DOCSLIB.ORG

Influences Affecting Compressive Strength of Modern Non-Hydraulic Lime Mortars Used in Masonry Conservation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Influences Affecting Compressive Strength of Modern Non-Hydraulic Lime Mortars Used in Masonry Conservation Transactions on the Built Environment vol 55, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509 Influences affecting compressive strength of modern non-hydraulic lime mortars used in masonry conservation J. Valek & P.J.M. Bartos Advanced Concrete and Masonry Centre, University of Paisley, Scotland Abstract Non-hydraulic lime based mortars are currently more and more often used for the repair of historic masonry. They are presumed to be compatible with the original mortarlmasonry and their properties are not always evaluated, mainly due to a lack of research into mortars produced in a traditional manner. Influences of curing conditions, quality of mixing and water content on compressive strength of a non-hydraulic lime mortar mix made of lime putty were reviewed and examined. The mortar specimens were prepared with various water contents, cured in outdoor and indoor conditions and tested after 1, 2, 4 and 6 months. Phenolphthalein pH indictor was used to measure the carbonation depth. The strongest mortar specimens were from the indoor ageing condition although the mortar was less carbonated. The addition of water into the fresh mix increased porosity and lowered the compressive strength, however there were other influences which affected this relationship. 1 Introduction In conservation practice there are two main ways to design a new repair mortar. The first one is based on the traditional conservation approach when the new mortar is a copy reproducing the original mortars as close as possible. The second one is more scientifically based, involving a detailed testing of properties of new and original mortars in order to ensure their compatibility. This approach is a more universal and advanced way of designing a compatible mortar Transactions on the Built Environment vol 55, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509 572 Structural Studies, Repairs and Maintenance ofHistorica1 Buildings as the first one is based merely on the presumption that the copied mortar will perform in the same manner as the original one. Although this presumption may not always be correct, as the historic mortars often undergo certain changes during their ageing [l], in the case of non-hydraulic lime mortars such application is probably close enough in terms of compatibility needs. However, the lack of research into the properties of lime-based mortars produced in the traditional ways inhibits accurate compatible design. The biggest hmdrance to this research is the complexity of influences on the mortar performance. To assess the performance of non-hydraulic lime mortars or their compatibility a number of tests are usually carried out [2]. Compressive strength testing remains a key factor in this assessment, however it should not be used as a sole measure of quality. In fact, for determination of compatibility of non-hydraulic lime mortars the value of the compressive strength alone may not be needed at all. However, in research of the mechanical and physical properties of lime mortars, compressive strength testing is a standard way to assess their hardening, setting and strength, and is related to carbonation, porosity and other physical properties [3]. Figure 1: Stone and lime mortar interaction and influencing factors after Bartos and Lawson [6]. 2 Influences on lime mortars performance Non-hydraulic lime based mortars are expected to have a relatively low compressive strength, approximately 0.5-3MPa and are expected to adjust to seasonal and minor structural movement without damage (4, S]. Durability of lime based mortars can vary depending on conditions and ageing but surviving examples of historic mortars well over 600 years old are available world-wide. Durability and performance of non-hydraulic lime mortars are limited not only by the material itself but also by workmanship, ageing and curing condtions and stone and mortar interaction, as presented in figure 1 [6]. Especially in the case of historic masonry, proper workmanship was determinative for the quality of work and therefore the performance of lime tnortars. Swiving masonry of historic structures is prove the quality of such practical and empirical knowledge of the past, however exact assessment is tnore difficult as the masonry and mortar have undergone durability testing over the centuries. Transactions on the Built Environment vol 55, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509 Structural Studies, Repairs and Maintenance of Historical Buildings 5 7 3 2.1 Influence of workmanship and masonry construction The performance of modem non-hydraulic lime mortars made of lime putty is considered to be strongly dependent on workmanship 111. The workmanship comprises not only the application of mortar but also particular constructional details, adequate workability, final surface finish, in-situ protection and curing. The workmanship should reflect the actual state of masonry and environmental conditions. Moisture suction parameters of masonry units together with often dBerent ageing conditions affect the bond between mortar and masonry. Properties of mortars cured in steel moulds are therefore dBerent from those of mortar cast between masonry 171. 