Investigation on Appropriate Admixtures for Use of Fly Ash in Masonry Bricks production

PROJECT REPORT2012

UNIVERSITY OF MALAWITHE POLYTECHNICFACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERINGD5CfRom: MWAWI KUMWENDA(eng/07/ne/012)SUPERVISOR: Dr. I. NGOMAsubmitted: 21ST DECEMBER 2012

Investigation on Appropriate Admixtures for Use of Fly Ash in Masonry Bricks production

A project submitted in partial fulfillment for the award of a Bachelor of Science degree in Civil Engineering.

ACKNOWLEDGEMENTSThe author wishes to express sincere gratitude to Dr I Ngoma for his suggestions, continuous supervision and guidance to complete this project.I would like to thank Mr Benedicto Munthali for his valuable contributions and for his assistance throughout the project.I would also like to thank Mr E Magona (LaFarge Cement), Mr G Kishindo (Presscane Limited) for providing me with valuable information throughout the project. Lastly, I would like to thank Civil Engineering Staff especially Mr I Ngoma for their assistance with the experiments.

TABLE OF CONTENTSACKNOWLEDGEMENTSiLIST OF TABLESivLIST OF FIGURESvLIST OF ACRONYMSviABSTRACTvii1Introduction11.1Background11.2Problem Statement and Justification21.3Objectives21.3.1Main Objective21.3.2Specific Objectives22Literature Review32.1Definition32.2Types of Bricks32.2.1Clay bricks42.2.2Calcium Silicate bricks42.2.3Concrete bricks52.2.4Fly ash bricks52.3Properties of Fly Ash52.4Environmental and Health Concerns82.5Other Materials102.5.1Lime102.5.2Sand102.5.3Gypsum102.6Classification102.7Physical Characteristics122.7.1Compressive Strength122.7.2Water Absorption132.7.3Efflorescence133Materials and Methods143.1Data Collection143.2Qualitative Data143.2.1Desk Study143.2.2Interviews143.3Experimental Study143.3.1Material Properties143.3.2Fly Ash153.3.3Cement183.3.4Lime193.4Experimental Procedures203.4.1Specimen Preparation203.4.2Water Absorption203.4.3Determination of Strength214Experimental Data224.1Manufacturing224.2Engineering Properties225Discussion325.1Fly Ash Composition325.2Effect of Admixtures325.2.1Water Absorption335.2.2Compressive Strength356Conclusion407Recommendations418References42Appendix A43Appendix B44Project Pictures44

LIST OF TABLEStable 2.1: Composition Of Fly Ash Based On Type Of Coal6Table 2.2: Physical And Geotechnical Parameters Of Fly Ash7Table 2.3: Classes Of Pulverized Fuel Ash-Lime Bricks11Table 4: Strength Requirements For Masonry Units And Mortar12Table 3.1: Particle Size Distribution By Wet Sieving15Table 3.2: Chemical Composition Of Fly Ash17Table 3.3: Engineering Properties Of Cement18Table 3.4: Chemical Composition Of Cement18Table 4.1: Control (7 Days)22Table 4.2: Control (28 Days)23Table 4.3: 60% Fa-40% Cement (7 Days)23Table 4.4: 60%Fa- 40% Cement (28 Days)24Table 4.5: 70% Fa- 30% Cement (7 Days)24Table 4.6: 70% Fa- 30% Cement (28 Days)25Table 4.7: 80% Fa- 20% Cement (7 Days)25Table 4.8: 80% Fa-20% Cement (28 Days)26Table 4.9: 90% Fa- 10% Cement (7 Days)26Table 4.10: 90% Fa- 10% Cement (28 Days)27Table 4.11: 60% Fa- 40% Lime (7 Days)27Table 4.12: 60% Fa- 40% Lime (28 Days)28Table 4.13: 70% Fa- 30% Lime (7days)28Table 4.14: 70% Fa- 30% Lime (28 Days)29Table 4.15: 80% Fa-20% Lime (7 Days)29Table 4.16: 80% Fa- 20% Lime (28 Days)30Table 4.17: 90% Fa- 10% Lime (7 Days)30Table 4.18: 90% Fa- 10 % Lime (28 Days)31Table 5.1: Summary Of Water Absorption Results33Table 5.2: Summary Of Compressive Strength Results35Table 5.3: Comparison Of Fly Ash Bricks With Standard Values39Table 9.1:Fly Ash Particle Size Distribution43

LIST OF FIGURESFigure 3.1: Particle Size Distribution GRAPH (Dry Sieving)16Figure 3.2: Fly Ash Sample17Figure 3.3: Physical Properties And Chemical Composition Of Ndola Lime19Figure 3.4: Bricks Immersed In Water For Water Absorption Test20Figure 3.5: Compressive Strength Test21Figure 5.1: Variation Of Water Absorption With Age34Figure 5.2: Variation Of Water Absorption With Admixture Type34Figure 5.3: Variation Of Free Cao With Time36Figure 5.4: Compressive Strength Variation With Age36Figure 5.5: Compressive Strength Variation With Age37Figure 5.6: Compressive Strength Variation With Admixture Type38Figure 5.7: Compressive Strength Variation With Admixture Type38Figure 9.1:Indoor Curing Of Bricks44Figure 9.2: Outdoor Curing Of Bricks44Figure 9.3: Internal Structure Of Brick45

LIST OF ACRONYMSASTM: American Society for Testing and MaterialsBS: British StandardFA: Fly AshIS: Indian StandardMSB: Malawi Standards BoardMBS: Malawi Bureau of StandardsOPC: Ordinary Portland Cement

