an investigation into the effect of rice husk ash on mortar when added in varying proportions -...

8/8/2019 An Investigation Into the Effect of Rice Husk ASh on Mortar When Added in Varying Proportions - Andrew Wood

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The University of Dublin

Trinity College

The Department of Civil, Structural and Environmental Engineering

AN INVESTIGATION INTO T HE E FFECT OF R ICEH USK ASH ON M ORTAR W HEN ADDED IN

VARYING P ROPORTIONS

Name: Andrew Wood

Supervised By: Dr. Sara Pavia


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By: Andrew Wood

Supervisor : Dr. Sara Pavia

A final year project report submitted in partial requirementfor the BAI Engineering degree

2006


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By: Andrew Wood

Supervisor : Dr. Sara Pavia

A final year project report submitted in partial requirementfor the BAI Engineering degree

2006


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DECLARATION

I declare that this dissertation, in whole or in part, has not been submitted to any University asexercise for a degree. I further declare that, except where reference is given in the text, it isentirely my own work. I further declare that the Library may lend out this dissertation foracademic purposes. I give permission for the Library to copy this thesis upon request.

____________

Andrew Wood


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ACKNOWLEDGEMENTS

Firstly I would like to thank my supervisor, Dr. Sara Pavia, for all her advice and guidance

throughout the year. I would also like to thank Eoin Dunne, Martin Carney for their helpand guidance with the testing, without which I dont know what I would ha ve done, and allof the technicians in the labs for their eagerness to help and for entertaining me over theyear. I thoroughly enjoyed it.

I also wish to thank Ryan Hanley, who was always available for queries and was mosthelpful whenever I called on him.

Finally, I had better thank my family and friends for putting up with me and keeping me sane,particularly towards the end of the project. Particular thanks must go to my mother,Pat-Ann, for all the late nights she fed me on my return from the library. Much appreciated!


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T ABLE OF C ONTENTS

Declaration ii

Acknowledgements iii

List of Tables vi

List of Figures vii

Abstract viii

Chapter 1 Introduction 1

1.1 Introduction 11.2 Main Objective 21.3 Aims 21.4 Outline 2

Chapter 2 Literature Review 4

2.1 Introduction 42.2 Introduction to Rice Husk Ash 52.3 Use of Rice Husk Ash in Concrete 52.4 Research on Lime Mortars 7

Chapter 3 Background Material: Lime 8

3.1 Limestone 83.2 Lime Cycle 83.3 Hydrated Lime 103.4 Lime Putty 10

3.5 Setting 11

Chapter 4 Mortar 13

4.1 Introduction 134.2 Properties of Lime Mortars 144.3 Materials used in Mortar 15


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L IST OF F IGURES

Figure 3.1, The Lime Cycle 9

Figure 5.1, Mortar Mixer 23

Figure 5.2, Cube Moulds for Mortar 24

Figure5.3, Prism Moulds for Mortar 24

Figure 6.1, Oven at + 5C 32

Figure 6.2, Capillary Suction tray 34

Figure 6.3, Shrinkage Gauge 36

Figure 6.4, Flexural Testing Machine 38

Figure 6.5, Flexural Strength Test 38

Figure 7.1, Water Absorption Results 42

Figure 7.2, Capillary Suction for all four mixes 45

Figure 7.3, Bulk Density for all four mixes 47

Figure 7.4, Real Density for all four mixes 48

Figure 7.5, Porosity Results for all four mixes 49

Figure 7.6, Shrinkage Results for all four mixes 51

Figure 7.7, Compressive Strengths for all four mixes 53

Figure 7.8, Flexural Strengths for all four mixes 55


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L IST OF TABLES

Table 5.1, Material Proportions for Pure Lime Putty 20

Table 5.2, Material Proportions for 25% RHA mix 21



Table 5.5, Sieve analysis of the sand used in all four mixes 23

Table 7.1, Example of Results from Capillary Suction Test 44


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ABSTRACT

This project investigates if the addition of Rice Husk Ash has a positive effect on limemortar, in particular lime putty. There has been a considerable amount of study into thebehaviour of concrete with the addition of RHA, with positive effects experienced. To seeif lime putty experiences similar positive effects, a number of simple laboratory tests werecarried out to test the physical performance of the mortar with the partial replacement of lime putty with RHA. Using the results from the tests completed, a conclusion can bedrawn on whether the addition of RHA is beneficial to the mortar and whether the use of RHA as a construction material is viable.


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1.2 Main Objective

To investigate the effect RHA has on lime putty when added in varying amounts, and see is itpractical for use in everyday construction.

1.3 Aims

To fully research the background to Rice Husk Ash

Research the effect of RHA on concrete

Learn and understand about the different types of lime

Learn how to mix and make lime mortar

Carry out a full set of tests on the mortar cubes made to get an indication of theeffects of RHA on lime putties

Use equations from chapter six to calculate the results of the tests

Analyse the results from the testing

Compare results with different results from similar mortars with the pure limeputty mix made in this project

Write up results and complete a report on the study undertaken

Report conclusions and findings from the study

1.4 Outline

Chapter Two consists of a review of literature on the background of RHA and itspossible uses in construction.

Chapter Three consists of a review and description of the background materials used in theproject, mainly the background and theory of lime.


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Chapter Four consists of a description of what mortar is and compares the differenttypes of mortar available.

Chapter Five consists of a description of the mix designs used for making the mortars forthe testing, the placement of the mortars.

Chapter Six consists of a description of the tests to be conducted, procedures for eachtest, and useful equations for calculating the results.

Chapter Seven consists of the presentation and analysis of the results.

Chapter Eight contains the conclusions drawn from the testing and therecommendations for further study in the field.


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C HAPTER 2

L ITERATURE R EVIEW

2.1 Introduction

This project focuses mainly on the effect RHA has on mortars rather than the type of mortarsused in the project. Firstly, some research must be done on RHA and its uses and benefits inconstruction. Unfortunately there is very little information on the use of RHA inconstruction. This is mainly because the idea of using RHA as a construction material isrelatively new. In the early 1990s, approximately, the first notion of using construction as a

means to recycle RHA was conceived. So because RHA is relatively young as a constructionmaterial, not much research has been done into its uses and possibleadvantages/disadvantages. Also, RHA is relatively unknown, so very little information isavailable in books on the subject. Most of the information on RHA used in this project wasfound on the internet, from published papers and articles from journals. The information inchapter three on lime was found on the internet, in books, and from various other sources asreferenced in the chapter.

As there is very little research done on RHA, there was a large field of possible subjects andtopics to investigate and research. The area with the most amount of research carried out wasthe addition of RHA to concrete. Therefore it would be interesting to see if the same positiveeffects were experienced when RHA was added to mortar. Non-hydraulic lime was preferredas pozzolans are often used to get an initial set in lime putties and then allow furtherhardening, by carbonation, to take place over time.