2.2 Influence of water content It has been suggested by Schafer et al. [S] that a correlation between porosity of an ancient and new lime mortar could be used as a method to estimate the compressive strength. The amount of water added determines porosity of a hardened mortar. Together with a degree of compaction they characterise a volume of voids in the mortar. A higher porosity means a lower strength. The mechanical properties of lime mortars are improved if the amount of water is reduced [9]. Lime putty usually contains enough water for mortar (bedding andtor pointing mortar) to be prepared without a firther addition of water 141. 2.3 Influence of workability Type of aggregate, its grading and lime puttylaggregate proportions control the amount of water needed to provide a good workability. The optimal waterhinder proportions differs depending on construction and application techniques. Good compaction of lime mortar is vital for its performance. Good workable Lime mortar possesses a greater degree of plasticity; it is often described as near to a modelling clay. 2.4 Influence of curing and ageing The curinglageing conditions for non-hydraulic lime mortars are to promote a combination of drying out (initial setting) and carbonation at such a rate that minimises shrinkage. The ideal environment has a temperature around 20°C and relative humid@ between 50-70% [10]. The strength development of the lime based mortars due to carbonation is inherently a very long-term process, depending on the curinglageing conditions. Curing described by British Standard [l11 for mortar specimens is not appropriate for non-hydraulic lime mortars. Moist curing in a container can possibly be used, however the container should not be airtight. According to literature [l21 and considering the nature of the hardening process of lime mortar such humid conditions can retard the carbonation and do not represent ambient conditions encountered in practice. Transactions on the Built Environment vol 55, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509 574 Structural Studies, Repairs and Maintenance of Historical Buildings 2.5 Influence of mixing and lime putty maturing The mixing and production methods of non-hydraulic lime mortars can also have a very strong influence on their performance. Maturing of some lime putties reduces their particle size and improves their water retentivity [13]. Sand [4]. carrying capacity should improve with reduction of particle size Hand or mechanical mixing can produced mortars of different quality. From practice it is known that the mortar plasticity can be improved by way of mixing. Traditional techruques of mixing 'by hand' involved beating, chopping and ramming on a wooden board until the mix was sticky and workable [4]. Ready-mixed mortar should be re-mixed before use. 3 Experimental The above review of influences on performance of lime mortars presented some factors that were considered before the experimental part was carried out. The objective of this research limited itself to examine only the influence of curing conditions on strength development with ageing and the effect of water addition during mixing. In order to eliminate the other influences and simpllfy the testing, one type of mortar, the same mixing method and 5Ox50x50mm cube specimens were used. The specimens were cured in laboratory conditions and not in realistic conditions withm masonry. Cube specimens were more practical and the experiment was seen as a first step in order to examine the basic principles. 3.1 Material and curing conditions A non-hydraulic ready-mixed lime mortar commonly used in conservation for repair works on stone masonry was used to cast sixty 50mm cubes. The lime mortar was a 1:3 mix, consisting of a minimum six-~nonth-oldnon-hydraulic Shapfell lime putty and Gowrie concrete sand. Density of the fresh mortar was determined as 2080 kg/m3. The specimens were cured in three different conditions marked as a, b and c. The curing condition a was the most stable. The temperature was, on average, around 20°C. The relative humidity (RH) was between 50% to 60%. The curing condition b was an indoor condition. The room was not heated, and therefore a whole range of temperatures above zero from 1°C to 23°C was monitored. On average, the temperatures were around 13°C to 16°C and RH from 58% to 65%. The condition c was a natural weather condition, where the specimens were exposed to temperatures below zero during winter. The exposure site was relatively sheltered and the temperatures and relative humidity were similar to typical average weather conditions in the west of Scotland. The lowest temperature was in winter (-S°C), and the hottest was during summer (+26"C). Transactions on the Built Environment vol 55, © 2001 WIT Press, www.witpress.com, ISSN 1743-3509 Structural Studies, Repam and Matntenance of Historical Buildi~gs 575 Relative humidity varied from 9% to 94% but on average the RH was quite high over all seasons between 75 - 85%.