ABSTRACTFly ash is a waste material produced by coal firing thermal plants and its accumulation causes pollution problems. This problem can be alleviated by utilization of the fly ash as a raw material for brick making. This will be a very beneficial solution in terms of economic and environmental aspects.The purpose of the project was to determine suitable admixtures for the use of fly ash in masonry brick production. The fly ash used in the study was obtained from PressCane in Chikhwawa district. In order to achieve this, a total of 108 bricks with 9 different mixes were manufactured. The first mix was the control with 100% fly ash while the rest of the mixes contained fly ash mixed in different proportions with either cement or lime. Each admixture mix contained 10%, 20%, 30% or 40% by weight of cement or lime mixed with the fly ash. After manufacturing the bricks were cured in the open and sprinkled with water every day until age of testing. After curing, the water absorption and compressive strength of the bricks were tested.Investigation on Appropriate Admixtures for Use of Fly Ash in Masonry Bricks production2012

The results from the laboratory tests showed that the compressive strength of the bricks increased and the water absorption reduced with increasing amount of admixture. It was also found that the fly ash-cement bricks had better compressive strength than fly ash-lime bricks. In the case of water absorption, the results showed that the fly ash-lime bricks had superior water absorption properties compared to the fly ash-cement bricks. Overall, the study showed that 5 out of the 8 admixture mixes meet MSB specifications for common and industrial load bearing bricks. Based on the results, it was thus concluded that quality masonry bricks can be made from fly ash when cement or lime is used as an admixture.Mwawi KumwendaPage | i

IntroductionBackground Fly ash is one of the by-products of the combustion of coal and comprises the fine particles that rise with the flue gases. The composition of fly ash depends on the source and makeup of coal, the type of combustion equipment used and the fly ash collection mechanism. However, all fly ashes contain significant proportions of silicon dioxide (SiO2) and calcium oxide (CaO). Fly ash is considered an environmental and health concern hence legislation requires that it be captured prior to release (Liu, Burkett, & Haynes, Improving Freezing and Thawing Properties of Fly Ash Bricks, 2005). This is achieved through the use of electrostatic precipitators or other particle filtration equipment before it reaches the chimneys of coal fired plants. The fly ash is then collected and disposed.The problem with fly ash disposal is that it requires large quantities of land, water and energy. In addition, its fine particles, if not well managed, by virtue of their weightlessness can become airborne leading to air pollution and health hazards. One of the ways of alleviating this problem is through the re-use of the fly ash in different sectors of the economy industry, infrastructure and agriculture. In the infrastructure sector, one use of fly ash is as a raw material for the manufacture of masonry bricks.The American Society for Testing and Materials (ASTM) classifies fly ash as Class C or Class F according to ASTM C618 (Standard Specification for Coal Fly Ash and Raw or Calcined Pozzolan for Use As a Mineral Admixture in Concrete). Class F fly ash is normally produced from burning anthracite or bituminous coal and contains a minimum of 70% by weight of SiO2, Al2O3, and Fe2O3 combined. Class C fly ash is normally produced from lignite or sub-bituminous coal and contains a minimum of 50% by weight of SiO2, Al2O3, and Fe2O3 combined. Class F fly ash has pozzolanic properties while Class C fly ash has pozzolanic and some cementitious properties.

Problem Statement and JustificationIt has been established through previous research, as cited by Liu (2005), that fly ash bricks can be produced by mixing fly ash with approximately 10% water, compacting at approximately 20KPa and then curing. This produces relatively strong bricks in the case of Class C fly ash however the bricks produced from Class F fly ash do not have satisfactory properties due to the lack of cementitious properties. The purpose of this project was to investigate appropriate admixtures for uses in fly ash brick production in order to improve their physical properties which include compressive strength and water absorption. Improving the quality of the bricks will make them more technically and commercially acceptable, and allow stakeholders in the construction industry adopt the use of fly ash bricks as a superior alternative to burnt clay bricks. As already stated this will also help in solving the problems associated with the disposal of fly ash. In addition, the fly ash bricks also help the environment by reducing the use of burnt clay bricks. In making clay bricks, the green bricks are cured by heating using energy from burning fossil fuels. Since the manufacture of fly ash bricks does not require heating, it helps reduce the release of greenhouse gases into the atmosphere (Liu, Burkett, & Haynes, 2005).ObjectivesMain ObjectiveThe main objective was to investigate appropriate admixtures for the use of fly ash in masonry bricks production.Specific ObjectivesThe project was intended to specifically fulfil the following:1. To acquire and characterise fly ash.2. To manufacture fly ash bricks with varying proportion of admixtures.3. To carry out laboratory tests to determine physical properties of the fly ash bricks.4. To assess the suitability of admixtures for the fly ash bricks.

Literature ReviewDefinitionBricks are one of the oldest manufactured building materials. The art of brickmaking and the craft of bricklaying can be traced back to 6000BC. Bricks have been a major building material since the end of the fourteenth century (Chudley & Greeno, 2007). A brick is defined in BS 3921 as a walling unit with coordinating or format size of 225 mm length, 112.5 mm width and 75 mm height. Bricks are known by their format size that is, the actual or work size plus a 10 mm mortar joint allowance to three faces. Therefore the standard brick of 225 mm 112.5 mm 75 mm has actual dimensions of 215 mm 102.5 mm 65 mm (Chudley & Greeno, 2007) . Bricks are used inmasonryconstruction, usually stacked together, or laid using various kinds ofmortarto hold the bricks together and make a permanent structure. Mortar is a mixture of sand, a binder such as lime or cement, and water. The mortar used in brickwork transfers the tensile, compressive and shear forces uniformly between adjacent bricks (Chudley & Greeno, 2007). Types of BricksThere are several ways of classifying bricks. One of the ways is by using the raw materials the bricks are made from. The types of bricks according to raw materials are as follows:1. Clay bricks.2. Calcium Silicate bricks.3. Concrete bricks.4. Fly ash bricks.

