UNIVERSITY OF NAIROBIcivil.uonbi.ac.ke/sites/default/files/cae/engineering/civil... · UNIVERSITY OF NAIROBI ... The fine aggregates and coarse aggregate were graded and tested for

UNIVERSITY OF NAIROBI

AN INVESTIGATIVE STUDY OF THE EFFECTS OF USING

DIFFERENT TYPES OF CEMENTS ON BOTH MORTAR

STRENGH DEVELOPMENT AND PROPERTIES OF

CONCRETE

BY ABDULKADIR .M .ABUBAKAR, F16/3727/2010

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

award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

APRIL 2015

i

Abdulkadir .M .Abubakar F16/3727/2010

ABSTRACT The mortar cube crushing strength, compressive and tensile strength of concrete from three

locally manufactured cements were tested.

The three cements tested were manufactured by Bamburi Cement brand name Nguvu, E.

African Portland Cement company brand name Blue triangle and Mombasa Cement brand name

Nyumba all Portland cement 32.5 were tested for mortar strength separately and results

compared.

The fine aggregates and coarse aggregate were graded and tested for Aggregate crushing value

(ACV) and flakiness index. Concrete was mixed for each cement brand, casted cured and tested.

The fresh concrete was tested for workability i.e. slump test and compaction factor test. In the

hardened state, Compressive and tensile tests were done.

The concrete from the three brands met the required 25 N/ (mix ratio M25 adopted) though

there were variations in both the fresh and hardened test done, the variation can be attributed to

different chemical composition and degree of quality control adopted by both the manufactures

and the carrying out the test. The 28 day cube crashing test result for class 25 concrete (M25)

showed that Bamburi Cement had the highest strength 31.3 N/ followed by Mombasa

cement 27.9N/ then finally 25.5N/ for Blue triangle .All the binders had a value higher

than the minimum required strength of 25 N/ .

For the mortar strength test all the binders did not achieve the required strength of 32.5 N/

due to use of river sand that was necessitated by unavailability of Standard sand. Bamburi had

the highest 30 N/ followed by Blue triangle 28.6 N/ then finally Mombasa cement

28.2 N/ .

ii


DEDICATION To my parents, brothers, sisters, family, friends and lecturers. Thank you for being there for me

throughout my entire life and studies

iii


ACKNOWLEDGEMENT

In The name of Allah, the Most Gracious, the Most Merciful. Praise is to God, the Cherisher and

Sustainer of the Worlds. Peace and Mercy be upon our beloved Prophet Muhammad (PBUH).

Thanks to my supervisor Dr. (Eng.) John Mere for his comments, knowledge shared guidance

and encouragement during the course of this project. His invaluable assistance, dedication and

objective criticism have resulted in the successful completion of this project.

Thanks to my friends just to mention a few Noor din, Moses, Haran, Abdullah, Yessing and

colleagues in the Department of Civil and Construction Engineering who have been a source of

encouragement and support. It was a wonderful journey. My thanks and appreciation also goes

to all the lecturers in the department for sharing immense knowledge and helping me with their

guidance.

I would also like to thank the Laboratory Technicians Mr. Machine, Mr. Nicholas from

Concrete Laboratory, and Mr. Martin from the soils laboratory Civil and Construction

Department, University of Nairobi for their kind help during lab work and also in assisting me

with this project.

Lastly, I wish to thank to my family my father, my mother, my sister and brothers for their

constant support throughout my life.

God Bless you All

Abdulkadir (2015)

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Table of Contents

ABSTRACT ................................................................................................................................................................... i

DEDICATION .............................................................................................................................................................. ii

ACKNOWLEDGEMENT ............................................................................................................................................iii

LIST OF FIGURES ....................................................................................................................................................viii

LIST OF TABLES........................................................................................................................................................ ix

LIST OF PLATES ......................................................................................................................................................... x

LIST OF CHARTS ....................................................................................................................................................... xi

CHAPTER ONE ............................................................................................................................................................ 1

INTRODUCTION ......................................................................................................................................................... 1

1.1 Background .......................................................................................................................................................... 1

1.2 Problem statement ............................................................................................................................................... 3

1.3 Objectives ............................................................................................................................................................ 4

Specific Objectives ................................................................................................................................................ 4

CHAPTER TWO ........................................................................................................................................................... 5

LITERATURE REVIEW .............................................................................................................................................. 5

2.1 Introduction ......................................................................................................................................................... 5

2.2 History and Manufacture of Cement.................................................................................................................... 5

2.2.1 Portland Cement ........................................................................................................................................... 7

2.2.2 Properties of Cement .................................................................................................................................... 8

2.3 Mortar Strength .................................................................................................................................................. 11

2.4 Concrete ............................................................................................................................................................. 12

2.5 Aggregates ......................................................................................................................................................... 12

2.5.1 The Grading of Aggregates......................................................................................................................... 13

2.6 Water ................................................................................................................................................................. 14

2.7 Admixture .......................................................................................................................................................... 14

2.8 Batching ............................................................................................................................................................. 15

2.8.1 Volume of Batching .................................................................................................................................... 15

2.8.2 Weight of Batching ..................................................................................................................................... 15

2.9 Properties of Plastic Concrete ............................................................................................................................ 16

2.10 Workability ...................................................................................................................................................... 16

2.11 Slump test ........................................................................................................................................................ 16

2.12 Compaction ...................................................................................................................................................... 17

2.13 Curing .............................................................................................................................................................. 18

2.14 Strength of Concrete ........................................................................................................................................ 18

2.3.2.1 Compressive strength of concrete ........................................................................................................... 18

2.3.2.1 Tensile Strength of Concrete ................................................................................................................... 20

CHAPTER THREE ..................................................................................................................................................... 21

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3.0 METHODOLOGY ................................................................................................................................................ 21

3.1 Sampling Collection and Preparation of Aggregates ........................................................................................ 21

3.2 Laboratory Testing of Properties of Aggregate................................................................................................. 21

3.2.1 Particle Size Distribution (BS: 812:PART1:1975) ..................................................................................... 21

Objectives ................................................................................................................................................................ 22

Procedure ................................................................................................................................................................. 22

3.6 Sieve Analysis and Grading of Fine Aggregates ................................................................................................. 23

3.7 Coarse Aggregates - (BS 882: 1992) .................................................................................................................. 23

3.7.1 Flakiness Index ........................................................................................................................................... 23

3.7.2 Aggregate Crushing Value (ACV).............................................................................................................. 25

Objective .................................................................................................................................................................. 25

Apparatus ................................................................................................................................................................. 25

Procedure ................................................................................................................................................................. 25

Calculation and expression of results ......................................................................................................................... 26

3.12 Concrete Test ................................................................................................................................................... 26

3.12.4 Preparation of Test Samples for Concrete Tests ....................................................................................... 26

3.13 Portland Cement .............................................................................................................................................. 26

3.14 Aggregates ....................................................................................................................................................... 27

3.15 Water ............................................................................................................................................................... 27

3.16 Mix Ratio ......................................................................................................................................................... 27

3.17 Mixing ............................................................................................................................................................. 27

3.18 Properties of Plastic Concrete .......................................................................................................................... 28

3.18.1 Slump Test (BS 1881: PART 102). .......................................................................................................... 28

3.18.2 Compaction Factor test ............................................................................................................................. 29

3.19 Testing of the Properties of Hardened Concrete .............................................................................................. 32

3.19.1 Determination of Compressive Strength –Cube Test................................................................................ 32

3.12 Mortar Test ...................................................................................................................................................... 36

3.12.1 Test Specimen ........................................................................................................................................... 36

3.12.3 Testing Procedure ..................................................................................................................................... 37

CHAPTER 4 ................................................................................................................................................................ 38

RESULTS AND DISCUSSION .................................................................................................................................. 38

4.2 Aggregate Crushing Value (ACV) ........................................................................................................................ 41

4.3 Plastic Concrete ..................................................................................................................................................... 42

4.3.1 Workability ..................................................................................................................................................... 42

4.3.2 Mechanical Test .............................................................................................................................................. 44

4.3.2.1 Cube Crashing Test .................................................................................................................................. 44

4.3.2.2 Mortar Test Results ............................................................................................................................... 49

CHAPTER FIVE ......................................................................................................................................................... 53

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CONCLUSION AND RECOMMENDATION ........................................................................................................... 53

5.1 General .............................................................................................................................................................. 53

5.2 Conclusion ......................................................................................................................................................... 53

5.3 Recommendation ............................................................................................................................................... 54

REFERENCES ............................................................................................................................................................ 55

APPENDICES ............................................................................................................................................................. 56

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viii


LIST OF FIGURES

Fig 1 showing the cement consumption in Kenya over the years .................................................. 3

Fig 2 Factors affecting the compressive strength of concrete ..................................................... 19

Fig 3 Grading of fine aggregate ..................................................................................................... 38

Fig 4 coarse aggregate grading ...................................................................................................... 39

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LIST OF TABLES

Table 1 Chemical composition of Portland cement (Brooks and Neville 1987) ............................. 7

Table 2 oxide composition limits of Portland cements ................................................................... 8