Load more

Recommended publications
  • Different Types of Building Limes
    Different types of building limes Natural hydraulic limes are made from limestone that contains impurities such as clay or silicates. Unlike lime putty which is non-hydraulic lime, NHLs can set in damp conditions, indeed they require water for a minimum period of around 72 hours to gain maximum strength. They also have some free lime available for carbonation. There are three European classifications NHL 2, NHL3.5 and NHL5 based on the compressive strength of laboratory mortars after 28 days. These are often somewhat misleadingly termed feebly hydraulic, moderately hydraulic and eminently hydraulic. We generally recommend the use of NHLs where the need for breathability and lower strength is outweighed by the desire for an earlier and harder set such as working on bedding hard masonry, wall copings, chimneys and slate floors. In some circumstances hydraulic lime mortars can be used for rendering or plastering. The strength of a hydraulic lime mortar (HLM) varies depending on the manufacturer of the hydraulic lime as some NHL will be high in the band or low. HLM will also vary depending on the ratio of lime binder to aggregate and the type of aggregate or sand used. Natural Hydraulic Lime (NHL) NHL or Natural Hydraulic Lime, comes from limestone that has natural impurities of clay and other minerals, the amount of impurities within it determines how hard it will set. NHL works by setting in the presence of water, hence the term Hydraulic: Natural hydraulic lime powders come in 3 European grades: GRADE STRENGTH(MPa) EXAMPLES OF USE NHL2 >2 to <7 Pointing internally or with soft masonry, plastering NHL3.5 >3.5 to <10 Bedding, pointing NHL5 >5 to <15 Flooring, below DPC or chimney flaunchings NHL's can be used when speed is essential as it sets much quicker than a Lime Putty based mortar.
    [Show full text]
  • Hot-Mixed Mortars: the New Lime Revival
    ALISON HENRY Hot-mixed mortars: the new lime revival Appreciation of the limitations of lime putty mortars and concerns about the strength of natural hydraulic limes have triggered renewed interest in traditional mortars, and in hot mixing. When non-hydraulic lime-putty mortars are used in exposed locations or, as here, for demanding applications such as on wall tops, failure due to frost damage is not uncommon. Quicklime made in The last five years or so have seen a revival in use of hot- traditional kilns often mixed mortar.While many people have welcomed this as contained under- or over- burned limestone which did a way of making more authentic mortars for conservation, not slake when the mortar others are sceptical or even hostile to what they see as a was made, and remained in new fad. Before exploring the pros and cons of hot-mixed the mix as rounded whitish particles, often referred to as mortars, it is worth reflecting on the past 40 years of lime ‘lime lumps’. Fragments of use and how we have arrived at the current situation. black fuel ash from the lime kiln sometimes found their way into the mortar too. The lime revival These are clearly visible in As the damage caused by hard, impervious cement many hot-mixed mortars. mortars became apparent from the mid- 20th century, However, for very high- quality work, quicklime was the revival in use of lime from the 1970s was naturally ‘BHP’ – ‘best hand-picked’ welcomed by conservation practitioners. Emerging – and did not contain lime practice borrowed from materials and methods used lumps or ash.
    [Show full text]
  • Precis of Use of the Natural Hydraulic Lime NHL
    ACCURATE OF USE OF THE NATURAL HYDRAULIC LIME Precis of use of the natural hydraulic lime NHL « Or, how to use nature to protect us from its whims ». Olivier Labesse. 1 ACCURATE OS USE OF THE NATURAL HYDRAULIC LIME To my father, a man, i own everything. 2 ACCURATE OF USE OF THE NATURAL HYDRAULIC LIME Preface There has been an on-going renaissance in working with lime throughout Europe during the last twenty years or so. Some countries had abandoned lime completely in favour of cement; when lime was used it was only to increase the workability of cement mortars. Working with lime was all but forgotten, repairs to old buildings were carried our us- ing cement mortars and concrete. As a result problems began to occur. It was realised that old structures originally built with lime were best repaired using lime. In simple terms old buildings needed to breathe in order to stay dry and healthy, and to remain flexible so as not to crack from inevitable minor movement. Working with lime had to be re-learnt again. In some countries nobody still living had worked with lime or only the very old had the dimmest memory of doing so. Written sources were scarce and some- times confusing. Initially mistakes were made but bit by bit knowledge and skills were re-developed. There is still some way to go. France was fortunate not to have abandoned its natural hydraulic lime production, which it has maintained since the 19th century. Today it has a thriving export business because of renewed demand worldwide.
    [Show full text]
  • Development of Bond Strength in Hydraulic Lime Mortared Brickwork
    Development of Bond Strength in Hydraulic Lime Mortared Brickwork Submitted by ZHAOXIA ZHOU for the degree of Doctor of Philosophy UNIVERSITY OF BATH Department of Architecture and Civil Engineering January 2012 COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and that they must not copy it or use material from it except as permitted by law or with the consent of the author. This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. Signature of Author........................................................... ii Acknowledgements The work in the thesis was carried out in the Department of Architecture and Civil Engineering at the University of Bath between January 2006 and January 2009. The author would like to thank Professor Pete Walker and Dr Dina D'Ayala, joint supervisors of this study. They have provided continuous support and professional guidance throughout the duration of the research. Their help, patience and time ensured that the project was completed successfully. The author would like to thank Professor Pete Walker in particular, who has been a great supervisor all the way through this long journey, not only contributing considerable expertise to the research, but also providing endless encouragement and support to help me through this most difficult time in my life. Special mention should be made to Dr Andrew Heath for designing the pneumatic loading system on the bond wrench test apparatus, and all of the laboratory staff in the department, Neil, Brian, Will, Sophie, Graham and Paul, who offered a big hand during the large amount of experimental work.