Clay bricksClay bricks are made by pressing a prepared clay sample into a mould, extracting the formed unit immediately, drying and then heating it in order to sinter the clay. They are the most common type of bricks.Many different types of bricks may be produced, depending on the nature of the clay used, the moulding process and the firing process. There are three basic subdivisions of type according to Taylor (2002):I. Common bricks.II. Facing bricks.III. Engineering bricks.Common bricksThese are ordinary bricks which have low strength and are not designed to provide good finished appearance. Facing bricksThese are designed to give an attractive appearance and are free from imperfections such as cracks. They are also durable and are used in external walls. They are by far the most popular type of brick and come in a huge variety of colours and sizes (Taylor, 2002). Engineering bricksThese are designed primarily for strength and durability. They are usually of high density and well fired. They are rated as either class A or B; with A being the strongest and they are ideal for use below ground level and for Damp proof courses.Calcium Silicate bricksThese bricks are made from carefully selected clean sand and/or crushed flint mixed with controlled quantities of lime and water. The semi-dry mixture is compacted into moulds and then autoclaved, at about 170oC at a specified pressure. The process takes from 7-10 hours and causes a surface reaction between the sand and lime, producing calcium silicate hydrates which glue the sand particles into a solid mass. The bricks are very accurate in shape and size and have good overall durability. They have the same format size as standard clay bricks (Chudley & Greeno, 2007) .

Concrete bricksThese are made from a mixture of inert aggregate and cement in a similar fashion to calcium silicate bricks, and are cured either by natural weathering or in an autoclave. They are used for load bearing and nonload-bearing walls; piers, fireproofing over steel structural members; fire safe walls around stairwells, elevators, and other enclosures; retaining walls and garden walls; chimneys and fireplaces; concrete floors; and many other purposes (Chudley & Greeno, 2007).Fly ash bricksThese are made from fly ash obtained from coal fired plants. The bricks may be made exclusively from fly ash or they may contain fly ash mixed with other raw materials. Properties of Fly AshUpon ignition in a furnace, most of the volatile matter and carbon in coal are burned off. During combustion, the coals mineral impurities (such as clay, feldspar, quartz, and shale) fuse in suspension and are carried away from the combustion chamber by the exhaust gases. In the process, the fused material cools and solidifies into spherical glassy particles called fly ash. The fly ash is then collected from the exhaust gases by electrostatic precipitators or bag filters. Fly ash is a finely divided powder resembling Portland cement (Team-Envis, 2007). Fly ashes are generally heterogeneous, consisting of a mixture of glassy particles with various identifiable crystalline phases such as quartz, mullite, and various iron oxides (Wikipedia, 2012). The particle sizes in fly ash vary from less than 1 m (micrometre) to more than 100 m with the typical particle size measuring less than 20 m. Fly ash is primarily composed of silicate glass containing silica (SiO2), alumina (Al2O3), iron (Fe2O3), and calcium oxide (CaO). Minor constituents are magnesium, sulphur, sodium, potassium, and carbon. Crystalline compounds are present in small amounts.The concentrations of the above components depend on the type of coal combusted to produce the ash. The properties also depend on the degree of pulverization, design of boiler unit, loading and firing conditions, handling and storage methods. The typical values for different types of coal are summarized in the table below:Table 2.1: COMPOSITION of fly ash based on type of coalComponent (%)BituminousSubbituminousLignite

SiO220-6040-6015-45

Al2O35-3520-3020-25

Fe2O310-404-104-15

CaO1-125-3015-40

LOI0-150-30-5

The physical and geotechnical parameters e.g. specific gravity, grain size, Atterberg limits, compaction characteristics, permeability coefficient, shear strength parameters and consolidation parameters are the same as those for natural soils (Team-Envis, 2007). The properties are summarized in the table below:

Table 2.2: physical and geotechnical parameters of fly ashEngineering Properties of Fly Ash