Table 3 workability and compaction factor .................................................................................. 17

Table 4 showing flakiness test result ............................................................................................. 40

Table 5 aggregate crushing value results ....................................................................................... 41

Table 6 showing results for slump and compaction factor test result ........................................... 42

Table 7 Compressive concrete cube 7 day results ......................................................................... 44

Table 8 Compressive concrete cube 14 day results ....................................................................... 45

Table 9 Compressive concrete cube 28 day results ....................................................................... 45

Table 10 showing result of tensile split test .................................................................................. 47

Table 11. 7 day mortar test result .................................................................................................. 49

Table 12. 14 day mortar test result ................................................................................................ 49

Table 13. 28 day mortar test result ................................................................................................ 50

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LIST OF PLATES

Plate 1 Washing of fine aggregate ................................................................................................. 22

Plate 2 Flakiness index test ............................................................................................................ 24

Plate 3 Mixing of constituents of aggregate .................................................................................. 28

Plate 4 Showing determination of slump test ................................................................................ 29

Plate 5 showing the compaction factor test apparatus ................................................................... 31

Plate 6 showing curing of concrete ................................................................................................ 32

Plate 7 showing cube crushing test of concrete ............................................................................. 34

Plate 8 showing tensile split test .................................................................................................... 35

xi


LIST OF CHARTS Chart 1 showing variation of slump test result .............................................................................. 43

Chart 2 Chart showing variation of the cement with age .............................................................. 46

Chart 3 showing the 28 day tensile split result .............................................................................. 48

Chart 4 showing mortar strength of different types of cement with age ...................................... 51

1

CHAPTER ONE

INTRODUCTION

1.1 Background

The most important use of cement is the production of mortar and concrete .Mortar strength

depends on adhesion of sand grains and cementing materials while concrete quality depends

upon the quantity and quality of the aggregate and the cement used as well as the bond

between them.

Cement is the most expensive component in both mortar and concrete and hence the need to

study and test to determine if indeed the cements meet the minimum set standards. The cost of

the cements in the country are not the same and vary therefore consumers may tend to go for

the cheapest of them to save a shilling without investigating the reliability and consistency of

every batch manufactured and used.

Cement is an adhesive substance of all kinds but in a narrow sense, it is the binding materials

used in building and civil engineering projects. Cement is a finely ground powder that when

mixed with water sets to a hard mass. The most important use of cement is the production of

mortar and concrete.

Mortar has been in use as a bond for brickwork for several thousand years dating as back as the

building of Egyptians pyramid. The standing of such ancient structures to date is a clear

indication of the durability of mortar. It is noted particularly for its strength and capacity to

adhere to bricks and masonry blocks. These properties make it an obvious choice for load

bearing joint materials. Compressive strength of mortar finds its widest application in

determination of the strength of masonry walls loaded perpendicularly to the joint bed. Mortar

derives its strength from adhesion of sand grains and cementing materials. Ordinary Portland

cement and hydrated lime are the usual cementing materials. The strength of a brick wall for

example is 25% to 50% the strength of brick.

Concrete is the most widely used material in the world. About a ton of concrete produced per

person per year worldwide, 6 billion metric tons produced annually. Concrete constitutes fine

aggregates, coarse aggregates, cement, water and if required an admixture. There are so many

2

types of concrete with different applications for example; pre-stressed concrete and reinforced

concrete are used for carrying enormous loads. Different types of concrete are produced

depending upon the required end application. The modern types of concrete include cellular or

aerated concrete which is light weight and durable, making it easy to be handled.

General use of are architectural structures, Pavements (concrete), motorways/roads,

bridges/overpasses, parking structures, brick/block walls and footing for gates, fences and poles.

Concrete will remain in use as a construction material well into the future. With such extensive

use, discovery of any shortcomings or problems associated with concrete structures or

reinforced concrete will become a matter of considerable public concern both from a safety

perspective and associated cost of reactivation.

In this project three most used ordinary Pozzolanic Portland cement (PPC) namely Bamburi

cement made at Mombasa brand name Nguvu, East African Portland cement company made at

Athi river brand name Blue Triangle and Mombasa cement limited (MCL) made at Athi river

brand name Nyumba were tested.

The practical utility of cements in general depends on the power which they gain strength with

age. The hardened concrete strength established depends on several factors such as the grading

of the sand or coarse aggregates as used in this study, the water-cement ratio, the degree of

mixing, the temperature and humidity of curing, the method of sample preparation, testing and

age of samples at testing. It was therefore imperative that these parameters remain reasonably

constant for this mix study whose aim is to compare the strengths of the various binders. The

same mix (Class 25 concrete) proportion is used to prepare samples and mortar cubes also tested

for compressive mortar strength tested. Temperature and humidity cannot be completely

controlled hence the preparation, curing and testing of specimens is all done within the same

environment.

3

Fig 1 showing the cement consumption in Kenya over the years by Kenya National Bureau

of Statistics (KNBS)

1.2 Problem statement

The cost of cement has been fluctuating over the years and thereby consumers go for the cheaper

cement to save cost without considering the effects of using different cements in the same

structures. As a procedure every batch that arrives in site should be tested to find out if it

conforms to the minimum specification required from Kenya Bureau of Standards (KEBS)

although it is not practical thereby testing sample batches .A major consideration of cement is it

consistency and little variation from the assumed strength. This project is tailored to look at the

variation if any that are there in using the three locally available binders. Since no cheap control

method that has been devised so far at site level, the quality control of the cement delivered to the

sites is left entirely on the manufacturer’s guarantee of good quality. The guarantee of good

quality in this case is the form of a Kenya Bureau of Standards seal on the cement bags. The

cement delivered to the sites is used without any rigorous checking, apart from occasional visual

inspection

This study is necessary because there have been many cases of collapse of buildings and

the major blame goes to the structural engineers. Determining the properties of concrete made

from different cement suppliers will help in partly solving the problem and raising

4

consciousness to the people (Contactors, Project managers, proponents/clients/employer etc.)

on site during construction.

Cement is widely used as a bonding material in concrete but most consumers do not

understand the mechanism by which it works. Since various cements have different physical

and chemical properties and an understanding of its rate of strength development of the

different locally available binders over specified time is essential.

1.3 Objectives

The main objective of this project is to determine and make a comparison of the compressive

strength of each brand of cement by compressive mortar strength and the corresponding

compressive strength of concrete.

Specific Objectives

1. To determine and make a comparison of the compressive and tensile strength of

concrete by using different types of cement.

2. To determine and make a comparison of the mortar strength of and variation if any by

using different types of cements.

3. To determine how slump and compaction factor of concrete are influenced by different

types of cements.

5

CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction Concrete should not be confused with cement. Cement refers to only the dry powder substance

used to bind the aggregates materials in concrete. Concrete is a construction material composed

of cement itself, coarse and fine aggregates, water and maybe admixtures if required.

2.2 History and Manufacture of Cement Since civilization started exploring construction of buildings, a material has been sought that

would bind stones into a solid, formed mass .The Assyrians and Babylonians used clay for this

purpose, and the Egyptians advanced to the discovery of lime and gypsum mortar as binding

agent for building such structures as the pyramid .The Greeks made further improvement and

finally the Romans developed cement that produced structures of remarkable durability.

Cement is manufactured from four basic raw materials namely: lime obtained from limestone or

chalk, silica obtained from shale, alumina obtained from bauxite or shale and iron oxide. The

raw materials are ground into a very fine powder, mixing them intimately in predetermined

proportions and burning in a large rotary kiln at a temperature ranging from 900 O

C -1400 O

C

where the material sinters and partially fuses into clinker. The clinker is cooled and ground to a

fine powder, with some gypsum added, and the resulting product is the commercial Portland

cement (Neville and Brooks 1987)

The process of manufacturing can be either be dry or wet(the mixing and grinding of raw

materials being done in dry and wet conditions respectively).The mixture is fed into a rotary

kiln that is slightly inclined. The mixture is fed at the upper end while pulverized coal (or other

source of heat) is blown in by an air blast at the lower end of kiln, where the temperatures may

6

reach about 1500oc .The amount of coal required is between 100kg and about 350kg, depending

on the process used. (Neville and Brooks 1987)

Although the cost of grinding cement to a high fineness is considerable and also leads to rapid

deterioration of the cement on exposure to the atmosphere, it is nevertheless a very important

factor in increasing the rapid development of strength, since it increases the rate of hydration. A

slight improvement in the workability of concrete is achieved when the cement used is made

finer, as this increases the water content. The water content of a cement paste of standard

consistency is greater the finer the cement, also fineness of the cement improves cohesiveness

of a concrete mix, thus reducing the possibility of the segregation of the concrete. The quantity

of water rising to the surface of the concrete known as bleeding is also reduced. The factors

discussed above enhance the strength of concrete, but if variable will cause a variable strength

concrete to be produced.

Cements which gain strength rapidly are prone to cracking due to early thermal expansion or

contraction. This implies that increasing the fineness of cement increases its rate of hardening or

of development of strength and so indirectly increases the risk of crack formation.