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2.2 Introduction to Rice Husk Ash

Rice Husk Ash is a by-product of the rice industry. When rice is harvested and milled,

roughly 78% of the paddy is rice and bran. The remaining 22% is the husk which surroundsthe rice paddy is called the husk. In countries of large rice industries, such as India orBrazil, the rice harvested is par-boiled in rice mills. These rice mills are fuelled by burningthe husks of the rice. When the husk only contains 75% organic matter, this leaves 25%inorganic matter, which makes up the ash after the firing process. This ash is called RiceHusk Ash (RHA). It is a highly siliceous material with an amorphous silica content of roughly 85 90%. The ash remains amorphous when burned in a controlled environment,below 600 - 700 Celsius. Each tonne of rice harvested produces roughly 220kgs of husk,leaving roughly 55kgs of ash after burning. As the Rice Husk Ash is very siliceous, it posesa serious threat to the environment, stated by [2, 21]. Various methods of recycling anddisposing of this waste are currently being explored. If the use of this Rice Husk Ash canhave a positive effect when added to concrete or mortar this would be a useful way to recyclepotentially harmful material such as Rice Husk Ash.

2.3 Use of Rice Husk Ash in Concrete

There has not been a lot of research carried out using Rice Husk Ash in mortar but, inconcrete, Rice Husk Ash has been used as a partial cement replacement in concrete inrelatively small amounts (5-10%). As the silica content in the Rice Husk Ash is so high(85 90%), it is considered a Super - pozzolan [1]. Super -pozzolans (e.g. silica fume) areused in high performance concrete. Super-pozzolans dramatically enhance the workability,compressive strength and impermeability. This decrease in permeability, results inconcretes which are highly durable to chemical attack and corrosion of the reinforcementsteel, due to the inability for the chlorides to penetrate the concrete.


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Rice Husk Ash is a very fine substance with a particle size of 25 microns and is also lessreactive than cement. During the hydration of cement, calcium hydroxide is formed. Thiscalcium hydroxide reacts with the silica in the Rice Husk Ash to form calcium hydridesilicate [1, 19]. This calcium hydride silicate fills the pores and strengthens themicrostructure of the concrete, particularly around the coarse aggregate. This porerefinement transforms the concrete from an open pore system to a closed pore system whichaffects the permeability more so than the compressive strength of the concrete. This willobviously aid the durability if the concrete as a direct result of the decreased permeability.Also stated by [19], when pastes with 10% RHA, without admixtures and with 10% silicafume are left for 28 days and tested for anhydrous materials, the RHA showed the lowestpercentage of anhydrous material in its paste. Therefore, verifying that RHA probablyaccelerates the hydration of cement. Rice Husk Ash also can reduce the heat of hydrationby up to 25 % [1]. Both of these indicate that less water is inclined to evaporate duringhydration, therefore, less water required in the first place. The less water required in themix, the lower the probability of shrinkage. A lot of research was completed in this area, of adding RHA to concrete, by [19, 20]. Positive effects were experienced by these authorswhen adding RHA to concrete. However, when RHA was tested in its natural state (on its

own) it displayed no pozzolanic properties [19].

As stated previously, there is no previous research done on the addition of RHA tomortars. Therefore, the results from concrete are the only results, regarding RHA, tocompare with. The other comparisons that can be made are with similar lime mortarswith no RHA used in the construction. The effects of RHA on lime mortars can becompared with normal lime mortars to see if the results are positive and worthwhile ornot.


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2.4 Research on Lime Mortars

For the mortar research, there were many useful books, papers and websites for informationon lime and lime mortars. Much of this research will be covered in chapter three

(background materials) under the Lime headings. The research on mortars will be coveredin chapter four (mortar) and suitable references given.


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C HAPTER 3

BACKGROUND M ATERIAL : L IME

3.1 Limestone

Lime does not occur naturally and is produced by burning a source of calcium carbonate,usually either chalk or limestone. Limestone is a sedimentary rock formed due to thedeposition of calcium carbonate from its solution in water.

3.2 Lime cycle

3.2.1 Summary

Lime is a term used to describe calcium carbonate which comes from chalk or limestone.

The limestone is burned first in a process called calcining [3], where the calcium carbonate isheated. The product of this calcining is Calcium Oxide, also called Quicklime. ThisQuicklime is then added to water to produce a calcium hydroxide, known as slaked lime.This calcium hydroxide then takes in carbon dioxide in order to harden, through a processcalled carbonation, and creates calcium hydroxide, therefore, completing the cycle. Theresulting calcium hydroxide can vary in its strength as the carbonation process can take years,in some cases, to complete its reaction. Carbonation is the main method of hardening inlimes, although some limes can harden by way of hydration.


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Fig 3.1 , The Lime Cycle

3.2.2 Lime Burning

The burning, or calcining, of lime is the first step in the lime cycle. The calcium carbonate

is burned in a kiln and gives off carbon dioxide, leaving an oxide, quicklime,

(Calcium carbonate burningcalcium oxide + carbon dioxide)

CaCO 3 burningCaO (quick lime) + CO 2

For calcium carbonate to burn and change to calcium oxide, the temperature must be at least880C. It is estimated that, to ensure that this temperature is reached in the core of thestone, a surface temperature of approx. 1000C must be obtained [6]. The product of thisburning is calcium oxide (quicklime), which is used in the next stage. The best


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quicklimes are the ones which are most reactive. These are obtained when the burningtemperature is kept as low as possible and burned slowly, while still ensuring that thecalcium carbonate is burnt. This is referred to as soft burnt quicklime [7].

3.2.3 Slaking

Slaking is the process where water is added to the quicklime, resulting in a reaction betweenthem. The water reacts with the oxide to produce a hydroxide. This is an exothermicreaction which can generate very high temperatures, so it is generally thought to be better toslake the quicklime as soon as possible after burning.

Calcium oxide (quicklime) + water calcium hydroxide

CaO + H 2O Ca (OH) 2

3.3 Hydrated Lime

If a minimal amount of water is used, just enough to facilitate slaking, the quicklimeproduces a powder known as hydrated lime. The exothermic reaction in slaking causesany slight excess of water to be evaporated. The powder produced is supplied normally inbags [4].

3.4 Lime Putty

When excess amounts of water are used in the slaking process, a milkyliquid is formed. This milky substance is left to sit, allowing the solids inthe liquid to settle to the bottom


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and form lime putty. Lime putty can mature for months, even years [8].As the slaking period of the putty is increased, the water retention and theplasticity are also increased. Lime putty is the purest form of lime as it is apurely non-hydraulic lime.

3.5 Setting

3.5.1 Non-Hydraulic Setting

Non-hydraulic lime does not need water to facilitate hardening. It hardens due to exposure

to the air, where it dries out and then absorbs carbon dioxide. The lime reacts with theabsorbed carbon dioxide in a process known as carbonation. No reaction with water isneeded for hardening to take place. Non-hydraulic lime is generally considered to be thepurest form of lime it is totally non-hydraulic. This indicates that there were no impuritiespresent in the original limestone or chalk, just pure calcium carbonate. Non-hydraulic limesare generally more flexible and more porous than hydraulic limes. This increased porosityhelps the air penetrate the mortar, which in turn helps the carbonation of the lime, due toincreased exposure to the carbon dioxide. Non-hydraulic limes therefore harden over alonger period of time than hydraulic limes do, due to the carbon dioxide having to permeatethrough the mortar over time. Initial set can be helped to harden more quickly by adding apozzolan, as in this project.