ParameterValue

Specific Gravity1.90-2.55

PlasticityNon-Plastic

Proctor Compaction-MaxDry density (gm/cc)0.90-1.60

Optimum Moisture Content (%)38.0-18.0

Angle of Friction (O)30O-40O

Cohesion (kg/cm2)Negligible

Compression Index0.05-0.4

Permeability (CM/SEC)105-103

Clay Size Fraction (%)1-10

Silt Size Fraction (%)8-85

Sand Size Fraction (%)7-90

Gravel Size Fraction (%)0-10

Coefficient of Uniformity3.1-10.7

Adopted from Parisara ENVIS Newsletter (4th January, 2007).The American Society for Testing and Materials (ASTM) divides fly ash (FA) into two classes: Class F and Class C based on the combined weight of SiO2, Al2O3, and Fe2O3. Unlike Class C fly ash, Class F fly ash needs to react with lime at ordinary temperature, in the presence of water in order to exhibit cementitious properties. The reaction of the fly ash and lime produces calcium silicate hydrates which are responsible for the high strength of the compound. A similar reaction takes place in class C fly ash in the presence of water but without lime. This is because class C fly ash contains a significant proportion of calcium oxide which acts as a natural binder. The bricks produced from the reactions are thus chemically bonded. Fly ashes are essentially slow setting cements.Research has shown that fly ash-lime bricks have superior compressive strength and require less mortar compared to clay bricks (Dighade, Ambekar, & Pande, 1999). It is important to note that in order to achieve this, there is need for proper and adequate support and guidance to brick manufacturers. Environmental and Health ConcernsFly ash bricks contain small amounts of pollutants including heavy metals hence there is need to show that they are environmentally safe construction products. It is also important to find out whether bricks made from fly ash would release pollutants into the environment when buildings are demolished and the bricks are reused or disposed of in landfills (Liu, Burkett, Haynes, & VanEngelehoven, 2009). Liu et al (2009) describe four critical environmental concerns about building products made from fly ash. These are:1. Potential for mercury vapour emission from the products. Mercury is a potential environmental and health hazard. It is found in fly ash in liquid form hence it can evaporate and cause health concerns.2. Potential for radon emission from the products. Radon is a radioactive gas that causes lung cancer. The higher the concentration of radon in the air and longer we breathe the air, the higher the risk of getting lung cancer.3. Fly ash is often contaminated with pollutants (heavy metals). It is important to evaluate the risk of these pollutants leaching when fly ash products are exposed to rain. 4. Potential for polluting landfills when a building is demolished and the broken fly ash products enter landfills.These concerns were tested in the laboratory and the results showed that: 1. Fly ash bricks made from Class C fly ash do not emit mercury into the air. On the contrary, the absorb mercury from the air. The air usually has about one to ten nanograms of mercury per cubic meter, hardly enough to poison anyone. Liu et al (2009) found that when fly ash bricks were put in a sealed chamber containing air, the air was found to contain only half a nanogram at the end of the study.2. Fly ash emits radon but the rate of emission is safe. This is justified as the rate is only half of that emitted by concrete and concrete products. Emissions from concrete and concrete products are considered safe (Liu, Burkett, Haynes, & VanEngelehoven, Environmental Properties of Fly Ash, 2009).3. Leaching of pollutants from fly ash bricks caused by rain is negligible (Chou, Chou, Patel, Pickering, & Stucki, 2006).4. Fly ash bricks pass the Environmental Protection Agency (EPA) mandated Toxicity Characteristic Leaching Procedure (TCLP) hence they are non-hazardous for landfill and handling (Chou, Chou, Patel, Pickering, & Stucki, 2006).Liu et al (2009) also observed that long term strength development in fly ash is due to carbonation caused by absorption of carbon dioxide from the atmosphere. This means that fly ash bricks help in reducing global warming.It is important to note that the results from the work of Liu and others apply to class C fly ash. There is need for further research to see if they also apply to class F fly ash. Further research on the environmental impacts and health concerns associated with FA was carried out by the U.S. Geological Survey. This led to the publication of Fact Sheet FS-163-97 which describes an approach to investigate the distribution and modes of occurrence (chemical form) of trace elements in coal and coal combustion products. The approach involves:1. Ultra-sensitive chemical or radiometric analyses of particles separated on the basis of size, density, mineral or magnetic properties.2. Analysis of chemical extracts that selectively attack certain components of coal or fly ash.3. Direct observation and micro beam analysis of very small areas or grains.4. Radiographic techniques that identify the location and abundance of radioactive elements.Using results from the above, the U.S. geologic survey concluded that radioactive elements in coal and fly ash should not be sources of alarm. The majority of fly ashes are not significantly enriched in radioactive elements, or in associated radioactivity, compared to common soils or rocks.Other MaterialsLimeLime to be used for fly ash bricks should be hydrated. Lime reacts with class F fly ash in presence of water at ordinary temperatures and gives it cementitious properties (Basumajumdar, Das, Bandyopadhyay, & Maitra, 2005).SandThe sand should be of good quality and should contain less than 5% of deleterious materials such as clay and silt.GypsumGypsum is a crystalline combination of calcium sulphate and water. It improves the quality of the bricks, especially the physical appearance (Sivapullaiah & Moghal, 2011).In general, all the materials used should not be detrimental to the bricks. ClassificationFly ash bricks lime bricks are classified on the basis of average wet compressive strength as given in the table 2.3.

Table 2.3: Classes of Pulverized Fuel Ash-Lime BricksClass DesignationAverage Wet Compressive Strength Not Less Than

N/mm2kgf/cm2

123

3030300

2525250

2020200

17.517.5175

1515150

12.512.5125

1010100

7.57.575

5550

3.53.535

Since the project was conducted in Blantyre, it is important to ensure that the bricks conform to the Blantyre City Assembly Building Code Bylaws. The table below shows the requirements for masonry and mortar units as specified in the bylaws.

Table 4: STRENGTH REQUIREMENTS FOR MASONRY UNITS AND MORTARWall TypePositionMinimum Average Compressive Strength, MpaClass of Mortar Required

Solid UnitsHollow Units

Structural other than foundation and retaining wallsSingle storey External or building internal7.03.5II

Double storey External or building internal10.5 or 147.0II

Non-structural other than parapet, balustrade and free-standing wallsExternal7.03.5II

Internal7.03.5II

Free-standingExternal or Internal10.57.0II

FoundationSupporting single storey7.03.5II

FoundationSupporting single storey10.5 or 147.0II

Parapet-7.03.5II

Balustrade-7.03.5II

Retaining-10.57.0II

Physical CharacteristicsCompressive StrengthCompressive strength is the capacity of a material or structure to withstand axially directed pushing forces. The minimum average strength of fly ash bricks when tested shall not be less than the value specified for each class above. In addition, the compressive strength of each individual shall not be less than minimum average strength by more than 20 percent.

Water AbsorptionThe Malawi Standard specification for burnt clay bricks does not specify any values for water absorption. The Indian Standard (IS) specification for fly ash-lime bricks however, states that when the bricks are tested after immersion in cold water for 24 hours, they should have average water absorption not more than 20 percent by mass up to class 12.5 and 15 percent by mass for higher classes.EfflorescenceEfflorescence refers to when salts are brought to the surface of a material as a result of movement of water in a wall or water being driven out as the result of heat of hydration. The bricks when tested shall have the rating of efflorescence not more than moderate up to Class 10 and slight for higher classes.

