UNIVERSITY OF NAIROBI

A Research on the use of Saw Dust Ash as a Potential Partial

Cement Replacement Material

By Akhubi A. Ochango, F16/3908/2009

A project submitted as a partial fulfillment for the requirement for the

award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2014

i

Abstract

The sustainable utilization and minimization of industrial and domestic wastes provides secondary

raw materials that lead to sustainable technologies. This research proposal looked into the viability

of the use of saw dust ash as a partial cement replacement material and compared the fresh and

hardened concrete properties of the saw dust ash concrete and Portland cement concrete. The

methodology of the study was mainly laboratory testing of the materials.

The scope of the research covered the potential of using saw dust ash in Kenya as a cement

replacement material. From the research, it was found out that saw dust ash concrete compared

well with Portland cement concrete up to 10% cement replacement. Further replacement, however,

would be detrimental to the strength of the concrete. The saw dust ash concrete was also found to

be cheaper and friendlier to the environment than Portland cement concrete in proportion to the

percentage of cement replaced. The main recommendation therefore was to replace cement with

10% saw dust ash as this particular proportion of replacement would enable cost savings, reduction

of environmental pollution and achievement of normal strength concrete as well.

The findings of this research call for the safe use and disposal of saw dust and its ash and should

also ignite an interest in the cement industry to produce cement that is friendlier to the environment

– “green cement”.

ii

Dedication

This project is dedicated to my parents, Mr. and Mrs. Akhubi for their support and encouragement

throughout my life to date.

iii

Acknowledgement

I wish to acknowledge the immense contribution of my supervisor Mrs. Monica Wokabi for her

support and guidance throughout this project from its inception to completion.

I also appreciate the support I received from the laboratory technicians: Mr. Muchina (Concrete

Lab); Mr. Ruto (Timber Lab); Mr. Mwangi (Chemistry Lab) and Mr. Bartiloi (Nuclear Science

Lab).

My classmates who assisted me and peer-reviewed my project also played a very vital role towards

its successful completion.

iv

Table of Contents

Abstract........................................................................................................................................................ i

Dedication ................................................................................................................................................... ii

Acknowledgement ..................................................................................................................................... iii

List of Tables ............................................................................................................................................. vi

List of Figures ........................................................................................................................................... vii

List of Plates ............................................................................................................................................ viii

List of Acronyms ....................................................................................................................................... ix

Chapter One ................................................................................................................................................ 1

1.0 Introduction ....................................................................................................................................... 1

1.1 Problem Statement ........................................................................................................................ 2

1.2 Purpose of the Study ..................................................................................................................... 2

1.3 Significance of the Study .............................................................................................................. 3

1.4 Delimitations of the Study ............................................................................................................ 3

1.5 Limitations of the Study ................................................................................................................ 3

Chapter Two ............................................................................................................................................... 4

2.0 Literature Review.............................................................................................................................. 4

2.1 Overview ....................................................................................................................................... 4

2.2 Microstructure of Concrete ........................................................................................................... 4

2.3 Manufacture of Portland Cement .................................................................................................. 9

2.4 Steps in the manufacture of cement............................................................................................. 10

2.5 Environmental effects of the Manufacture of Cement ................................................................. 12

2.6 Specialized Types of Cement ...................................................................................................... 14

2.7 The Use of Wood Ash in Cement Replacement .......................................................................... 20

Chapter Three ........................................................................................................................................... 22

3.0 Methodology ................................................................................................................................... 22

3.1 Overview ..................................................................................................................................... 22

3.2 Mix Design ................................................................................................................................. 22

3.3 Preparation and Tests on Saw Dust Ash ...................................................................................... 30

v

3.4 Tests on Aggregates .................................................................................................................... 33

3.5 Tests on Properties of Fresh Concrete ......................................................................................... 34

3.6 Tests on Properties of Hardened Concrete .................................................................................. 35

3.7 Desk Studies ............................................................................................................................... 36

3.8 Data Collection Aids ................................................................................................................... 36

Chapter Four ............................................................................................................................................. 38

4.0 Results ............................................................................................................................................ 38

4.1 Saw Dust Ash Tests .................................................................................................................... 38

4.2 Tests on Aggregates .................................................................................................................... 41

4.3 Tests on Properties of Concrete................................................................................................... 43

4.4 Desk Study .................................................................................................................................. 45

Chapter Five ............................................................................................................................................. 49

5.0 Analysis and Discussion ................................................................................................................. 49

5.1 Objectives ................................................................................................................................... 49

5.2 Properties of SDAC .................................................................................................................... 49

5.3 Properties of Saw Dust Ash ........................................................................................................ 59

Chapter Six ............................................................................................................................................... 63

6.0 Conclusion and Recommendations ................................................................................................. 63

6.1 Conclusion .................................................................................................................................. 63

6.2 Recommendations ....................................................................................................................... 64

Bibliography ............................................................................................................................................. 65

Appendices ............................................................................................................................................... 68

A1: Preparation and testing of fresh concrete ....................................................................................... 68

A2: Testing of hardened concrete ......................................................................................................... 70

A3: Hydrometer analysis ...................................................................................................................... 71

vi

List of Tables

Table 1: Proportions of Raw Materials used in the production of cement ................................................ 10

Table 2: Slump Ranges for Specific Applications .................................................................................... 25

Table 3: Approximate Mixing Water and Air Content Requirements ...................................................... 26

Table 4: Water-Cement Ratio and Compressive Strength Relationship ................................................... 27

Table 5: Volume of Coarse Aggregate per Unit Volume of PCC............................................................. 28

Table 6: Table for collection of specific gravity of saw dust ash data ...................................................... 36

Table 7: Table for collection of hydrometer analysis data........................................................................ 37

Table 8: Table for collection of data of particle size distribution of fine/coarse aggregates ..................... 37

Table 9: Results of the specific gravity of saw dust ash .......................................................................... 38

Table 10: Results of Hydrometer Analysis of saw dust ash ..................................................................... 39

Table 11: Results of XRF Test on digested saw dust ash ......................................................................... 40

Table 12: Results of the sieve analysis of fine aggregates ........................................................................ 42

Table 13: Results of the sieve analysis of coarse aggregates .................................................................... 43

Table 14: Results of the workability tests for fresh concrete .................................................................... 43

Table 15: Results of the compression test for hardened concrete ............................................................. 44

Table 16: Results of the splitting tensile test for hardened concrete ......................................................... 44

Table 17: Results of the flexural test for hardened concrete..................................................................... 45

Table 18: Cost comparison of various proportions of mixes of SDAC and PCC ..................................... 45

Table 19: Approximation of the reduction in CO2 emission .................................................................... 48

Table 20: Compressive strengths of hardened concrete ........................................................................... 53

Table 21: Splitting tensile strengths of hardened concrete ....................................................................... 55

Table 22: Flexural strengths of hardened concrete ................................................................................... 56

vii

List of Figures

Figure 1: An electron micrograph of the interfacial transition zone .......................................................... 8

Figure 2: A diagrammatic representation of the interfacial transition zone ................................................ 8

Figure 3: A summarized flow chart for the manufacture of Portland cement ........................................... 12

Figure 4: Comparison of particle size distribution of cement, fly ash and silica fume ............................. 18

Figure 5: Standard deviation of characteristic strength of concrete ......................................................... 23

Figure 6: Wavelength dispersive XRF spectrum of the digested saw dust ash sample............................. 41

Figure 7: A graph of slump vs. % cement replacement ............................................................................ 51

Figure 8: Graph of compaction factor vs. % cement replacement ............................................................ 51

Figure 9: Correlation of compaction factor and slump ............................................................................. 52

Figure 10: Graph of compressive strength development .......................................................................... 54

Figure 11: Graph of splitting tensile strengths ......................................................................................... 57

Figure 12: Graph of flexural strengths ..................................................................................................... 57

Figure 13: Grading curve for saw dust ash............................................................................................... 60

Figure 14: Grading curve for fine aggregates .......................................................................................... 61

Figure 15: Grading curve for coarse aggregates....................................................................................... 61

viii

List of Plates

Plate 1: Burning of saw dust to ash using open kiln process .................................................................... 30

Plate 2: Specific gravity test on saw dust ash sample ............................................................................... 31

Plate 3: Hydrometer analysis on saw dust ash .......................................................................................... 31

Plate 4: Saw dust ash passing Seive No. 200 ........................................................................................... 32

Plate 5: Heating of reagents in fume chamber .......................................................................................... 33

Plate 6: Sieve analysis of fine aggregates ................................................................................................. 34

Plate 7: Slump test ................................................................................................................................... 35

Plate 8: True slump for fresh concrete .................................................................................................... 50

Plate 9: Spalling in 28 day control cube under compression test .............................................................. 58

Plate 10: Main fracture plane of 28 day control cylinder under splitting tensile test ................................ 58

Plate 11: Major crack from soffit of 28 day control beam under flexure test ........................................... 59

ix

List of Acronyms

ACI – American Concrete Institute

ASTM – American Society for Testing and Materials

BS – British Standards

EACPA – East Africa Cement Producers Association

KS – EAS – Kenyan Standards

NESC – National Economic and Social Council

OPC – Ordinary Portland Cement

PCC – Portland Cement Concrete

SDAC – Saw Dust Ash Concrete

XRF – X-ray Fluorescence

1

Chapter One

1.0 Introduction

Globally, the only substance people use the most in massive volume more than cement is water.

This is because cement is an excellent building material, being inexpensive, pourable and also

hardens as rock overtime. The only problem is that cement is dirty as it pollutes the environment.

This is because the main constituent of cement is limestone which is the main contributor to the

pollution caused by the manufacture and use of cement.

The limestone is preferred as it is readily available and is found in most countries. Also, the

limestone is easily obtained by means of excavation from the ground. In the manufacturing

process, the limestone is heated to get the required mineral, calcium carbonate, which is a major

ingredient in cement manufacture.

Limestone is preferred as it contains a large amount of calcium carbonate, being the remains of

shelled marine creatures. The limestone requires heating which uses up fossil fuel. When heated,

the limestone gives off carbon dioxide which contributes to the greenhouse gases. Unfortunately,

cement’s huge contribution to air pollution is overlooked by the general public (Rosenwald, 2011).

Limestone is used as it contains calcium carbonate which on heating (calcination), forms calcium

oxide which is the main chemical ingredient in the manufacture of both hydraulic and non-

hydraulic cement.

Having established some basic chemistry as pertaining to the reactions involved in the manufacture

of cement, a good question to ask is how the same benefits derived from cement can be achieved

while the cement remains friendly to the environment. The answer lies in using a substance that is

less pollutant to the environment but which can achieve the same mineral constituents as those

brought about by limestone.

A contemporary popular way has been the use of ash, a good example being the construction of

the Hoover Dam in the United States in which fly ash from the steel manufacturing industries was

largely used as a cement replacing material.

2

A lot of research has been put into the study of ash from steel manufacturing industries and this

has provided a lot of information and positive steps into the replacement of cement with fly ash

from the steel manufacturing industries. Much, however, remains to be researched as pertaining

the use of timber ash as a cement replacement alternative.

1.1 Problem Statement

The use of cement is a huge contributor to greenhouse gases and the resultant associated global

warming. This is brought about by the manufacturing process in which limestone is used

extensively. The limestone, however, is an important ingredient to the cement manufacturing

process given it contains the vital compound needed, that is calcium carbonate. If the same quality

of cement, especially in terms of strength, can be obtained with little or no limestone used, then

this would mitigate against the negative environmental impacts that the limestone has. The cost of

cement is also on the rising trend (Waithaka, 2014) due to increased demand and rising mining

levies and a solution to this increase in prices would be a relief to the consumers of cement in the

construction industry.

This study therefore shall set to look into the viability of using saw dust ash as a partial cement

replacement to mitigate against the pollution problem and also provide a cheaper concrete.

1.2 Purpose of the Study

The objectives of the research are:

i. To analyze the properties of the saw dust ash concrete as compared to Portland cement

concrete.

ii. To test some of the properties of saw dust ash.

iii. To do a cost comparison of the saw dust ash concrete with Portland cement concrete.

iv. To approximate the reduction of carbon emissions that would result from the use of saw

dust ash as a partial replacement to cement.