The strength of concrete generally increases with the cement content, although an increases

cement content will increase the shrinkage .When the water/cement ratios is maintained constant,

an increase in the cement content improves the workability of the mix without affecting the

strength .It should be noted that an increase in workability will result in the achievement of better

compaction, hence increasing the strength.

The last main factor which contributes to the quality of cement, hence of the concrete, is the

storage conditions of the cement .The cement bags must be placed in stacks in a shed and be kept

as dry as possible. A raised floor covered with water proofing material, may be provided to

prevent moisture from infiltrating and coming into contact with the cement bags. When stored

under good conditions bagged cement may lose 20% of its strength after 2 months storage, and

up to 40% after six months storage. It is therefore very necessary to reduce the storage time of

cement bags as much as practicable. This may be achieved by stacking the bagged cement in

such a way that the first lot to be delivered is used first.

7

2.2.1 Portland Cement

Portland cement is an artificial product obtained by finely pulverizing the clinker produced by

claiming to incipient fusion a natural or artificial mixture of finely ground argillaceous and

calcareous materials (Baker 1930)

Four compounds are regarded as the major constituents of cement:

Table 1: Chemical composition of Portland cement (Brooks and Neville 1987)

Name of Compound Oxide Composition Abbreviation

Tricalcium Silicate 3CaO.Si02 C3S

Dicalcium silicate 2CaO.Si02 C2S

Tricalcium Aluminate 3CaO.AlO3 C3A

Tetra calcium Aluminoferrite 4CaO.Al2O3.Fe2O3 C4AF

The silicates C3S and C2S are the most important compounds, which are responsible for the

strength of hydrated cement paste.C3S contributes most to the strength development during the

first four weeks and C2S influences the later gain in strength. In reality the silicates are not pure

compounds but contain minor oxides in solid solution. These oxides have significant effects on

the atomic arrangements, crystal form, and the hydraulic properties of the silicates.

C3A presence in cement is undesirable as it contributes little or nothing to the strength of cement

at early ages and when hardened it is attacked by sulphates, leading to formation of calcium

sulphoaluminate may cause disruption. C3A benefits in the manufacture of cement lies in that

fact that it facilitates the combination of lime and silica. C4AF is also present in small quantities

and compared to other three compounds does not affect the behavior of cement significantly. It

however reacts with gypsum to form calcium sulphoferrite and its presence may accelerate the

hydration of silicates.

The amount of gypsum added to the clinker is crucial. It depends upon the C3A content and the

alkali content of cement. Increasing the fineness of cement has the effect of increasing the

8

quantity of C3A available at early stages and this raises gypsum requirement. An excess of

gypsum leads to expansion and consequent disruption of the set of cement paste. The table below

gives the oxide composition limits of Portland cements

Table 2: Oxide Composition limits of Portland Cements

OXIDE CONTENT,PER CENT

CaO 60-67

SiO2 17-25

Al2O3 3-8

Fe2O3 0.5-6.0

MgO 0.1-4.0

Alkalis 0.2-1.3

SO3 1-3

2.2.2 Properties of Cement

The most important property in cement is:

a. Color

b. Specific gravity

c. Activity

d. Soundness

e. Strength

f. Fineness of cement

2.2.2.1 Color

Color of cement has little bearing upon the quality and may indicate an excess of some

ingredient, and for any given brand, variation in shade may indicate differences in the character

of rocks used, or in the degree of burning. Usually Portland cement should be dull grey, bluish

gray probably indicates an excess of lime, dark green indicates a high percentage of iron, brown

9

indicates an excess of clay and yellowish shade indicates over burning. Usually some site

engineers rely on color for inspection.

2.2.2.2 Specific Gravity

The specific gravity of a substance is the ratio of its weight to the weight of an equal volume of

water. Specific gravity of cement maybe be said to give a true indication of the thoroughness of

burning and well burned cement is known to have certain definite limits. Too high a specific

gravity will therefore indicate over burning and over burning tends to break up some of the

compounds which should be present in normal cement and form others which may compromise

the quality of cement

A low specific gravity indicates under burning, adulteration and hydration. An under burnt

cement contains large proportion of uncombined, or insufficiently combined elements, some of

which are sources of great danger. If such cement is used, these elements may cause

disintegration and the ultimate failure of the structure. The specific gravity of Portland cement

varies between 3.00-3.25 while for natural cement the variation was between 2.75-3.05.

2.2.2.3 Activity and Setting

The term is used to describe stiffening of cement paste. If cement is mixed into a paste with

water allowed to stand, it gradually hardens. The rate of hardening is termed the time of setting

or activity. Cements differ widely in their rate and manner of settling. A knowledge of the

activity of a cement is of importance both in testing and in using a cement, since its strength is

seriously impaired if the mortar is disturbed after it has begun to set. Ordinarily, the moderately

slow setting cements are preferable, since they need not be handled so rapidly and may be mixed

in large quantities (Baker 1905)

There are two distinct stages in setting the initial and the final set. The initial set takes place

when the mass begins to harden, and the hard set, when the hardening has reached a point where

the mass cannot be appreciably disturbed without fracture. The best cements should be slow in

acquiring initial set but should harden quickly afterwards. Natural cements are generally much

10

quicker in setting than Portland cements. In natural cements, the hard set frequency occurs within

a few minutes after the initial set, sometimes within a period of 15 minutes and should develop

hard set from 30 minutes to 3 hours. Initial set should in no case develop in less than 10 minutes.

The composition degree of burning, age, fineness of grinding, amount of water used in mixing

and the temperature and the humidity of the air, affect the activity of cement. The initial and final

setting time are approximately related by the following equation (Reid 1907)

Final set time (min) =90+1.2(initial set time in minutes)

2.2.2.4 Soundness

It is essential that cement paste once it has set does not undergo a large change in volume. The

restriction is that they must be no large appreciable expansion which under condition of restraint

could result in disruption of the hardened cement paste. Such expansion occur due reaction of

free lime, magnesia and calcium sulphate and cements exhibiting this type of expansion are

classified as unsound

Free lime cannot be determined by chemical analysis since it is not possible to distinguish

between unreacted CaO and Ca(OH)2 produced by a partial hydration of the silicates when the

cement is exposed to the atmosphere.

Magnesium and Calcium sulphate are also liable to cause expansion through formation of

magnesium hydroxide and calcium sulphoaluminate respectively. (A.M Neville and J.J Brooks

revised1990).

11

2.2.2.5 Strength

Strength tests are not made on neat cement paste because of difficulties in obtaining good

specimen and in testing with a consequent large variability of test results. Cement-sand mortar

and in some cases concrete of prescribed proportions made with specified materials under strict

controlled conditions, are used for purpose of determining the strength of cement.

There are several tests forms of strength test: direct tension, compression and flexure. Tension

tests have been gradually superseded by compression tests. They are two British Standards

methods for testing compressive strength of cement: one uses mortar and the compressive and

tensile strength of concrete.

2.2.2.6 Fineness of Cement

"Fineness", defined as "the total surface area of the cement that is available for hydration", has

great influence on properties of fresh and hardened concrete.

The rate of hydration deepens on the fineness of cement particles and for a rapid development of

strength a high fineness is necessary. The more finer the particles of cement the higher its

compressive strength and higher workability. However, the cost of grinding and the effects of

fineness on properties like gypsum requirement, workability of fresh concrete and long-term

behavior must be borne in mind.

2.3 Mortar Strength

Mortar strength development is the process through which a cement, sand and water are mixed

and increases in strength over time. In the presence of water, the aluminates and silicates of

which cement is composed form products of hydration that are responsible for firming and

hardening that occurs in cement paste. The strength is influenced by cohesion of the cement

paste, adhesion of the cement to the sand particles and to a certain extent the strength of the sand

itself. The mechanical strength of the hardened cement is the property of the material that is most

obviously required for structural purposes.it is for this particular reason that the strength tests

plays an important role in the use of binders as building materials. There exists several forms of

strength test namely direct tension, direct compression and flexural. Compressive strength of

cement is determined by compressive strength test on mortar cubes compacted by means of a

standard vibration machine. Standard sand (IS: 650) is used for the preparation of cement mortar.

The specimen is in the form of cubes 70.6mm×70.6mm×70.6mm. Mortar compressive strength is

12

influenced by the cement type, or more precisely the compound composition and fineness of

cement, water-cement ratio, type and grading of sand.

Since cement gains strength over time, the time at which strength test is to be conducted must be

specified. Typical times are 1 day (for high early strength cement), 3days, 7days, 28days and

90days (for low heat of hydration cement)

It is important to note that the strength test of cement is carried out on the cubes of hardened

cement –sand mortar and not on a neat cement paste because of difficulties of moulding and

testing with a consequent large variability of test results. It should be assumed that two types of

cement meeting the same minimum requirements will produce the same strength of mortar or

concrete without modification of mix proportions

In this study, the sand proportions 66% of the mortar mix and thus may greatly influence its

properties. Some types of organic matter present in aggregate may reduce the hydraulic activity

of the cement and thus compromising normal setting and hardening time. Dust or clay matter on

the surfaces of the aggregate particles may reduce the bond between them and cement paste.