3.5.2 Hydraulic Setting

Hydraulic limes have similar properties to non-hydraulic lime as it still sets partially bycarbonation, but there is also hydraulic setting taking place also. Hydraulic setting is due toreaction with water, similar to the hydraulic set experienced with OPC. These limes stilloriginate in limestone and chalk but the limestone is not as pure as the limestone used forNon-Hydraulic limes. If there are clay particles present in the limestone before


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burning, these particles cause the resulting calcium oxide to have hydraulic properties [5]. Theamount of impurities in the limestone affects the resulting properties of the lime. Limestonecontaining less than 12% clays results in feebly hydraulic limes, which have the closestrelationship to lime putties out of all the hydraulic limes.

Hydraulic limes are not as flexible as non-hydraulic limes, but they are stronger and lessporous than non-hydraulic limes. Hydraulic lime mortars are more widely used due to theease in which they can be mixed and used. They generally are supplied in powder form inbags.


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C HAPTER 4

M ORTAR

4.1 Introduction

Mortar is defined as A material used in masonry to fill gaps between stones or bricks inconstruction and bind them together [9] . The term mortar can also be used to describeplaster or render, used to give a smooth, durable finish to a wall. They both consist of thesame materials, but the renders cover a more vast area in relation to their volume, whereasmortars work over a much smaller area.

A good mortar should act as a conduit for the moisture in the wall, preserving the masonryfrom decay due to percolating water, moisture and salt solutions. The mortar is therefore thesacrificial material in such structures, with a life span much lower than that of thesurrounding masonry. Mortars should absorb any moisture or water and encourage it to beevaporated through the mortar joints rather than through the masonry.

There are many types of mortars, each with defining properties. A suitable mortar must bechosen for differing conditions and circumstances. In older buildings, a more flexible softermortar must be used in order to withstand any movement within the structure that most, olderbuildings experience. Non-hydraulic limes are generally used for re-pointing of softmasonry due to the softer nature of the mortar. A lime putty or feebly-hydraulic lime wouldbe used for such a task. In areas subject to damp conditions or more harsh weatherconditions, a hydraulic lime would be more suitable. For this reason, most buildings wouldcontain more than one type of lime mortar, depending on the conditions the mortars are beingused in.


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4.2 Properties of Lime Mortars

Lime mortars are more porous than stone and so allow the water to pass through the mortarrather than through the stone. Therefore damage due to crystallisation occurs in the mortar

oint, instead of in the masonry, as mortar can be replaced more easily. As statedpreviously, lime mortars allow for more movement in structures. With this freedom tomove, the need for expansion joints is very low. Lime mortars will allow for minorstructural and seasonal movements by forming numerous minute hairline cracks, rather thanone large crack. If there is water present, it will dissolve any free lime in the mortar andflow through the cracks. The water will evaporate depositing the lime and seal the cracks ina process called autogenous healing [16].

Lime mortars allow buildings to breathe and moisture to escape. Failure to do so can resultin dampness problems in the structure due to the inability for trapped moisture to permeateout through the mortar or the masonry. This is particularly important in timber framedhouses; an impermeable render can lead to timber decay. For limes, the permeability is alsoimportant for the hardening process of the lime itself as it allows carbon dioxide to penetratethe mortar aiding the carbonation process. Softer mortars such as lime putty allow greatermovement of fluids and so they are used extensively in older buildings so the water can flowfreely to the surface and not decay the masonry itself in doing so. Lime mortars are moreporous than OPC mortars and considered more workable also. OPC mortars do not allowthe same flow of water that lime mortars do.

As lime mortars allow the movement of fluids quite easily, this provides a morecomfortable environment inside buildings. The relative humidity is more stable as aresult; reducing condensation formation and mould growth.

Most of the time lime mortars are weaker than OPC mortars. Generally, the softer andmore porous the lime mortar, the lower the strength is. When strengths for OPC mortars arecompared with lime mortars, the tests are usually carried out after 28 days, which is anaccurate representation for OPC, but not for lime. As lime hardens largely due to


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carbonation over time, the lime mortar strength at, say 12 months, would be a lot closer to theOPC mortar strength. This has certain benefits when a building is new the lime is stillrelatively soft and can accommodate such movement, as could be experienced in a newbuilding. If a weak, rapidly setting material is used in such a case, the mortar can bereplaced easily. However if a strong mortar is used that is stronger than the masonry, themasonry could fail if subjected to slight movement.

4.3 Materials used in Mortar

4.3.1 Lime

The type of lime required depends on the functions the mortar is required to perform. Thetwo fundamental options are hydraulic or non-hydraulic limes. Hydraulic limes generallycome in bags of dry hydrate powder. Non-hydraulic usually comes in the form of a limeputty. Non-hydraulic limes are more pure than the hydraulic, as the impurities (or clay) arewhat causes the lime to be hydraulic, as stated in chapter three.

4.3.2 Aggregate

The aggregate used in mortars is sand. The sand should be clean, hard and durable. Sandoriginating from the sea should be avoided due to the salt content, which can affect thehardening, durability, strength or the appearance of the mortar. The grading of the sand isalso important, so that there is an even distribution of particle sizes throughout the sand.However, the amount of particles smaller than 75m must be kept to a minimum as particlesof this size classify as clay. Clay can have pozzolanic effects on the lime. A sieve analysisshould be conducted on the sand to determine the percentage clay in the sand.


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It is preferable that the sands be angular; sharp sands interlock well with each other betterthan rounded ones do and there are fewer voids as a result. Also the size of the particlesaffect the amount of binder required. The larger the particle size, the more binder that isneeded. This indicates that the binder to sand ratio should be decided after analysis of thesand. An excess of binder can result in lower strength mortar.

4.3.3 Water

Water used in mortar must be clean and should not contain any material in suspension orsolution, in a quantity sufficient to cause harmful effects on the mortar or the materials usedwithin the mortar. The proportion of the water to binder should be the least possible required

to give adequate workability to the mortar. It should also conform to BS 3148:1990.

4.3.4 Additives

Other materials can be added to mortar to enhance its performance. Traditional additives inthe past for plasters or mortars were tallow oil, sugar, hair. Cement can be added but it mustbe added with care as it can affect the long term durability of the mortar, preventingcarbonation from happening [17].

4.3.5 Pozzolans

Pozzolans are materials that obtain cementitious properties when added to water. Theparticles of these materials are very fine and sometimes have been subjected to great heat.Some examples are pulverized fuel ash (PFA) and fired china clay. They are sometimesadded to non-hydraulic limes to accelerate the initial set and improve the strength of themortar also.


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4.4 Mixing

The mix used for mortars depends on the required strength but generally the proportions arethree parts sand to one part binder (lime), 3:1mix, once the mortar maintains good plasticity.

If the poorer lime is used, the proportions may be reduced to a mix of, say, 2:1. However,when mortar is made with a high content of sand, more water must be added and so theprobability of cracking is higher, due to higher water content.

Due to the variations in the different types of lime, a trial mix is advised before employing acertain mix on site. This will help determine the correct sand to binder ratio and the mostappropriate lime to be used.

4.5 Testing

The following tests are suitable for testing the various properties of mortars.