The research shall seek to find out the mineral composition of saw dust ash and further test it as a

cement replacement alternative. The research shall also seek to find out the optimum mix design

for the use of saw dust ash as a partial replacement of cement.

This study shall positively contribute to future advances in green cement production in which the

use of limestone will have been reduced or eliminated altogether.

3

1.3 Significance of the Study

As aforementioned in the purpose of the study, the significance of this study will impact the

industry both theoretically and practically, thus adding to the knowledge-base on the use of timber

ash and ash in general as a cement replacement alternative and also add more potential for modified

cement products to the industry that can be of the same use as ordinary cement.

In Kenya, the Vision 2030 blueprint for the development of the country focuses more on

infrastructure given that infrastructure is the first item in Chapter 2 that outlines the foundations

for Socio-Economic Transformation (Kenya: Vision 2030, 2007). Infrastructural development is

positively correlated with cement demand thus it would follow that advances towards greener

cement would help prevent the increased environmental pollution that would be bought about by

the infrastructural development.

It therefore should be in order that all advances towards greener cement would be beneficial for

our Kenyan economy at this particular point in time where all projections and trends as far as

infrastructural development and cement demand is concerned are positive (Davidson, 2013).

1.4 Delimitations of the Study

This study focused on saw dust ash therefore a delimitation was the availability of the timber ash.

It was also limited to Kenya, being a country that uses timber as fuel and furnishing, and may not

be applicable to other countries that do not use timber as much.

1.5 Limitations of the Study

The ash obtained from timber was not consistent as the burning temperature was not constant.

Also, obtaining the saw dust in sufficiently large quantities was a challenge and it had to be sought

from a large saw mill. These large saw mills may not be present in some areas of the country.

Some producers of timber waste and timber ash also preferred using the ash for agricultural

purposes and as such they may not consider using it in cement replacement (Hume, 2006).

These limitations may be overcome by training and information being provided on the use of

timber ash in cement replacement.

4

Chapter Two

2.0 Literature Review

2.1 Overview

A cement is a binder. It is a substance that sets and hardens independently and can bind other

materials. The most important use of cement is as an ingredient in the production of mortar in

masonry and concrete. Cement is made by heating limestone (calcium carbonate) with small

quantities of other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination,

whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium

oxide, or quicklime, which is then blended with the other materials that have been included in the

mix. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum

into a powder to make 'Ordinary Portland Cement', the most commonly used type of cement (often

referred to as OPC). Portland cement is a basic ingredient of concrete, mortar and most non-

specialty grout. The most common use for Portland cement is in the production of concrete.

Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As

a construction material, concrete can be cast in almost any shape desired, and once hardened, can

become a structural load bearing element (Portland Cement, 2014).

2.2 Microstructure of Concrete

Modern Material Science focuses more on the microstructural composition of concrete (Mehta &

Monteiro, 2006). In order to exercise some control on the properties of concrete, a knowledge of

the microstructural composition and properties is necessary. The microstructural properties of

concrete are vital when it comes to the overall strength, dimensional stability and durability of

concrete.

Definition wise, the microstructure of concrete is the type, amount, size, shape, and distribution of

phases present in it (Mehta & Monteiro, 2006). The gross elements of the microstructure of

concrete may be seen by cutting through a cross-section thereof while the finer elements are

usually resolved by the help of a microscope. For the gross elemental view, the term

macrostructure is usually used while the term microstructure is used for the microscopic

magnification of the macrostructure.

5

Even though concrete is the most widely used structural material, its microstructure is

heterogeneous and highly complex. Thus, the microstructure-property relationships in concrete are

not yet fully developed. However, some basic knowledge of the essential elements of the

microstructure of concrete is useful in the understanding of the factors that influence the important

engineering properties of concrete such as strength, elasticity, shrinkage, creep and cracking.

2.2.1 Complexities

An examination of the cross section of concrete would reveal two distinguishable phases, that is,

the aggregate particles of varying size and shape, and the binding medium composed of an

incoherent mass of hydrated cement paste (Mehta & Monteiro, 2006). Thus at the macroscopic

level, concrete may be considered as a two-phase material.

When the structure is observed at the microscopic level, the complexities of concrete are readily

seen. It becomes evident that the two phases of the microstructure are neither homogeneously

distributed nor are they homogeneous themselves.

The unique description of the concrete microstructure can be looked at in three main distinguishing

parts. First, there is the interfacial transition zone which is the region next to the particles of coarse

aggregate. Generally, the interfacial transition zone is weaker than either of the two main

components of concrete. This fact makes this particular zone to be of particular interest when it

comes to the mechanical behavior of concrete. Second, each of the three phases is in itself a multi-

phased component. An example would be the aggregates which contain several minerals, micro

cracks and voids. Third, unlike other materials, the microstructure of concrete is not an intrinsic

characteristic of the material because the two components of the microstructure, the interfacial

transition zone and the hydrated cement paste, are subject to change with time and environmental

properties.

2.2.2 The Microstructure of the Aggregate Phase

The three properties of concrete contributed by the aggregate phase are the unit weight, elastic

modulus and the dimensional stability of concrete. These properties depend upon the bulk density

and strength of the concrete and are thus determined more by the physical rather than chemical

characteristics of the aggregates. This implies that the physical characteristics of the aggregates

supersede the chemical characteristics in importance and overall influence.

6

The shape, texture and porosity of the aggregates affect the properties of concrete. It is also

important to note that the size and shape of the aggregates can affect the strength of the concrete

indirectly. If an aggregate has a large number of particles with large sizes and also a large number

of elongated and flat particles, there will be a higher probability of water films accumulating next

to the aggregate face thus weakening the interfacial transition zone. This phenomenon is known

as bleeding.

2.2.3 The Microstructure of the Hydrated Cement Paste

The hydrated cement paste refers to pastes that are made from OPC. The hydrated cement paste

develops as a result of the chemical reactions between OPC and water. Anhydrous Portland cement

is a gray powder in colour whose particle size ranges from 1 to 50 micrometers. Clinker is heated

to a high temperature together with calcium sulfate and this high temperature results in reactions

between calcium oxide and silica, iron oxide and alumina. The major chemical constituents of the

clinker compounds are C3S, C2S, C3A and C4AF. The approximate percentages of the chemical

constituents may be inferred from Table 1.

Dispersion of OPC in water causes the calcium sulfate and some other compounds of calcium to

go into solution. This causes the liquid to be saturated with ions of calcium. Within a few minutes

of the cement hydration, ettringites appear. These are needle-shaped crystals of calcium

trisulfoaluminate hydrate. They are formed due to the interaction between calcium, sulfate,

aluminate and hydroxyl ions.

Some hours after the dispersion into water, large crystals of calcium hydroxide that are shaped as

prisms and small fibrous crystals of calcium silicate start to fill the empty spaces occupied by

water. After some days, ettringite may become unstable and form monosulfaoaluminate hydrate

with a hexagonal-plate morphology.

The solids that are present in the hydrated cement paste are calcium silicate hydrate, calcium

hydroxide, calcium sulfoaluminate hydrates and unhydrated clinker grains (Mehta & Monteiro,

2006). The types, amounts, and characteristics of these four principal solid phases in the hydrated

cement paste are determined by use of an electron microscope.

7

The hydrated cement paste also contains voids and these are made up of interlayer space in C-S-

H, capillary voids and air voids. These voids have a significant influence on the properties of the

hydrated cement paste. Of particular mention, they adversely affect the strength of the concrete.

Water is also of special mention when it comes to discussing about the hydrated cement paste.

Water may exist in the hydrated cement paste in many forms depending on the difficulty or ease

with which the water may be removed from the cement paste. There are, therefore, four types of

water in the hydrated cement paste. These are: capillary water, adsorbed water, interlayer water

and chemically combined water. The capillary water is the bulk water that is free from the

influence of the attractive forces exerted by the solid surface. Adsorbed water is the one that is

close to the surface. Due to attractive forces, water molecules are adsorbed onto the surface of the

solids in the hydrated cement paste. Interlayer water is closely associated with the C-S-H structure

while the chemically combined water forms an integral part of the microstructure of the cement

hydration products.

2.2.4 The Interfacial Transition Zone in Concrete

This zone exists between the large particles of the aggregate and the hydrated cement paste. It is

treated as a different concrete microstructure as its microstructure and properties differ from those

of the hydrated cement paste. Among the interesting properties of concrete that are attributable to

this zone include:

i. Concrete being brittle in tension and tough in compression.

ii. Concrete being inelastic while its constituent components being elastic when tested

separately.

iii. The compressive strength of concrete being higher than its tensile strength by an order of

magnitude.

iv. Cement mortar being stronger than concrete of the same cement content, water-cement

ratio, and age of hydration.

v. The rapid drop of the elastic modulus of concrete when exposed to fire as compared to its

compressive strength.

8

An electron micrograph of the interfacial transition zone is as shown in Figure 1:

Figure 1: An electron micrograph of the Interfacial transition zone (Source: Mehta P.K. &

Monteiro P.J.2006)

The interfacial transition zone may also be represented as shown in Figure 2:

Figure 2: A diagrammatic representation of the Interfacial transition zone (Source: Mehta P.K.

& Monteiro P.J. 2006)

9

The strength of the interfacial transition zone at any point depends on the volume and size of voids

present. At early stages, the interfacial transition zone may possess a strength lower than that of

bulk mortar but with increasing age, this strength may measure up or even surpass that of the bulk

mortar. This increase in strength may be attributable to formation of new products in the voids

contained in the interfacial transition zone. Poor strength of the interfacial transition zone may also

be caused by the presence of micro cracks.

The interfacial transition zone is generally considered as the strength limiting phase in concrete.

This zone causes the concrete to fail at a lower stress level than that of either of the two main

components. This zone is also responsible for the stiffness/elastic modulus of the concrete.

Durability is also affected by the interfacial transition zone because corrosion occurs in the areas

where there are voids that let in air and water.

2.3 Manufacture of Portland Cement

2.3.1 Introduction

Modern cements, having Portland cement as the main constituent, have the following broad

groupings according to EN 197-1:

i. Portland cement Comprising Portland cement and up to 5% of minor additional

constituents

ii. Portland-composite

cement Portland cement and up to 35% of other single constituents

iii. Blast furnace cement Portland cement and higher percentages of blast furnace slag

iv. Pozzolanic cement Portland cement and up to 55% of pozzolanic

constituents(volcanic ash)

v. Composite cement Portland cement, blast furnace slag or fly ash and pozzolana

In Kenya, cement is made to KS – EAS 18 which conforms to European Standard EN 197-1. The

approximate proportions of the raw materials (oxides) which go into the manufacture of cement

are as outlined in Table 1 (Neville, 2012).

10

Table 1: Proportions of Raw Materials used in the production of cement

Raw

Material

Chemical

composition

Symbol

Designation

Source Proportion (%)

Lime CaO C Limestone/Chalk 60-67

Silica SiO2 S Shale/Clay 17-25

Alumina Al2O3 A Bauxite/Shale 3-8

Iron oxide Fe2O3 F Iron ore 5-6

Not all the raw material contains the required oxides and the proportion of the oxide in the raw

material must be determined by chemical analysis. The content of the oxide in the raw materials

will determine the proportions of the raw materials mixed together to make cement.

2.3.2 Operations in the Manufacture of Cement

The following operations are key in the manufacture of cement.

i. The quarrying of raw material and stock piling at the factory.

ii. Mixing of raw materials in pre-determined quantities.

iii. Grinding of the material into fine powder, a process known as raw mealing.

iv. Homogenizing of the raw meal.

v. Clinkering i.e. burning the raw meal at high temperature to produce hard pellets known as

clinkers.

vi. Grinding the clinker together with any other additive to produce the desired cement.

Grinding of the clinker to fine particles greatly helps in enhancing the strength of concrete

(Hewlett, 2012). Homogenizing of the raw meal can be done by mixing in water (wet process) or

by mixing in dry conditions (dry process). The wet process usually requires additional energy to

dry the raw meal before burning, but reduces dust emissions. Modern technology, however

incorporates efficient dust arrestors making the wet process obsolete.