Some natural aggregates contain as little as possible amounts of constituent that might adversely

affect the hardening of cement paste. For this reasons and uniformity a standard sand (IS: 650) is

used for this purpose. Standard sand is used to assess the quality of cement, lime, pozzolana and

other mineral admixture used in construction industry. It is imported from the United Kingdom

(UK)

2.4 Concrete

Concrete as mentioned in the introduction is a man-made composite which constitutes cement as

the binder, aggregates i.e. fine (sand) and course (gravel), water and admixture (if required).it is

defined by properties in its fresh and hardened state.

2.5 Aggregates

The original view that aggregates were an inert material dispersed through the cement paste

largely for economic reasons is now obsolete since recent research has shown that the properties

of aggregate greatly affect the durability and strength performance of concrete. Only natural

aggregates will be considered as they may be deemed relevant in production of normal concrete.

Artificial aggregates are mainly used in the production of special concrete such as lightweight

13

concrete. Out of the materials which form concrete, aggregate is the most abundant, comprising

of at least ¾ of the volume of concrete.it may hence be said that the quality of the aggregates is

of considerable importance of concrete with consistent properties.

The other properties of aggregate include crushing strength, resistant to impact and factors which

affect the bond between the aggregates and the cement paste. The factors which affect the bond

between aggregates and the cement paste are the shape, surface texture and the size of the

individual aggregate particles. Since aggregates are cheaper than cement it is therefore of

economic interest to include into the mix as much of the former and as little of the latter as

technically possible.

Aggregates are divided into two basic size groups fine aggregates, often referred to as sand, and

coarse aggregates, also referred to as ballast. Aggregates can also be conveniently grouped into

two main categories, i.e. According to source or occurrence; Natural aggregates and artificial

aggregates. According to densities; Light weight, normal weight and heavy weight aggregates.

2.5.1 The Grading of Aggregates

Grading means mixing of two or more aggregates sizes to achieve specific proportions of fine

aggregate and coarse aggregate as desired. The grading of aggregates does not affect the strength

of fully compacted concrete with a given water/cement ratio hence in the project water/cement

ratio was kept constant and same aggregate used .grading is important since it affects

workability. Workability determines the amount of compaction that can be achieved and in turn

determines the strength achieved

The main factors governing desired aggregate grading are surface area of aggregates, which

determines the amount of water necessary to wet all the solids, the relative volume of the

aggregate, the workability of the mix and the tendency to segregation.

For a concrete mix to be satisfactory workable, it is requirement for it to contain a sufficient

amount of materials finer than no.50 BS sieve. The water /cement ratio of mix is generally fixed

from strength considerations, but as the same time the amount of cement paste has to be

sufficient to cover the surface of all aggregates, this implies that the lower the surface area of

14

aggregates, the lesser the paste required and therefore less water is required. This implies that

coarse aggregates having less surface area will produce concrete of high strength

In practice when trying to approximate to some type of grading, it should be noted that the

properties of the mix will remain largely unaffected when compensation of a small deficiency of

fine by a somewhat larger excess of coarse particles is applied, provided the departure is not too

great. The workability of a concrete mix is largely controlled by the grading of the aggregate

contained therein. The workability, in turn affects the water and cement requirements, controls

segregation and its compaction that can be achieved

2.6 Water

Water is the third ingredient necessary for making concrete. The water is usually required not to

contain impurities such as organic matter, suspended and dissolved solids and salts which will

affect the concrete adversely. Water in addition to reacting with cement thereby causing it to set

and harden, also facilitates mixing, placing and compacting of the fresh concrete. Water is also

used for washing the aggregates and for curing purpose. Water fit for drinkable is acceptable for

mixing concrete.

2.7 Admixture

Are substances introduced into a batch of concrete during or immediately before its mixing in

order to improve the properties of the fresh or hardened concrete

Rixom1997; Concrete Society Technical Report No.18, 1980).

15

2.8 Batching

The process of proportioning the various constituent of concrete materials to produce concrete is

known as batching. The batching process is normally carried out in two ways either weigh

batching or volume batching. Each of these methods of batching has its advantage and

disadvantage in terms of accuracy of measurement, cost and time. However, the weight batch

system has been found to produce a more consistent concrete compared to volume batching.

Following below is a brief discussion of the two methods.

2.8.1 Volume of Batching

Is a batching method which utilizes volume measurements as means of proportioning the various

materials to make concrete. The volume measurements units in use today include gauge box pans

and (karais) buckets etc.

The accuracy of the volume measurements depends on closeness with which the materials pack.

If the material packs closely with few air voids, the solids volume of the materials is greater than

when the material is loosely packed. The above, in addition to errors in the measurements are the

two main sources of variation of cube crushing strength when the volume batching is adopted.

The increase in volume of sand due to increase in moisture content known as bulking is another

important cause of the inconsistency of this method.

2.8.2 Weight of Batching

This is a method of batching whereby weight units are used for the purpose of proportioning the

various constituent concrete materials. This method holds one special advantage over volume

batching that is, it eliminates errors due to the variation in the amount of voids present in a

special volume, a point of importance in connection with the batching of sand (fine aggregate)

provided proper maintenance service is given to the weighing machine, thus retaining its

accuracy on site. Errors in proportioning are generally negligible.

Where good and regular maintenance is available, Weigh is the method of choice, outstanding

advantage being in the consistency of the quality of the resulting successive batches of concrete.

In weight batching constant changes in the amount of mixing water should be effected to

compensate changes in the moisture of the aggregate

16

2.9 Properties of Plastic Concrete Plastic mixed concrete can be considered as a suspension of particles of varying sizes (coarse

aggregate, fine aggregate and cement) in water. Surface attractive forces are significant for

cement particles, but less so for aggregate particles. Aggregate account for 65-80% of the

volume of concrete and will control the performance of fresh concrete. The main resistance to

flow will therefore be the interference and friction between aggregate particles. The main

properties of interest in fresh concrete are:

a) Compatibility -the property of concrete that determines how easily it can be compacted

to remove air voids.

b) Mobility - that property which determines how easily the concrete can flow into moulds

and around the reinforcement.

c) Stability - that property which determines the ability of the concrete to remain a stable

and coherent mass during handling and vibration.

Even though there is no single test that has been devised to satisfactorily measure all the

properties associated with workability. There are some types of consistency test that act

as an index to workability: the slump test, the compacting factor test and the vebe (VB)

consistometer test (Evans and kong1987).

In this project, the slump and the compacting factor test were used as an index to workability.

2.10 Workability Defined as that property of freshly mixed concrete or mortar that determines the ease and

homogeneity with which it can be mixed, placed, compacted and finished. It’s significant

because it affects the quality of several aspects of the construction process including finishing.

Good workability provides indirect benefits to the hardened concrete as well due to full

consolidation (density) are easier to achieve.

2.11 Slump test This test was done in accordance to BS1881:part 102:1983.this test is paramount since it helps

in determining batch to batch variations in the uniformity of concrete production .Uniformity or

17

consistency is important to a successful project. Slump is a much better way of describing

consistency of concrete than terms like wet, dry, runny etc.

Table 3: Workability and Compaction Factor

Description of workability slump mm compaction factor

No slump 0

Very low 0-25 0.78

Low 25-50 0.85

Medium 50-100 0.92

High 100-175 0.95

2.12 Compaction Compaction is usually performed on a workable mix to achieve maximum density. The

principle behind compaction is to eradicate air voids. Concrete should not be to dry

necessitating the use of excessive efforts in achieving the necessary compaction which is

uneconomical. Concrete also should not be too wet to avoid segregation therefore workability of

concrete is a governing factor as far as compaction is concerned. Compaction can be done by

1. Compaction by hand: whereby a tamping rod is used by hand .due to the amount of

effort which must be used in this method its can be satisfactory applied on a fairly

workable mix. When carried out properly compaction by hand gives a good result and

because of its simple equipment required its more economical method of compaction.

2. Compaction by vibration: This method has made it possible to use less workable mix

which cannot otherwise be compacted by hand methods. The available external vibrators

are hydraulic, pneumatic or electric power. Vibration tables or shaken tables (the ones

we have in our concrete laboratory) can be used for making cubes to be tested.

18

2.13 Curing The curing of cubes has an important influence on the strength attained. Particular attention

should be given to the avoidance of any possible drying out and to the curing temperature.

BS1881:part3: gives details for the curing of test tubes. For specimen made on site it is required

that the cubes shall be stored immediately after making under damp matting or other suitable

damp materials covered with polythene at a temperature of 20+-5oc for 16-24hours. After

demoulding they are submerged in a tank maintained at 20+_2oc until the time for testing

2.14 Strength of Concrete Strength is considered the most valuable property of concrete. Strength gives an overall picture

of the quality of concrete and is directly related to the structure of cement paste.

2.3.2.1 Compressive strength of concrete

Compressive strength is the most common performance measure used by engineers in design of

buildings and other structures.

Measured by considering failure under the action of a uniaxial compressive force. Under

uniaxial compression, the failure pattern is such that the cracks are approximately parallel to the

applied load though some cracks form at an angle to the applied load as shown in the figure

below. The parallel cracks are caused by a localized tensile stress in a direction normal to the

compressive load. The inclined cracks are due to collapse caused by development of shear plate

19

Fig 2 Compression test of Concrete

Water cement ratio, degree of compaction and age: Under full compaction, at a given age and at

normal temperature, the strength of concrete is inversely proportional to the water cement ratio.