    [Show full text]
  • Lime and Its Place in the 21St Century: Combining Tradition, Innovation, and Science in Building Preservation∗
    International Building Lime Symposium 2005 Orlando, Florida, March 9 -11, 2005 LIME AND ITS PLACE IN THE 21ST CENTURY: COMBINING TRADITION, INNOVATION, AND SCIENCE IN BUILDING PRESERVATION∗ Lauren B. Sickels-Taves, Ph.D.1 Philip D. Allsopp, D.Arch, RIBA2 Abstract Lime is a long-established material in mortars and renders, with its use dating back centuries. Its properties are time-tested, both in-situ and in laboratories. However, lime’s marketability and the increased need for faster building in the 19th and 20th centuries decreased its widespread use. During this period, masonry integrity problems, and, later, sustainability concerns and increased mold risk were introduced into the built environment resulting from the widespread use of impervious materials including Portland cement for mortars and external renders. Evidence shows that lime has always been and remains a practical, sustainable, and healthy alternative to cement worthy of far more widespread deployment across the building industry. ∗ © Copyright NLA Building Lime Group 2005 The views presented in this paper are solely those of the authors. The National Lime Association (NLA) and the Building Lime Group assume no liability or responsibility for any errors, omissions, or other limitations in this paper or for any products, services, or methods presented. This paper is intended for use by professional personnel competent to evaluate the significance and limitations of the information provided and who will accept full responsibility for the application of this information. NLA and the Building Lime Group do not intend to infringe on any patent or other intellectual property right or induce any other party to do so, and thus users of this document are responsible for determining whether any method, technique, or technology described herein is protected by patent or other legal restriction.
    [Show full text]
  • Experimental Study on Lime Mortar Using Flyash and Gallnut As Additives
    Special Issue - 2016 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 SNCIPCE - 2016 Conference Proceedings Experimental Study on Lime Mortar using Flyash and Gallnut As Additives B. Dhilipkumar1 M. Dhivakar Karthick2 Assistant Professor Assistant Professor Department of Civil Engineering Department of Civil Engineering Kongunadu College of Engineering & Technology Kongunadu College of Engineering & Technology Thottiam, Trichy Thottiam, Trichy Abstract— As concern the environmental impacts and high strength and tensile strength of lime mortar have been cost of cement which is widely used, clearly requires alternate studied. protective binder. But in the first civilization, lime is used as II. METHODOLOGY biodegradable binding material which is also composed of additives such as pozzolana and traditional herbs. In the present Lime is a binder which is in general, the purpose of the study lime mortar with composition of flyash as pozzolana binder is to hold the sand particles together and to fill the which enables mortar to set rapidly in the ratio of 1:1:2 voids in between the grains of sand. Hydraulic lime used in (lime:pozzolana:sand) as per IS:4098 – 1983. Also used extracts building construction. Sand is the most common aggregate in of kadukkai (gallnut) and palm’s jaggery in the proportion of 5%, 10% and 15% of the weight of binder. As the result, on mortars. the potable water should be used in appropriate addition of 5% herbal extract in pozzolanic lime mortar amount till attain required consistency. Flyash , kadukkai improves workability and increases tensile strength, also ( Terminalia chebula) and palm’s jaggery are additives of enhanced increased compressive strength about 55% compared lime mortar.
    [Show full text]
  • Hydraulic Lime an Introduction
    HYDRAULIC LIME AN INTRODUCTION Hydraulic lime was an important cementitious material before the arrival of Portland cement but it is little used now, except in conservation work. Production of good hydraulic lime is as much a craft as a technology, even more than ordinary lime but, with the decline in use of hydraulic lime, there are few skilled producers left and new producers often need to learn the required skills from scratch. Hydraulic lime hardens partly by reaction with water and so differs from other types of lime which harden by chemical reaction with carbon dioxide in the air. Hydraulic lime has properties intermediate between ordinary lime and Portland cement but is produced in a similar way to ordinary lime. In addition to containing calcium hydroxide, the chemical which makes up ordinary lime, hydraulic lime also contains calcium silicates similar to the main cementitious components of Portland cement. A cement with properties similar to hydraulic lime can also be obtained by mixing ordinary lime with a pozzolanic material. Hydraulic lime can be made stronger than ordinary lime and can be used in some applications for which ordinary lime is not suitable, particularly where water is present. In developing countries hydraulic lime is rarely produced. There is probably considerable potential for increased production in situations where Figure 1: Slaking. Hydrated lime is produced by adding water to quicklime. Portland cement is scarce or very expensive. Chenkumbe Hills Area, Malawi ©Practical However, in general, little mapping of reserves of Action/David Mather raw materials or assessment of their quality has been carried out.