2.4 Steps in the manufacture of cement

2.4.1 Raw Mealing

This is the process of making raw meal. Pre-determined quantities of raw materials are mixed

together and ground into fine powder known as “raw meal”. After this the raw meal is led to a silo

11

where it is homogenized through thorough mixing. Homogenization is important in that it

enhances the combination of oxides during burning. Regular tests are employed as quality control

measures in the chemical composition and fineness of the raw meal.

2.4.2 Clinkering

This is the process of burning raw meal to produce clinker. The raw meal is fed into a pre-heating

chamber where hot air is blown over it to dry it and make it easy to burn. The raw meal is then led

into a rotary kiln with temperature ranging from 900oC at the inlet to 1450oC at the hottest end.

The kiln is inclined downwards at about 5o and rotated so that raw meal moves slowly towards the

hotter end.

Powdered coal and industrial oil are the major fuels used to provide heat. Between the temperature

ranges of 900oC-950oC, the calcium carbonate in limestone or chalk breaks down to calcium oxide

and carbon dioxide by the equation shown below:

CaCO3 CaO + CO2 {calcining}

It is noteworthy to mention that this process of calcining is a big contributor to the carbon dioxide

that forms a key pollutant in the cement manufacturing process.

Between 1250oC and 1450oC, the oxides combine and fuse into hard pellets known as clinkers.

The clinker is then cooled by blowing cold air over it and is then led into a shed for storage. The

air used to cool the clinker heats up and is used to preheat the raw meal before burning.

2.4.3 Grinding

This is the process of crushing clinker to produce cement. The chemical composition and fineness

of cement is closely monitored at all times during the grinding process.

2.4.4 Packaging

After grinding is complete, the cement produced can be stored in silos or fed into specialized

cement trucks for immediate delivery. The other option is to package the cement into bags of 25kg

or 50kg with the details of the cement type printed on the bags.

The processing may be summarized in the flow chart in Figure 3.

12

Figure 3: A summarized flow chart for the manufacture of Portland cement

2.5 Environmental effects of the Manufacture of Cement

In all stages of its manufacture, Portland cement causes pollution of the environment. These

include emission of airborne pollution in the form of dust and gases which are the foremost

pollutants. The other forms of pollution arise due to the vibration of the blasting equipment, release

of CO2, consumption of large portions of fossil fuels and the damage of land masses due to

quarrying. All these forms of pollution contravene the foremost principle in the Kenyan

Environmental Management and Coordination Act: “Every person in Kenya is entitled to a clean

and healthy environment and has the duty to safeguard and enhance the environment”

(Environmental Management and Co-ordination Act, 1999). There is, therefore need to mitigate

the pollution arising from the manufacture of cement.

The amount of CO2 produced in concrete is directly proportional to the amount of cement used in

the concrete mix. 900 kg of CO2 are produced for the fabrication of every ton of cement

(Mahasenan, Natesan, Smith , Humphreys, & Kaya, 2003).

Of all the pollutants in the cement manufacturing industry, CO2 gas emission is the most prevalent.

This particular pollutant is produced in three distinct processes:

13

i. Source 1: CO2 produced by the decarbonation of limestone in the calcining process (US

Department of Energy, 2006).

ii. Source 2: CO2 produced by the kiln fuel combustion.

iii. Source 3: CO2 produced by the vehicles in the cement manufacturing plant and that

produced by the vehicles used in the distribution of the already manufactured cement (The

Cement Sustainability Initiative, 2007).

Of all the three sources, source 1 is fairly constant with an average production of about 0.5 kg of

CO2 produced for every kg of Portland cement produced. It is this source that makes the cement

manufacturing process dirty as far as pollution of the environment is concerned.

Source 2 is dependent upon the efficiency of the manufacturing plant and the mitigating measures

that the plant has in place. The low efficiency wet process (which has since been done away with)

results in the production of CO2 at the rate of about 0.65 kg per kg of cement produced. The amount

of CO2 that results from the modern practices average about 0.30kg per kg of cement produced

while the amount of overall gases produced by the kiln would average as high as twice the amount

of cement produced (Hewlett, 2012). The installation of filters in the kilns also helps greatly in the

reduction of the amount of the CO2 produced in the kiln fuel production process (Peray, 1998).

Source 3 is relatively insignificant when compared with the former two. It results to about 0.08 kg

of CO2 produced with every kg of finished cement.

2.5.1 Mitigation Measures

Cement manufacturing companies have of late tried to mitigate against the pollution caused by the

industry by including gas filters in their chimney designs so as to trap the emission gases that are

otherwise thrown off into the atmosphere. Trap filters have also been installed and used to trap

dust in the quarrying process so as to reduce the dust emission.

There has also been efforts to reclaim defaced pieces of land as a result of quarrying. A good

example of successful reclamation in Kenya is the Haller Park in Bamburi, Mombasa that was

reclaimed by Lafarge, Bamburi Kenya to create a wildlife habitation which has grown in fame and

has attracted both local and international tourists.

14

With the improvements in the energy sector and efficient manufacturing processes such as the

Kalina cycle, the overall CO2 generation can be as low as 0.7 kg per kg of cement produced.

Innovation helps in the reduction of sources 1 and 2 through improved chemistry of cement,

utilization of wastes such as ashes and adoption of more efficient processes.

In some applications, lime mortar, which reabsorbs the same amount of CO2 that was produced in

its manufacture, is used other than ordinary cement that doesn’t possess this ability. Other types

of contemporary cements such as Novecam (Imperial Innovations, 2011) and Ecocement (Eco-

cement, 2013) also have the ability to absorb CO2 from ambient air during the hardening process

(Alok, 2008).

This research also aims at mitigating the negative effects of the manufacture and use of OPC as

the cement replacement will help in the reduction of mainly sources 1 and 2 which are the main

causes of pollution.

2.6 Specialized Types of Cement

Over the years, specialized cements have been manufactured which have specialized

characteristics. This has been achieved by the use of admixtures. Admixtures are additives to

concrete other than the usual cement, water and aggregates. The admixtures are added before,

during or after the mix. The chief purpose of the admixtures is to reduce the cost of concrete and

the other purposes include:

i. To modify the properties of hardened concrete.

ii. To ensure the quality of concrete during mixing, transportation, placing and curing.

iii. To overcome emergent situations during concrete operations.

2.6.1 Functions of Admixtures

The classification of admixtures is done according to the purpose of the admixtures. As far as

chemical admixtures are concerned, there are five distinct kinds of admixtures: air-entraining,

water-reducing, retarding, accelerating and plasticizers. There is another special category of

admixtures into which all the other admixtures fall. This group has admixtures with a number of

functions such as corrosion inhibition, reduction of shrinkage, workability enhancement, bonding,

damp proofing and colouring (Portland Cement Association, 2013).

15

2.6.1.1 Retarding Admixtures

These slow down the setting of concrete and are used especially in the hot regions. This in turn

eases up placing and finishing which would otherwise be hard to achieve in the hot regions. Thus

the concrete is made workable during placement. Many retarding admixtures also serve as water

reducers and may entrain some air in the concrete.

2.6.1.2 Accelerating Admixtures

Accelerating admixtures increase the rate of early strength attainment in concrete. They work in

the opposite way that the retarding admixtures work and are used in the cold weather. They assist

in reducing the time required for proper curing and protection

2.6.1.3 Super Plasticizers

These are high range water reducers. They reduce water required by 12 to 30 percent (Portland

Cement Association, 2013). The effect of the plasticizer lasts for 30 to 60 minutes, depending on

the brand and the dosage rate and this is followed by rapid reduction in workability. For this reason

and coupled with the fact that plasticizers result in slump loss, they are usually added at the jobsite.

2.6.1.4 Corrosion Inhibiting Admixtures

These fall in the special admixture category and are added to slow down the corrosion of

reinforcement steel in concrete. They are used as a defensive strategy in marine structures,

highways and parking garages and anywhere else where the concentration of chloride is expected

to be high.

2.6.2 Naturally Occurring Pozzolans

Most of the naturally occurring pozzolans are derived from volcanic activity. During an explosive

volcanic eruption, quick cooling of the magma, composed mainly of aluminosilicates, results in

the formation of glass or vitreous phases with a disordered structure. During the solidifying of

magma, the evolution of gases causes a porous texture and high surface area in the resulting rock.

This enhances the chemical reactivity of the resultant rock. Aluminosilicates with a distorted

structure are unstable in alkaline solutions thus the high reactivity of volcanic glasses with lime or

Portland cement in an aqueous environment.

2.6.2.1 Volcanic Glasses

In volcanic glasses, small amounts of nonreactive crystalline minerals are generally found

embedded in the glassy mixture. Examples of these minerals are quartz, feldspar and mica.

16

Examples of materials that derive their lime-reactivity characteristics mainly from unaltered

aluminosilicate glass are Santorinin Earth of Greece, Bacoli Pozzolan of Italy and Shirasu

Pozzolan of Japan.

2.6.2.2 Volcanic Tuffs

Volcanic tuffs are usually a by-product of alteration of volcanic glass. Zeolite tuffs are fairly strong

and can possess compressive strengths on the order of 10 to 30 MPa. The cementitious

characteristics of volcanic tuffs are akin to those of volcanic glasses.

2.6.2.3 Calcined Clays or Shales

Clays and shales do not show appreciable reactivity with lime until the crystal structures of the

clay minerals are destroyed by heat treatment. The temperature of the heat treatment usually varies

from between 600˚ to 900˚ C and it serves to distort the aluminosilicate structure of the clays thus

enhancing the pozzolanic activity of the clay or shale.

2.6.3 The Use of By-Product Materials

Many industrial by-products are useful as mineral admixtures in Portland cement concrete. This

helps reduce the mass of wastage from the industries that would otherwise become pollutant while

at the same time assisting the cement industry come up with new innovative types of cements.

2.6.3.1 Iron Blast-furnace Slag

In the production process of cast/pig iron, when the slag is cooled slowly in air, the mineral

components present usually do not react with water. These minerals are present as crystalline

melilites (C2AS-C2MS2 solid solution). This material is nominally pozzolanic when ground to fine

powder. If the liquid slag is rapidly quenched, the resultant solid is of a noncrystalline or glassy

state and is usually called granulated or pelletized slag depending on the appearance of the solid.

Generally, particles of slag that are less than 10 µm contribute to early strength of concrete up to

28 days; particles of 10 to 45 µm contribute more to later strength, while particles coarser than 45

µm are difficult to hydrate.

2.6.3.2 Silica Fume

Silica fume is also known as condensed silica fume, micro silica or volatilized silica. It is a

byproduct of the induction arc furnaces in the silicon metal and ferrosilicon alloy industries.

Compared to normal Portland cement and typical fly ashes, silica fume particles show particle size

distribution of two orders of magnitude finer (Figure 4). Silica fume is highly pozzolanic but its

17

major disadvantage is that it increases the water requirement of concrete appreciably if water

reducing admixtures are not utilized in mitigation.

2.6.4 The Use of Ash in Cement Replacement

As early as 1914, the potential of ash in cement replacement was discovered and early use of fly

ash begun in 1937 (Halstead, 1986).

2.6.4.1 The use of Fly Ash

Fly ash was discovered early in the 20th century as a good cement replacement material. The

aqueducts and the Pantheleon in Rome were constructed using volcanic ash or pozzolana that has

the same properties as fly ash (Moore, 1995). Class C fly ashes are the ones that are well known

to be used as partial replacement for Portland cement. Other types of fly ashes such as Class F can

have undesirable effects such as volatility on the entrained air in concrete. Up to 30% mass of

Portland cement can be replaced by use of fly ash. However, this amount can be increased for

some limited applications.

In modern thermal power plants during the combustion of powdered coal, a majority of the mineral

impurities for example clays, quartz and feldspar melt at high temperature. Matter fuses and is

transported to areas of low temperature. In these areas of low temperature, it solidifies as spherical

particles of glass. Some minerals agglomerate and form bottom ash while most of the particles that

are finer fly out with the stream of gas thus the name fly ash (pulverized fuel ash in UK). (Mehta

& Monteiro, 2006).

Most of the fly ash occurs as solid spheres of glass. Sometimes, a small number of hollow spheres,

called cenospheres (completely empty) and plerospheres (packed with numerous small spheres)

may also be present. Particle size distribution shows that the particles in fly ash generally vary

from <1µm to nearly 100 µm in diameter with more than 50 percent by mass less than 20 µm

(Figure 4). Fly ash normally affects the water requirement and workability of fresh concrete, and

the rate of strength development in hardened concrete.