Shrinkage

Capillary suction/Water

absorptionBulk/Realdensities

Porosity

CompressiveStrength

FlexuralStrength

These tests will be described in greater detail in chapter six.


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4.6 Health and Safety

Lime can be caustic and cause irritation to the skin if exposed to it for long periods of time.When handling lime putty, gloves should be worn, particularly when skin is broken. The

RHA is a very fine dust and when lime is in dry powder form, dust masks should be wornto prevent inhalation. If inhaled, the dust can cause upper respiratory track problems.

First Aid Measures

If lime comes in contact with the eyes wash out with fresh water. Protective creamshould be applied to any skin exposed to lime for any amount of time.


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C HAPTER 5

M IX DESIGN AND P ROPORTIONS

5.1 Materials Used

Non-Hydraulic lime comes in the form of a putty which is stored under water, as it does notreact with water to set, but with carbon dioxide, so the water prevents this from happening.This putty is an off white colour and has the consistency of a sort of hard cheese and needs tobe cut with a pallet knife. As the putty is slaked for over a year, it contains a lot of water.This indicates that very little water is needed to make the mortar, unlike the hydraulic limeswhich come as a dry powder.

The Rice Hush Ash came as a very fine powder. RHA has pozzolanic properties andtherefore also has hydraulic properties also. A pozzolan is a siliceous material whichreacts with Calcium hydroxide and water to obtain hydraulic set at room temperature.This reaction is very similar to that of cement.

The aggregate used was natural, river bed sand. The same sand was used throughout all of the tests, for consistency, so that comparisons can be drawn between each of the mixes.

5.2 Proportions

For each of the following mixes, the humidity was between 50 60%, and thetemperature was kept between 15 -17C. This indicates that the evaporation of waterduring the mixing process is negligible as conditions for each mix was relativelyconstant.


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5.2.1 Pure Lime Putty (0% mix)

Each of the mixes had an aggregate to binder ratio of 3:1, by weight. As lime putty is well

slaked lime, with a large amount of water in it, generally very little water added to the mix asthere is no water needed to hydrate the lime. The aggregate used was very dry and so asmall amount of water was needed to replace any pore water that has been evaporated fromthe aggregate.

Table 5.1 Material Proportions for Pure Lime Putty

5.2.2 25% RHA Mix

This mix was the first mix made, and so the behaviour of the lime with the addition of RHAwas unknown. As RHA has pozzolanic properties, and is a very fine material, it needs acertain amount of water. Otherwise the water contained in the lime putty will be sucked out,by the RHA, and so making the mortar a lot less workable. Also the RHA will need a certainamount of water also for hydration. This all indicates that water needs to be added to themix in order to facilitate the RHA and also to help make the mortar more workable and easierto compact into the moulds. Initially, there was 80 g of water added and the prisms weremade. Before making the cubes, a further 30 g was added to make it more workable.

Material Lime Putty

Sand

Water


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Table 5.2 Material proportions for 25% RHA mix

5.2.3 50% RHA mix

The required consistency was now known and so adequate water was added in order toachieve suitable workability and adequate hydration of the RHA.


5.2.4 75% RHA mix

As we can see now, there is 75% RHA replacement of the lime putty, therefore morewater is needed.

Material Lime Putty

Sand

Water

Material Lime Putty

Material Lime Putty

SandWater

Material Lime Putty


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5.3 Sand

As this study is not about the aggregate used but the RHA, typical mortar sand was used.This sand was used in all the mixes in order to keep the mortars consistent and allow forcomparison at the end. As demonstrated in Table 5.5, the particle size varies from 5mm to0.075mm and is quite well graded also. 1.8 % of the sample passed through the 75 m sieve,particles smaller than 75 m are considered clay. These clay particles are regarded asimpurities, and cause problems on the mortar as they can cause hydraulic set in the lime;affecting the results of the mortar as it is lime putty being used in this project.

This sample of sand contains fairly large, round particles. This means that the packingwill not be as good as if it were angular.

Material Lime Putty

Sand

Water

Material Lime Putty


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Table 5.5 Sieve analysis of the sand used in all four mixes

5.4 Mixing Procedure

5.4.1 Equipment

1. Scales with an accuracy of +1g

2. Mortar mixer with three speedsettings

3. PalletKnife/Spatula

4. Dust Mask and Gloves (the RHA is so fine, it creates a fine dust which canbe inhaled and could be quite dangerous if done so, also the putty canbe unpleasant if in contact with broken skin so gloves must be worn)

Fig5.1 Mortar Mixer

Material Lime Putty 8

Sand 2

Water ~

Material Lime Putty 6

RHA 2

Sand 2

Water 8


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5.4.2 Mixing

As there are no standards for mixing lime putty, the guidelines from St. Astierrecommendations were used. As the amount of RHA varies, the amount of water added isdetermined by the consistency and the workability of the mortar during the mixing

1. Each ingredient was weighed carefully on the scales

2. Half of the sand was placed in the mixing bowl

3. The Lime Putty(along with RHA) is then added

4. These are mixed for approximately five minutes

5. Gradually the remainder of the sand is added to the mix

6. Water is added accordingly throughout the mixing process7. the mortar is left to mix for a further ten to fifteen minutes

5.5 Moulds

The testing in this project required 50 mm3

cubes. Steel moulds (50 mm x 50 mm x 50mm) were used for these cubes. Prisms of the dimensions, 40 mm x 40 mm x 160 mm,were required. Steel moulds were also used for these prisms.

Fig 5.2 Cube Moulds for Mortar Fig 5.3 Prism Moulds for Mortar


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For each of the mixes, six cubes and three prisms were made. The prisms are used for theshrinkage tests and for measuring the flexural strength of the mortar. The cubes were usedfor the remaining tests, water absorption, capillary suction, densities, porosity andcompressive strength.

The moulds were checked to ensure they were clean. Once this was verified, they werethoroughly brushed with de-moulding oil. This helps remove the samples from the mouldsonce they hardened. After the moulds were brushed with oil; they were left upturned so noexcessive oil remains, as this would have affected the mortar. The mortar could now beplaced in the moulds.

5.6 Placement

1. The method used for placing each of the cubes and the prisms were thesame.

2. The mortar was placed in the moulds using the spatula or pallet knife intwo layers.

3. The first layer was then compacted using a metal tamping rod to compactthe mortar and therefore reduce the air voids as much as possible.

4. With concrete or hydraulic limes, the samples are tamped a number of times, but as putty is stiffer, the sample must be tamped until themortar is unable to compact any more.

5. The second layer of mortar must be above the edge of the mould andtamped down as above.

6. The surface is then levelled off using the pallet knife.

7. The cubes/prisms are covered with plastic or damp Hessian to preventinitial shrinkage.


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5.7 Curing

The mortar remained in the moulds until they were sufficiently hard, so they could beremoved from the moulds. Each of the mixes remained in the cubes for at least two days.

The mixes with higher proportion of RHA took a shorter time to harden as they hardened byhydraulic means as well as carbonation.