    [Show full text]
  • Potential of Using Wood Biomass Ash in Low-Strength Composites
    materials Article Potential of Using Wood Biomass Ash in Low-Strength Composites Ana Bariˇcevi´c 1,* , Ivana Carevi´c 1, Jelena Šantek Bajto 1, Nina Štirmer 1 , Marija Bezinovi´c 1 and Keti Kristovi´c 2 1 Department of Materials, Faculty of Civil Engineering, University of Zagreb, Fra Andrije Kaˇci´caMioši´ca26, 10000 Zagreb, Croatia; [email protected] (I.C.); [email protected] (J.Š.B.); [email protected] (N.Š.); [email protected] (M.B.) 2 Trames Ltd., Šipˇcine2, 20000 Dubrovnik, Croatia; [email protected] * Correspondence: [email protected]; Tel.: +385-1-4639-536 Abstract: Reducing greenhouse gas emissions and dependence on fossil fuels is the cornerstone of all European climate and energy strategies. Consequently, renewable energy sources are becoming more competitive with fossil fuels. The largest source of bioenergy in the European Union is biomass-fired power plants. Therefore, the European coal phase-out strategy led to an increased use of wood biomass as a sustainable fuel, generating large amounts of wood biomass ash (WBA). In the research studies reported so far, WBA has been mainly used in cementitious composites. However, given the similarities between the chemical composition of WBA and hydraulic lime (HL), this research focused on its potential classification as a building lime. Overall, three different sources of fly WBA were considered for the preparation of binders as mixtures of WBA and coal fly ash (CFA) in different ratios. The contribution of each binder mixture on the paste and mortar properties was analyzed based on the chemical composition, setting time, volume stability, and contribution to the mortar strength (compressive and flexural).
    [Show full text]
  • SOIL STABILIZATION USING LIME and FLY ASH N.Krithiga1, D.Pujitha *2,T
    SOIL STABILIZATION USING LIME AND FLY ASH N.Krithiga1, D.Pujitha *2,T. Palayam*3 , A.revathy*4 1Assistant Professor(civil Eng),Department of Civil Engineering,Sri Muthukumaran Institute of Technology,*234 UG students, Department of Civil Engineering, ABSTRACT Now a days, inefficient properties of soils are a critical issue in engineering projects. In some cases, improve the characteristic of unsuitable soil is a fundamental step for making construction.Pavement structures on poor soil sub grades show early distress causing the premature failure of the pavement. Clayey soil usually have the potential to demonstrate undesirable engineering behaviour , such as low bearing capacity , high shrinkage and swell characteristics and high moisture susceptibility. Stablilsation of these soil is a usual practice for improving the strength.Soil stabilization performed the use of technique to adding a binder to the soil in order to improve the engineering performance of soil .This study reports the improvement in the strength of a locally available cohesive soil by addition of both lime and fly ash. Researches were illustrated that adding the additives leads to progress in workability and mechanical behaviour of soil after stabilization lime and fly ash as local natural and industrial resources were applied for chemical stabilization. Lime alone has traditionally been used in clay-bearing, highly cohesive soil whereas fly ash has been used to bind non-cohesive soil, granular or poorly cohesive soil. Fly ash is mainly used to stabilize the sub base or base course. 1 1. INTRODUCTION The swelling and shrinkage characteristic of expansive soil depend upon the percentage of moisture content in it.