18

Figure 4: Comparison of particle size distribution of Portland cement, fly ash and condensed

silica fume. (Source: Mehta P.K et al. 2006)

High volume fly ash has been proven to increase the workability of concrete. Processed ash has

been used as a cement replacement material in great volumes (up to 70%) for example in the

construction of Ghatghar dam project in Maharashtra, India. According to the U.S. Federal

Highway Administration, the spherical shape of the fly ash enhances the workability of concrete

and also aids in the reduction of water demand in the mixing of concrete (U.S Federal Highway

Administration, 1995).

It is also argued that by adding fly ash to concrete, the greenhouse gas contribution of concrete is

reduced. This is because a tone of Portland cement produced results in a tone of CO2 emitted

(Malhotra, 1998), as compared with no CO2 generated with fly ash. According to the International

Energy Association, cement production is expected to grow by between 0.8% and 1.2% between

the years 2006 and 2050 (International Energy Agency, 2014) which would translate in a tonnage

of way above 2 billion annually. This implies that replacement of a significant portion of this

cement by fly ash would significantly reduce the emission of carbon associated with construction

as long as the production of fly ash is taken as a given. Many researchers have pointed out that the

use of fly ash in concrete has led to the improvement of the interfacial zone in the microstructure

of the concrete (Chaid , Jauberthie, & Randell , 2004).

19

In countries that produce steel and coal, for example some of the European countries, obtaining

fly ash is quite easy as these industries produce huge amounts of fly ash as wastes. When coal is

used in a power plant, it is first ground into powder to increase the surface area of reaction and

then blown into the power plant boiler. After the coal is consumed, it leaves behind molten particles

rich in silica, alumina and calcium which solidify into microscopic spheres that are then collected

from the power plants before they fly away and that is why they are referred to as fly ash. Fly ash

improves the workability and densification of concrete, reacts with free lime to produce hydrated

calcium silicates and has pozzolanic properties. This is what makes fly ash a good material for use

in cement replacement. One of the most notable example in which fly ash was used extensively in

cement replacement was in the construction of Hoover Dam in The United States.

2.6.4.2 The Use of Other Types of Ash in Cement Replacement

Apart from fly ash from steel industries, that has gained much ground as a cement replacement

material, other types of ash from varied sources have also been used in cement replacement. The

other ashes that have been tested as potential cement replacement materials include wood and

charcoal ash, rice husk ash, coal ash, saw dust ash and power plant fly and bottom ash. The great

advantage that these ashes provide is the reduction of waste due to dumping and also replacement

of the cement which would have been used instead. The main limitation of the use of these ashes

lies in the workability of the concrete as the percentage of the ash is increased. This limitation

however can be mitigated by using finer ash that has particle size that is as close to the cement

particle size as possible.

Of particular mention is the rice husk ash. Rice husks are the shells produced during the de-husking

of paddy rice. Rice mills often have enormous problems in depositing this bulky material as each

tonne of paddy rice produces about 200 kg of husk. This husk yields 20% ash upon combustion.

In order to develop some pozzolanic activity, the rice husk ash is normally ground to finer powder.

A higher degree of pozzolanic activity may also be developed when the husks are burnt in a

controlled environment so that the silica is retained in a non-crystalline form and in cellular

microstructure. Mehta (US Patent No. 4105459, 1978)/ (US Patent No. 5346548, 1999) reported

on the effect of processing conditions and how they affect the characteristics of rice husk ash and

the advantageous effects of the amorphous ash on concrete properties. Together with Folliard

(Mehta & Folliard, 1995), Mehta also investigated on the durability aspects of blended Portland

20

cement–rice husk ash mixtures. Zhang and Malhotra (Zhang & Malhotra, 1996) have also

confirmed that reactive rice husk ash is similar to silica fume.

2.7 The Use of Wood Ash in Cement Replacement

2.7.1 Industrial Production of Wood Ash

Wood is a renewable source of energy and also relatively environmentally friendly when compared

to other sources of energy such as coal and oil. This fact has led to increased use of wood ash as a

source of energy production (Tarun , Kraus, & Kumar , 2001). This would result in increased

generations of wood ash from industries such as pulp and paper mills and steam power plants that

use wood partially or wholly in their boilers. The ash is normally deposited in landfills. This causes

these industries to have problems with environment regulators and it is also costly to them to obtain

more land to deposit more wood ash. A solution to this problem lies in the use of wood ash as a

cement replacement material.

2.7.2 The Use of Saw Dust Ash in Cement Replacement

In Kenya, where the steel and coal industries are not established, the use of ashes from agricultural

sources such as rice husk and biomass is much common. The use of wood and saw dust ash

however, has not gained extensive use as the saw dust is usually put to other uses such as in poultry

farming, making briquettes for use as fuel, preservation of agricultural produce e.g. potatoes, and

also using it as fuel by burning it directly. Saw dust is also very common due to the availability of

saw mills in almost every township in the country. Much study has also not been done in the use

of saw dust ash as a cement replacement material. Among the few authors of recent studies done

so far include Marthong (Marthong, 2012) and Raheem (Raheem A.A, Olasunkanmi, & Folorunso,

2012). This fact implies that there is more to be studied and done in relation to the use of saw dust

ash as partial cement replacement material. This is thus a ripe area for more research work.

2.7.3 The Industrial Management of Saw Dust

The short survey taken in the sawmills around Nairobi area showed that many of them do not value

the saw dust produced and usually dump it in landfills. An oral interview with Mr. Bhavji, who is

one of the persons in charge of the milling section in the Timsales Saw Mill in Nairobi, along

Enterprise Road revealed that for cypress species alone, the saw mill produces 10 drums per day

which is the equivalent of 2000 kilograms of saw dust daily. The mill however, does not convert

the saw dust to other uses but dumps it in landfills.

21

Other medium and small scale sawmills were also visited and it was found out that some do sell

their saw dust, especially those located near residential areas such as Kawangware and Rongai.

These sold their saw dust at averagely KSh.100 per 50 kg sack load which is quite a good bargain.

This study sought to justify a good alternative use of saw dust as opposed to it being dumped in

landfills. A good highlight of the big threat that saw dust can pose, if not managed well, was done

by Terra Nuova, an international sustainability organisation, in 2007 (Njenga, Yonemitsu, Karanja,

& Jamnadass, 2011) in which the researchers showed just how vulnerable the lakes in the Rift

Valley region were because of the dumping of saw dust.

22

Chapter Three

3.0 Methodology

3.1 Overview

The Methodology section covers the means by which the objectives of the research were attained.

It covers the determination of different proportions of materials for the mix design, the preparation

and tests on aggregates, the preparation and tests on saw dust ash and the tests on properties of the

fresh and hardened concrete. These tests were done pursuant to objectives (i) and (ii) in section

1.2.

For objectives (iii) and (iv) (Section 1.2), desk study method was used in the comparison of the

saw dust ash concrete and normal Portland cement concrete in terms of cost and carbon emission

reduction. The desk studies are explained further in section 4.4.

Tables that were used in the collection of experimental results are shown in section 3.8 and the

detailed procedures for some of the experiments are appended in Appendices A1, A2 and A3.

3.2 Mix Design

This was the process by which the proportions of various constituents of concrete were determined

with the objective of producing concrete with the required fresh and hardened properties. The

concrete was then tested for both fresh and hardened properties as a fulfilment of Objective (i) in

section 1.2.

3.2.1 Factors Influencing the Choice of Mix Design

i. Compressive strength.

ii. Workability.

iii. Type and grading of aggregates.

iv. Aggregate/cement ratio.

v. Maximum size of aggregate.

vi. Durability requirement.

The method used in this design was American Concrete Institute method.

23

3.2.2 Steps in Determination of the Mix Design

Step 1: Determination of target mean strength

Characteristic strength of concrete under consideration = 25 N/mm2.

This is cube strength below which only 5% of the results would be expected to fall.

Target mean strength = target average cube strength of sample tested.

Figure 5: Standard deviation of characteristic strength of concrete (Source: ACI, 2000)

Since the test results were below 40 the standard deviation for the tests was 8. The target mean

strength 𝑓𝑚 was given by:

𝑓𝑚 = 𝑓𝑐𝑢 + 1.64s

𝑓𝑚 = target mean strength

𝑓𝑐𝑢 = characteristic strength

S = standard deviation

From Figure 5, s = 8

𝑓𝑐𝑢 = 25N/𝑚𝑚2

24

𝑓𝑚 = 25 + (1.64×8) = 38.12Mpa

Target mean strength = 38.12Mpa

Step 2: Required material information

i. Maximum aggregate size = 20mm = 0.79inches

ii. Specific gravity of cement = 3.15

iii. Specific gravity of river sand = 2.65 and its fineness modulus = 2.7

iv. Unit weight of water = 1000kg/𝑚2

v. Bulk specific gravity of granitic coarse aggregate = 2.7

Slump

Required slump for structural strength of beams, reinforced walls and columns was found in

Table 2, from which the required slump ranged between 25mm – 100mm

25

Table 2: Slump Ranges for Specific Applications

Source: ACI, 2000 Table 5.14

Step 3: Estimating mixing water

Using Table 3 and taking a slump of 50mm = 2inches and considering a maximum aggregate

size of 20mm = 0.79inches;

Mixing water = 312lb/𝑦𝑑3 = 185.45kg/𝑚3

The above value applied to non-entrained air concrete.

Type of Construction

Slump

(mm) (inches)

Reinforced foundation walls and

footings 25 - 75 1 – 3

Plain footings, caissons and

substructure walls 25 - 75 1 – 3

Beams and reinforced walls 25 -

100 1 – 4

Building columns 25 -

100 1 – 4

Pavements and slabs 25 - 75 1 – 3

Mass concrete 25 - 50 1 – 2

26

Table 3: Approximate Mixing Water and Air Content Requirements for Different Slumps and

Maximum Aggregate Sizes

Mixing Water Quantity in kg/m3 (lb./yd3) for the listed Nominal

Maximum Aggregate Size

Slump

9.5 mm

(0.375

in.)

12.5

mm

(0.5 in.)

19 mm

(0.75

in.)

25 mm

(1 in.)

37.5

mm

(1.5 in.)

50 mm

(2 in.)

75 mm

(3 in.)

100 mm

(4 in.)

Non-Air-Entrained PCC

25 - 50

(1 - 2)

207

(350)

199

(335)

190

(315)

179

(300)

166

(275)

154

(260)

130

(220)

113

(190)

75 - 100

(3 - 4)

228

(385)

216

(365)

205

(340)

193

(325)

181

(300)

169

(285)

145

(245)

124

(210)

150 - 175

(6 - 7)

243

(410)

228

(385)

216

(360)

202

(340)

190

(315)

178

(300)

160

(270) -

Typical entrapped

air

(percent)

3 2.5 2 1.5 1 0.5 0.3 0.2

Source: ACI, 2000 - Table 5.16

Step 4: Water/cement ratio

This was the proportion of water by mass to that of cement used in the mix. Water/cement ratio

needed to be as low as possible commensurate to proper placing and compacting to ensure

minimum void content. The lower the water cement ratio the higher the strength. Since the target

mean strength at 28 days was 38.12Mpa for concrete class 25. Table 4 gave the value of w/c ratio.

27

Table 4: Water-Cement Ratio and Compressive Strength Relationship

28-Day Compressive

Strength in MPa (psi)

Water-cement ratio by weight

Non-Air-

Entrained Air-Entrained

41.4 (6000) 0.41 -

34.5 (5000) 0.48 0.40

27.6 (4000) 0.57 0.48

20.7 (3000) 0.68 0.59

13.8 (2000) 0.82 0.74

Source: ACI, 2000 - Table 5.17

From Table 4, 38.12Mpa or 5528.84Psi gave a w/c ratio of 0.445

Water/cement ratio = 0.445

Step 5: Cement content

Weight of cement = 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟

𝑤/𝑐 =

185.45

0.445 = 416.74kg/𝑚3

Cement content = 416.74kg/𝑚3

Step 6: Estimation of coarse aggregate content

Using the fineness modulus for river sand = 2.7 and a maximum aggregate size = 20 mm. Table 5

gave the corresponding values of the percentage coarse aggregate in concrete.

