EFFECTS OF DIFFERENT SIZE OF COARSE AGGREGATE ON THE COMPRESSIVE

STRENGTH OF CONCRETE

BY

MUONEKE, VIVIAN CHISOM

REG. NO: NAU/2016224045

A PROJECT WORK SUBMITTED TO THE DEPARTMENT OF CIVIL ENGINEERING,

FACULTY OF ENGINEERING.

NNAMDI AZIKIWE UNIVERSITY, AWKA

JANUARY, 2022.

i
 CERTIFICATION

This is to certify that this work titled “Effects of different size aggregate on the compressive

strength of concrete” was carried out by me, Muoneke Vivian Chisom with registration number

2016224045 in the Department of Civil Engineering, Faculty of Engineering, Nnamdi Azikiwe

University, Awka.

…………………………... … ……………………………
Muoneke, Vivian Chisom Date
(Student)

ii
 APPROVAL

This project titled “Effects of different size of coarse aggregate on the compressive strength of

concrete” has been approved for submission in the Department of Civil Engineering, Faculty of

Engineering, Nnamdi Azikiwe University, Awka.

…………………………... ………………………………
Engr. I. K. Omaliko Date
(Project Supervisor)

…………………………... ………………………………
Engr.Dr. C. A. Ezeagu Date
(Head of Department)

…………………………... ………………………………
Engr, Prof. D.O. Onwuka
(External Supervisor) Date

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 DEDICATION

I dedicate this work to God Almighty for his providence, grace and love he showed me

throughout my stay in this university.

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 ACKNOWLEDGEMENT

I give tremendous thanks to Almighty God who made this work a success. My sincere gratitude

goes to my impeccable project supervisor, Engr. I. K. Omaliko for his efforts, guidelines and

encouragement which led to the success of this work.

I appreciate the Head of Department, Dr. A.C. Ezeagu for his dedication towards the affairs of

the department, my lecturers and the entire staff of the Department of Civil Engineering for their

various forms of assistance.

This acknowledgment will be incomplete without mentioning my beloved parents Chief and Lolo

Lawrence Muoneke for your lovely care and dedication towards my life and my education, May

God reward you. To my siblings, Chinenye, Kosi, and Chinaemerem I say, “I love you”. I

appreciate my supportive uncle, Hon, Chief Fabian Muoneke. I cherish also the time we shared

my darling friends of mine, Chinenye, Chidera, Ruth, Bernard, Eke Emmanuel, Mairo, and

Rafaela.May the good Lord continue to bless and guide you all in Jesus name.

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 ABSTRACT

Coarse aggregates, which is the interest of this study, make the difference. Three different types
of coarse aggregates, with 20mm maximum size, employed in this investigation, these are;
12mm, 16mm, and 20mm. The grading and compressive strength of the aggregates were studied.
The mix ratio and water/cement ratio adopted for the study was 1:2:4 and 0.55 respectively.
Two concrete cubes (150mm x 150mm x 150mm) were cast for eachcoarse aggregate type of
which two were crushed at each curing age namely; 7, 14, 21, and 28 days. The 28 day strengths
of the concretes made with 20mm, 16mm, and 12mm were 26.20N/mm 2, 24.02N/mm2, and
22.03N/mm2 respectively, The 21 day strengths of the concretes made with 20mm, 16mm, and
12mm were 23.23N/mm2, 21.85N/mm2, and 18.17N/mm2 respectively, The 14 day strengths of
the concretes made with 20mm, 16mm, and 12mm were 21.24N/mm2, 20.03N/mm2, and
17.47N/mm2 respectively and The 7 day strengths of the concretesmade with 20mm, 16mm, and
12mm were 19.34N/mm2, 17.55N/mm2, and 15.53N/mm2 respectively. Therefore, result shows
that as the aggregate size increases, the compressive strengthincreases also with increasing
curing days.

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 LIST OF FIGURE

Figure 4.1: sieve Analysis for Fine Aggregate 42

Figure 4.2: Sieve Analysis Graph for 20mm Coarse Aggregates 43

Figure 4.3: Sieve Analysis Results for 16mm Coarse Aggregate 44

Figure 4.4: Sieve Analysis Results for 12mm Coarse Aggregate 45

Figure 4.5: Variation in Slump with Different Coarse aggregate 47

Figure 4.6: Graph of Compressive Strength against Curing Age 50

Figure 4.7: Compressive Strength Analysis of the Effects of Coarse Aggregate 51

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 LIST OF TABLE

Table 3.1: Mix Design for One Concrete Cube 34

Table 4.1: Sieve Analysis Results for Fine aggregates 41

Table 4.2: Sieve analysis results for coarse aggregate (20mm) 42

Table 4.3: Sieve analysis results for coarse aggregate (16mm) 43

Table 4.4: Sieve analysis results for coarse aggregate (12mm) 44

Table 4.4: Slump Test Result 47

Table 4.5: Compressive Strength of Concrete Test Results for 12mm Coarse Aggregate 48

Table 4.6: Compressive Strength of Concrete Test Results for 16mm Coarse Aggregate 49

Table 4.7: Compressive Strength of Concrete Test Results for 20mm Coarse Aggregate 49

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 LIST OF PLATE

Plate 2.1: Slump Test Apparatus 23

Plate 2.2: Compaction Factor Test Apparatus 24

Plate 2.3: Flow Test Apparatus 25

Plate 2.4: Vee-Bee Test Apparatus 26

Plate 2.5: Kelly Ball Test Apparatus 26

Plate 3.1: Sharp Sand 30

Plate 3.2: Coarse Aggregate 31

Plate 3.3: Hand Mixing of Concrete 40

Plate 1: Sieve Analysis on Coarse Aggregate 60

Plate 2: Sieve Analysis on 20mm Coarse Aggregate. 60

Plate 3: Batching of Concrete. 61

Plate 4: Removal of Cubes from Metallic Molds 61

Plate 5: Getting Cubes Ready for Curing. 62

Table of Contents
CERTIFICATION.............................................................................................................................................ii

APPROVAL...................................................................................................................................................iii

DEDICATION................................................................................................................................................iv

ix
ACKNOWLEDGEMENT..................................................................................................................................v

ABSTRACT....................................................................................................................................................vi

LIST OF FIGURE...........................................................................................................................................vii

LIST OF TABLE............................................................................................................................................viii

LIST OF PLATE..............................................................................................................................................ix

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

1.0 INTRODUCTION..................................................................................................................................1
1.1 BACKGROUND OF STUDY...................................................................................................................3
1.2 STATEMENT OF PROBLEM.................................................................................................................3
1.3 AIMS AND OBJECTIVES.......................................................................................................................4
1.4 SCOPE OF WORK................................................................................................................................5
1.5 SIGNIFICANCE OF STUDY....................................................................................................................5
CHAPTER TWO.............................................................................................................................................6