Once removed from the moulds, the cubes/prisms were placed in the curing chamber. Forlime putty the major method of hardening is carbonation. This indicates that the cubes cannot be cured under water like cement based mortar cubes are, as the lime would not be ableto absorb CO

2. Therefore, these cubes are kept in the curing room. In this room the

constant temperature is between 15 - 20C and the humidity is kept quite high ~50 60%humidity is maintained as much as is possible. The cubes were kept in this room for the full35 days of curing and hardening, the prisms were kept in the room for 50 days as they wereused for the shrinkage tests which were set up in this room also.

5.8 Discussion

When the 25% RHA mix was made there was not enough water added and the workabilitywas compromised. This was mainly due to inexperience, and lack of knowledge on thebehaviour of lime putties and RHA. The resulting cubes and prisms were brittle and werequite dusty to touch. Other problems experienced during this mix were the quantitiesprepared as there was barely enough mortar for all of the cubes. With the 75% RHA mix,there was a lot of water required to hydrate the RHA and improve workability. This extrawater made the mortar more fluid, and behave more like a hydraulic lime. This meant it wasunlike the other mixes when being placed. Again inexperience and lack of knowledge meant

it was hard to judge when enough compaction was achieved.


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C HAPTER 6

T ESTING

6.1 Introduction

To understand the behaviour of the lime putty with the addition of RHA, a number of testswere carried out on the cubes and prisms made. The tests used were decided upon afterconsidering the possible positive effects that could be experienced with the addition of RHA.The possible effects of RHA on mortar can be estimated after looking at the effectsexperienced in concrete, with the addition of RHA. The results from these tests are thenused to ascertain beneficial conclusions on the behaviour of RHA with lime putty.

6.2 The Tests

6.2.1 Water Absorption and Capillary Suction

The water absorption is a good indication of how permeable the mortar is and how easilywater can pass through the mortar. This movement of water also applies to gases such ascarbon dioxide. For lime mortars, in particular, this is important as the mortar is allowed toabsorb the CO

2and therefore facilitate carbonation within the mortar and aide the setting of

the lime within the mortar. Therefore more porous the lime mortar is, the quicker it willreach full maturity.

Penetrability is the term used for the overall movements of fluids through a material. Thisflow includes diffusion, sorption and permeability [10]. The flow through a material under adifferential pressure is called permeability. Diffusion is the movement of a fluid under aconcentration differential. Sorption is the capillary movement through the


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capillary pores in the material. These three methods of fluid movement are all groupedtogether as penetrability, but permeability is the accepted term for the movement of fluidsthrough a material. The permeability of the mortar is particularly important, as the moistureneeds to be able to pass through the mortar more easily than through the surroundingmasonry. This prevents the masonry decaying unduly due to moisture being forced to flowthrough the masonry. Therefore the more porous the mortar is the better for the surroundingmasonry as the mortar is sacrificial to the masonry.

Two tests were carried out to examine the movement of fluids through the mortar. The firsttest conducted was the water absorption test. This test measures the volume of pore spacein the mortar by fully immersing the cube in water at atmospheric pressure and at roomtemperature. Deionised water is used in accordance with the RILEM standards. The

second test is to measure the rate of water absorption due to capillary suction in the mortar.The capillary test was carried out in accordance with BS EN 1925; 1999 [11]. Both of these tests were carried out on unsaturated cubes, which were placed in contact with water.The water is under atmospheric pressure only.

6.2.2 Bulk Density and Real Density

The density of a material is a measure of the degree of consolidation of a solid. Densityinvestigates the grain packing of the material and therefore can inform of the chemicalresistance also due to the closeness of the particles [12]. Bulk and real densities areimportant in assessing the extent of some forms of decay in the mortar and in determining theextent to which the pore space can be filled by an impregnation treatment RILEM

Bulk Density (also called Apparent Density) is the ratio of the dry mass to the bulk volumeof the sample, or the volume of all solids in the cube. Bulk Density is expressed inkilograms per cubic metre.


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Real Density is the volume mass of the impermeable material, measured as a ratio of the drymass of the sample to the bulk volume of the sample. Real Density is also expressed inkilograms per cubic metre. Both of these tests were carried out according to the RILEMstandards.

6.2.3 Porosity

Porosity is the ratio of the volume of pores accessible to water to the bulk volume of thesample. It is generally expressed as a percent. It gives the total number of voids in themortar. Porosity of the mortar is very important as it affects the durability of the mortar.This test can therefore be useful in assessing the water absorption in mortars and thereforeassess the durability also.

It is assumed for this project that the pores are interconnected in the mortar. Consequently,the total porosities and open porosities are equal. As the RHA has very small particles, thepores could be filled by the RHA and therefore the porosity may vary with the varyingproportions of RHA in the mixes. In this project the porosity was obtained from the bulk and real density results using a simple formula [13].

6.2.4 Shrinkage

The shrinkage of mortar is an important test in the analysis of mortars as it can be detrimentalif the shrinkage is too great. The bond between the mortar and the masonry can be brokenand so does not perform the desired function. The rate of shrinkage is dependent onhumidity, temperature and other atmospheric variables. The amount of shrinkage is

dependent on the amount of water in the mortar during mixing. Lime putty generally hashigh shrinkage due to the amount of water already in the putty, and also the non-hydraulicnature of the putty.


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6.2.5 Compressive Strength

Compressive strength is the load per unit area under which a sample fails. In mortars thecompressive strength is related to the amount of hydraulic set in the mortar. This hydraulicset also relates to the durability of the mortar [12]. Therefore, the lime putty, which setsmainly due to carbonation, has relatively low compressive strengths in comparison with otherlime mortars. As RHA has certain pozzolanic properties and sets by hydraulic set, the aim isto see what effect the RHA has on the mortar. In this test the cubes were tested incompression to determine the maximum load they could carry before failure occurred.

6.2.6 Flexural Strength

The Flexural strength is a test of the flexibility of the mortar. Flexural strength is importantfor mortars as it allows movement without the necessity for expansion joints. Generally,the more hydraulic the mortar, the less flexible it is. The flexibility for lime putty isgenerally greater than that of non-hydraulic lime mortars and so this project will observe theeffect RHA has on the lime putty mortar. The centre-point loading method [14] was used

to determine the strength. As the standard used is for cement, the modifications for lime,from BS EN 459-2; 5.1.2, are used.

6.3 Testing Standards

The standards used in the testing for this project were the RILEM standardsand the BS/BS EN standards. The BS standards for mortars are generallymodified cement standards and so there are very few specific standards formortars. For this reason, some of the RILEM standards were used insteadof the BS or BS EN. For compression and


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flexural strengths the BS EN 196-1: 1994 was used with the modificationsfor mortars. For the capillary suction, BS EN 1925: 1999, for use on stone,was used. The RILEM standards were used for the densities tests, porosityand water absorption tests. This was due to the lack of suitable standards inBS/BS EN. For the capillary test the duration between readings wasadjusted so to accommodate a faster rate of absorption of water in mortar, incomparison to stone. The standard used for mixing lime putty was BS6463-99 (part 103)

6.4 Testing Procedures

6.4.1 Water Absorption Test

As stated above, there are no suitable standards in the BS/BS EN codes. Therefore theRILEM standards were used.