28

Table 5: Volume of Coarse Aggregate per Unit Volume of PCC for different Fine aggregate

Fineness Moduli

Nominal Maximum

Aggregate Size

Fine Aggregate Fineness Modulus

2.40 2.60 2.70 2.80 3.00

9.5 mm (0.375 inches) 0.50 0.48 0.47 0.46 0.44

12.5 mm (0.5 inches) 0.59 0.57 0.56 0.55 0.53

19 mm (0.75 inches) 0.66 0.64 0.63 0.62 0.60

25 mm (1 inches) 0.71 0.69 0.68 0.67 0.65

37.5 mm (1.5 inches) 0.75 0.73 0.72 0.71 0.69

50 mm (2 inches) 0.78 0.76 0.75 0.74 0.72

Source: ACI, 2000 - Table 5.18

From the Table 5, the percentage of coarse aggregate was found to be 0.63

From ACI – 2000 the oven dry unit weight for granitic aggregate = 1601 kg/𝑚3

Proportion of coarse aggregate = 1601×0.63 = 1008.63 kg/𝑚3

Step 7: Estimation of fine aggregate

Considering a volume of 1 𝑚3 and a density of water of 1000kg/𝑚3

Volume of water = 185.45

1000 = 0.18545 𝑚3

Volume of cement = 416.74

3.15×1000 = 0.13229 𝑚3

Volume of coarse aggregate = 1008.63

2.7×1000 = 0.3735 𝑚3

29

Volume occupied by small aggregates = 1-(0.18545+0.13229+0.3735) = 0.30876 𝑚3

Mass of fine aggregate = density × volume

2.65×1000×0.30876 = 818.214 kg/𝑚3

3.2.3 Estimated Batch Weights per Cubic Metre

Water = 185.45 kg

Cement = 416.74 kg

Coarse aggregate = 1008.63 kg

Fine aggregate = 818.214 kg

The proportions of cement to saw dust ash varied with the different percentages of replacement

as follows:

i. 0% cement replacement

Cement = 416.74 kg

ii. 5% cement replacement

Cement = 395.90 kg; Saw dust ash = 20.837 kg

iii. 10% cement replacement

Cement = 375.066 kg; Saw dust ash = 41.674 kg

iv. 25% cement replacement

Cement = 312.555 kg; Saw dust ash = 104.185 kg

v. 40% cement replacement

Cement = 250.044 kg; Saw dust ash – 166.696 kg

vi. 60% cement replacement

Cement = 166.696 kg; Saw dust ash = 250.044 kg

30

3.3 Preparation and Tests on Saw Dust Ash

3.3.1 Preparation of Saw Dust Ash

The saw dust was obtained from Timsales®, Enterprise Road in Industrial Area, Nairobi City. It

was then burnt using open kiln process in the University of Nairobi’s Architecture, Drawing and

Design Department kiln. The yield of ash on combustion was found out to be about 30%. The total

quantity of saw dust ash needed for the research was about 50 kg. Therefore, 200 kg of saw dust

was burnt in the open kiln process to produce a total of about 60 kg of saw dust ash and the extra

amount was used to account for losses in the course of the experiment.

The temperature of operation of the kiln ranged between 300˚C and 500˚C. The resultant ash was

then ground to fine powder and tested as a fulfilment of Objective (ii) in section 1.2.

Plate 1: Burning of saw dust to ash using open kiln process

3.3.2 Specific Gravity of Saw Dust Ash

About 50 g of the saw dust ash was passed through Sieve No. 7. The sample was then oven dried

and specific gravity tests using density bottles carried out.

31

Plate 2: Specific gravity test on saw dust ash sample

3.3.3 Hydrometer Analysis on Saw Dust Ash

This test was done to quantitatively determine the particle size distribution of the saw dust ash that

passed the Sieve No. 200. 50g of the sample was used in the hydrometer analysis.

Plate 3: Hydrometer Analysis on saw dust ash

32

Plate 4: Saw dust ash passing Sieve No. 200

3.3.4 Elemental Analysis of Saw Dust Ash

This test was done in two laboratories: The Chemistry Laboratory in Chiromo Campus, University

of Nairobi and The Nuclear Science Laboratory in Main Campus, University of Nairobi. The

Chemistry Laboratory was used to digest 1 g of the saw dust ash sample so that it could be used

for the X-Ray Fluorescence test at the Nuclear Science Laboratory. The apparatus and reagents

that were used in the test included:

i. Measuring cylinder

ii. Beaker (2)

iii. Nitrous acid (50 ml)

iv. Hydrochloric acid (50 ml)

v. Perchloric acid (40 ml)

vi. 1 g sample of saw dust ash

vii. Distilled water

The procedure of the digestion was as follows:

i. The measuring cylinder was rinsed with distilled water.

ii. Aqua Regia (mixture of nitrous acid and hydrochloric acid in the ratio of 1:3) was

prepared.

iii. The beakers were rinsed with the aqua regia and then with the distilled water.

iv. In one beaker, 1 g of the saw dust ash was mixed with 50 ml of aqua regia.

33

v. In the second beaker, 50 ml of aqua regia was put and used as a control experiment.

vi. Both beakers were heated in a fume chamber.

vii. 20 ml of perchloric acid was added to each beaker when almost dry.

viii. The mixtures were heated to almost dryness.

ix. 100 ml of distilled water was used to top the mark in each beaker.

Plate 5: Heating of reagents in fume chamber

The digested saw dust ash was then forwarded to the Nuclear Science Laboratory for the XRF

test.

3.4 Tests on Aggregates

3.4.1 Tests on Coarse Aggregates

The coarse aggregate (maximum size 20 mm) was subjected to water absorption test. A sample

was weighed then submerged under water for 24 hours. The sample was then surface dried, oven

dried and weighed.

3.4.2 Tests on Fine Aggregates

The fine aggregates were subjected to sieve analysis to obtain the particle size distribution. 200 g

of the sample was weighed then passed through a series of sieves and the results tabulated then the

distribution curve drawn.

34

Plate 6: Sieve analysis of fine aggregates

3.5 Tests on Properties of Fresh Concrete

3.5.1 Slump Test

This well-established test was carried out in form of a frustum of a cone with an upper diameter

of 100 mm, and a lower diameter of 200 mm and a height of 300 mm. The mould was placed on a

smooth, horizontal, vibration free and non-absorbent surface and filled in three equal layers with

the concrete, each layer tamped 25 times with a standard tamping rod. The slump was then

measured using a meter rule.

35

Plate 7: Slump test

3.5.2 Compaction Test

This test was used to determine the compacting factor. The fresh concrete was poured in the

compacting apparatus and then reduced to occupy the minimum volume by means of vibration.

Work was done in overcoming friction between the concrete and the containing surface and this

work was measured indirectly by the difference between the weight of the compacted and the

weight of the uncompacted concrete.

3.6 Tests on Properties of Hardened Concrete

3.6.1 Compressive Strength

6 batches of test cubes (each with 3 test cubes) of side 150 mm were crushed using a universal test

machine complying with BS 1881 part 115 – 1986 specifications (methods for testing concrete).

The test procedure was applied in accordance to BS EN 12390-3:2003.

3.6.2 Flexural Strength Test

6 Beams of size 100 mm x 100 mm x 500 mm were cast and tested on a span of 400 mm in

accordance to BS 1881 part 109-1983 (methods for making test beams from fresh concrete). These

beams were tested, using the 3-point test method, using the compression test machine with a

special adapter for flexural test.

36

3.6.3 Splitting Tensile Test

The Splitting tensile test was used to find the ability of concrete to resist tension. A total of 6

cylinders were used (1 in each mix). The dimensions of the cylinders were 150 mm internal

diameter and 300 mm height. The cured cylinders were tested with their horizontal axes between

the platens until failure. This test was done in accordance to ASTM C496-11.

3.7 Desk Studies

Desk studies were used in the comparison of the cost of normal cement and that of the saw dust

ash cement. The studies were also used in the approximation of the carbon emission reduction that

would result from the replacement of cement with saw dust ash.

3.8 Data Collection Aids

3.8.1 Specific Gravity of Saw Dust Ash

Table 6 was used in the collection of the results for the test on the specific gravity of the saw dust

ash.

Table 6: Table for collection of specific gravity of saw dust ash data

Bottle Description Bottle 1 Bottle 2

Mass of Empty Bottle (g)

Mass of Bottle + Soil (g)

Mass of Bottle + Soil + Water (g)

Mass of Bottle full of Water (g)

Mass of Water used (g)

Mass of Soil used (g)

Volume of Soil (cm3)

Specific gravity of Soil

Average GS

37

3.8.2 Hydrometer Analysis on Saw Dust Ash

Table 7 was used in the collection of results for the hydrometer analysis of the saw dust ash.

Table 7: Table for collection of hydrometer analysis data

Date/Time Time elapsed

(min)

Temp

˚C

Hydrometer Reading

Rh1

Rh HR D

mm

K

%

3.8.3 Sieve Analysis of Fine/Coarse Aggregates

Table 8: Table for collection of data of particle size distribution of fine/coarse aggregates

CLIENT

Test date: FINE/COARSE

AGGREGATES

Specification

Pan mass (gm)

Initial dry sample mass + pan (gm)

Initial dry sample mass (gm) Fine mass (gm)

Washed dry sample mass + pan (gm) Fine percent (%)

Washed dry sample mass (gm) Acceptance Criteria (%)

Sieve size (mm) Retained

mass (gm) % Retained (%)

Cumulative passed

percentage (%)

Acceptance Criteria

Min (%) Max (%)

14

10

4.76

2.36

1.18

0.6

0.3

0.15

0.075

38

Chapter Four

4.0 Results

4.1 Saw Dust Ash Tests

4.1.1 Ash Yield on Combustion

The yield of ash from the saw dust upon combustion was found out to be about 30%. The total

quantity of saw dust ash needed for the cement replacement and chemical testing was about 50kg.

Therefore, 200kg of saw dust was burnt in the open kiln process to produce a total of about 60kg

of saw dust ash and the extra amount was used to account for losses in the course of the experiment.

4.1.2 Specific Gravity of Saw Dust Ash

Table 9: Results of the specific gravity of saw dust ash

Bottle Description D F

Mass of Empty Bottle (g) 60.08 61.85

Mass of Bottle + Soil (g) 69.60 71.72

Mass of Bottle + Soil + Water (g) 173.32 175.69

Mass of Bottle full of Water (g) 170.73 171.00

Mass of Water used (g) 103.72 103.97

Mass of Soil used (g) 9.52 9.87

Volume of Soil (cm3) 6.93 5.18

Specific gravity of Soil 1.37 1.91

Average GS 1.64

The average specific gravity of the saw dust ash was found to be 1.64 which is just above half of

the average specific gravity of ordinary Portland cement which is 3.15 as was mentioned in Step

2 of section 3.1.2.