LITERATURE REVIEW................................................................................................................................6
2.1 INTRODUCTION............................................................................................................................6
2.2 LIMITATIONS OF CONCRETE...............................................................................................................7
2.3 CLASSIFICATION OF CONCRETE....................................................................................................8
2.4 PROPERTIES OF CONCRETE................................................................................................................9
2.4.1 PROPERTIES OF FRESH CONCRETE..............................................................................................9

2.4.2 PROPERTIES OF HARDENED CONCRETE....................................................................................12

2.5 REVIEW OF THE EXISTING LITERATURE............................................................................................27

CHAPTER THREE.........................................................................................................................................30

MATERIALS AND METHODOLOGY..........................................................................................................30

3.1 MATERIALS.................................................................................................................................30
3.1.1 CEMENT..............................................................................................................................30

3.1.2 FINE AGGREGATES..............................................................................................................30

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 3.1.3 COARSE AGGREGATES........................................................................................................31

3.1.4 WATER................................................................................................................................31

3.2 METHODOLOGY...............................................................................................................................32
3.2.1 MIX PROPORTION...............................................................................................................32

3.2.2 PRELIMINARY TEST.............................................................................................................34

CHAPTER FOUR..........................................................................................................................................41

RESULTS AND DISCUSSIONS...................................................................................................................41

4.1 SIEVE ANALYSIS FOR FINE AGGREGATES..........................................................................................41
4.2 SIEVE ANALYSIS FOR COARSE AGGREGATES....................................................................................42
4.3 SLUMP..............................................................................................................................................46
4.4 COMPRESSIVE STRENGTH................................................................................................................47
CHAPTER FIVE............................................................................................................................................52

CONCLUSION AND RECOMMENDATION................................................................................................52

5.1 CONCLUSION..............................................................................................................................52
5.2 RECOMMENDATION...................................................................................................................53
REFERENCES...............................................................................................................................................54

APPENDICE.................................................................................................................................................60

xi
 CHAPTER ONE

INTRODUCTION

1.0 Introduction

Concrete is a composite material made of aggregate bonded together by liquid cement, which

hardens over time (Woodford, 2016). The major components of concrete are cement, water, and

aggregates (fines and coarse aggregate) with aggregates taking about 50 to 60% of the total

volume, depending on the mix proportion. The amount of concrete used worldwide is twice that

of steel, wood, plastics, and aluminum combined (Rajith and Amritha, 2015). According to

Yaqub and Bukhari (2006), concrete’s use in the modern world is exceeded only by that of

naturally occurring water.

Concrete can be used either singular or reinforced with steel in order to achieve the required

strength. Concrete builds durable, long lasting structures that will not rust, rot, or burn. It is

widely used for making architectural structures, foundations, brick walls, bridges and many other

civil engineering works. Concrete is used in large quantities almost everywhere humanity has a

need for infrastructure because of its high compressive strength and durability (Ajamu and Ige,

2015).

Concrete is one of the most widely used construction materials. The raw material from which it

is prepared: cement, aggregates and water affect both the quality and cost of construction.

Aggregates are usually cheaper than cement and constitute over 70% of the volume of concrete.

The availability and proximity of aggregate to the construction site also affect the cost of

construction.

The compressive strength of concrete is one of its major properties that structural engineers take

into consideration before erecting any structure (Hollaway, 2010). This property can be affected
1
by many factors including water to cement ratio, degree of compaction, aggregate size and

shape.

Aggregate gradation plays an important role in concrete mixing. Unsatisfactory gradation of

2
aggregates leads to segregation of mortar from the coarse aggregates, internal bleeding, need for

chemical admixtures to restore workability, excessive water use and increased cement use

(Loannides and Mills, 2006).

Aggregates constitute about 50 to 60% of the concrete mix depending on the mix proportion

used. The larger the aggregate percentage in concrete mix, the stronger the concrete becomes

(Waziri et al., 2011). Aggregates are the most mined material in the world. They are a component

of composite materials such as concrete and asphalt concrete.

Curing can be achieved by keeping the concrete element completely saturated or as much

saturated as possible until the water-filled spaces are substantially reduced by hydration products.

According to (Hassan and Mohammed, 2014), curing concrete increase strength by up to 50%

and also improve durability, making it more water tight and improve its appearance. If the

concrete is not cured and is allowed to dry in air, it will gain only 50% of the strength of

continuously cured concrete (Raheem, 2013).

A number of concrete structures around the globe cracks and lose stiffness when subjected to

external load. Having premature deterioration of concrete is an international problem; the

building industry needs to increase the load carrying capacity of structures by using concrete of

high strength. In concrete structures, the mix proportion of the different components together

with the aggregate type and size determine the compressive strength of hard concrete. According

to (Adiseshu and Ganapati, 2011), larger aggregates demand lower water on its mix thus

reducing the workability and increasing the compressive strength of concrete.

3
1.1 Background of study

Coarse aggregate plays an important role in concrete. To predict the behavior of concrete under

general loading requires an understanding of the effects of aggregate type, aggregate size, and

aggregate content. This understanding can only be gained through extensive testing and

observation.

In normal-strength concrete, failure in compression almost exclusively involves deboning of the

cement paste from the aggregate particles at what, for the purpose of this report, will be called

the matrix-aggregate interface (Rozalija K., David D., 1997). In contrast, in high-strength

concrete, the aggregate particles as well as the interface undergo failure, clearly contributing to

overall strength. As the strength of the cement paste constituent of concrete increases, there is

greater compatibility of stiffness and strength between the normal stiffer and stronger coarse

aggregate and the surrounding mortar. Thus, micro cracks tend to propagate through the

aggregate particles since, not only is the matrix-aggregate bond stronger than in concretes of

lower strength, but the stresses due to a mismatch in elastic properties are decreased. Thus,

aggregate strength becomes an important factor in high-strength concrete.

1.2 Statement of problem

It is a common practice in Nigeria to use locally found aggregates (washed and unwashed

gravels) for construction purposes. The integrity of these aggregates should be investigated to

ascertain their performance in structural members. Recent constructions in Nigeria, especially in

Awka and its environs make indiscriminate use of aggregates notwithstanding their sources and

not considering their physical condition at the time of use.

4
Coarse aggregates are obtained naturally or artificially and occupies up to 60% by weight or

volume of the concrete, depending on the mix proportion adopted which, in turn, depends on the

expected compressive strength. The compressive aggregate strength is an important factor in the

selection of aggregate. When determining the strength of normal concrete, most concrete

aggregates are several times stronger than the other components in concrete and therefore not a

factor in the strength of normal strength concrete. For this reason, the quality of the coarse

aggregates is essential when considering the quality of the concrete itself. The properties of

coarse aggregates do grossly affect the durability and structural performance of concrete. Such

properties as size, shape, and surface conditions of aggregates are considered alongside the

mineral composition of the rock material from which theaggregate formed a part.