Materials and MethodsData CollectionBoth qualitative and quantitative data was collected.Qualitative Data Desk Study This involved the study of available literature from books, standards, related research reports, journals and the internet in order to be familiar with the properties of fly ash, the use of fly ash for masonry brick production and the admixtures to be used in this project.InterviewsInterviews were conducted with officials from the Ethanol Company to obtain information about their coal usage, fly ash generation, and method of handling and storage of the fly ash. Interviews were also conducted with professionals with relevant information about fly ash and its use in masonry brick production.Experimental StudyThe objective of the project was to determine suitable admixtures for the use of fly ash in masonry bricks production. In this respect, two admixtures were prepared, namely; cement and lime. A total of nine mixes were prepared and the engineering properties namely; compressive strength and water absorption were tested. An observation of the shape of the cured bricks was made prior to testing.

Material PropertiesThis section presents the chemical and physical characteristics of the materials used in the project. The tests were carried out according to procedures described in British Standards.Fly AshThe fly ash used in the experimental program was obtained from PressCane limited in Chikhwawa. The coal used at the factory comes from Mchenga and Kaziwiziwi coal mines in Rumphi. The coal is crushed to pea size (6mm) before being fed into the Cethar Fluidix Boilers which operate at temperatures between 800 and 920 C. The factory uses 24 tonnes of coal per day and produces approximately 10 tonnes of fly ash per day (24 hours). The fly ash is then heaped and sprinkled with water to prevent the particles of FA from becoming airborne. The gradation of the FA was determined by sieve analysis and a chemical analysis was carried out to determine the chemical composition. The results are shown in the tables below: Table 3.1: particle size distribution by wet sievingPropertyValueUnits

Fineness (retention 45 m) 54.6%

LOI29.9%

PSD GRAPHDEPARTMENT OF CIVIL ENGINEERINGMwawi Kumwenda MATERIAL:PURE COAL ASHClaySiltSandGravelCobblesBouldersFineMediumCoarseFineMediumCoarseFineMediumCoarse200mm1020304050607080901000.0010.0100.1001.00010.000100.0001000.000Percentage Passing (%)Particle Size (mm)

Figure 3.1: particle size distribution GRAPH (dry sieving)Table 3.2: chemical composition of fly ash

Figure 3.2: fly ash sample

CementDuracrete cement manufactured by Lafarge Malawi was used in the investigation. Duracrete is a class N cement with strength of 32.5N/mm2. The physical properties and the chemical composition of the cement as provided by the manufacturer are presented in the tables below.Table 3.3: engineerinG properties of cementProperty ValueUnits

Density2.96g/cm3

Fineness7.68m

Strength

2 days12N/mm2

7 days25N/mm2

28days32.5N/mm2

Table 3.4: chemical composition of cementParameterUnitsValue

CaO%65.41

Al2O3%5.61

Fe2O3%5.21

SiO2%20.42

FCaO%0.50

C3S%63.30

C3A%6.06

LOI%1.00

L/Wt.1388.00

It is important to note that duracrete differs from Ordinary Portland cement as it contains between 5 and 10% reactive silica. LimeHydrated lime manufactured by Ndola Lime Company was used in the investigation. The figure below presents the physical properties and the chemical composition of the lime used throughout the study.

Figure 3.3: physical properties and chemical composition of ndola limeSource: Ndola Lime Company websiteExperimental ProceduresSpecimen PreparationThe specimens were prepared by proportioning and dry-mixing of batch materials; fly ash, cement and lime in a mixer. Water was then added to the mixture and it was blended until it became workable. After mixing, the brick was shaped by placing it in a mould. The bricks were then removed from the moulds and cured indoors for three days. After indoor curing, the bricks were taken outdoors, sprinkled with water and then covered with black PVC sheets. Water was sprinkled on the bricks daily until age of testing.Water AbsorptionThe dried specimen was immersed in clean water at a temperature of 22C for 24 hours. The specimen was then removed and any traces of water were wiped off with a damp cloth and the specimen was weighed.

The water absorption is given by the formula

Figure 3.4: bricks immersed in Water for water absorption testDetermination of StrengthThe specimen was placed with flat faces horizontal between 4mm thick sheets and carefully cantered between plates of the testing machine. A load was then applied axially at a uniform rate of 10 N/mm2 per minute till failure occurred and the maximum load at failure was noted. The load at failure was the maximum load at which the specimen failed to produce any further increase in the indicator reading on the testing machine.

Figure 3.5: compressive strength test

Experimental DataManufacturingOne control mix and eight mixes with admixtures were prepared for the investigation. The control contained 100% fly ash while the other mixes contained either FA and cement or FA and lime in varying proportions. The fly ash was partially replaced with either cement or lime ranging from 10% to 40%.Engineering PropertiesThe engineering properties; water absorption and compressive strength were determined for all the nine mixes. Twelve bricks were manufactured for each of the nine mixes and 6 were tested at 7 days while the remaining 6 were tested at 28 days. The bricks were tested at different ages to examine the development of strength in the bricks. The results are shown in the tables below. N.B: The tables do not include water absorption values for 90% FA-10% Cement and 90% FA-10% Lime bricks as they became severely disfigured. Table 4.1: control (7 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)Shape

Good FairPoor

12085223105652341550.14

22235222105652331080.22

32180223105652341560.16

4159522510565236252.80.08

51615225105652362540.11

6161022510565236254.40.12

Table 4.2: control (28 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)Shape

Good FairPoor

1206522510565236255.40.14

2221522310565234157.40.20

3205522510565236256.20.17

4208522210565233105.40.15

5210522310565234156.40.17

6227522310565234157.80.21

Table 4.3: 60% FA-40% CEMENT (7 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1247522510868243002506.5226055.25