39

4.1.3 Hydrometer Analysis on Saw Dust Ash

Table 10: Results of Hydrometer Analysis of saw dust ash

Date/Time Time elapsed

(min)

Temp

˚C

Hydrometer

Reading Rh1

Rh HR D

mm

K %

1200 0.5 20 27.0 27.5 9.3 2.9 100.00

1 20 24.5 25.0 10.3 2.1 90.6

2 20 22.5 23.0 11.1 1.6 83.0

4 20 20.5 21.0 11.9 1.2 75.5

8 20 17.0 17.5 13.3 0.9 62.3

15 20 13.5 14.0 14.7 0.7 49.1

30 20 11.0 11.5 15.7 0.5 39.5

60 20 9.0 9.5 16.5 0.4 32.1

120 20 6.5 7.0 17.4 0.3 22.6

240 20 5.5 6.0 17.9 0.2 18.9

1440 20 4.5 5.0 18.3 0.1 10.4

40

4.1.4 Elemental Analysis of the Saw Dust Ash (XRF Test)

Table 11: Results of XRF Test on digested saw dust ash

Element Content in Solid Sample

(µg/g)

Content in Solid Sample

(%)

K 486778 48.68

Ca 414176 41.41

Ti 4614 0.46

V 737 0.07

Cr 464 0.05

Mn 14411 1.44

Fe 69586 6.96

Ni 46 0.00

Cu 279 0.03

Zn 781 0.08

Ga 0 0.00

Rb 3239 0.32

Sr 3969 0.40

Y 115 0.01

Pb 37 0.00

41

Figure 6: Wavelength dispersive XRF spectrum of the digested saw dust ash sample

4.2 Tests on Aggregates

4.2.1 Water Absorption of Coarse Aggregates

Wet weight = 599.5 g

Dry weight = 579.5 g

% water absorption = 𝑤𝑒𝑡 𝑤𝑒𝑖𝑔ℎ𝑡−𝑑𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡

𝑑𝑟𝑦 𝑤𝑒𝑖𝑔ℎ𝑡 𝑥 100

=599.5−579.5

579.5 𝑥 100

= 3.45

0 5 10 15 20

- keV -

10

102

103

104

105

Pulses

Na Mg Al

Si

Si

P

P

S

S

Cl

Cl

Ar

Ar

K

K

Ca

Ca

Ti

Ti

V

V

Cr

Cr

Mn

Mn

Fe

Fe

Ni

Ni

Cu

Cu

Zn

Zn

Ga

Ga

As

As

Se

Se

Br

Br

Rb

Rb

Rb

Sr Sr

Sr

Y

Y

Y

Mo

Mo

Mo

Cd

Cd

Cd

Au

Au

Au

Hg

Hg

Hg

Pb

Pb

Pb

U

U

U

42

4.2.2 Sieve Analysis of Fine Aggregates

Table 12: Results of the sieve analysis of fine aggregates

CLIENT F16/3908/2009

Test date: 10-Jan-14 FINE

AGGREGATES

Specification

Pan mass (gm) 100

Initial dry sample mass + pan (gm) 300

Initial dry sample mass (gm) 200 Fine mass (gm) 30

Washed dry sample mass + pan (gm) 270 Fine percent (%) 15.0

Washed dry sample mass (gm) 170 Acceptance Criteria (%)

Sieve size (mm) Retained

mass (gm) % Retained (%)

Cumulative passed

percentage (%)

Acceptance Criteria

Min (%) Max (%)

14 0 0.0 100.0

10 0 0.0 100.0

4.76 0 0.0 100.0

2.36 22.7 11.4 88.7

1.18 46 23.0 65.7

0.6 39.8 19.9 45.8

0.3 39.9 20.0 25.8

0.15 38.5 19.3 6.6

0.075 13.1 6.6 0.0

200

43

4.2.3 Sieve Analysis of Coarse Aggregates

Table 13: Results of the sieve analysis of coarse aggregates

CLIENT F16/3908/2009

Test date: 10-Jan-14 COARSE

AGGREGATES

Specification

Pan mass (gm) 100

Initial dry sample mass + pan (gm) 2100

Initial dry sample mass (gm) 2000 Fine mass (gm) 0

Washed dry sample mass + pan (gm) 1800 Fine percent (%) 0.0

Washed dry sample mass (gm) 1700 Acceptance Criteria (%)

Sieve size (mm) Retained

mass (gm) % Retained (%)

Cumulative passed

percentage (%)

Acceptance Criteria

Min (%) Max (%)

20 0 0.0 100.0

14 1304 65.2 34.8

10 46 2.3 32.5

4.76 0 0.0 32.5

2.36 628 31.4 1.1

1.18 22 1.1 0.0

0.6 0 0.0 0.0

0.3 0 0.0 0.0

0.15 0 0.0 0.0

0.075 0 0.0 0.0

2000

4.3 Tests on Properties of Concrete

4.3.1 Tests on Fresh Concrete (Workability)

Table 14: Results of the workability tests for fresh concrete

Control 5%

replacement

10%

replacement

25%

replacement

40%

replacement

60%

replacement

Slump (mm) 40.2 33.6 28.5 20.4 13.6 10.3

Uncompacted weight (kg) 27.3 28.5 25.6 28.4 25.7 25.8

Compacted weight (kg) 29.0 30.4 28.0 31.6 28.8 29.7

𝐶𝑜𝑚𝑝𝑎𝑐𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟

=𝑈𝑛𝑐𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡

𝐶𝑜𝑚𝑝𝑎𝑐𝑡𝑒𝑑 𝑤𝑒𝑖𝑔ℎ𝑡

0.94 0.94 0.91 0.90 0.89 0.87

44

4.3.2 Tests on Hardened Concrete

The tests on hardened concrete were performed after 7, 14 and 28 days in order to find out the

variation of the characteristics with the age of the concrete.

4.3.2.1 Compressive Test

Table 15: Results of the compression test for hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

0 Day

crushing

value (kN)

0 0 0 0 0 0

7 Day

crushing

value (kN)

354 320 276 265 130 110

14 Day

crushing

value (kN)

488 443 405 322 213 138

28 Day

crushing

value (kN)

569 520 462 425 240 160

4.3.2.2 Splitting Tensile Test

Table 16: Results of the splitting tensile test for hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

28 Day

splitting

value

(kN)

185 160 120 110 100 70

45

4.3.2.3 Flexural Test

Table 17: Results of the flexural test for hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

28 Day

failure

value

(div)

62 57 48 41 28 25

4.4 Desk Study

4.4.1 Overview

The desk study was based on material prices, theoretical and empirical data. These were then used

in the calculation of the reduction of concrete costs and the reduction in the carbon emissions.

4.4.2 Cost Comparison of SDAC and PCC

Table 18: Cost comparison of various proportions of mixes of SDAC and PCC*

% Cement

Replacement

Cost of Material (Ksh.) %

Reduction

in Cost

Cement Fine

Aggregate

Coarse

Aggregate

Saw

Dust

Ash**

Total Cost Reduction

in Cost

0 6,647 1,965 2,084 0 10,696 - -

5 6,315 1,965 2,084 157 10,521*** 175 1.63

10 5,982 1,965 2,084 315 10,346 350 3.27

25 4,985 1,965 2,084 787 9,821 875 8.18

40 3,988 1,965 2,084 1,259 9,296 1,400 13.09

60 2,659 1,965 2,084 1,889 8,597 2,099 19.62

46

* The cost of transportation of materials was not considered in the calculations.

** Cost of saw dust = Ksh. 100 per 50 kg bag and ash yield on combustion = 30%

*** Sample Calculation for 5% cement replacement:

Cement: 0.95

5.38 𝑥 1.55 𝑥 1442 𝑥

1

50 𝑥 800 = 𝐾𝑠ℎ. 6,315

Fine aggregates: 1.96

5.38 𝑥 1.55 𝑥 1600 𝑥

1

1000 𝑥 2175 = 𝐾𝑠ℎ. 1,965

Coarse aggregates: 2.42

5.38 𝑥 1.55 𝑥 1473 𝑥

1

1000 𝑥 2030 = 𝐾𝑠ℎ. 2,084

Saw dust ash: 0.05

5.38 𝑥 1.55 𝑥 1640 = 23.62 𝑘𝑔 𝑜𝑓 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡 𝑎𝑠ℎ 𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑

50 𝑘𝑔 𝑜𝑓 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡 𝑦𝑖𝑒𝑙𝑑𝑠 15 𝑘𝑔 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡 𝑎𝑠ℎ (30% 𝑦𝑖𝑒𝑙𝑑)

∴ 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡 𝑡𝑜 𝑦𝑖𝑒𝑙𝑑 23.62 𝑘𝑔 𝑜𝑓 𝑎𝑠ℎ

= 50

15 𝑥 23.62 = 78.73 𝑘𝑔 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡

50 𝑘𝑔 𝑜𝑓 𝑠𝑎𝑤 𝑑𝑢𝑠𝑡 𝑐𝑜𝑠𝑡𝑠 𝐾𝑠ℎ. 100

∴ 78.73 𝑘𝑔 𝑤𝑖𝑙𝑙 𝑐𝑜𝑠𝑡 𝐾𝑠ℎ. 157

Total cost: 𝐾𝑠ℎ. 10,521

In the above calculations, the following figures were adapted from The Joint Building Council-

Nairobi Zone with the Price List REF: 7/2012

Cement in bags: (1442 kg/m3) 20,677/= per cubic metre (14,399/= per ton) F.O.R, W.E.F

01.03.2009. Index = 145.74

Sand: (1600 kg/m3) 3,132/= per cubic metre delivered Nairobi Area (2,175/=

per ton W.E.F 01.08.2011). Index = 245.25

Aggregate: (1473 kg/m3) 2,927/26 per cubic metre (2,030/= per ton) W.E.F.

01.08.2011. Index = 229.36

47

The costing was done on the materials that went into the production of 1 m3 of concrete. There was

an assumption of 50% shrinkage of concrete and 5% loss of all the materials. The value of density

of saw dust ash was inferred from Table 9. From Table 18, it was deduced that there was a general

decrease in the cost of a cubic metre of concrete with an increase in the proportion of the saw dust

ash in the concrete. The 60% cement replacement concrete achieved 19.62% cost saving while the

5% cement replacement concrete achieved 1.63% cost saving compared to normal concrete

without replacement.

4.4.3 Estimation of the Green House Gas Emission Reduction

As it was noted in section 2.5, the manufacture of Portland cement has adverse effects on the

environment mainly due to the emission of greenhouse gases. Reduced clinker production that

results from the replacement of cement will result in a reduction in the emission of air pollutants

such as oxides of nitrogen and particulate matter.

The reduction of clinker production will also result in less material being consumed in the kiln

primarily limestone. At the same time, the use of the saw dust ash in cement replacement will

result in the reduction of harmful effects to the environment due to the stockpiling of the saw dust

or inappropriate disposal.

Therefore, CO2 produced from the calcining process and that produced by the kiln fuel combustion

will be reduced as a result of the use of SDAC instead of PCC.

Potential increased environmental impacts may result from the transportation of the saw dust/saw

dust ash to the mixing plants. The mode of transport may cause the release of conventional air

pollutants but this is also dependent on the distance travelled. Therefore, the CO2 produced by the

transporting vehicles may not be effectively reduced by the partial replacement of cement with

saw dust ash. To mitigate this, the saw dust/ saw dust ash should be located close to the mixing

plants. The open kiln process may also result in the discharge of conventional air pollutants and

this may be reduced by use of chimney filters.

Table 19 approximates the reduction in CO2 emission that would result from the replacement of

cement with saw dust ash:

48

Table 19: Approximation of the reduction in CO2 emission per tonne of cement fabricated

% Replacement CO2 Emission

(kg)

Reduction in CO2

Emission (kg)

% Reduction in CO2

Emission

0 900 - 0

5* 855 45 5

10 810 90 10

25 675 225 25

40 540 360 40

60 360 540 60

* Sample calculation for 5% cement replacement:

1 𝑡𝑜𝑛𝑛𝑒 𝑜𝑓 𝑐𝑒𝑚𝑒𝑛𝑡 = 900 𝑘𝑔 𝑜𝑓 𝐶𝑂2

∴ 0.95 𝑡𝑜𝑛𝑛𝑒𝑠 = 0.95 𝑥 900 𝑘𝑔 = 855 𝑘𝑔 𝑜𝑓 𝐶𝑂2

% 𝑅𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛 𝑒𝑚𝑖𝑡𝑡𝑒𝑑 = 100

900 𝑘𝑔 𝑥 (900 𝑘𝑔 − 855 𝑘𝑔) = 5%

As it was mentioned in section 2.5, 900 kg of CO2 are produced for the fabrication of every tonne

of cement. This basis was used to come up with table 19 from which it can be deduced that the

percentage reduction in CO2 emission is directly proportional to the percentage replacement of

cement.

49

Chapter Five

5.0 Analysis and Discussion

5.1 Objectives

As mentioned in Section 1.2, the objectives of the study were: to test the properties of SDAC as

compared to PCC; to test properties of saw dust ash; to compare cost of SDAC to PCC and to

approximate the reduction in carbon emissions with the replacement of cement.

5.2 Properties of SDAC

5.2.1 Properties of Fresh SDAC

The tests on the properties of fresh SDAC were done in fulfilment of the first objective. The results

of the tests were as shown in Table 14. From the results, there was a general decrease in the

workability of the concrete as the proportion of saw dust ash was increased as illustrated in Figures

7 and 8. The PCC (0% replacement) had a slump and compaction factor value of 40.2 mm and

0.94 respectively. These values decreased as the saw dust ash was increased in proportion.