1.3 Aims and objectives

The aim of this project is to investigate the effects of different size of coarse aggregate on the

compressive strength of concrete.

The objectives of this research are as follows:

1 To gather an abundance of pertinent information through an in-depth review of previous

studies and pinpoint the areas that need to be addressed.

2 To carry out a sieve analysis of the fine and coarse aggregate.

3 To design the mix proportions.

4 To determine the workability of the fresh concrete.

5 Curing of all the concrete specimens for 7, 14, 21 and 28 days.

6 To determine the compressive strength of the hardened concrete.

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1.4 Scope of work

The present work aims to determine the effects of different coarse aggregate sizes on the

compressive strength of concrete using aggregates of sizes; 12mm, 16mm and 20mm, sieve

analysis conducted to grade the aggregate. A cement mix ratio of 1:2:4, water cement ratio of

0.55 and curing days of 7, 14, 21 and 28 days was adopted for 24 cubes of size

150mm×150mm×150mm. They were casted with the components of the concrete batched by

weight. The concrete cubes cured in water 24 hours after casting using the ponding method of

curing. The compressive strength of the concrete at each aggregate size is determined using the

load-testing machine available at the Engineering Laboratory Nnamdi Azikiwe University Awka.

1.5 Significance of study

Aggregate is commonly considered an inert filler, which accounts for 60 to 80 percent of the

volume and 70 to 85 percent of the weight of concrete. Although aggregate is considered an inert

filler, aggregates are necessary component that defines the concrete’s thermal and elastic

properties and dimensional stability.

For this reason, the quality of the coarse aggregates is essential when considering the quality

of the concrete itself. The results from the work aim to serve as a guide in the building and

construction industry while recommending the optimum size of coarse aggregate to use at a mix

ratio of 1:2:4 and a water cement ratio of 0.55 to achieve maximum strength of hardened

concrete after curing.

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 CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction

Concrete is a relatively new construction material when compared to earth, stone, timber and steel.

However it is now the most widely used material for building and civil engineering constructions.

In 2011 alone, over of 27 billion tons was used (in comparison to only about 0.7 billion used in

1993) (Garba, 2014). Besides, if a concrete is to be suitable for a particular purpose, it is

necessaryto select the constituent materials and combine them in such a manner as to develop

constituents of concrete depends on the quality and economy of the particular concrete required.

Concrete is a composite material composed of coarse granular material (the aggregate) embeddedin

a hard matrix of material (the cement or binder) that fills the space between aggregate particlesand

glues them together. We can also consider concrete as a composite material that consists of a

binding medium within which are embedded particles of fragments of fine aggregates (sand) and

coarse aggregate (crushed granite, quartzite, or river gravel). So basically the simplest

representation of concrete is;

Concrete = cement + fine aggregate +coarse aggregate +water

In light of the controversy, this report describes work that is aimed at improving the

understandingof the role that coarse aggregate plays in the compressive strength of concrete. The

role of coarse aggregate in concrete is central to this report. While the topic has been under study

for many years,an understanding of the effects of coarse aggregate has become increasingly more

important with

7
the introduction of high strength concretes, since coarse aggregate plays a progressively more

important role in concrete behavior as strength increases.

Concrete is the most widely used construction material in the world. It is used in many different

structures such as dams, pavements, building frames and bridges. Also its worldwide production

exceeds that of steel by a factor of 10 in tonnage and by more than a factor of 30 in volume. The

present consumption of concrete is over 10 billion tons a year. It is more than 10 times of the

consumption of steel by weight.

Concrete is the most inexpensive and the most readily available material. The cost of production

of concrete is low compared with other engineering construction materials. Because concrete is a

low temperature bonded inorganic material and its reaction occurs at room temperature, concrete

can gain its strength at ambient temperature.

It can be formed into different into different desired shapes and sizes right at the construction

sites. Concrete has low energy consumption for production compared with that of steel. Unlike

wood and steel, concrete can harden in water and can withstand the action of water without

serious deterioration. This makes concrete an ideal material for building structures to control,

store and transport water examples include dams and concrete pipelines. Concrete conducts heat

slowly and is able to store considerable quantities of heat from the environment and thus can be

used as protective coating for steel structures.

2.2 Limitations of concrete

Besides being an ideal construction material, it does have the following limitations. Concrete has

low tensile strength and hence cracks easily. Therefore, concrete is to be reinforced with mild

steel bars, high tensile steel or mesh. Concrete expands and contracts with the changes in

temperature.
8
Hence expansion joints are to be provided to avoid the formation of cracks due to thermal

movements.

Fresh concrete shrinks on drying. It also expands and contracts with wetting and drying.

Provision of contraction joints is to be made to avoid the formation of cracks due to dry

shrinkage and moisture movements. Concrete is not entirely impervious to moisture and contains

soluble salts which may cause efflorescence. This requires special care at the joints. Creeps

develop in concrete under sustained loads and this factor is to be taken care of while designing

dams and pre- stressed concrete structures.

2.3 Classification of concrete

based on Unit Weight

1. Ultra-light concrete: < 1,200 kg/m3

2. Lightweight concrete: 1200- 1,800 kg/m3

3. Normal-weight concrete: 2,400 kg/m3

4. Heavyweight concrete: > 3,200 kg/m3

Based On Strength

1. Low-strength concrete: < 20 MPa compressive strength

2. Moderate-strength concrete: 20 -50 MPa compressive strength

3. High-strength concrete: 50 - 200 MPa compressive strength

4. Ultra high-strength concrete: > 200 MPa compressive strength

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2.4 Properties of concrete

To obtain a good quality concrete, its properties in both fresh and hardened states play important

rules.

2.4.1 Properties of fresh concrete

Workability

Workability is a general term to describe the properties of fresh concrete. Workability is often

defined as the amount of mechanical work required for full compaction of the concrete without

segregation. This is useful definition because the final strength of the concrete is largely

influenced by the degree of compaction. A small increase in void content due to insufficient

compaction could lead to a large decrease in strength. The primary characteristics of workability

are consistency (or fluidity) and cohesiveness. Consistency is used to measure the ease of flow of

fresh concrete. And cohesiveness is used to describe the ability of fresh concrete to hold all

ingredients together without segregation and excessive bleeding.

Segregation

Segregation of concrete means separation of ingredients from design fresh concrete resulting in

the non-uniform mix. More specifically this implies the separation of coarse aggregates from the

mortar because of differences in size, density, shape and other properties of ingredients in which

they are composed. Because of segregation honeycomb is created in the concrete and it basically

affects the strength of the concrete and its porosity. During construction work, segregation and

concrete can occur on site and it affects the durability of your structures. If you are constructing

your own house or working on a site you have to understand about segregation and concrete. In

good concrete all the ingredients are properly distributed and make a homogeneous mixture. If a

concrete sample exhibits a tendency for separation of coarse aggregates from the rest of the

10
ingredients, it indicates segregation and concrete depending upon the dryness or wetness of the

concrete mix.