2243522410968244162025.2425404.31

3263522510968245253208.2727805.50

4257522510968245253047.8627205.63

5227522511068247502085.3324959.67

6232022511068247502175.5625309.05

Table 4.4: 60%fa- 40% cement (28 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

72350228110692508042210.66275517.23

8216023011067253003929.82261020.83

9216023011065253003508.77260020.37

102365225110672475041810.70276016.70

11192523011068253003328.32240024.68

122375229110672519045011.32274015.37

Table 4.5: 70% fa- 30% cement (7 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1222022611065248601002.5524108.56

222602281106725080842.1224458.19

3225022811067250801002.5324408.44

4222522611070248601604.08257015.51

5205022610970246341343.45236015.12

6212522511070247501303.33252018.59

Table 4.6: 70% fa- 30% cement (28 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1186022811068250801503.79243030.65

2177522811065250801543.89232030.70

3156022911068251901353.40217039.10

4200522511070247501584.05244521.95

5213022611070248601704.33257020.66

6196522511070247501563.99242023.16

Table 4.7: 80% fa- 20% cement (7 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

120052261107024860481.22251025.19

222302261107024860421.07248511.43

319252251107024750491.25244026.75

421452251107024750401.02251017.02

518352261097024634461.18237029.16

620252261057023730401.07241019.01

Table 4.8: 80% fa-20% cement (28 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

122402261087024408501.30254513.62

222052251107024750521.33244510.88

319702251107024750541.38241522.59

421902261097024634561.44249013.70

521602251087024300501.30242512.27

618802251107024750511.31254035.11

Table 4.9: 90% fa- 10% cement (7 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

12065227110702497012.20.31

218352271107024970120.30

31985225110702475012.60.32

42065229110702519013.30.33

520402251107024750130.33

62025227110702497012.80.32

Table 4.10: 90% fa- 10% cement (28 days)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

11830225110702475012.50.32213516.67

22265224110702464015.40.4024156.62

32320225110702475016.20.4125409.48

41930225110702475013.60.35213510.62

52025224110702464012.50.32

62105225110702475013.10.34

Table 4.11: 60% fa- 40% LIME (7 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

123702231107024530862.2224151.90

224302271057023835782.0724802.06

323652221087023976782.0624051.69

423152221087023976822.1723702.38

523652251087024300802.0924051.69

623752251107024750802.0524151.68

Table 4.12: 60% FA- 40% LIME (28 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1177022811067250801563.9419057.63

2220522811067250801744.4023757.71

3180022811067250801684.2419558.61

4179522811067250801583.9919206.96

5222022811067250801483.7423957.88

6217022811067250801543.8923458.06

Table 4.13: 70% FA- 30% LIME (7DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

120752251106824750701.79231511.57

220602251106824750581.49234513.83

321302271106824970601.5222907.51

421402251107024750701.79236010.28

521352251107024750641.6423459.84

620502251086724300561.46233013.66

Table 4.14: 70% FA- 30% LIME (28 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1201522510967245251704.39237017.62

2206522510868243001503.91238015.25

3206522610867244081654.28235514.04

4214022510768240751383.63241012.62

5204522510768240751042.74236515.65

6205522610868244081323.43236515.09

Table 4.15: 80% FA-20% LIME (7 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

121652231106824530962.4823659.24

221652251106624750982.5123558.78

321702251107024750902.3023508.29

4211522510770240751002.63234010.64

5211022511070247501042.66235011.37

6212022511067247501062.71235511.08

Table 4.16: 80% FA- 20% LIME (28 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

1197022511067247501203.07229516.50

2206022310968243071403.65235514.32

3201022511070247501283.28232015.42

4184022511069247501183.02231025.54

5196022511068247501263.23232018.37

6195022510970245251223.15232018.97

Table 4.17: 90% FA- 10% LIME (7 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

120102241076723968220.58231014.93

221202241106724640230.59234010.38

320102251106824750210.54226512.69

419752201106824200200.52

52045223110682453020.20.52

61925223110682453020.40.53

Table 4.18: 90% FA- 10 % LIME (28 DAYS)Brick NoWeight (g)Length (mm)Width (mm)Height (mm)Area (mm2)Load (KN)Strength (N/mm2)Soaked (1 day) (g)AbsorptionShape

Good FairPoor

11610225108682430022.50.59

21760228108672462423.80.61

31640228109682485227.60.70

419952251086724300260.68

51925227110682497028.50.72

61630228109672485227.90.71

DiscussionFly Ash CompositionThe chemical composition of the fly ash was determined and presented as metal oxide composition and the amount of unburned carbon was measured as the loss on ignition (LOI) value. The chemical composition indicated that the fly ash samples contained three major oxides (SiO2, Al2O3, and Fe2O3). The values of SiO2, Al2O3, Fe2O3 and CaO are consistent with values for bituminous coal however the value LOI of 29.88% is outside the typical the values. The amount of unburnt carbon is a function of type of coal; operational parameters (O2level, residence time of coal particles inside the furnace, turbulence, and furnace temperature profile) and coal fineness. The high carbon content has the potential of increasing the water absorption of the brick. It may also allow water to flow through the brick thereby reducing its strength. Particle size analysis showed that the fly ash had less fine material than specified in relevant standards. The coarser gradation of the FA resulted in less reactive ash and was also a contributing factor to the high carbon content. The XRF analysis results showed that the fly ash contained 0.93% CaO hence it was classed as class F fly ash. As already stated class F fly ashes only have pozzolanic properties and require an activator in order to exhibit cementitious properties. Effect of AdmixturesWhen the results in the tables are examined, one of the first observations is the increase in strength and improvement in water absorption when admixtures are added to the mix. These two properties will now be investigated separately in the following sections.