At a given degree of hydration, the water/ cement ratio determines the porosity of the cement

paste.

Aggregate properties: Size, shape, grading, surface texture, strength, stiffness and

maximum size of aggregates.

Aggregate/ cement ratio: for a constant water/cement ratio, a smaller proportion of paste

to the total volume of mix leads to higher strength of concrete.

20

2.3.2.1 Tensile Strength of Concrete

Concrete is not expected to resist direct tension because of it has low tensile strength and is brittle

in nature. Tensile strength is used in the design of structural members to evaluate the shear

resistance provided by concrete and determine the steel requirement. Determination of tensile

strength is however necessary in order to determine the load at which concrete members may

crack. Cracking in concrete is a form of tension failure and has detrimental effects on a concrete

member by promoting corrosion of reinforcement or eventual total failure. Cracking problems

occur when diagonal tension arising from shearing stresses develops.

Determination of tensile strength is mostly done by indirect methods in which a compressive force

is applied to a concrete specimen in such a way that the specimen fails due to the tensile stresses

developed in the specimen. The splitting tensile test is the most commonly used indirect test

method and its advantages are:

The same moulds and testing machine used for compression tests are used for

splitting tensile tests.

The tests is simple to perform and gives more uniform results than that given by other tests

and the values obtained are closer to the actual tensile strength of concrete than the

modulus of rapture value.

Tensile strength is of interest in unreinforced concrete structure under earthquake conditions and

in structures designed on the basis of flexural strength, which involves strength in tension e.g.

highways and pavement

21

CHAPTER THREE

3.0 METHODOLOGY

3.1 Sampling Collection and Preparation of Aggregates The fine aggregates used in this project were provided by the civil engineering laboratory. The

source of the fine aggregates (sand) was from Machakos River. It was noted that the aggregates

were not protected from rainfall, sunlight or impurities. A sample was prepared by quartering

and dried in the oven for one day then graded according to BS 812:Part 1:`1975.

The coarse aggregated were provided by the civil engineering laboratory. It was noted that there

was no effort to protect the aggregates from neither rainfall nor impurities. They were well

graded natural coarse aggregates obtained from Ndarugu quarry near Juja. Aggregates passing 19

mm sieve but retained in 10 mm sieve were used. The natural coarse aggregates were further

sieved in order to remove traces of quarry dust and other small particles. They were cleaned and

dried in the oven for a day. A sample was prepared by quartering and graded according to BS

882-1992.Excess fines in the coarse aggregates were removed by sieving through 4.76mm sieve

to conform to requirements of BS 8500-2-2002.

3.2 Laboratory Testing of Properties of Aggregate

3.2.1 Particle Size Distribution (BS: 812:PART1:1975)

This test consists of dividing up and separating by means of a series of test sieves, a material

into several particle size classification of decreasing sizes. The mass of the particles retained on

the various sieves is related to the initial mass of the material. The cumulative percentages

passing each sieve are reported in numerical and graphical form.

22

Plate 1 Washing of fine aggregate

Objectives

1. To determine the particle size distribution of specified aggregates.

2. To draw grading curves for the aggregates specified.

Procedure

The test sieves were arranged from top to bottom in order of decreasing aperture sizes with pan

and lid to form a sieving column. The aggregate sample was then poured into the sieving

column and shaken thoroughly manually. The sieves were removed one by one starting with the

largest aperture sizes (top most), and each sieve shaken manually ensuring no material is lost.

All the material which passed each sieve was returned into the column before continuing with

the operation with that sieve. The retained material was weighed for the sieve with the largest

aperture size and its weight recorded. The same operation was carried out for all the sieves in

the column and their weights recorded. The screened material that remained in the pan was

weighed and its weight recorded. The cumulative mass retained and passing on each sieve was

23

calculated as a percentage of the original mass. The results of the sieve analysis were presented

graphically in charts known as grading charts.

3.6 Sieve Analysis and Grading of Fine Aggregates

. The sieve sizes in general used for particle size distribution of fine aggregates were 14, 10, 5,

2.36, 1.18 mm and 600, 300,150 and 75μm. This test consisted of dividing up and separating by

means of a series of test sieves named here above, a material into several particle size

classifications of decreasing sizes. The cumulative percentages passing each sieve were reported

in numerical and graphical form.

3.7 Coarse Aggregates - (BS 882: 1992) The sieve sizes general used for particle size distribution of coarse aggregates were 50, 37.5,25,

19, 10, and 4.75 for coarse aggregate. The aggregates were collected approximately 2kg by

mass. The proportions of the different sizes of particles making up the aggregates are found by

sieving and are known as the 'grading' of the aggregates, the grading was given in terms of the

percentage by mass passing the various sieves. The cumulative percentages passing through

each sieve were reported in both numerical and graphical form.

3.7.1 Flakiness Index

Approximately 1kg of aggregate was taken and each particle of the 7/8 in. (22.4 mm) to 5/8 in.

(16.0mm) sample was passed through the 3/8 in. (9.5 mm) slot of the thickness gauge. The

particles passing through the gauge were separated from those retained on the gauge. Each

particle of the 5/8 in. (16.0 mm) to 3/8 in. (9.5 mm) sample was passed through the 1/4 in.

(6.3mm) slot of the thickness gauge. The particles passing through the gauge were separated

from those retained on the gauge. Each particle of the 3/8 in. (9.5 mm) to 1/4 in. (6.3 mm)

sample was passed through the 5/32 in. (4.0mm) slot of the thickness gauge. The particles

passing through the gauge were separated from those retained on the gauge.

24

All particles retained on the gauge were combined and counted. The total is the Retained

Sample. The particles passing through the appropriate slots were combined and counted; this is

the total passing sample.

Analysis

Flakiness index = Sample passing ÷ (sample passing + sample retained) x 100%

Plate 2 Flakiness index test

25

3.7.2 Aggregate Crushing Value (ACV)

ACV is a relative measure of the aggregates resistance to crushing under gradually applied load

conducted on aggregates to check their individual resistance

Objective

1. To determine the relative measure of the resistance of an aggregate to crushing under

gradually applied compressive load.

Apparatus

1. An open ended steel cylinder of nominal 150mm internal diameter with plunger and open

plate.

2. Round ended steel tamping rod 16mm and 600mm long.

3. Weighing balance.

4. BS Test sieves 14mm, 10mm and 2.36mm.

5. A compressive testing machine capable of applying 400KN, at a uniform loading rate.

6. A cylindrical metal measure of internal dimensions: 115 mm by 180 mm deep.

Procedure

The surface –dry aggregate was sieved through 14mm and 10mm sieves and the material

retained on 10mm sieve adopted for test. The retained material was placed in the cylindrical

measure and its weight of aggregate determined and recorded at Wt. (A).

The cylinder of the test apparatus was put in position and the test sample placed in three layers

each layer being subjected to 25 strokes of the tamping rod.

The surface of the aggregate was then leveled and the plunger inserted and insured it rested

horizontally on the surface of the aggregates.

26

The apparatus with the test sample and plunger were then placed in position between the platens

of the testing machine and loaded at 400KN in 10 minutes.

After loading the crushing material was removed from the cylinder and sieved through 2.36mm

sieve.

Calculation and expression of results

Calculate the aggregate crushing value (ACV) expressed as a percentage to the first decimal

place, of the mass of lines formed to the total mass of the test specimen from the following

equation

ACV

Where:

M1 is the mass of the specimen (in g)

M2 is the mass of the material passing the 2.36 mm test sieve (in g).

3.12 Concrete Test

3.12.4 Preparation of Test Samples for Concrete Tests

Batching by weight by use of a weighing machine was chosen in this project. The calculated

amount of each constituent will be tabulated in the mix proportion section. Three batches were

made.

3.13 Portland Cement Nguvu Ordinary Portland cement Cem IVlB 32.5N, Blue Triangle Ordinary Portland cement

Cem IVlB 32.5N and Mombasa Ordinary Portland cement Cem IVlB 32.5N were used in each

batch respectively.

27

3.14 Aggregates Fine aggregates (sand) that was stored in the yard of the laboratory was used (the sand was from

Machakos river).The coarse aggregates in the laboratory were two types 10mm diameter and

20mm diameter. The 10mm diameter was used because the moulds provided were 100mm by

were from Ndarugo quarry from Juja. The aggregates were stockpiled into 3 distinct piles .The

was no effort to protect the aggregates from impurities or from Rain water.

3.15 Water The water used in this project was sourced from the laboratory tap .The technician assured that

the water was fresh, free from organic matter and drinkable. To get a comparable basis of the

result, a constant water/cement ratio of 0.5 was assumed.

