______

Question 6 The lower the W/C Ratio (Water/Cement) the greater the strength of the concrete, however if the W/C Ratio is to low what effect does this have on its workability. ______

Question 7 List 3 x Curing methods

(1)______(2)______(3)______

Question 8 How many days are generally accepted before concrete will gain a large part of its ultimate strength.

______

Question 9 To achieve maximum concrete density it is necessary to remove air voids, explain how this is done

______

Question 10 What is “Tensile Strength” in relation to concrete?.

______

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Question 11 Durability is the measure of the concrete’s resistance to the ravages of time and weather, list 4 x factors that can influence “Durability” (1)______(2)______(3)______(4)______

Question12 List 4 x factors that affect the workability of concrete.

(1)______(2)______(3)______(4)______

Question 13 What is a “Slump Test” and what does it measure.

______

Question 14 List 2 x factors that may contribute to “Shrinkage Cracks” and give an example of a precaution you would take to help minimise this effect.

(1)______(2)______

Question 15 List the 4 x Basic materials used in the manufacture of “Portland Cement”

(1)______

(2)______

(3)______

(4)______

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Question 16 In relation to the different types of cement powder, explain a situation where Type LH Cement (Low Heat) may be used. ______

Question 17 “POZZOLANS” are a substance which reacts to the presence of moisture and lime which help produce compounds with a cementing action, one of which is Fly Ash. Explain where Fly Ash is obtained from and list 2 x advantages it offers

(1)______

(2)______

Question 18 In general Aggregates used in concrete should have a number of properties list 2 of these properties

(1)______

(2)______

Question 19 What effect does particle shape and surface texture of “crushed rock” aggregates have on the overall strength of concrete ______

Question 20 Why is the storage of aggregates stock piles important.

______

Question 21 What effect does sea water and bore water have on a concrete mix?

______

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Question 22 List 4 x different scenarios where “ADDMIXTURES” may be added to a concrete mix.

(1)______(2)______(3)______(4)______

Question 23. Explain the advantages of using plywood-sheeting formwork?

______

Question 24. What is a “Release Agent” and list 2 x different types?

1)______(2)______

Question 25 Explain how you would store and maintain formwork so it is kept in good workable condition?

______

Question 26 Concrete is strong in tension and week in Compression strength? (Answer True or False)

______

Question 27 Why is sufficient concrete cover important in relation to steel reinforcement bars? ______

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Question 28 List 3 x different types of Reinforcement steel commonly used on a construction site.

(1)______(2)______(3)______

Question 29 In relation to “Deformed Bar” what does the following abbreviation mean? – Y28

______

Question 30 In relation to “Square Fabric Mesh” what does the following abbreviation mean? – F82

______

Question 31 Why is it important to secure reinforcement bars to the formwork?

______

Question 32 For slabs what is the recommend distance “Plastic Bar Chairs” should be spaced apart.

______

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Question 33 What is the primary purpose of Reinforcement Bar chairs?

______

Question 34 List 3 x types of concrete finishing tools?

(1)______(2)______(3)______

Question 35. What is the maximum recommended delivery time Concrete should be delivered onsite after mixing has been completed. ______

Question 36 What effect does prolonged mixing in hot weather have on concrete? ______

Question 37 Describe 3 x ways concrete can be distributed onto a job site.

(1)______

(2)______

(3)______

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Question 38 There are 4 principals that should be followed when placing concrete, List 2 of them?

(1)______

(2)______

Question 39 List 2 of the main objectives for compacting Concrete?

(1)______(2)______

Question 40 Briefly explain the correct method for using an immersion type vibrator?

______

Question 41 What effect does the presence of “free water” have on top of a slab if finishing work was to take place. ______

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Question 42 There are a number of purposes for floating concrete after screeding, list 3 of them.

(1)______(2)______(3)______

Question 43 In your own words, explain why trowelling is used as part of the concrete finishing process ______

Question 44 Briefly explain how an “Exposed Aggregate” finish is achieved? ______

Question 45 Explain 2 x different Curing methods that are commonly used today ______

Question 46 List the 4 x different types of concrete to concrete joints that are commonly used? ______

Question 47 After a concrete slab has been laid what time frame is recommended to make a Dummy Contraction Joint with a Quick Cut Saw?

______

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Question 48 What is the recommended distance between expansion joints? ______

Question 49 Why are expansion joints necessary? ______

Question 50 Give an example of where an isolation joint may be used. ______

NOTE If you cannot find answers in the learning pack you are also welcome to look them up on line.

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Practical Exercise 1

1. Calculate material quantities from plan drawings

1. Existing plan TRACEY ( 3 Bedroom House )

2. Calculate the amount of concrete required for the house slab with a thickness of 150mm.

3. Calculate the amount of bedding mix required for the bathroom and laundry (wet areas)

4. Calculate the amount of concrete for the courtyard (flush with line of terrace and a joining 600mm pathway to the terrace at 100mm thickness.

5. Make up a very neat and legible order list for all materials that you will need to order.

6. Now make up a neat and legible list of tools & equipment that you will require for this job.

7. Identify any problems or requirements that you will have especially considering the environment.

8. Can you work out how much the job would cost using the concrete cubic price of $150 and mesh at $25 / sqm. Expansion strip foam at $35 a 25m roll, chairs at $30/100

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. Practical Exercise 2

Make up a job safety plan & fill out a risk assessment form base on above

. Practical Exercise 3

Check all aspects of Concrete Specifications from a plan if need be go on line and check the different concrete types. What type of concrete would you order for the slab, and what type for the path and courtyard.

. Practical Exercise 4

Make a list of the formwork you will need for the above job and any extra gear that may have been overlooked.

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Job Safety Analysis – 1 Copy to be handed in for each unit

Student Name : Student Signature:

Project : Trainers Name:

Location : Date : Accepted : Yes ! No !

Procedure - List Possible Hazards – What things can Safety Control – How can I stop or of steps happen or go wrong, also what hidden Risk minimize these things happening or Risk in doing a Job on dangers are there on this Job Site? going wrong or injuries occurring? a site.

Signature Trainer / Site Leader______

Signature Building Supervisor______

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Job Safety Analysis – Risk Matrix

Consequence

1 2 3 4 5 Likelihood Insignificant Minor Moderate Major Catastrophic

11 16 20 23 25 A (Almost Certain)

7 12 17 21 24 B (Likely)

4 8 13 18 22 C (Possible )

2 5 9 14 19 D (Unlikely)

1 3 6 10 15 E (Rare)

Low Medium High Extreme

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