    [Show full text]
  • Technical Data Sheet Natural Hydraulic Lime (En 459-1)
    TECHNICAL DATA SHEET NATURAL HYDRAULIC LIME (EN 459-1) Raw materials: Natural hydraulic lime is a hydraulic binder in powder-form, partially hydrated, that is obtained calcining limestones that contain between 15 and 20% of clay and other impurities, correctly denominated marls. During the calcination (aprox. 1200ºC, lower firing temperature than Portland cement) calcium reacts in the kiln with the clay minerals to produce silicates, aluminates and ferro-aluminates that enable the hydraulic lime to set faster than quicklime or slaked lime and without exposure to air (including under water). Any unreacted calcium is transformed into calcium hydroxide. This part of the lime reacts non-hydraulic, precise water or environmental humidity and carbon dioxide gas of the air, and is responsible for the progressive resistance of the natural hydraulic lime. It varies according to its hydraulic index. Special mortar properties made with natural hydraulic lime, beneficial for RESTORATION AND ECO-BUILDING: Great plasticity (therefore easy to progress), fort adhesion in diverse materials and surfaces, great capacity of water retention, low tendency of cracking (low modulus of elasticity), good durability, good water-impermeability, permeability to water steam, allows buildings to breathe (the less hydraulic the most) and has a good aspect. Lime mortars are up to 34% more insulating than those of cement. Natural hydraulic limes are free of additives and have a low index of radiation. Technical qualities of our NHL 5 NHL 3,5 NHL 3,5 blanca NHL 2 natural
    [Show full text]
  • Mechanical and Durability Performance Improvement of Natural Hydraulic Lime-Based Mortars by Lithium Silicate Solution
    materials Article Mechanical and Durability Performance Improvement of Natural Hydraulic Lime-Based Mortars by Lithium Silicate Solution Zijian Song 1,2,*, Zhongyuan Lu 1,* and Zhenyu Lai 1 1 State Key Laboratory for Environment-Friendly Energy Materials, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China; [email protected] 2 Department of Material Engineering, Mianyang Vocational and Technical College, Mianyang 621000, China * Correspondence: [email protected] (Z.S.); [email protected] (Z.L.) Received: 21 October 2020; Accepted: 19 November 2020; Published: 23 November 2020 Abstract: Natural hydraulic lime (NHL) as a building material has been widely used to restore the historic structure. However, the slow growth rate of strength and durability limits its engineering application. In this work, the NHL-based mortars were pretreated by lithium silicate (LS) solution impregnation and surface spraying. The results show that the compressive strength, surface hardness, and freeze-thaw cycle (FTC) resistance of NHL-based mortar were greatly improved after LS pretreatment. Specifically, the compressive strengths of the sample increased by about 32.7–52.0%. LS was sprayed on the sample’s surface (about 0.2 kg/m2) and the surface hardness increased by up to 10 grades. Compared with the control samples, the weight loss of treated samples decreased by about 31.6–43.8%. A rehydration process to generate the hydrated calcium silicate gel (C-S-H) was observed between calcium hydroxide (CH) and LS, which can decrease the sample’s porosity and form a silicate coating on the surface. With an increase in the concentration of LS, the macropores (50–10,000 nm) content decreased, while the mesopores (10–50 nm) and nanopores (less than 10 nm) increased.
    [Show full text]
  • Mechanical and Hygric Properties of Natural Hydraulic Lime (NHL) Mortars with Pozzolans
    Mechanical and hygric properties of natural hydraulic lime (NHL) mortars with pozzolans Marwa Aly1, Sara Pavia2 1, 2 Dep. of Civil, Structural and Environmental Engineering, Trinity College Dublin, Dublin, Ireland ABSTRACT: Currently, hydraulic limes are used as binders to strengthen and repair traditional and historic masonry. For hundreds of years, pozzolans have been used in combination with lime binders to improve the properties and durability of masonry mortars and concrete. This paper studies flexural and compressive strength, porosity, water absorption and capillary suction of natural hydraulic lime (NHL5) mortars prepared with two pozzolanic additions (ground granulated blastfurnace slag –GGBS- and rice husk ash-RHA). Portland limestone dust was used as a filler. The mixing, curing, binder/aggregate ratio and flow were kept constant in order to attribute variation of mortar properties to the type of additive. Two pozzolan/lime percentages were used (10% and 20%). The results indicate that at age of 28 days, the partial replacement of NHL5 by 20 % GGBS (i) greatly increased compressive and flexural strength by 125% and 67% respectively compared to a control mortar (without additive); and (ii) decreased porosity, water absorption and capillary suction by 46%, 44% and 66% respectively when compared to a control mortar. 1 INTRODUCTION Natural hydraulic limes have been used as a binder for building since antiquity. They are produced by burning limestone which naturally contains impurities mainly in the form of silica and alumina. Nowadays, these limes are used for new building and repairs to existing masonry. They are often chosen as a compatible materials to repair traditional and historic masonry.
    [Show full text]