Water Absorption The tables (4.3-4.18) show results of water absorption of the 8 mixes. The control bricks (100% Fly Ash) disintegrated when immersed when immersed in water and the absorption percentage was taken as 100. As the admixtures were added, there was a marked improvement in the water absorption of the bricks. Further, the water absorption improved as the percentage of admixture increased for both cement and lime. This observation was in line with the expectation that admixtures improve the water absorption of fly ash bricks.Table 5.1: summary of water absorption resultsFA-Cement (%)FA-Lime (%)

Mix (%)7 Days28 days7 Days28 days

60-406.5719.201.907.81

70-3012.4027.0711.1115.04

80-2018.0334.569.9018.19

The results show that both the FA-Cement and FA-Lime bricks have lower water absorption rates at 7 days than at 28 days. As already stated, the bricks were dried in doors for the first three days before being taken out and sun dried hence the higher absorption percentage at 28 days. At 28days, the water added in fresh state had evaporated and the matrix was basically dry, hence bricks absorbed more water.

Figure 5.1: variation of water absorption with age The results of the water absorption test also show that the FA-lime bricks have better water absorption than FA-Cement bricks. This leads to the conclusion that lime is a better admixture in terms of water absorption as compared to cement at both ages. Figure 5.2: variation of water absorption with admixture typeMBS 6:1994, burnt clay bricks specification recommends a maximum water of 4.5% and 7% for class A and class B engineering bricks respectively. The standard does specify any limit for water absorption values for common and industrial load bearing bricks however a limit of 20% is generally used. Comparing these recommended values with the results shows that all the mixes fail for both classes of engineering bricks. All the FA-Lime bricks (except the 90% FA- 10% Lime mix) have water absorption values below 20% hence they can be described as quality bricks. On the other hand, only the 60% FA-40% Cement mix has water absorption below 20% with the rest of the mixes having higher values. Compressive Strength Table 5.2 presents the results of the compressive strength of the fly ash bricks at 7 and 28 days. As seen from the table, compared to the control mix, the admixtures improved the strength of the bricks. The control mix had an average strength of 0.14N/mm2 and 0.17N/mm2 at 7 and 28 days respectively. The results also show that the compressive strength of all the bricks increased as the amount of admixture increased regardless of the age of the bricks.Table 5.2: summary of compressive strength resultsFA-Cement (N/mm2)FA-Lime (N/mm2)

Mix7 Days 28 Days7 Days28 Days

60-406.469.932.114.03

70-303.013.911.623.73

80-201.141.341.363.23

90-100.320.360.550.67

The results further show that both FA-Cement and FA-Lime bricks have higher strength at 28 days than at 7 days. The strength in FA-Limes bricks is due to the formation of hydrates from the reaction of lime with oxide components like silica, alumina and iron oxide in the presence of water. Ma and Brown (1997) showed that the amount of free CaO in FA-Lime was directly related to the strength of the mix and that as FA-lime reactions progress, the amount of free CaO dropped producing a stronger mix. Basumajumdar, Das, Bandyopadhyay, & Maitra, 2005 carried out a study that showed that the amount of free CaO in FA-Lime mix decreases with time. This shows that the results obtained from the tests are in line with previous research and that the development of strength in FA-Lime bricks is gradual. It was noted that strength development in the FA-Cement bricks was directly influenced by cement. Fly ash is less reactive than cement hence the strength of the bricks decreased with increasing amount of FA used. The gradual development of strength of the bricks was due the slow nature of the pozzolanic reaction between FA and Cement. Figure 5.3: variation of free cAo with Time

Figure 5.4: Compressive Strength Variation With Age

Figure 5.5: Compressive Strength Variation With AgeFurthermore, the results show that the FA-Cement bricks have higher strength than the FA-Lime bricks at mixes of 60-40 and 70-30 while the FA-Lime bricks have superior strength at mixes of 80-20 and 90-10. The higher strength of the FA-Cement bricks may be due to bonds with higher strength than the calcium silicate hydrate bonds formed in the FA-lime bricks. At lower concentrations of cement and lime, the FA-lime mixes might have had higher free CaO concentration hence the higher strength. This is illustrated in the figures below.

Figure 5.6: Compressive strength variation with admixture type

Figure 5.7: Compressive strength variation with admixture typeComparing the results obtained with values in MS 6 shows that the bricks qualify for class 30-75 in the common and industrial load bearing bricks as shown in the table below.

Table 5.3: comparison of fly ash bricks with standard valuesDesignationClassCompressive Strength (N/mm2), min Water Absorption % by mass, maxBricks Qualified

FA-CementFA-Lime

Load bearing bricks757.5-10not specified60-40 (28 days)

505.0-7.560-40 (7 days)

353.5-5.070-30 (28 days)70-30 (28 days)

303.0-3.580-20 (28 bays)

ConclusionAs result of this experimental study, the following conclusions could be made: The fly ash used in the study had a small percentage of particles finer than 45 m hence it had reduced reactivity. In addition the fly also had a small percentage of CaO resulting in reduced reactivity. The high proportion of LOI resulted in reduced reactivity and also increased water absorption. From these characteristics it can be concluded that the fly ash used in the study was a poor raw material. The addition of admixtures to fly ash bricks reduces their water absorption. The improvement continues with increased amount of admixture. The study showed that cement was a better admixture in terms of water absorption as compared to lime. The FA-Lime water absorption values at 28 days ranged from 7.81 to 18.19 % while FA-Cement values ranged from 19.2- 34.56 %. Four out of the eight admixture mixes qualify as usable bricks when a 20% absorption limit is adopted. The addition of cement and lime to fly ash increases the compressive strength of the fly ash bricks. Cement proved to be a better admixture at high concentrations (60-40 and 70-30) while Lime was better at lower concentrations (80-20 and 90-10). The compressive strength values at 28 days ranged from 0.36-9.93 N/mm2 and 0.67- 4.03 N/mm2 for the FA-Cement and FA-Lime bricks respectively. The results showed that 5 out of the 8 mixes prepared had strength above 3.5 N/mm2 and therefore were of acceptable quality as per MBS standard requirements. Overall, from the study it can be concluded that masonry bricks can be made from fly ash mixed with either cement or lime. The bricks have sufficient strength and water absorption characteristics to be used as load bearing bricks for common and industrial use as per MBS: 6 requirements. However, only the 60% FA- 40% cement bricks have sufficient strength to be used as masonry units according to the Blantyre City Assembly Building Regulations Code of Practice (table 9.2) which specifies a minimum compressive strength of 7.0 N/mm2.