Types of Segregation of Concrete

There are mainly 2 types; the coarser and the heavier particles tend to separate out or setting

down from the rest of the mix because they tend to travel faster along a slope or settle more than

finer materials. This type of segregation may occur if the concrete mix is too dry. Grout (water +

cement) separating out from the rest of the material because of lowest specific gravity. This type

of segregation may occur if the concrete mix is too wet. A well-designed concrete does not

segregate if rightly mixed and batched.

Causes of Segregation in Concrete

The following are the major causes:

1. The difference in the specific gravity of the mix constituents (fine aggregates and coarse

aggregate).

2. The difference in the size of aggregate.

3. Improper grading of aggregates.

4. Improper handling of aggregates.

5. Bad practices and handling and transporting of concrete.

6. Too much vibration of concrete.

7. Concrete that is not proportioned properly and not mixed adequately for 2 workable mix.

8. Placing of concrete from a greater height.

9. Concrete is discharged from a badly designed mixer or from a mixture with worn-out blades.

11
 How to Prevent Segregation of Concrete

1. At the time of construction, especially while using transit mixers care should be taken that

the concrete is not poured from a height greater that 1.5 meter.

2. Aggregates should be properly graded as it will prevent the segregation.

3. To improve the viscosity of concrete which prevents the segregation, air entraining agents

can be used.

4. In case of mass concreting where mechanical vibrators are used care should be taken that

they are not used for longer period.

Bleeding

Concrete mix design is a very precise science to achieve design concrete strength. If concrete

ingredients are not mixed properly many concrete related problems can result and affect the

strength and durability of concrete. Bleeding is one of the concrete related problems. It is mostly

observed in a highly wet mix and badly proportioned concrete ingredients after placing of the fresh

concrete. Free water in a mix rises upward to the concrete surface due to the settlement of solid

particles by gravity action. This process is known as ‘Bleeding of Concrete”. In certain situation

though bleeding water does not come up to the surface but bleeding does take place. The bleeding

water gets trapped on the underside of coarse aggregates or of reinforcements. This is known as

internal bleeding.

Effects of bleeding of concrete

1. The main effect of is that the concrete mixture loses its homogeneity, which results in

weak and porous concrete.

2. It affects the bond between hardened cement paste and aggregates for reinforcement on

account of higher water cement ratio.

12
 3. Such concrete is easily prone to the micro cracking due to shrinkage stresses caused by

dissipation of heat of hydration and drying shrinkage.

4. If the bleeding water carries with it more amount of the cement particles, a layer of

laitance will be formed.

5. Due to bleeding the ability of pumping is very much reduced, which makes it difficult

where concrete is to be pumped for higher elevations.

How to prevent bleeding of concrete

1. Bleeding of concrete depends on the properties of cement. Bleeding gets decreased by

increasing the fineness of cement because finer particles hydrate earlier and also their rate

of sedimentation is lower.

2. The properties of cement are not an only soul factor influencing the bleeding of concrete.

3. The presence of fine aggregates and higher water cement ratio also lead to bleeding. A

higher rate of the water cement ratio can lead to excessive bleeding and if evaporation of

water from the surface of the concrete is faster than the bleeding rate plastic shrinkage

cracking may result.

4. Use of air entraining admixtures can also reduce the bleeding in concrete

2.4.2 Properties of Hardened Concrete

Hardness

The hardness of concrete is referenced by its compressive strength. The higher the compressive

strength, the harder the material.

13
Strength

Strength with regard to concrete for structural purposes it can be defined as the unit force

required to cause rupture. Concrete is considered by many to be a strong and durable material,

and rightfully so. But there are different ways to assess concrete strength. Perhaps even more

importantly, these strength properties each add different qualities to concrete that make it an

ideal choice in various use cases

Compressive strength

Concrete is used mainly so as to exploit its good compressive strength. The compressive strength

of concrete is the load applied on hardened concrete per unit area of the specimen symbolized by

N/mm2. Neville and Brooks (2000) consider the fracture mechanics approach for concrete under

bi-and tri-axial stresses and under uniaxial compression.

Tensile strength of concrete

Tensile strength is the ability of concrete to resist breaking or cracking under tension. It

affects the size of cracks in concrete structures and the extent to which they occur. Cracks

occur when tensile forces exceed the tensile strength of the concrete.

Traditional concrete has a significantly lower tensile strength as compared to compressive

strength. This means that concrete structures undergoing tensile stress must be reinforced with

materials that have high tensile strength, such as steel.

It is difficult to directly test the tensile strength of concrete, so indirect methods are used. The

most common indirect methods are flexural strength and the split tensile strength.

The split tensile strength of concrete is determined using a split tensile test on concrete cylinders.

The test should be performed according to the ASTM C496 standard.

14
Flexural strength of concrete

Flexural strength is used as another indirect measure of tensile strength. It is defined as a

measure of an unreinforced concrete slab or beam to resist failure in bending. In other words, it is

the ability of the concrete to resist bending.

Flexural strength is usually anywhere from 10 to 15 percent of the compressive strength,

depending on the specific concrete mixture.

There are two standard tests from ASTM that are used to determine the flexural strength of

concrete C78 and C293. Results are expressed in a Modulus of Rupture (MR) in psi.

Flexural tests are very sensitive to concrete preparation, handling, and curing. The test should be

conducted when the specimen is wet. For these reasons, results from compressive strength tests

are more typically used when describing the strength of concrete, as these numbers are more

reliable.

Factors affecting the strength of concrete

The strength of concrete is usually affected by many factors, in this project work, such factors are

discussed with particular reference to the compressive strength. The factors include:

Cement

Cement is considered as the main constituent of concrete in terms of strength development.

(Gupta and Gupta 2012) define cement as a material having adhesive and cohesive properties

which makes it capable of bonding material fragments into a compact mass. Cement and water

constituents of concrete chemically react to form a binding medium (Garba, 2014). When cement

paste hardens, it binds the aggregate into an artificial stone-like material called concrete.

According to

15
Dunuweera (2017), Cement is produced by utilizing an extensive amount of raw materials

treated and reacted at extreme conditions such as high temperatures.

Aggregate

Aggregates constitute the skeleton of concrete. Approximately three-quarters of the volume of

conventional concrete are occupied by aggregate. It is inevitable that a constituent occupying

such a large percentage of the mass should contribute important properties to both the fresh and

hardened product. Aggregate is usually viewed as an inert dispersion in the cement paste.