Apparatus

Oven maintained at 105 + 5C

WaterBasin

SteelRibs

Weighing Scales accurate to 0.01g


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Fig 6.1, Oven at 105C + 5C

Method

1. After 35 days of hardening, the cube was placed in the oven at105C and left for 24 hours.

2. Once the cubes were completely dry the cube was removed fromthe oven and left to cool to room temperature.

3. The cubes were weighed (Wd) and then submersed in deionised

water fully. The cubes were rested on raised steel ribs soeach surface of the cube was exposed to the water.

4. The cubes were left in the water for 24 hours and weighed. Thisweight recorded and the cubes immersed again in the water.

5. The cubes were weighed again after a few hours to check if thecubes were saturated (i.e. had they absorbed any more water).

6. Once the cubes were saturated, they were weighed again toget the saturated weight of the cubes (W

a).

Notes

The cubes had droplets of water on the surface after being removed from the tank. Thesewere removed by blotting the surfaces of the cube with a wet cloth, so not to absorb some of the pore water in the pores on the surface.


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5. The wet face of the cube is blotted with a damp cloth to removeexcess water on the surface before being weighed and the wetmass recorded.

6. This procedure is then repeated for varying intervals up to 60 minutes.

Notes

The water level was maintained by measuring the depth of water at regular intervals andreplacing any absorbed water. Unlike the recommendations of the standards whichmaintain consistency by having a constant flow of water in and out of the tray. In thelaboratory, these conditions are impractical to implement and therefore this moreconvenient, alternative method was employed.

Also suggested in the standards was to continue the tests for as long as 1440 minutes. Thissuggested time is for stone and therefore, for mortar, the more practical time was 60 minutes.

Fig.6.2 Capillary Suction tray


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6.4.3 Bulk and Real Density/Porosity

These tests were conducted in accordance with RILEM [13].

Apparatus

Oven maintained at 105 + 5C

Weighing scales with accuracy of 0.01g

Hydrostatic weighing scales accurate to 0.01g

Evacuationvessel

Method

1. The cubes were dried in an oven for 24 hours until a constantmass was achieved (m

d)

2. The cubes were then placed in the evacuation vessel underwater and a vacuum placed on the vessel

3. The cubes were left in the vessel under vacuum for24 hours

4. After this period the vessel was returned to atmospheric pressureand the cubes left submerged for a further 24 hours

5. The cubes were removed and the hydrostatic weight measured (mh)

(under water)

6. The cubes are dried with a damp cloth and weighed again atatmospheric pressure (m

s), whilst still saturated

The values for bulk and real density were calculated from these results. The porosityresults were also calculated from these results. For the calculations it is assumed that all of the pores are linked and so the open porosity is equal to the total porosity.


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6.4.4 Shrinkage

The shrinkage test monitors how much a prism of mortar shrinks over time. Shrinkage isgenerally related to the amount of water in the mortar, as shrinkage occurs due to the unused

water leaving the mix. This test simply requires the prisms to be set up under a shrinkagegauge, accurate to 0.02mm, and monitored over time. The gauges are placed in the curingroom to avoid fluctuations in humidity and temperature. The curing room maintains ahumidity of 50% 60% and temperature of 15C 20C. A graph is then drawn up usingsimple equations so the mixes can be compared easily.

Fig 6.3, Shrinkage Gauge

6.4.5 Compressive Strength

Some standards suggest the cubes being saturated, but as these cubes are lime puttysubmersing them in water would hinder the hardening as it would restrict the carbonation of the lime putty. This test was performed according to the BS 196-1 [13]. The cubes areplaced in the centre of the plate in the testing machine and a uniformly distributed load isapplied. This load is continuously increased until failure occurs.


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Method

1. Cross sectional area of the cube measured and cube placed in thecentre of the plate.

2. The cube was then continuously loaded at a very low rate until

failure stress, F, was noted.

The stress rate on the machine was manually controlled so to get a more accurate value as themortar cubes are so weak.

Although it is stated earlier that the testing began after 35 days of hardening, it was in factcloser to 50 days after placement in the moulds. This is due to the limited number of cubesand prisms made. There were a number of non-destructive tests performed on the cubesbefore crushing. The results from these tests are directly compared with other results thatwere taken on 28, 35 or 56 day strength. This must be kept in mind when comparing thedifferent mortars.

6.4.6 Flexural Strength

As there are no standards for mortars in particular, the standards for cement were employed,as in above (BS 196-1) [14]. The centre-point loading technique was also used [14]. Theapparatus required is simply a flexural testing rig with two bars on the bottom 100 mm apartand a bar above in the middle between these bars. The load is then applied to the prism,through the top bar, steadily until failure occurs.


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Fig 6.4, Flexural Testing machine

Method

1. Place the prism across the two lower bars at a right angleto them.

2. The top bar is then wound down on top of the prism.

3. The load is steadily applied to the prism until failure stress isreached and the maximum load noted.

Fig 6.5, Flexural Strength Test


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6.5 Key Equations for Calculation of Results

6.5.1 Water Absorption Test

Expression for calculating the water absorbed:

(%)(6.1)

6.5.2 Capillary Suction Test

The water absorption coefficient [12] (by capillary suction) is expressed as:

(g/m2.s

0.5)

(6.2)

6.5.3 Densities and Porosity Tests

Bulk Density ( ) is given by the equation where the dry mass is divided by the bulk volume [12]

(6.3)


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Real Density ( r), given by dividing the dry mass by the impermeable volume [12]

( g/cm3

) (6.4)

Porosity (P), assuming that total porosity and open porosity are equal, this equation willgive a value for porosity [11]

P =

(%)(6.5)

6.5.4 Shrinkage Test

The shrinkage results were simply the amount (mm) the samples shrunk over time (days) and

a graph drawn up of this.

6.5.5 Compressive Strength Test

The test was carried out on three cubes from each of the mixes to get a more accurateresult, when the averages of the three were taken. The compressive strength was thencalculated using the formula:


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(Mpa)(6.6)Where F is the failure load in Newtons, and A, being the area expressed in mm

2. R

cis

calculated to three significant figures.

6.5.6 Flexural Strength Test

Three prisms were used for each mix, as above in compression; the following equation isused to calculate the flexural strength.

R f

=

(6.7)

Where Rf is flexural strength (N/mm

2or MPa), b is the side of the square section (mm), F

f is

the load applied to the middle of the prism at failure (N) and l is the distance between thesupports (mm)


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C HAPTER 7

R ESULTS

7.1 Water Absorption Test

This test was completed after 35 days of maturing in the curing chamber; it was the first of the non-destructive tests to be completed. The test was carried out in according to themethod outlined in chapter six. The cubes were submerged in the water until a constantweight was obtained and then the final, saturated weight was measured. The amount of water absorbed was then measured and given as a percentage of the saturated weight. A barchart was drawn using excel showing the percentage water absorption for each mix.