Recommendations The quality of fly ash bricks depends on the quality of raw materials, proportioning of raw materials, handling and mixing of raw materials hence the following recommendations can be made from the study: The quality of fly used for masonry brick production should be improved. This can be achieved by using pulverised coal instead of pea size coal. This will improve the fineness of the fly ash and the CaO content. Pulverised coal also burns more efficiently than pea size coal hence reducing the LOI content of the fly ash. The quality of the fly ash can also be improved by grinding the fly ash to improve the fineness and benefication of the fly ash to reduce the carbon content. Ordinary Portland Cement (OPC) should be considered in the production of fly ash bricks as it has a higher CaO content than the cement used for study. Use of OPC could result in higher compressive strengths for the bricks. In this study, no compaction was in the manufacture of the bricks since the focus was on the strength development of the FA and admixtures. Further research should be carried out to find out the effect of compaction on the quality of the bricks. There is need for further research on the effect of curing methods on the quality of FA bricks. It is important to remember that before FA bricks can be commercially produced, there is need to conduct an economic assessment and evaluate the critical economic factors in using fly ash and selected admixtures as raw materials for masonry brick production. In addition, there is need to conduct an environmental feasibility study to ensure that the product does not have detrimental effects on the environment.

ReferencesBasumajumdar, A., Das, A. K., Bandyopadhyay, N., & Maitra, S. (2005). Some Studies on the Reaction Between Fly Ash and Lime. Bulletin of Materials Science, 131-136.British-Standards-Institution. (2005). Fly Ash for Concrete-Part 2: Conformity evaluation. London: British Standards Institution.British-Standards-Institution. (2007). Fly Ash for Concrete-Part 1: Definitions, specifications and conformity criteria. London: British Standards Institution.Bureau of Indian Standards. (1993). Burnt Clay Fly Ash Building Bricks - Specification. New delhi: Bureau of Indian Standards.Bureau-of-Indians-Standards. (1992). Methods of Tests of Burnt Clay Building Bricks. New Delhi: Bureau of Indian Standards.Bureau-of-Indian-Standards. (1990). Fly Ash-Lime Bricks - Specification. New Dellhi: Bureau of Indian Standards.Chou, M.-I., Chou, S.-F., Patel, V., Pickering, M., & Stucki, J. (2006). Manufacturing Fired Brick With Class Fly From Illinois Basin Coals. Illinois: US State Geological Survey .Chudley, R., & Greeno, R. (2007). Construction Technology. London: Pearson Education Limited.Dighade, R. R., Ambekar, S. V., & Pande, A. M. (1999). Fly Ash Lime Gypsum Bricks. Fly Ash Utilisation for Value Added Products, 54-58.Liu, H., Burkett, W., & Haynes, K. (2005). Improving Freezing and Thawing Properties of Fly Ash Bricks. Lexington, Kentucky: World of Coal Ash.Liu, H., Burkett, W., Haynes, K., & VanEngelehoven, J. (2009). Environmental Properties of Fly Ash. Lexington,Kentuky: World of Coal Ash (WOCA).Malawi-Standards-Board. (1994). Burnt Bricks - Specification. Blantyre: Malawi Standards Board.Sivapullaiah, P. V., & Moghal, A. A. (2011). Role of Gypsum in the Strength Development of Fly Ashes with Lime. Journal of Materials in Civil Engineering, 210-219.Taylor, G. D. (2002). Construction Materials. London: Pearson Education Limited.Team-Envis. (2007, January 4). Utility Bonanza from Fly Ash. Parisara. Bangalore, Karnataka, India: Department of Forests, Ecology and Environment.U.S.-Geological-Survey. (1997). Radioactive Elements in Coal and Fly Ash:Abundance, Forms and Environmental Significance. Denver: U.S. Geological Survey.

Appendix aTable 9.1:Fly ash particle size distribution

InitialMass Retained (g)PercentageCumulative

Dry Mass (g)ActualCorrectedRetained% Passing

m1510M(m/m1)x100

75mm

63mm

50mm00.00.0100.0

37.5mm00.00.0100.0

20mm00.00.0100.0

Passing 20mmm2510

Total(Check with m1)510

Riffledm3260

Riffled and washedm4260

Correction factor(m2/m3)1.9615

14mm00.00.0100.0

10mm00.00.0100.0

5.0mm00.00.0100.0

Passing 5.0mmm5260

Total (Check with m4)260

Riffledm6260

Correction factor(m2/m3)x(m5/m6)1.9615

1.18mm00.00.0100.0

0.6mm1529.45.894.2

0.425mm2549.09.684.6

0.300mm1529.45.878.8

0.212mm2039.27.771.2

0.150mm2039.27.763.5

0.063mm55107.921.242.3

0.045mm95186.336.55.8

Passing 45m(Pan)1529.45.80.0

APPENDIX bProject Pictures

Figure 9.1:Indoor Curing of Bricks

Figure 9.2: Outdoor Curing of Bricks

Figure 9.3: Internal Structure of Brick