However, strictly speaking, aggregate is not truly inert because physical, thermal, and,

sometimes, chemical properties can influence the performance of concrete (Neville and Brooks,

2000).

Water

Water is one of the most important ingredients of concrete as it actively participates in the

chemical reaction with cement. This is why (Neville and Brook2000) reiterates that the quality of

water is important because impurities in it may interfere with the setting of cement, may

adversely affect the strength of the concrete or cause staining of its surface, and may also lead to

corrosion of reinforcement.

However, according to Shetty (2009), MacCarthy (2010), Sabraini (2010) Garba et al. (2014),

mixing water induce hydration process in concrete production (which is responsible for strength

development) and assist in workability (which enables concrete to be easily mixed, transported

placed and compacted). The reaction between cement and water is as follows;

2Ca3SiO5 + 6H2O → 3Ca(OH)2 + Ca3Si2O7.3H2O (2.1)

Ca3(AlO3)2 + 6H2O → Ca6(AlO3)2.6H2O (2.2)

16
Numerous studies have been carried out on the effect of water quality on the strength and durability

characteristics of a cement concrete. It was generally observed by virtually all the researchers

suchas McCarthy (2010), Sabraini (2010), Gupta and Gupta (2012) and Garba (2014) that the

quality of mixing water for concrete production should be as good as drinking water. However, this

statement was not agreed by Shetty (2009), he argues that some water containing small amount

ofsugar could be suitable for mixing concrete and conversely water suitable for mixing concrete

maynot necessary be fit for drinking.

He emphasizes that the best course to find out whether a particular type of water is suitable for

concrete making or not, is, to make concrete with this water and compare its 7 days’ and 28 days’

strength with comparison cubes made with distilled water. If the compressive strength is up to 90%,

the source of water may be accepted. Besides that, there is relationship between the quality of

mixing waters used in the construction of a structure with the setting time strength, stability, safety

and serviceability of that structure. Noruzman et al. (2012) carried out a research in which they

noted that the initial setting time of cement paste and the compressive strength tests are the two

methods by which questionable water may be tested with respect to its suitability for concrete

production.

Also, the presence of harmful oxides, such as MgO, SO 3 and other alkalis, in mixing water affects

the quality of the hardened concrete (Reddy, 2013). Since water may contain some impurities

suchas clay, sugar, oil, salt etc., which may not be within the tolerable concentration as clarified by

(Shetty 2009). The quality of water is to be critically monitored and controlled during the process

of concrete making.

17
Water to cement ratio

Water to cement ratio (W/C) ratio is one of the most important parameters governing the strength

of concrete. The density of hardened cement (in terms of a gel/space ratio) is governed by the

water/cement ratio. With higher w/c ratio, the paste is more porous and hence the strength is

lower. The strength continues to increase with decreasing w/c ratio only if the concrete can be

fully compacted.

For concrete with very low w/c ratio, if no water-reducing agent is employed, the workability

can be so poor that a lot of air voids are entrapped in the hardened material. The strength can

then be lower than that for concrete with higher w/c ratio. For a given set of materials and

environment conditions, the strength of a concrete age depends only on the water-cement ratio,

providing full compaction can be achieved. The standard water-cement ratio is 0.5.

Coarse to fine aggregate ratio

The following points should be noted for coarse/fine aggregate ratio:

1. If the proportion of the aggregate is increased in relation to the coarse aggregate, the

overall aggregate surface area will increase.

2. If the surface area of the aggregate has increased, the water demand will also increase.

3. Assuming the water demand has increased, the water-cement ratio will increase.

4. Since the water-cement ratio has increased, the compressive strength will decrease.

Aggregate to cement ratio

The following points should be noted for aggregate-cement ratio:

1. If the volume remains the same and the proportion of cement in relation to that of sand is

increased, the surface area of the solid will increase.

18
 2. If the surface area of the solid has increased, the water demand will stay the same for the

constant workability.

3. Assuming an increase in cement content for no increase in water demand, the water-

cement ratio will decrease.

4. If the water-cement ratio reduces, the strength of the concrete will increase.

Age of concrete

The degree of hydration is synonymous with the age of concrete provided that the concrete has

not been allowed to dry out or the temperature is too low. In theory, provided that the concrete is

not allowed to dry out, then it will always be increasing albeit at an ever reducing rate. For

convenience and for most practical applications, it is generally accepted that the majority of the

strength has been achieved by 28 days.

The 7th day strength can range from 60% - 80% of the 28th day strength, with a higher percentage

for a lower w/c ratio. After 28 days, the strength can continue to go up. Experimental data

indicates that the strength after one year can be over 20% higher than the 28 days strength. The

reliance on such strength increase in structural design needs to be done with caution, as the

progress of cement hydration under real world conditions may vary greatly from site to site.

Compaction of concrete

Once the concrete has been placed, it is ready to be compacted. The purpose of compaction is to

get rid the air voids that are trapped in loose concrete. Air voids reduce the strength of the

concrete. For every 1% of entrapped air, the strength falls by somewhere between 5% and 7%

(Gambhir, 1999). This means that concrete containing a mere 5% air voids due to incomplete

compaction can lose as much as one third of its strength. Air voids also increase concrete

permeability. That in turn reduces its durability.

19
If the concrete is not dense and impermeable, it will not be watertight. It will be less able to

withstand aggressive liquids and its exposed surfaces will weather badly. The difference between

air voids and entrapped air bubbles should be noted at this stage. The air bubbles that are

entrained are relatively small and spherical in shape, increase frost resistance. Entrapped air on

the other hand tends to be irregular in shape and is detrimental to the strength of the mix. In order

to remove both, the concrete must be properly compacted.

Curing of Concrete

It should be clear from what has been said above, that the detrimental effects of storage of

concrete in a dry environment can be reduced if the concrete is adequately cured to prevent

excessive moisture loss. Curing is the process of protecting the freshly poured concrete from

evaporation and temperature extremes which might adversely affect cement hydration. Curing

ensures the continuation of hydration of cement and the strength gain of concrete. Concrete

surfaces are cured by sprinkling with water. Most of the strength gain and take place within the

first month of concrete's life cycle but hydration continues at slower rate for many years.

Concrete continues to get stronger as it gets older.

Durability

Concrete has been considered as a material that can bear both internal and external exposure

conditions requiring little or no maintenance. This assumption proved valid except when it is

subjected to severe or aggressive environment. A durable concrete is one that serves the purpose

for which it was designed for, for the specified service condition and the lifespan. Gambo (2014),

defines durability of cement concrete as its resistance to deteriorating agencies to which it may

be exposed during its service life or which may inadvertently reside inside the concrete itself.