7.1.1 Results

Fig 7.1, Water Absorption Results


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7.1.2 Discussion

As seen in the bar chart above, the water absorption increases with the increasing proportionsof RHA added. Lime putty is generally more porous and permeable than other hydrauliclimes due to the excess water in the lime putty after slaking. When RHA is added to the limeputty, it absorbs a lot of the water in the mix and so water must be added to the mortar tomake it more workable and easier to compact into the moulds. Some of this extra water isused in the hydration of the RHA. However, any of the idle water is then expelled from themortar during its maturing and therefore resulting in shrinkage. As the amount of RHA ineach mix rises, the amount of water that is added also rises. This extra water leaves voids inthe mortar when it is expelled from the mortar during the maturing and also the dryingprocesses.

This water absorption also applies to other fluids and gases. The absorption of gases such ascarbon dioxide can help to speed up the carbonation process, resulting in the mortar hardeningmore quickly.

7.1.3 Conclusion

The increased water absorption can be beneficial to the mortar but not if the absorption is toogreat, as in the 75 % RHA mix. There is too much free water available in the 75 % mix andthis could affect other properties of the mortar.

7.2 Capillary Suction Test

This test was carried out on three cubes from each mix as specified in chapter six. Thecubes were placed in the tray for varying time intervals, starting at one minute up to onehour. The cubes were weighed at these intervals to measure the amount of water absorbedby the cubes in the previous time interval. These results were used to calculate values whichcan be graphed. Below is an example of one set of results and calculations:


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Table 7.1, Example of Results from Capillary Suction Test

Material Amount Lime Putty 800 g

Sand 2400 g

Water ~20 g

Material Amount

Lime Putty 600 g

RHA 200 g

Sand 2400 gWater 80 g (+30 g)

Material Amount

Lime Putty 400 g

RHA 400 g

Sand 2400 g

Water 230 g

Material

Amount

Lime Putty 200 g


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7.2.1 Results

Fig 7.2, Capillary Suction for all four mixes

7.2.2 Discussion

As seen in the graph, the pure lime putty (0% RHA Mix) was not as linear as the other mixes;this could be due to the larger sized pores in this mortar. In the mixes with RHA, the RHAwill fill a number of the gaps and so will result in smaller pores in the end. A largedifference can be seen between the pure lime putty and the 25% RHA mix. A similardifference can be seen between 25% mix and the 50% mix. Even though the 50% mix hadhigher water absorption than the 0% and the 25% mixes, the capillary results for the 50% mixare far lower. This could be due to a few reasons; the high water absorption will show arelatively large number of pores, but they may not be connected throughout the mortar. Theproportion of RHA will have an effect on the pores as it will fill a lot of the gaps in betweenthe aggregate and the binder. Another factor affecting the capillary suction would be theadded water to the mortar at the mixing stage. Due to the high


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proportion of RHA there would not be a huge amount of free water after hydration of theRHA was fulfilled.

The 0% mix might not have the same volume of pores that the other mixes do but the pores

are probably interconnected and this is the reason for the rapid saturation of the cube due tocapillary suction. These cubes were saturated after approximately 30 minutes; whereas theother cubes were not saturated even after 60 minutes, apart from the 75% mix.

The 75% mix was quite disappointing as these cubes were saturated after approximately 45minutes. As the main ingredient of the mortar was the RHA, which has such small particles,a lot of water was required to, firstly hydrate the RHA, and secondly make the mix more

workable and compactable. As there is so much water added to the mix, there is thepossibility of more free water. This free water, when not used in the mortar, evaporates,leaving very small capillary pores. These capillary pores, if interconnected, can cause a highcapillary suction. This high water content could be a contributory factor in the high rate of water absorption in this mix also.

7.2.3 Conclusion

The best results in this test were the 50% mix as it absorbed nearly half of what any other mixdid. The test did show that the addition of RHA does have a positive effect on the mortar.It did display a more positive effect when in smaller proportions when the setting method of carbonation is more dominant, rather than hydraulic setting. This could be one of the reasonswhy the 75% mix did not display the same positive effects that the rest of the RHA mixesdisplayed.


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7.3 Bulk and Real Density Test

This test was carried out on 3 cubes from each mix. After the test was completed and resultsobtained, the values for the bar charts were calculated from the equations (6.3) and (6.4).

7.3.1 Results

Fig 7.3, Bulk Density for all four mixes


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Fig 7.4, Real Density for all four mixes

7.3.2 Discussion

It can be seen from the above charts that the 75% mix shows the greatest difference between

the bulk and real densities indicating that this mortar has the greatest amount of pores. Thebulk density results indicate that the pure lime putty has the densest microstructure followedby the 25% mix and 50% mix. The 75% mix has very low bulk density in comparison to theother mixes. When these results are compared with the results from the study by Pavia andTreacy [15], the bulk density results for the pure lime putty are a bit higher in this project thanin [15]. The real density results however are only very slightly higher. This could be due toa number of reasons. The sand used in this study might not be the same and also the testingprocedure could also have differed from the procedures used in this study. However, themixes with RHA included show very positive results when compared with the fat lime,feebly-hydraulic and OPC mortars tested in [15]. Both the bulk and the real densities for25% and 50% mixes are far greater than both the feebly-hydraulic and OPC mortars. Againthis could be due to the differing sand used or the testing methods.


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7.3.3 Conclusion

The results from [15] are useful for comparison, but they will be different due to the reasonslisted above. Therefore it is better to compare between the four mixes made for this projectas there has been a trial mix of pure lime putty made with the same sand and mixingtechniques used throughout all of the tests.

7.4 Porosity Test

These results were calculated using the bulk and real densities using the equation (6.5)

7.4.1 Results

Fig 7.5, Porosity Results for all four mixes


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7.4.2 Discussion

As can be seen from the chart, the porosity can be related to the amount of water added duringmixing; and therefore the amount of free water available in each mortar. The highest porosityis the 75% mix which had the most water added during the mixing stage. The lowest is thepure lime putty which had very little water added to the mix due to the high water content of the putty to begin with. The small amount of water added to this mix was to counteract thedryness of the sand used. A lack of pore water in the sand could cause the sand to absorbsome of the water from the mix. The 25% and 50% mixes showed very similar porosityresults. Even though the 50% contained a lot more water, the 25% mix was the first mixmade, therefore the compaction and packing of the 25% mix might not be as good as the 50%mix was.

7.4.3 Conclusion

Even though the porosity in the pure lime putty is lesser than any of the other mixes, becausethe RHA has such fine particles and fills voids between aggregate, it can be concluded thatthe pores are larger, but not as numerous as the other mixes. And also the capillary resultsshow that the 25% mix and the 50% mix show the best performance under capillary suction.This shows that even though they have the largest number of pores, they are smaller and not

as interconnected. The 75% mix has poor capillary results and high porosity, which indicatesa high number of interconnected pores. This is bad for mortars as it could affect the strengthand other properties of the mortar.


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7.5 Shrinkage Tests

These tests were performed on three prisms from each mix. The results then drawn up onexcel.

7.5.1 Results

Fig 7.6, Shrinkage Results for all four mixes

7.5.2 Discussion

As stated in chapter six, shrinkage is related to the amount of water in the mortar, and theexpulsion of the water during the drying causes shrinkage in the mortar. The 50% mix hasthe highest shrinkage result which indicates a large amount of free water in the mix.