This trend is similar to the one found by other researchers (Raheem A.A, Olasunkanmi, &

Folorunso, 2012). The workability (effort required to manipulate a concrete mixture with a

minimum of segregation) of fresh concrete depends on the water content in the mix. In this

experiment, the water content was kept constant at 185.45 kg per cubic meter for each percentage

replacement of cement. The implication is that the higher ratios of replacement required more

water in order for their workability to compare favorably to PCC. This would be disadvantageous

for large construction works involving the partial replacement of cement with saw dust ash as the

cost of more water would increase the overall costs of materials.

It is important also to note that the results of the compaction factor test can be correlated to the

slump test although the relationship is not linear as seen in Figure 9 although the slump test is

widely used as compared to the compaction factor test due to some inherent disadvantages of the

compaction factor test which include:

i. Bulky apparatus required for the compaction factor test.

ii. The use of a balance, which may not be available in some instances/places.

iii. Inaccurate results due to the friction in the compaction factor apparatus.

50

The incorporation of finely divided particles in the concrete improves its workability as it reduces

the number and size of voids in the concrete. A reason for the reduction in workability of the

SDAC could be the variation of size in the saw dust ash. Therefore, a probable way of mitigating

this problem would be to grind the ash into very fine and consistent particle sizes which would be

comparable to the particle sizes of the cement.

The control, 5% cement replacement and 10% cement replacement concrete achieved a slump

value of more than 25 mm. These three can therefore be used in all the applications listed in Table

2 such as foundation walls, plain footings, substructure walls, building columns and pavements

and slabs. All the mixes achieved a true slump as shown in Plate 8 thus all the mixes conform to

the requirement of ASTM C143 that the only permissible type of slump is the true slump whereby

the concrete remains intact and maintains a symmetrical shape.

Plate 8: True slump for fresh concrete – 60% cement replacement

51

Figure 7: A Graph of Slump vs. % Cement Replacement

Figure 8: Graph of Compaction Factor vs. % Cement Replacement

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50 60 70

SLU

MP

(m

m)

% REPLACEMENT

GRAPH OF SLUMP vs % REPLACEMENT

0.86

0.87

0.88

0.89

0.9

0.91

0.92

0.93

0.94

0.95

0 10 20 30 40 50 60 70

CO

MP

AC

TIO

N F

AC

TOR

% REPLACEMENT

GRAPH OF COMPACTION FACTOR vs % REPLACEMENT

52

Figure 9: Correlation of Compaction Factor and Slump

5.2.2 Properties of Hardened SDAC

The properties of hardened concrete were also determined in fulfilment of the first objective. Table

15 gives the values of the forces required to compress the concrete cubes. These values can be

converted to compressive strengths using the formula:

𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ =𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛 𝐹𝑜𝑟𝑐𝑒

𝐶𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎

A sample calculation (28 day compressive strength for the control) is as shown below:

𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 569,000 𝑁

22500 𝑚𝑚2= 25.29 𝑁/𝑚𝑚2

The respective compressive strengths (Table 20) were then used to come up with Figure 10 which

is a comparison of the respective compressive strengths with the respective ages of the concrete in

days.

0

5

10

15

20

25

30

35

40

45

0.86 0.87 0.88 0.89 0.9 0.91 0.92 0.93 0.94 0.95

CO

MP

AC

TIO

N F

AC

TOR

SLUMP (mm)

CORRELATION OF COMPACTION FACTOR AND SLUMP

53

Table 20: Compressive strengths of hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

0 Day

compressive

strength

(N/mm2)

0 0 0 0 0 0

7 Day

compressive

strength

(N/mm2)

15.73 14.22 12.27 11.78 5.78 4.89

14 Day

compressive

strength

(N/mm2)

21.69 19.69 18.00 14.31 9.47 6.13

28 Day

compressive

strength

(N/mm2)

25.29 23.11 20.53 18.89 10.67 7.11

54

Figure 10: Graph of Compressive Strength Development

The control (0% cement replacement) attained a 28 day strength of 25.29 N/mm2 which was an

expected value as the mix design was for Class 25 concrete. It was observed that as the proportions

of saw dust ash was increased, the compressive strength decreased with the 60% cement

replacement concrete attaining the lowest 28-day strength of 7.11 N/mm2.

Based on the 28-day compressive strengths, the concrete composed of up to 10% cement

replacement can be classified as moderate strength concrete (20 – 40 N/mm2). The concrete

composed of more than 10% cement replacement can be classified as low strength concrete (less

than 20 N/mm2). The implication is that the concrete with up to 10% cement replacement can be

used for most concrete works such as structural members in buildings.

As mentioned in section 2.2.4, the interfacial transition zone is the main strength limiting factor in

concrete. The steady increase in strength with age of the concrete may be attributable to the

formation of new products in the voids contained in the interfacial transition zone. A probable

reason for the reduction in compressive strength with an increase in the proportion of cement

replaced would be a change in the microstructure of the interfacial transition zone and also a

change in the microstructure of the hydrated cement paste composed of the saw dust ash.

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Co

mp

ress

ive

Str

en

gth

(N

/mm

2)

Days

COMPARISON GRAPHS OF CONCRETE COMPRESSIVE STRENGTH DEVELOPMENT

Control 5% Replacement 10% Replacement

25% Replacement 40% Replacement 60% Replacement

55

The compressive test is the main determinant of the strength characteristics of hardened concrete.

There are, however, other tests on hardened concrete that can be correlated to the compressive test.

These are the splitting tensile test and the flexural test. Concrete is strongest in compression and

weakest in tension. It is for this reason that reinforcement is provided in structural concrete

members to take the tensile forces in place of the concrete. The flexural strength of concrete is also

dependent on the section properties of the concrete member under consideration.

The results for the splitting tensile test and the flexural test on hardened concrete were recorded in

Tables 16 and 17 respectively. From these two tables, Tables 21 and 22 (from which the respective

Figures 11 and 12 were obtained) were obtained with the following sample computations:

𝑆𝑝𝑙𝑖𝑡𝑡𝑖𝑛𝑔 𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 2(𝑆𝑝𝑙𝑖𝑡𝑡𝑖𝑛𝑔 𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝐹𝑜𝑟𝑐𝑒)

𝐶𝑢𝑟𝑣𝑒𝑑 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎

𝑆𝑝𝑙𝑖𝑡𝑡𝑖𝑛𝑔 𝑇𝑒𝑛𝑠𝑖𝑙𝑒 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ (28 𝐷𝑎𝑦 𝐶𝑜𝑛𝑡𝑟𝑜𝑙) = 2 𝑥 185,000 𝑁

𝜋 𝑥 150 𝑚𝑚 𝑥 300 𝑚𝑚= 2.62𝑁/𝑚𝑚2

Table 21: Splitting tensile strengths of hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

28 Day

splitting

tensile

strength

(N/mm2)

2.62 2.26 1.69 1.56 1.41 1.00

𝐹𝑙𝑒𝑥𝑢𝑟𝑎𝑙 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 𝑃𝐿

𝑏𝑑2

𝑊ℎ𝑒𝑟𝑒: 𝑃 = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑙𝑜𝑎𝑑 𝑎𝑝𝑝𝑙𝑖𝑒𝑑 (𝑁); 𝐿 = 𝑆𝑝𝑎𝑛 𝑙𝑒𝑛𝑔𝑡ℎ (𝑚𝑚);

𝑏 = 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑤𝑖𝑑𝑡ℎ 𝑜𝑓 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 (𝑚𝑚); 𝑑 = 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑒𝑝𝑡ℎ 𝑜𝑓 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 (𝑚𝑚)

𝐹𝑙𝑒𝑥𝑢𝑟𝑎𝑙 𝑆𝑡𝑟𝑒𝑛𝑔𝑡ℎ (28 𝐷𝑎𝑦 𝐶𝑜𝑛𝑡𝑟𝑜𝑙) = 62 𝑑𝑖𝑣 𝑥 44 𝑥 4.536 𝑁 𝑥 400 𝑚𝑚

100 𝑚𝑚 𝑥 (100 𝑚𝑚)2= 4.95 𝑁/𝑚𝑚2

56

𝑁𝐵: 1 𝑑𝑖𝑣 = 44 𝑙𝑏; 1 𝑙𝑏 ≈ 4.536 𝑁

Table 22: Flexural strengths of hardened concrete

Control 5%

Replacement

10%

Replacement

25%

Replacement

40%

Replacement

60%

Replacement

28 Day

flexural

strength

(N/mm2)

4.95 4.55 3.83 3.27 2.24 2.00

The splitting tensile strengths and the flexural strengths correlate well with the compressive

strengths as there was a general decrease in both the tensile strength and the flexural strength with

an increase in the proportion of the cement replaced with saw dust ash. The splitting tensile

strength was averagely about 10% of the compressive strength of the concrete and this confirmed

that the tensile strength of concrete is lower than its compressive strength.

A quick comparison of the splitting tensile strengths and the flexural strengths would reveal that

the flexural strengths are higher than the splitting tensile strengths. This is because in the flexural

strength test, failure is controlled by the strength of the concrete on the tensile surface while in the

splitting tensile strength test, failure can be initiated anywhere in the portion of the diametrical

plane that is in tension. Therefore, based on the size effect principle, it would follow that the

flexural strengths would be higher that the splitting tensile strengths.

Ordinary Portland cement has typical flexural strength values of 3 – 5 N/mm2. This implies that a

cement replacement of up to 25% with saw dust ash would provide sufficient flexural strength.

57

Figure 11: Graph of Splitting Tensile Strengths

Figure 12: Graph of Flexural Strengths

0

0.5

1

1.5

2

2.5

3

0 10 20 30 40 50 60 70

Split

tin

g Te

nsi

le S

tre

ngt

h (

N/m

m2

)

% Replacement of Cement

GRAPH OF SPLITTING TENSILE STRENGTH VS % REPLACEMENT OF CEMENT

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70

Fle

xura

l Str

en

gth

(N

/mm

2)

% Replacement of Cement

GRAPH OF FLEXURAL STRENGTH VS % REPLACEMENT OF CEMENT

58

All the cubes, cylinders and beams of the various mix proportions exhibited the same failure

patterns for compression, splitting tensile and flexure tests respectively. There was not any marked

difference in the crack patterns. Generally, the cubes failed by their lateral sides getting spalled

and there was dense columnar cracking in the bulk of the specimen as shown in Plate 9. The

cylinders failed by having a main fracture plane throughout the cylinder as shown in Plate 10.

These differences in cracking patterns are due to differences in stress-strain relation between the

cubes and the cylinders. The beams that were subjected to the flexural test failed generally by a

major crack from the soffit of the beam (that was under tension) towards the centre of the beam as

shown in Plate 11.

Plate 9: Spalling in 28 day control cube under compression test

Plate 10: Main fracture plane of 28 day control cylinder under splitting tensile test

59

Plate 11: Major crack from soffit of 28 day control beam under flexure test

5.3 Properties of Saw Dust Ash

5.3.1 Specific Gravity of Saw Dust Ash

From Table 9, the average specific gravity of saw dust ash was found to be 1.64. This figure is

about half of the specific gravity of ordinary Portland cement which is 3.15. This implies that the

more the percentage replacement of cement in the concrete, the lesser the overall weight of the

concrete and structure at large. This would be an economic gain for the massive structures such as

storey buildings and bridges. Lighter concrete would mean less logistics and costs of handling it.

Lighter structures or members thereof would also result in lower reinforcement costs due to the

reduction in dead load.

However, a compromise would have to be made, in the percentage replacement of cement by use

of saw dust ash, between the weight and the strength of the resultant concrete. The strength of the

hardened concrete would still play a vital role in the final decision of the optimum proportion of

cement replacement with saw dust ash.

5.3.2 Grading of the Saw Dust Ash

Hydrometer analysis was done on the saw dust ash sample passing Sieve No. 200 and the results

were recorded in Table 10. The purpose of this test was to get the distribution of the saw dust ash

particles and to see how they compare with the curves for fine and coarse aggregates whose data

was recorded in Tables 12 and 13 respectively.