20
The durability of concrete is affected by physical, mechanical and chemical causes but is mostly

affected by chemical causes, which result in volume change, cracking of concrete and ultimately

leading to deterioration of concrete. This is the reason why Gupta and Gupta (2012) discussed

the effect of chemical causes on the durability of concrete under the following headings: sulphate

attack; acid attack; Sea water attack; alkali aggregate reaction; deicing salts effect and

carbonation. Impermeability

The impermeability of concrete refers to the property of concrete that cannot be pervaded by

water oil and other liquids with pressures. It plays an important role in the durability of concrete.

Dimensional change

The dimensions of concrete change when there is elastic deformation under applied loading,

creep deformation under sustained loading, thermal expansion or contraction under temperature

variation, and swelling or shrinkage under moisture content variation.

Workability of concrete

Workability is a general term to describe the properties of fresh concrete. Workability is often

defined as the amount of mechanical work required for full compaction of the concrete without

segregation. This is useful definition because the final strength of the concrete is largely

influenced by the degree of compaction. A small increase in void content due to insufficient

compaction could lead to a large decrease in strength.

The primary characteristics of workability are consistency (or fluidity) and cohesiveness.

Consistency is used to measure the ease of flow of fresh concrete. And cohesiveness is used to

describe the ability of fresh concrete to hold all ingredients together without segregation and

excessive bleeding.

21
Factors affecting workability

1. Water content: Except for the absorption by particle surfaces, water must fill the spaces

among particles. Additional water "lubricates" the particles by separating them with a

water film. Increasing the amount of water will increase the fluidity and make concrete

easy to be compacted. Indeed, the total water content is the most important parameter

governing consistency. But, too much water reduces cohesiveness, leading to segregation

and bleeding. With increasing water content, concrete strength is also reduced.

2. Aggregate mix proportion: For a fixed w/c ratio, an increase in the aggregate/cement

ratio will decrease the fluidity. (Note that less cement implies less water, as w/c is fixed.)

Generally speaking, a higher fine aggregate/coarse aggregate ratio leads to a higher

cohesiveness.

3. Maximum aggregate size: For a given w/c ratio, as the maximum size of aggregate

increases, the fluidity increases. This is generally due to the overall reduction in surface

area of the aggregates.

4. Aggregate properties: The shape and texture of aggregate particles can also affect the

workability. As a general rule, the more nearly spherical and smoother the particles, the

more workable the concrete.

5. Cement: Increased fineness will reduce fluidity at a given water-cement ratio, but

increase cohesiveness. Under the same water-cement ratio, the higher the cement content,

the better the workability (as the total water content increases).

6. Admixtures: Air entraining agent and super plasticizers can improve the workability.

22
 7. Temperature and time: As temperature increases, the workability decreases. Also,

workability decreases with time. These effects are related to the progression of chemical

reaction.

Workability test

Workability of concrete has never been precisely defined, but for practical purposes it generally

implies the ease with which a concrete mix can be handled from the mix to its final compacted

shape. The measurement of workability of fresh concrete is important in assessing the

practicability of compacting the mixture and also in maintaining consistency throughout the job.

In addition, workability tests are often used as an indirect check on the water content and

therefore on the water/cement ratio of the concrete (Barnbrook et al., 1979).

The types of workability test are;

a. Slump test.

b. Compaction factor test.

c. Flow test.

d. Vee-Bee consistometer test.

e. Kelly ball test.

Slump test

The concrete slump test or slump cone test is the most common test for workability of freshly

mixed concrete which can be performed either at the working site/field or in the laboratory. To

maintain the workability and quality of fresh concrete, it is necessary to check batch by batch

inspection of the concrete slump. This can be easily done with the concrete slump test. The

23
slump test is the simplest test to determine workability of concrete that involves low cost and

provides immediate results. Slump test is done in accordance to BS 1881: 103 :1993.

Three different kinds of possible slumps exist; true slump, shear slump, and collapse slump.

Conventionally, when shear or collapse slump occur, the test is considered invalid. However, due

to recent development of self-compact concrete, the term of collapse slump has to be used with

caution.

Plate 2.1: Slump Test Apparatus.

Compaction factor test

Compaction factor test works on the principle of determining the degree of compaction

achieved by a standard amount of work done by allowing the concrete to fall through a standard

height.

This is specially designed for laboratory use, but if the circumstances favours, it can also be

used on the working site/field.

24
Compaction factor test of concrete is more precise and sensitive than the concrete slump test;

hence it is more favorable and useful for low workable concrete or dry concrete which is

generally used when concrete is to be compacted by vibration. Compaction factor test is done in

accordance to BS 1881: 103 :1993.

Plate 2.2: Compaction Factor Apparatus

The flow test

The flow test is a laboratory test, which gives an indication of the quality of concrete with

respect to consistency or workability and cohesiveness. In the flow test, a standard mass of

concrete is subjected to jolting. This test is generally used for high/ very high workability

concrete.

25
Similar laboratory test named ‘Flow Table Test ‘was developed in Germany in1933 and it has

been described in ‘BS 1881:105: 1984’. This method is used for the high and very high workable

concrete which would exhibit the collapse slump.

Plate 2.3: Flow Test Apparatus

Vee bee consistometer test

Vee bee consistometer test is a good laboratory test on fresh concrete to measure the workability

in an indirect way by using a Vee-Bee consistometer. Vee bee test is usually performed on dry

concrete and it is not suitable for very wet concrete. Vee bee consistometer test determines the

mobility and to some extent compatibility of concrete. In the vee bee consistometer test vibrator

is used instead of jolting. Vee bee test determines the time required for the transformation of

concrete by the vibration. This test is done in accordance to BS EN 12350-3: 2009.

26
 Plate 2.4: Vee-Bee Apparatus

Kelly ball test

This test is developed by J.W Kelly, hence it’s known as a Kelly ball test. Kelly ball test is a

simple and inexpensive field test which measures workability of fresh concrete with the similar

to the concrete slump test, but it is more accurate and faster than a slump test. This test uses a

device that consist of metal hemisphere (ball) thereby indicating the consistency of fresh

concrete by its level of penetration when the metal hemisphere drops. Thus, in this test, depth is

determined through metal hemisphere, which sinks under its own weight into fresh concrete.

This test is done in accordance to ASTM C360-92 – For ball penetration test

Plate 2.5: Kelly Ball Apparatus

27
 Setting of concrete

Setting is defined as the onset of rigidity in fresh concrete. It is different from hardening, which

describes the development of useful and measurable strength. Setting precedes hardening

although both are controlled by the continuing hydration of the cement.

2.5 Review Of The Existing Literature

Young and Sam (2008) reported that smooth rounded aggregates was more workable but yielded a

lesser compressive strength in the matrix than irregular aggregates with rough surface texture. They

were also of the opinion that a fine coating of impurities such as silt on the aggregate surfacecould

hinder the development of a good bond and thus affects the strength of concrete produced with the

aggregates.