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7.6.1 Results

Fig 7.7, Compressive Strengths for all four mixes

7.6.2 Discussion

As the lime putty sets entirely by carbonation, the initial 35 day curing period would not besufficient to allow adequate setting for the pure lime putty. Even though these were testedat 50 days, a lot of the time, after the 35 days, the cubes were submerged in water or in theoven. This would impede the carbonation process substantially. These conditions wouldhowever be more favorable to the mixes containing RHA as it sets partially throughhydration.


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7.6.3 Conclusion

As seen in fig 7.7, the pure lime putty does not withstand compressive loads as well as theother mixes. The 50% mix is over eight times stronger in compression than the pure limeputty. This could be due to a better bond between the aggregates caused by the fine particlesin the RHA acting as an additional binder in the mortar. The 25% mix showed goodcompressive results also being higher than the 75% mix but still lower than the 50% mix.The addition of RHA obviously has a positive effect on the lime putty mortar but the bestresults can be achieved when the proportion of RHA is kept less than the proportion of lime.

7.7 Flexural Strength Tests

This test was performed on three prisms from each mix. It was carried out afterapproximately 50 days. The results for flexural strength were obtained from the equation(6.7) after the readings were taken.


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7.7.3 Conclusion

As demonstrated in fig 7.8, the 50% mix has three times the flexural strength the pure limeputty has. As stated above the 25% mix results were quite disappointing due to the reasonsgiven. The 75% mix performed as well as the pure lime putty did. This was probably dueto the majority of the binder used being RHA. The setting being mainly hydraulic ratherthan by carbonation would affect the flexural behaviour of the mortar. The 75% mix actedsimilarly to an OPC mortar. It can be seen clearly in the 50% mix, that the RHA has a verypositive effect on the mortar in this proportion. However if the 25% mix contained morewater the results for this mix could have been more encouraging.


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C HAPTER 8

C ONCLUSIONS

8.1 Introduction

The objective of this project was to investigate the effect RHA has on lime mortar whenadded in varying proportions, and is it a practical material to use in the construction industry.Experimental studies were carried out to demonstrate some of the properties of lime mortarwith the addition of RHA and the results compared with feebly hydraulic lime mortar andalso a reference mix with no RHA content. The theory of lime and lime mortars wasdescribed, followed by a description of the mortar mixes. The testing methods and testswere fully described, and the results were recorded from the testing were analysed using theequations given in chapter six.

8.2 Conclusions

The results obtained in this project show that the addition of RHA to lime putty has a lot of positive effects when added in the right proportions. The reference mix of pure lime putty isthe main source of comparison in the project, as the sand used and procedures were consistentthroughout all of the mixing and testing, the most accurate comparisons could be made.When comparing the results from this project with other results there are a number of variables which can affect the results. A different type of sand can affect the results, andalso the mixing procedure can be different if mixed or tested according to different standards.This is the reason a trial mix of pure lime putty was made using the same aggregate andmixing techniques as the other mixes.


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The addition of RHA improved the behaviour of the mortar in almost all of the tests exceptfor the shrinkage test. This is due to the extra water added to the RHA mixes in order tomake them more workable. The RHA had a tendency to draw the water from the putty,therefore affecting the workability of the mix. Due to inexperience and lack of knowledgeon RHA, the water content could probably be reduced and therefore decrease the shrinkage.The water absorption results were also quite similar to the shrinkage. The amount of waterabsorption rises with the amount of RHA added to the mortar. This is not necessarily a badresult as the water absorption also applies to absorption of gases such as carbon dioxide. Theability for carbon dioxide to penetrate the mortar means an increase in carbonation of the limeand therefore more rapid hardening of the mortar. as stated in chapter seven, the 25% RHAmix was the first mix made and so not enough water was added to the mix. Due to this someof the results for this mix were a little inaccurate, particularly the flexural strength andshrinkage. it would be expected that if the test for this mix were don again the results wouldbe a bit more consistent and satisfactory.

The results for the 75% mix were disappointing. The flexural strength and compressivestrength were lower than both the 50% mix and 25% mix. The shrinkage was the secondhighest behind the 50% mix. The density of the 75% mix was a lot lower than the two othermixes, and it also had the highest porosity. In shrinkage, the mix was saturated afterapproximately 30 minutes. One of the possible reasons for these disappointing results is theamount of water in the mix. Due to the high level of RHA a lot of water must be added inorder to achieve adequate workability. Another reason for the poor results could be the factthat RHA does not have pozzolanic properties when on its own. The high proportion of RHA in this mix could demonstrate this fact. This would explain the poor results in flexuraland compressive strengths. While the high water content would explain the porosity andcapillary suction results.

The 50% mix displayed the best results in most of the tests. The compressive strengths arecomparable with strong OPC mortars whilst also maintaining very high flexural strengthsalso. The low capillary suction indicates that the pores are not entirely


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interconnected. The only disappointing result from this mix was the shrinkage which wasvery high in comparison to the pure lime putty mix. This mix showed good density resultswith very similar porosity results to the 25% mix.

As demonstrated by the results, the addition of RHA to lime putty has very positive effectson the mortar, once the proportions of RHA added are kept relatively small. Particularlythe 50% mix which has only one really poor result (shrinkage), and the 25% mix, if carriedout again, it is estimated, it could display similarly positive results. As these results showthe same good results shown by non-hydraulic limes but with the bad aspects of these limerectified.

8.3 Recommendation for Further Study

Due to time restrictions and resources, the tests completed gave limited results. However theresults obtained were very positive and encouraging, and would warrant further study intothis topic.

To get more definitive results, a wider range of mortars must be made with wider variationsin mix proportions. The water added should be regulated a bit more with restrictionsplaced in order to avoid too much water affecting the results. This can only be done aftermuch experimentation.

As there is limited knowledge of RHA and how to use it, a considerable amount of testing and research needs to be carried out in order to understand its behaviour underdifferent circumstances and to get a definitive method for mixing RHA.


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R EFERENCES

[1] Singhania N. P ., 2004, Rice Husk Ash, The Institute of Concrete Technology Newsletter, Issue no.55 Autumn 2004, The Institute is a Professional Affiliate of the Engineering Council(UK).

[2] Singhania N. P ., March 2004, Concrete adding to the mix, Institute of Civil Engineers and Surveyors, March 2004 issue, publisher unknown

[3] Lime education sheet www.singletonbirch.com

[4] http://www.trp.dundee.ac.uk/research/glossary/lime.html

[5] Taylor J., Lime: The Basics, historic churches 2002,(www.buildingconservation.com )

[6] Ashurst J., Ashurst N ., Practical Building Conservation Mortar Plaster and

Renders , Aldershot: Gower Technical Press, (1988)

[7] Wingate M ., Small Scale Lime Burning The Journal of Building Limes forum , Vol.10, (2003)

[8] Cowper A.D ., lime and lime mortar , Department of scientific and industrialResearch, London, (reprint 1997)

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Ed., Houghton MifflinCompany, (2004)
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[14] BS 196-1:1995 , Methods of Testing cement. Determination of Strength

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[16] www.buildinglimesforum.org.uk/whyuselime

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[19] Hasparyk N.P., Farias L.A., Andrade M.A.S., Bittencourt R.M ., (2004)

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an investigation into the effect of rice husk ash on mortar when added in varying proportions -...

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