3.16 Mix Ratio The mix design adopted was class 25 commonly referred to M-25M stands for mix. The ratio is

1:1.5:3 in order of cement, fine aggregates and coarse aggregates respectively. The table below

shows each constituent by mass in each batch of cement type, attached a detail table of the

batches. See Appendix 1(page 6) for the comprehensive mix quantity calculation

Table 4 Showing Batches Mix Proportions

Sand (kg) Cement(kg) Coarse aggregate(kg) Water(litres)

13.5 9 27 4.5

3.17 Mixing With the weight of each constituent ready, first the coarse aggregates were poured followed by

fine aggregates then cement into the pan mixer. They were mixed for about five minutes until

they were evenly distributed. Water was then added as the mixing continued until it was even.

28

Plate 3 Mixing of Constituents of Aggregate

3.18 Properties of Plastic Concrete

3.18.1 Slump Test (BS 1881: PART 102).

The slump test is the most well-known and widely used test method to characterize the

Workability of fresh concrete. The inexpensive test, which measures consistency of concrete

batch mixes.

Apparatus

1. Truncated conical mould 100 mm diameters at the top, 200mm diameter at the

bottom and 300mmm high.

2. Steel tamping rod 16mm diameter and 600mm long with ends hemispherical.

Procedure

29

The slump test is carried on the design mixes. The standard slump cone with a base plate was

used. The inside of the mould was cleaned and oiled before the test and the mould made to

stand on a smooth hard surface. The mould was held down using the feet rested on the foot

rests, and the mould filled in three layers of approximately equal sizes. Each layer was then

tamped with 25 strokes using

Tamping rod and the strokes being uniformly distributed over the cross-section of the layer.

The surface was smoothened using the trowel, and the surface of the cone and base plate

wiped clean. The cone was then lifted vertically upright and the slump measured for each

sample design.

Plate 4 Showing Determination of Slump Test

3.18.2 Compaction Factor test

Compaction factor is obtained by passing the mix through an arranged system where the mix

falls through the apparatus and is compacted by gravity as it falls from one level to another to

establish the amount of work necessary to produce full compaction. The compression factor

apparatus was greased on the inner surface of the cylinder to prevent concrete from sticking on

the inside of the apparatus. The mass of the empty cylinder was first measured and labeled

M1.Using a spatula the upper hopper was filled with the fresh concrete gently without

compacting it. Afterwards, trap door was then released and concrete fell into the lower hopper.

Once the concrete had come to rest, the excess concrete above the lower hopper was removed

30

and trap door opened. Concrete then fell into the cylinder and excess was removed with a

trowel and outside of the cylinder cleaned and mass of the cylinder with un-compacted fresh

concrete taken and recorded as M2.Thereafter, the cylinder was vibrated on the vibration table

and more concrete was added until the cylinder was fully compacted and full. The new weight

M3 was taken and the compaction factor is obtained as the ratio of the weight of non-

compacted concrete sample divided by the compacted weight of the sample.

31

Plate 5 showing the compaction factor test apparatus

32

3.19 Testing of the Properties of Hardened Concrete

3.19.1 Determination of Compressive Strength –Cube Test

Casting of Cubes

The specimens were cast in iron moulds generally 100 mm cubes. This conforms to the

specification of BS 1881- 3:1970. The moulds surface were first cleaned and oiled on their inside

surface in order to prevent development of bond between the mould and the concrete. The

moulds were then assembled and bolts and nuts tightened to prevent leakage of cement paste.

After preparing trial mixes, the moulds were filled in three layers, each layer being compacted

using a poker vibrator to remove as much entrapped air as possible and to produce full

compaction of concrete without segregation. The moulds were filled to overflowing and excess

concrete removed by sawing action of steel rule. Surface finishing was then done by a means of

trowel. The test specimens were then left in the moulds undisturbed for 24 hours and protected

against shock, vibration and dehydration at a temperature of 20+_30oc

Plate 6 Showing Cast Concrete

33

3.19.1.2 Curing of Cubes

The specimens were removed from the moulds and marked with details of; type of mix, date of

casting, duration for curing and the determined crushing date, using a water proof marker then

placed in water of temperature about 200C such that they were completely submerged. Some

samples were cured for 7days, 14days and others 28days so as to determine how the duration

of curing would affect strength of concrete. Curing took place by hardening of the concrete.

The temperature controlled the rate of progress of the reactions of hydration and consequently

affected the development of strength of concrete.

3.19.1.2 Compressive Test

After curing the cubes for the specified period, they were removed and wiped to remove

surface moisture in readiness for compression test .the cubes were then placed with the cast

surface in contact with the platens of the testing machine that is the position of the cube when

tested should be at right angles to that as cast. The load was applied at a constant rate of stress

and load at which the cubes failed was recorded.The cube compressive strengh was determined

from the formula

F=

Where P= failure load(N)

A=Cross sectional area of the specimen,

for this project the size used was 100mm 100mm

34

Plate 7 showing Compressive Cube Crushing Test of Concrete

3.19.1.3 Splitting Tensile Test

Tensile splitting strength of the concrete cylinder was performed to comply with BS 1881-

117:1983-Method for determination of tensile splitting strength.

Apparatus

1. Standard test cylinder of concrete specimen (300mm length x 150mm diameter)

2. Compression testing machine

Procedure

The standard cylinder of concrete specimen was placed horizontally between the loading

surfaces of the Compression Testing Machine with strips of wood were placed between the

specimen to ensure uniform distribution of applied load. The compression load was then

35

applied uniformly along the length of the cylinder until failure of the cylinder along the

vertical diameter. Strips of ply wood were placed between the specimen and the loading

surfaces to ensure uniform distribution of the applied load and thus preventing high magnitude

of compressive loads near the points of application. The load at which failure occurred was

recorded for the different cement used.

The formula used to obtain the tensile splitting strength is shown below

F=

Where:

P=Maximum load at failure (KN)

L=length of the specimen (mm)

D=diameter of the specimen (mm)

Plate 8 Showing Tensile Split Test

36

3.12 Mortar Test

3.12.1 Test Specimen

3.12.1.1 Description of Test Apparatus

The halve of the cube moulds and base plates were thoroughly scrapped and wiped clean

especially on the inside surfaces and on the edges to remove coating .The joints between the

halves of the cubes were covered with the thin film of grease and the halves rigidly fixed

together. The inside faces of the cube mould were also coated with a thin film of oil. This was

also done for the plate before the mould was placed on top of it.

3.12.1.2 Description of Test Specimens

The test specimen was mortar cubes of size 70.7mm with the area of each cube face equal 5000

mm2.

3.12.1.3 Materials

Cements provided by the university was used throughout the study both for financial reasons and

to ensure a realistic and reliable determination of strength development.

3.12.1.4 Sand

The sand used in this study was fine river sand from machakos passing through 0.15mm sieve

and retained at sieve 0.075mm due to unavailability of British standard sand in the laboratory.

3.12.2 Preparation of Test Specimen

Cement - 185g

Sand - 555g

Water - 74g

37

The amount of sand and cement given in the mix proportion were weighed and the required

amount of water measured in the measuring cylinder.

The weighed sand and cement were dry mixed a non-porous plate for about for about 1 minute

then with water for approximately 3 ½ minutes. The mixing was done such that the resulting mix

was homogenous.

The paste was immediately transferred to the cubes mould hopper fixed on the vibration machine

in contact and directly above the cube mould clamped onto the table of the vibration machine.

The vibration machine was then turned on and the mortar compacted by vibration for 2 minutes.

At the end of vibration, the mould (still containing mortar) was removed from its clamped

position.

Excess materials above the mould edges were sliced off and the top face smoothed. The

specimen was then labeled and placed in an area free from any kind of interference. In order to

reduce evaporation, the exposed top of the cubes was covered with sheet of polythene paper

making contact with the upper edge of the mould. The test specimens were de-moulded after 24

hours and submerged in water in the curing room.

3.12.3 Testing Procedure

The cement mortar cubes were tested on the compression testing machine upon removal from

water and were tested in a wet condition. Before testing, the cube faces were wiped to remove

any surface grit. The cubes in contact with the machine’s platens were the smooth faces i.e. any

pair of the 4 perpendicular to the one facing up during casting.

For compression testing machine, with the aid of a load placer, the loading was steadily and

uniformly applied until the specimen failed as indicated by the backward motion of the black

pointer. The failure load was that denoted by the red pointer which remained at the maximum

value even after loading was stopped. It had to be reset for every subsequent cube.

For each binder at each age, 3 cubes were tested. The failure load was then recorded.

38

CHAPTER 4

RESULTS AND DISCUSSION

a

From the graph grading did lie between the upper and lower boundary as required by BS 882 -

1992. They are to the right meaning they are coarser than fine (sand).

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Pass

ing

(%)

Sieves (mm)

Min

Max

Fig 3 Grading of Fine Aggregate

39

Fig 4 Coarse Aggregate Grading

The graph showed that the grading did lie between the boundaries set by BS882-1992 for coarse

aggregate though the coarse aggregates are not of uniform size.