Chen and Liu (2004) as well as Rao and Prasad (2002) viewed aggregates as the skeleton of

concrete and consequently persuaded that all forms of coatings should be avoided in order to

achieve a good concrete. When a concrete mass is stressed, failure may originate within the

aggregates, the matrix, or at the aggregate-matrix interface. The aggregate-matrix interface is an

important factor determining the strength of concrete.

Bloem and Gaynor (1963) studied the effect of shape, surface texture, fine coatings, and

maximum size of aggregates on the water requirement and strength of concrete. The study

reported that at equal water/cement ratio, irregular shaped smaller sized aggregates without

coatings achieved a better strength than smooth rounded large sized aggregates. They also opined

that individual properties of aggregates and the magnitude of the size difference may lead to

increase or decrease in concrete strength at a fixed cement content.

28
Aginam et al. (2013) investigated the effect of coarse aggregate types on the compressive

strength of concrete on three different types of coarse aggregates, with 20mm maximum size, was

employed in the investigation, namely; crushed granite, washed gravel, and unwashed gravel.

The grading and relative densities of the aggregates was studied. The mix ratio and water/cement

ratio adopted for the study was 1:3:6 and 0.6 respectively. The target mean strength at 28 days

was 15N/mm2. Twelve concrete cubes (150mm x 150mm x 150mm) were cast for each coarse

aggregate type of which four were crushed at each maturity age namely; 7, 14, 21, and 28 days.

All cubes reached the target mean strength after 7 days of curing. The 28 days strengths of the

concretes made with crushed granite, washed gravel, and unwashed gravel were 25.1 N/mm 2,

20.0 N/mm2, and 16.9 N/mm2 respectively. Consequently, the authors concluded that the strength

of concrete depends greatly on the internal structure, surface nature and shape of aggregates.

According to Bruce and Ndlangamandla (2016), the effect of aggregate size on the compressive

strength of concrete. The experiment had three treatments, which were the aggregate sizes (9.5

mm, 13.2 mm and 19.0 mm) and the control. A constant mix of 1: 2: 4 with a water/cement ratio

of 0.5 used throughout the experiment. Three cubes (150 mm× 150 mm) were casted from each

batch and the compressive strength was determined using a concrete load-testing machine (Pro-

Ikon cube press) after 7 days curing. The results reflected that workability (slump) increased with

increasing aggregate size. The concrete made from the 9.5 mm, 13.2 mm and 19.0 mm aggregate

sizes had workability (slumps) of 10 mm, 13.5 mm and 20 mm, respectively. The mean

compressive strength for the 9.5 mm, 13.2 mm, and 19 mm were 15.34 N/mm2, 18.61 N/mm2 and

19.48 N/mm2, respectively. They concluded that concrete workability was directly proportional

to aggregate size. The mean concrete compressive strength increased with increasing aggregates

size.

29
Abdullahi (2012) investigated the effect of aggregate type on compressive strength of concrete

for a nominal mix (1:2:4), 75 cubes (150x150mm) were cast to allow the compressive strength to

be monitored at 3, 7, 14, 21, and 28 days. Test result showed that concrete made from river

gravel has the highest workability followed by crushed quartzite and crushed granite aggregates.

Highest compressive strength at all ages with concrete made from quartzite aggregate followed

by river gravel and then granite aggregate. The author proposed compressive strength models as

a function of age at curing. In addition, where concrete practitioners have options, aggregate

made from quartzite is advisable for concrete works.

30
 CHAPTER THREE

MATERIALS AND

METHODOLOGY

3.1 Materials

3.1.1 Cement

The Portland-Limestone cement with the brand name of Dangote cement was purchased at Agu-

Awka in Anambra state. It was stored in a dry environment to protect it from moisture to avoid

the occurrence of lumps before the experiment.

3.1.2 Fine Aggregates

Fine aggregate used was dry river sand sourced locally from Ezu River in Anambra state and

bought from the retailers in Agu-Awka. The sand was sun-dried before sieve analysis was

carried out to rid it of impurities such as crushed stones and twigs. It was sieved to a particle size

range between 0.15 -2.36mm which is within the range specified by BS112 (1971).

Plate 3.1: Sharp Sand

31
3.1.3 Coarse Aggregates

The type of coarse aggregate used throughout this investigation was washed granite. The effects

of three different sizes of coarse aggregates were investigated in this research these sizes are

20mm, 16mm, and 12mm. These sizes were sourced from the quarries of Abakaliki and were

bought from the local retailers in Agu-Awka in Anambra state. Sieve analysis tests were also

conducted on the coarse aggregates for adequate confirmation of the sizes of the samples after

they have been washed and dried.

Plate 3.2: Coarse aggregates

3.1.4 Water

Portable water at the Nnamdi Azikiwe University was used throughout this investigation and the

tests were carried out at the Civil Engineering laboratory of the same University.

32
 3.2 Methodology

The concrete mix proportions were batched by weight and the casting, curing and crushing were

done in accordance with the guidelines specified by BS1881; Part108 (1983), BS8110; Part1,

(1985), and BS1881; Part3 (1992).

150x150x150mm cubes were casted and the compressive strengths were investigated at 7, 14, 21

and 28 days of curing.

Each concrete mix proportion was the same except the variation in aggregate size. Eight cubes were

cast for each aggregate size, two cubes for each curing age. The hardened concrete cubes are

retrieved from the steel molds 24hours after casting and are placed in curing tanks. The concrete

cubes are withdrawn from water in the curing tanks and allowed to dry for some hours before

crushing. The average compressive strength is taken from the two cubes in each curing age

3.2.1 Mix Proportion

A nominal mix ratio of 1:2:4 (cement: fine aggregates: coarse aggregates) was adopted for the

purpose of this work and water-cement ratio of 0.55 was used throughout the investigation. The

mix composition was computed using the weight method and the batch compositions are shown

below. To calculate the quality of materials required to cast 1 concrete cube at a mix ratio of

1:2:4by batching by weight.

Parameters

i. Density of concrete = 2400kg/m³

ii. Size of cubes =150mm x 150mm

iii. Converting to meters = 0.15m by 0.15m

33
 iv. Volume of cube = 0.15m × 0.15m × 0.15m = 0.00375m³

v. Weight of cube = 2400kg/m³ x 0.153m³= 8.1kg.

To determine the weight of the individual components

1:2:4 = cement: sand: aggregates; 1:2:4 = 7

Cement: 1/7 × 8.1 = 1.157kg

Sand: 2/7 × 8.1 = 2.314kg

Coarse aggregates: 4/7 × 8.1 = 4.629kg

Provide additional 10% on all concrete components to take care of wastage;

Cement = 1.157 + (10/100 × 1.157) = 1.157 + 0.1157 =1.2727kg

Sand = 2.314 + (10/100 × 2.314) = 2.314 + 0.2314 = 2.5454kg

Aggregate = 4.629 + (10/100 × 4.629) = 4.629 + 0.4629= 5.0919kg

To estimate the weight of water for one concrete cube using the chosen water-cement ratio of

0.55; 1.2727 x 0.55 = 0.6999kg

Converting water in kg to liters

1kg of water is approximately 1liter of water therefore for each concrete cube

0.6999liters of water must be maintained.