60

From Tables 10, 12 and 13, the respective Figures 13, 14 and 15 were obtained. From Figures 13

and 14, it was noted that the saw dust ash falls within the region of the fine sand (0.1 – 1 mm). As

discussed in section 5.2.1, finer grinding of the saw dust ash would be required so as to improve

the workability of the fresh SDAC. Ordinary Portland cement, typically, has 15% of its particles,

by mass, being below 5 µm in diameter and 5% of its particles above 45 µm. Portland cement

therefore has a large proportion of its particles being below 45 µm. In order for the saw dust ash

to achieve this kind of consistency, a mechanical grinder may have to be used.

Figure 13: Grading Curve for Saw Dust Ash

0

20

40

60

80

100

120

0.1 1 10

% P

ASS

ING

SIEVE SIZE (mm)

GRADING CURVE - SAW DUST ASH

61

Figure 14: Grading Curve for Fine Aggregates

Figure 15: Grading Curve for Coarse Aggregates

0

20

40

60

80

100

120

0.01 0.1 1 10 100

% P

ASS

ING

SIEVE SIZE (mm)

GRADING CURVE - FINE AGGREGATES

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

% P

ASS

ING

SIEVE SIZE (mm)

GRADING CURVE - COARSE AGGREGATES

62

5.3.3 Elemental Analysis of Saw Dust Ash

The XRF results were shown in Table 11 and Figure 6. From Table 11, it can be seen that the ash

sample had a Calcium (the main element of our consideration) content of 41.41%. It is important

to note that this element occurs as an oxide (Tarun , Kraus, & Kumar , 2001) in the saw dust ash

due to the combustion of the saw dust. Comparing this content to the normal content of Calcium

Oxide in ordinary Portland cement in Table 1 (60 -67%), the saw dust ash has a lower content of

the oxide.

It is important to note that the combustion temperature has an effect on the final content of elements

in the ash. The temperature mainly affects the composition of the ash in two major ways:

i. Dissociation: the breakdown of carbonates and related compounds into oxides. Relatively

lower temperatures lead to incomplete dissociation and a lower content of oxides.

ii. Volatization: where the fly ash is not measured, some combustion products or portions

thereof may not be present at all in the ash sample.

Because of these reasons, the content of the Calcium oxide in the saw dust ash may be increased

by increasing the temperature of the kiln and trapping the fly ash from the chimney.

A source of error in the digestion of the saw dust ash sample resulted in an abnormally high Cl

content as seen in Figure 6. This content was ignored.

63

Chapter Six

6.0 Conclusion and Recommendations

6.1 Conclusion

The objectives of the research were met by means of the methods outlined in Chapter Three. The

results were recorded in Chapter Four and the analysis and discussions outlined in Chapter Five.

SDAC, up to a cement replacement of 10% by weight, can be used for applications requiring

moderate strength concrete as it exhibited adequate compressive strength. The splitting tensile

strength and the flexural strength of the SDAC also decreased with more replacement of the

cement. Concrete made up of 25% of cement replacement was found to be adequate in flexural

strength. The workability of the SDAC however decreased as greater proportions of cement were

replaced by the saw dust ash. Therefore, more water would be required to improve on the

workability of the concrete having greater proportions of saw dust ash as cement replacement.

The saw dust ash exhibited cementitious properties as shown by its ability to blend well with

ordinary Portland cement. It also has a lower specific gravity value than normal Portland cement

implying that it would make the resultant concrete lighter with more proportions of cement

replaced. The ash also had a content of calcium oxide that would compare well with that of OPC

though lower. The temperature and method used in burning the saw dust would also have an impact

on the properties of the resultant ash. Controlled burning would be the most suitable method as it

would ensure complete combustion of the saw dust into ash.

The cost of the SDAC was found to be lower than the cost of the PCC. This is because saw dust

concrete utilizes a waste product (saw dust) and converts it into economic and sustainable use.

Therefore, the replacement of cement with saw dust ash would be beneficial to low income areas

which may not afford to keep up with the rising costs of cement.

The reduction in carbon emissions was found to be positively correlated with the proportion of

cement replaced. Therefore, the more the proportion of cement replaced, the more would be the

reduction in carbon emissions.

64

6.2 Recommendations

Based on the results, discussions and conclusions, the following recommendations arise:

i. A compromise between the strength of concrete, cost savings of cement replacement and

reduction of carbon emission would allow a replacement of up to 10% for normal strength

concrete. The normal strength concrete may be put to uses such as the construction of

structural members in buildings. Any cement replacement above 10% would be cheaper

and friendlier to the environment but would produce low strength concrete. This may be

used in works such as paving and minor repairs.

ii. Further research should be done on the microstructure of SDAC. This would help find ways

of improving the SDAC so that higher percentages of replacement would still result to

normal strength concrete that would be usable for normal structural works such as

construction of buildings.

iii. A further study on the effect of different combustion temperatures and methods of

combustion on the mineral content of the saw dust ash to find out the optimum temperature

and method of combustion to yield ash with a good content of Calcium which will blend

well with the ordinary Portland cement. Also, further research should be done on a method

of combustion that would be friendlier to the environment.

65

Bibliography

Alok, J. (2008, December 31). Revealed: The Cement that Eats Carbon Dioxide. The Guardian.

Chaid , R., Jauberthie, R., & Randell , F. (2004). Influence of a Natural Pozzolan on High

Performance Mortar. Indian Concrete Journal, 22.

Davidson, J. (2013, January). Kenya's 1.2 million tpa cement plant on track for 2014 completion.

World Cement.

Halstead, W. (1986). Use of Fly Ash in Concrete. National Cooperative Highway Research Project.

Hewlett, P. (2012). Lea's Chemistry of Cement and Concrete. Elsevier.

Hume. (2006). Wood Ashes: How to use them in the Garden .

Imperial Innovations. (2011, January 26). Imperial Innovations. Retrieved from Imperail

Innovations: http://www.imperialinnovations.co.uk/news-centre/news/imperial-

innovations-portfolio-company-novacem-rai/

International Energy Agency. (2014). Cement Roadmap. Retrieved from International Energy

Agency:

http://www.iea.org/publications/freepublications/publication/Cement_Roadmap_Foldout

_WEB.pdf

Kenya Ministry of Environment and Natural Resources. (1999). Environmental Management and

Co-ordination Act. Government of the Republic of Kenya.

Kenya Ministry of Planning and National Development, NESC. (2007). Kenya: Vision 2030.

Government of the Republic of Kenya.

Mahasenan, Natesan, Smith , S., Humphreys, K., & Kaya, Y. (2003). The Cement Industry and

Global Climate Change: Current and Potential Future Cement Industry CO2 Emissions.

Greenhouse Gas Technologies - 6th International Conference (pp. 995-1000). Oxford.

Malhotra, V. (1998). The Role of Supplementary Cementing Materials in Reducing Greenhouse

Emissions. Concrete, Fly Ash and the Environment Proceedings. Building Green.

66

Marthong, C. (2012). Saw Dust Ash as Partial Replacement of Cement. International Journal for

Engineering Research and Applications.

Mehta , P. (1999). US Patent No. 5346548.

Mehta, P. (1978). US Patent No. 4105459.

Mehta, P. K., & Monteiro, P. J. (2006). Concrete, Microstructure, Properties and Materials.

McGraw Hill.

Mehta, P., & Folliard, F. (1995). Rice Husk Ash - A Unique Supplementary Cementing Material.

Nevada: International Symposium on Advances in Concrete Technology.

Moore, D. (1995). The Roman Pantheon: The Triumph of Concrete. Pinedale: Office Outlet

Publishing.

Neville, A. (2012). Properties of Concrete. Prentice Hall.

Njenga, M., Yonemitsu, A., Karanja, N., & Jamnadass, R. (2011). Making a Living From Dust.

Miti, 22.

Peray, K. (1998). The Rotary Cement Kiln. CHS.

Portland Cement. (2014, March 7). Retrieved from Wikipedia:

http://en.wikipedia.org/wiki/Portland_cement

Portland Cement Association. (2013). Retrieved from America's Concrete Manufacturers:

http://www.cement.org/basics/concretebasics_chemical.asp

Raheem A.A, Olasunkanmi, B., & Folorunso, C. (2012). Saw Dust Ash as Partial Cement

Replacement in Concrete.

Rosenwald, M. (2011, December). Building a Better World with Green Cement. Smithsonian

Magazine.

Tarun , R., Kraus, R., & Kumar , R. (2001). Wood Ash: A New source of Pozzolanic Material.

Mumbai.

67

The Cement Sustainability Initiative. (2007). Progress Report: World Business Council for

Sustainable Development.

U.S Federal Highway Administration. (1995). Fly Ash Facts for Highway Engineers. Federal

Highway Administration.

US Department of Energy. (2006). Emisions of Greenhouse Gases in the US. Energy Information

Administration.

Waithaka, J. (2014, January 15). Kenya Cement Prices Hiked On New Mining Levy. The Star.

Wikipedia. (2013, January 9). Eco-cement. Retrieved from Wikipedia:

http://en.wikipedia.org/wiki/Eco-cement

Zhang, & Malhotra. (1996). High Performance Concrete Incorporating Rice Husk Ash as a

Supplementary Cementing Material. ACI Materials Journal.

68

Appendices

A1: Preparation and testing of fresh concrete Introduction:

Workability is a measure of how easy it is to place and compact concrete.

Concrete of high quality can be produced by ensuring the materials, workmanship and machinery

used are up to standard. Workability can be measured in the laboratory by application of

consistency tests on the plastic concrete.

Objectives:

To measure the slump of wet concrete

To get the compaction factor for the same concrete

To measure the V-B time for the same

Procedure

Determine the slump, compaction factor, and slump of concrete with the following components:

Coarse aggregates: 3/8" and 3/4" maximum size ^

Fine aggregate: Sand

Cement

Water

(1) Weigh the empty bucket

(2) Measure the required quantities of cement, water, sand and aggregates.

(3) Put the quantities in the mixer in the following order:

Coarse aggregate

Sand

Cement

Water

(4) Mix the quantities with a rotating machine

(5) Remove the batch and divide into small portions fill a frustum of a cone in 4 layers each layer

receiving 25 stamps with a 16 mm diameter steel rod.

(6) Remove the frustum and measure the fall.

(7) Use the provided conical container to fill the bottom cylinder with a portion of wet concrete

(uncompacted).

69

Measure the weight of compacted concrete.

(8) Put another portion of in another cylinder and use vibrating table to compact it,

(9) Measure the weight of compacted concrete.

(10) Fill another portion into a conical mould in four layers each receiving 25 blows with a 16 mm

diameter rod in V -B apparatus.

(11) Remould the concrete by switching on the machine,

(12) Measure the remoulding time.

(13) Put the concrete samples together into a batch and fill three cubical moulds and 2 cylindrical,

moulds using the vibrating table to compact them.

(14) Cover the five moulds with wet rags for 24 hours.

(15) Put the moulds in a curing room.

RESULTS AND DISCUSSION

(1) Report the batch quantities used and the workability tests results.

(2) Discuss your results.

(3) Determine the degree of workability of the concrete.

70

A2: Testing of hardened concrete Introduction:

Strength of concrete is not very directly affected by workability.

Method of manufacture and curing have direct effect on the strength,

Most concrete mixes attain over 70% if their strength after 7 days and almost maximum strength

after 28 days.

Procedure:

1. Get the cubes and cylinders prepared after workability tests after 14 days of curing,

2. Divide the cubes into 4 parts on each of the smooth surfaces.

3. Get the rebound number on each part for two smooth surfaces.

4. Put the cube in the compressing machine and load it until it crushes. Get the crushing force,

5. Test to be performed for the three cubes.

6. Place the cylinder on the compression machine lengthwise.

7. Place a pair of splints on the cylinder, one on top and the other one at the bottom,

8. Switch on the machine and measure the force required to split the cylinder along the centroid,

9. Repeat the same for the second cylinder.

RESULTS AND DISCUSSION:

1. Get-the average of the rebound numbers.

2. Get the compressive strength which corresponds to the average rebound number (kg/mm2)

3. Calculate the tensile strength of concrete from strength = 2𝑃

𝜋𝐷𝐿

Where P = load

D = cylinder - diameter

L = cylinder length

Discuss your results and compare with the workability previously determined.

71

A3: Hydrometer analysis

72

73

74

75