The gradation of aggregate is important since it determines the paste requirement of a workable

concrete. Paste requirement itself controls the cost of the project since cement is the most

expensive component in concrete. The best way to achieve a workable concrete is by adoption of

a good gradation of aggregate. The better the gradation, the lesser the paste requirement hence

saving in economy, higher strength, lower shrinkage and greater durability .This is due to the fact

that the more the paste the more concrete is permeable and susceptible to chemical attacking.it

should be noted that they are no ideal requirements for grading since workability is not only

dependent on grading alone but on surface area of the aggregates which determines the amount

of water to wet all the solids. Workability also depends on the relative volume occupied by the

aggregate, tendency to segregate and amount of fines in the mix. The result in this project shows

that the sand and the coarse aggregates did conformed to the specification to BS 882-1992 .

0

10

20

30

40

50

60

70

80

90

100

1 10 100

Pass

ing

(%)

Sieves (mm)

Min

Max

40

4.1 Flakiness index

Table 5: Flakiness Test Result

Sieve size(mm) 12.7 to 9.525 9.525 to 6.35 Total

Weight passing(g) 45.2 182.9 228.1

Weight retained(g) 68.2 257.2 325.4

Flakiness index =

100 = 41.2%

According to BS882-1992 it is undesirable to have aggregates containing flaky particles in

excess of 10%-15%.The results tabulated report that the aggregates are indeed flaky and had

failed to be within the specified standard and hence affects workability of the concrete.

Flakiness tests are useful only in general assessment of aggregates and don not adequately

describe the shape of the particles since the aggregate shape can be conveniently assessed by test

for angularity, flakiness and elongation indices.

41

4.2 Aggregate Crushing Value (ACV)

Table 6: Aggregate Crushing Value Results

Weight passed, M2 490

Weight retained 2210

Total weight, M1 2700

ACV Calculated

×100

×100=18.15%

The ACV result is 18.15% which is alright since the BS 882-1992 requirement is not to exceed

35%. Technically when the ACV of the aggregates exceeds 30% the results may be unusual and

10% fine test is carried out. Due to the fact that the result18.15% is lower than 30%, 10% fine

test was not done. The aggregate did not fail by ACV.

42

4.3 Plastic Concrete

4.3.1 Workability

As indicated earlier, the slump test and the compaction factor test were done on plastic concrete

to determine workability of the concrete. The tests were conforming to BS 1881-102:1983.The

test result is tabulates as shown below.

Table 7: Results for Slump and Compaction Factor Test

Type of cement Portland

(32.5N)

Slump Compaction factor

Bamburi cement 34 0.91

E. African Portland cement 36.4 0.94

Mombasa cement 33.6 0.90

43

Chart 1 Showing Variation of Slump Test Result

From the experiment it was realized that there was a variation on the consistency and workability

depending on the type of cement used. The result obtained show that slump ranging from 30m-

35mm and compaction factor ranging from 0.9 to 0.94 the degree of compaction was low in all

the three cement used. This was a result of using the same w/c ratio (0.5) .The difference in both

the slump and compaction factor is due to the fact that mix water being absorbed by aggregates

had different saturation level (looking at the result the difference in saturation level of the

aggregates used was very small) since each batch of cement was done on different days due to

unavailability of casting cubes. The usual practice in site is the amount of water to be added to

the concrete constituent is left to the mixer operator to decide due to his experience with the W/C

ratio calculated in mind.

32

32.5

33

33.5

34

34.5

35

35.5

36

36.5

37

Bamburi cement E.african portlandcement

Mombasa cement

Slu

mp

(m

m)

A graph of Slump against type of cement

slump

44

4.3.2 Mechanical Test

4.3.2.1 Cube Crashing Test

Table 8: Results of Compressive Strength Test at 7 Day

Type of

cement

Sample 1(KN) Sample 2(KN) Average

load(KN)

Compressive

strength

(N/ )

Bamburi

cement

160 180 170 17

African

Portland

cement

155 167 161 16.1

Mombasa

cement

140 143 142 14.2

45

Table 9: Compressive Concrete Cube 14 Day Results

Type of

cement

(32.5N)

Sample 1(KN) Sample 2(KN) Average load

(KN)

Compressive

strength

(N/ )

Bamburi

cement

260 248 254 25.4

African

Portland

cement

231 239 235 23.5

Mombasa

cement

235 251 243 24.3

Table 10 : Compressive Concrete Cube 28 Day Results

Type of

cement

(32.5N)


(KN)

Compressive

strength

(N/ )

Bamburi

cement

326 300 313 31.3

African

Portland

cement

250 260 255 25.5

46

Mombasa

cement

278 280 279 27.9

Chart 2 Chart showing variation of the compressive strength of cements with age

From the results shown Bamburi cement had the highest strength in 7 day followed by Blue

triangle than lastly Mombasa cement.

Their 7 day strengths are 17, 16.1 and 14.2 (N/ ) respectively. Bamburi exhibited a faster

rate of gain of strength from early ages which gives advantage of removing formwork earlier.

The 14 day test result shows Bamburi has the highest strength followed by Mombasa and finally

Blue triangle cement. Their 14 day strengths are 25.4, 24.3 and 23.5 (N/ ) respectively.

The 28 day test result shows Bamburi has the highest strength followed by Mombasa and finally

blue triangle. Their 28 day strengths re 31.3 27.9 and 25.5 (N/ ) respectively.

0

5

10

15

20

25

30

35

7 day 14 day 28 day

.Co

mp

ress

ive

Str

en

gth

(M

Pa)

Age of Concrete in Days

A Bar chart of compressive strengh against age

Bamburi

Mombasa

Blue triangle

47

Different cements have different chemical constituent’s proportions and degree of fineness

which determine the purpose and type of cement. The strength of concrete is controlled by

many factors other than the type of cement used. These factors range from characteristics of

aggregate, W/C ratio and voids in concrete. In this research the aggregate used were the same

and a constant W/C ratio adopted to get a comparable result. It’s true that some cements gain

strength more rapidly than others but for a given W/C ratio the difference are only 10 %

(Evans and Kong 1987). All the brands of cements surpassed the minimum required strength

of 25 (N/ ).

Table 11: Result of Tensile Split Test

Type of

cement(32.5N)

Sample

1(KN)

Sample

2(KN)

Average(KN) Tensile split

strength(N/ )

Bamburi

cement

200 190 195 2.76

African

Portland

cement

150 155 153 2.16

Mombasa

cement

140 160 150 2.12

48

Chart 3 Showing 28 Day Tensile Split Result

From the results of tensile strengths Bamburi had the highest followed by blue triangle and

finally Mombasa Cement. The 28 day results were 2.76, 2.16 and 2.12 (N/ ).The results of

tensile strengths of the cements used did not range between 1/8 to ½ of cube strength, as

recommended range by Evans and Kong 1987.

0

0.5

1

1.5

2

2.5

3

28 Day

Ten

sile

Str

en

gth

(M

Pa)

Age of Concrete in Days

A Bar chart of Tensile strengh against age

Bamburi

mombasa

blue triangle

49

4.3.2.2 Mortar Test Results

Table 12: 7 Day Mortar Test Result

Type of

cement

Sample 1(KN) Sample 2(KN) Average

load(KN)

Compressive

strength

Bamburi

cement

20 22 21 4.3

African

Portland

cement

17.5 18.5 18 3.8

Mombasa

cement

19 22 21 4.3


Type of cement Sample 1(KN) Sample 2(KN) Average load

(KN)

Compressive

strength

Bamburi

cement

115 110 113 23.1

African

Portland

cement

120 123 122 24.9

Mombasa

cement

118 104 111 22.7

50


Type of

cement

Sample 1 Sample 2 Average

load(KN)

Compressive

strength

Bamburi

cement

145 148 147 30

African

Portland

cement

140.5 139.5 140 28.6

Mombasa

cement

135 140 138 28.2

51

Chart 4 Showing Mortar Strength of different Types of cement with Age

From the results shown Bamburi cement has the highest strength in 7 day followed by Mombasa

cement than lastly African Portland cement. Their 7 day strength is 4.3, 4.3 and 3.8 (N/ )

respectively. Bamburi exhibited a faster rate of gain of strength from early ages which gives

advantage of removing formwork earlier

The 14 day test result shows Bamburi has the highest strength followed by blue triangle and

finally Mombasa cement. Their 14 day strength 23.1, 24.9 and 22.7 (N/ ) respectively.

The 28 day test result shows Bamburi has the highest strength followed by blue triangle and

finally Mombasa. Their 28 day strength is 30, 28.6 and 28.2(N/ ) respectively.

Different cements have different chemical constituent’s proportions and degree of fines of the

cement. The result shows that Bamburi has the highest Mortar strength amongst them followed

Blue triangle and finally Mombasa cement. The result were lower than the 32.5(N/ )

expected due to the size of the mortar cube (70mm cube), it was hard to compact and test hence a

major source of error in the results .A prism would have given a more accurate results if it were

available. The sand used was from machakos and not the standard cement imported from Britain

which was not available. The sand used was out in the open with no effort to protect it from

rainwater and impurities .clay ,mud and oil interfere with the bonding of the cement and sand

0

5

10

15

20

25

30

35

7 Day 14 Day 28 Day

Mo

rtar

Str

en

gth

(M

Pa)

Age of Mortar in Days

A Bar chart of Mortar strengh against age

Bamburi

mombasa

blue triangle

52

reducing strength and although care was taking by washing the sand particles, the reduction of

strength is attributed to the impurities present in the river sand after washing. Chemical

contaminants such as sulphates, acids and chlorides affect the durability of concrete which cannot

be accounted for since durability issue is a long term investigation.

53

CHAPTER FIVE

CONCLUSION AND RECOMMENDATION

5.1 General

In this research, three brands of cement were tested for mortar strength, concrete was prepared

for each brand of cement and both its compressive and tensile strength compared. The

conclusion drawn are based on the results obtained and are summarized below.

5.2 Conclusion

1. For given water content the slump varied from 34-37mm while compaction Factor varied

between 0.90-0.94.Bamburi was the most workable followed by Blue triangle then

Mombasa cement.

2. The 28 day cube crushing test result for class 25 concrete (M25) showed that Bamburi

Cement had the highest strength 31.3 N/ followed by Mombasa cement 27.9N/

then finally 25.5N/ for Blue triangle .All the binders passed the minimum required

strength of 25 N/ .

3. For the 28 day tensile split test Bamburi had the highest strength 2.76 N/ followed

by Blue triangle cement 2.16 N/ and finally Mombasa cement 2.12 N/ .

4. For the mortar strength test all the binders did not achieve the required strength of 32.5

N/ due to use of river sand that was necessitated by unavailability of Standard sand.

Bamburi had the highest 30 N/ followed by Blue triangle 28.6 N/ then finally

Mombasa cement 28.2 N/ .

5. All the cement increased strength with age, Bamburi cement was found to be the most

consistent cement among all and had achieved a more strength than the 25 N/

minimum strength required.

6. Both The fine aggregate and coarse aggregate were not the specified grading of BS882-

1992. The Coarse Aggregate failed Flakiness index test .The aggregate in the laboratory

should be protected from Rainfall and impurities to get a more Accurate results.

54

5.3 Recommendation

1. A chemical analysis of the local cement to explain the strength development in addition

fineness test be done to fully explain the variation in strength.

2. A through research done on the locally available cement by testing all of them and

casting various mixes that will give a comparison so as to support this project results a

get more accurate results.

3. Provision of more moulds in the concrete laboratory to cater for more samples to done

to get a more accurate result. The moulds were few that the students had to book earlier

and cast less so as to allow others also to finish the test.

4. The laboratory technicians should put effort to get aggregates that are well graded and

protect the aggregate from external harsh weather and impurities.

5. The flexural strength test be conducted and the samples observed for a longer time than

this project to get more conclusive and accurate results.

6. Standard sand was not available hence the sand should be used for all the locally

cements to get a more accurate results.

7. For future research on this topic other locally available binders and limes are tested and

standard be made for them.

8. The Mortar Test be done with care due to the size of the cubes and a prism should be

used for the test as the practice in the ministry testing laboratory.

55

REFERENCES

1) Joseph F.Lamond, J.H.Pielert (Jan1, 2006) Significance of Tests and Properties of

Concrete and Concrete-Making Materials, Chapter 12 on Strength, ASTM STP 169B.

2) BS 1881-108: 1993. Testing Concrete – Method for making test cubes from fresh

concrete, British Standard Institute.

3) 1881-110: 1993. Testing Concrete – Method for making test cylinders from fresh

concrete, British Standard Institute.

4) BS 1881-116: 1983. Testing Concrete – Method for determination of compressive

strength of concrete cubes, British Standard Institute.

5) BS 1881-117: 1983. Testing Concrete – Method for determination of tensile splitting

strength, British Standard Institute.

6) Studies of Flexural Strength of Concrete, Part 3 (ASTM Proceedings, Volume 57,

1957). , Effects of Variations in Testing Procedures, by Stanton Walker and D.L.

Bloem, NRMCA Publication No. 75

7) Rixom 1997; concrete society Technical report No.18 1980

8) Baker, C.E (1930) -A Treative on Masonry construction, 9th Edition, John Wiley &

sons Inc.

9) Hughes, B.P & Bahramian, B (December 1965) -cube tests and uniaxial compressive

strength of concrete, Mag.of concrete research, vol 17, No.53

10) L. J Murdock, K. M. Brook and J. D. Dewar (1991), Concrete Materials and practice,

6th Edition; London Melbourne Auckland, London.

11) Newman, J. and Choo, B.S. (2003). Advanced Concrete Technology, Elsevier Ltd.

12) Neville, A.M and Brook, J.J. (2001). Concrete Technology, Pearson Education

Limited, Edinburg Gate, England.

13) Neville, A.M (1981). Properties of Concrete, 3rd

Edition, Longman Scientific and

Technical.

14) BS 1881-102: 1983. Testing Concrete - Method for determination of slump, British

Standard Institute.

56

APPENDICES

1

List of appendices

Appendix 1: Tables of aggregate grading 1

Appendix 2: Compressive cube strength and tensile split results for each type of cement 4

Appendix 3: Mortar test results 6

Appendix 4: Plates 8

2

Appendix 1: Tables of aggregate grading

Table A1: fine aggregate grading results

Sieve

analysis(mm)

Retained

mass(gm.)

% retained Cumulative

passed

percentage

Lower limit

criteria

Upper limit

criteria

14 0 0.0 100.0

10 4 1.6 98.4 100

4.76 5 1.9 96.5 89 100

2.36 12 4.7 91.9 60 100

1.18 21 8.1 83.7 30 100

0.6 73 28.3 55.4 15 100

0.3 107 41.5 14.0 5 70

0.15 28 10.9 3.1 0 15

0.075 4 1.6 1.6

254

Table A2: coarse aggregate grading results

Sieve

analysis(mm)

Retained

mass(gm.)

% retained Cumulative

passed

percentage

Lower limit

criteria

Upper limit

criteria

20 0 0.0 100.0

14 0 0.0 100.0 100

10 114 10.0 90.0 85 100

5 780 68.5 21.4 0 25

2.36 244 21.4 0.0 0 5

1138

Pan mass(gm.) 126

Initial dry mass

+pan(gm.) 384

Initial dry mass(gm.) 258 Fine mass(gm.) 4

Washed dry mass

+pan(gm.) 380

Fine percent % 1.6

Washed dry

mass(gm.) 254

Acceptance criteria %

3

Table A4: BS and ASTM requirements for grading of fine aggregate

Table A5: Grading requirements for coarse aggregates according to BS 882: 1992

4

CLASS 25 MIX DESIGN QUANTITIES

Cube size of 100x100x100 mm was used

Volume of one cube = 0.001 m3

Density of concrete = 2400 Kg/m3

Mass of concrete required for one cube = 0.001 x 2400 = 2.4 Kg

Total number of cubes required = 2 cubes for averaging, 3 types of cement to be tested cubes at 7

and 14 and 28 day strength = 18 cubes in total.

Cylinder size of 150 mm diameter and 300 mm height was used.

Volume of one cylinder = 0.053 m3

Mass of one cylinder = 12.72 Kg

Total number of cylinder required = 2 cylinders for averaging, 3 types of cements to be tested,

cylinders at 28 day strength required = 6 cylinders

A water cement ratio of 0.5 to be used

A 15% to cater for wastage during the laboratory tests was added

For each batch (6 cubes +2 cylinders) =2.4 6+2 12.72=39.84

Sand=1.5/5.5 1.15 39.84=13.5Kg

Cement=1/5.5 1.15 39.84=9Kg

Coarse Aggregate=3/5.5 1.15 39.84=27Kg

The quantities were rounded to the nearest whole number for ease of measurements.

Appendix 2: Compressive cube strength and tensile split results for each type of cement

Table A6 Compressive concrete cube 7 day results

Type of cement Sample 1(KN) Sample 2(KN) Average

load(KN)

Compressive strength

(N/ )

Bamburi cement 160 180 170

African Portland

cement

155 167 161

Mombasa

cement

140 143 142

5


Type of cement

(32.5N)


(KN)


(N/ )

(


African Portland

cement

231 239 235

Mombasa

cement

235 251 243


Type of cement

(32.5N)


(KN)


(N/ )


African Portland

cement

250 260 255

Mombasa

cement

278 280 279

6

Table A9 showing result of tensile split test

Type of

cement(32.5N)

Sample 1(KN) Sample 2(KN) Average(KN

)

Tensile split

strength(N/ )

=


African Portland

cement

150 155 153

Mombasa

cement

140 160 150

Appendix 3: Mortar test results

Table: 7 day mortar test result

Type of cement Sample 1(KN) Sample 2(KN) Average

load(KN)

Compressive

strength


African Portland

cement

17.5 18.5 18

Mombasa

cement

19 22 21

7

Table 14 day mortar test result

Type of cement Sample 1(KN) Sample 2(KN) Average load

(KN)



African Portland

cement

120 123 122

Mombasa

cement

118 104 111

Table 28 day mortar test result

Type of cement Sample 1 Sample 2 Average

load(KN)



African Portland

cement

140.5 139.5 140

Mombasa

cement

135 140 138

8

Appendix 4: Plates

Plate A1: showing flakiness index performed

Plate A2: Showing sieving of coarse aggregates from outside the laboratory.

9

Plate A3: showing application of concrete to construct a swimming pool

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