34
 Table 3.1: Mix design for one concrete cube

CEMENT SAND COARSE AGGREGATE WATER

(Kg) (Kg) (Kg) (Kg)

1.2727 2.5454 5.0919 0.6999

3.2.2 Preliminary Test

In controlling the quality of aggregates, it is important to ensure that the aggregate is clean and

does not contain any organic impurities which might retard or prevent the setting of the cement

and that the proportions of the different sizes of the particles within a graded material remain

uniform. Sometimes excessive silt and clay contained in the fine and coarse aggregates may

result in increased shrinkage or increased permeability in addition to poor bond characteristics. It

may also necessitate greater water requirement for workability.

Accurate tests for determining the proportions of clay, silt and dust in fine or coarse aggregates

are given in clause 12 and 13 of BS 812 (Barnbrook et al., 1979), but these tests are suitable only

for the laboratory. On site cleanness can be assessed visually, though for natural sands the field

settling tests will give an approximate guide to the amount of clay or silt. Cleanness tests on the

coarse aggregates was not considered as the coarse aggregate was visibly clean from silt and

clayey components as the aggregates used were washed crushed quarry stones.

Sieve Analysis

Sieve analysis is referred to as the simple operation of separating a sample of aggregates into

factions (groups) each consisting of particles of the same size. The main aim is to determine

various sizes of particles present in aggregates and appropriately grading the aggregates.

35
Apparatus

a. Standard B.S test sieve

b. A weighing scale

c. Container used in the weighing.

Procedure for the sieve analysis

i. The aggregate specimen to be used (fine aggregate) is dried for 24 hours to rid specimen

of any traces of moisture.

ii. Sieves are arranged from top to bottom in descending order.

iii. Weight of the container to be used in the specimen measurements is ascertained.

iv. Before the sample is used, they are sieved through a 4.75mm sieve for uniform sample;

and the portion retained in the sieve was discarded while those passing were used to

perform the particle size analysis.

v. A considerable measured quantity of the aggregate is placed in the sieves from the top.

vi. Sieving is done for about 5 hours manually.

For the coarse aggregate used, the aggregate was sieved through the 1inch sieve (25mm sieve)

and those passing the sieve aperture and retained in the (20 mm) sieve were used to obtain that

particular size of aggregate as those not passing the 1 inch sieve were discarded. This was to

bring about uniformity in the aggregate used. The same procedure was repeated for sieve sizes

16mm, 12mm. Aggregates subsequently retained in sieve sizes 6.3mm, 5mm, 3.35mm and the

pan were discarded.

36
Testing on fresh concrete

Slump Test

Workability of concrete has never been precisely defined, but for practical purposes it generally

implies the ease with which a concrete mix can be handled from the mix to its final compacted

shape. The measurement of workability of fresh concrete is important in assessing the

practicability of compacting the mix and also in maintaining consistency throughout the job. The

slump test was carried out on the fresh concrete after the mixing of each batch, the slump value is

taken down and the used concrete is poured back into the mix and reblended. The slump test was

carried according to specifications on BS EN 12350-2: 2009.

Determination of workability of concrete is as follows;

Apparatuses Used

a. A truncated slump cone (Truncated conical mold)

b. A tampering rod (16mm diameter and 600mm long)

c. Metallic rule

d. Flat tray (metallic)

e. Trowel

f. Spirit level

Procedure of the Test

i. Concrete is mixed with a water/cement ratio of 0.55 for 12mm, 16mm and 20mm

aggregate size for uniformity throughout the project research.

ii. The inside of the mold should be cleaned before each testing and mold applied with

lubricant (diesel oil) to prevent concrete from sticking to mold surface. The mold is then

placed on the flat hard tray such that the wider surface is on the flat form or tray.

37
 iii. The mold (height 300mm, top diameter 100mm and bottom diameter 200mm) is then

filled with concrete in 3 layers of equal height with the use of a trowel. Compacting or

rodding is carried on each layer with a minimum of 25 strokes with the tampering rod.

After the top layer has been rodded, the surface of the concrete is struck off level with the

top of the mold with a trowel.

iv. After leveling and smoothing top of the concrete with the mold/cone height, any spillage

around the mold is cleaned away from around the base of the mold, and the mold is the

lifted vertically from the concrete.

v. The slump is the difference between the height of the concrete before and after the

removal of the mold. The tampering rod is placed on top of the cone to span across the

concrete slump. The metallic rule is the used to measure the difference in height between

the top of the cone and the top of the cone and the top of the slumped concrete.

Testing on hardened Concrete

Compressive test cubes

For aggregates with nominal size of 20mm (¾ inch) or less can be done in 100mm (4 inches)

cubes. The 150mm cube was used in this investigation.

𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒
𝐿𝑜𝑎𝑑,𝑃 (𝐾𝑁)
Compressive strength =
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎,𝐴 (𝑚𝑚2)
(3.1)

Details of the testing cubes, beams and cores as stated before are given in part 4 of BS 1881. The

testing procedure is as follows;

Apparatuses Used

a. Steel molds (150 x150x150) mm3 with base plates.

b. Tampering rods

38
 c. Shovels for the concrete mixing

d. Hand trowels

e. Weighing balance

Procedure for the Manufacturing of the Test Cubes

i. The molds for the testing would be properly assembled, cleaned up and lubricated to

prevent concrete from sticking to the molds surfaces or sides.

ii. Freshly prepared concrete mix is then placed in the molds in 3 layers, with each layer

being effectively rammed with the tampering/ramming rod. The ramming of the concrete

is carried out methodically, the strokes being evenly distributed over the surface of the

concrete in regular pattern and not concentrated in one particular spot.

iii. The test specimens are kept in conditions of constant room temperature and allowed to

set for 24hrs of which they are subsequently demolded and marked before putting them in

curing tanks until time of testing.

iv. Cube is removed from the curing tank and dimensions and weight of the cube is duly noted.

v. The bearing surface of the testing machine is wiped clean and the cube placed in the

compression machine in such a way that the load is applied to the surface of the cube.

The axis of the cube must be carefully aligned with the center thrust of the machine.

vi. The load from the machine is applied to the cube by pulling on the machine level handle

repeatedly until such a point when the concrete cube show signs of failure or crushing.

vii. The compressive strength is then recorded.

Batching

Generally, the components of concrete in various proportions can be batched by weight or

volume. The batching process was done by weight as this is preferable in most cases because of

its degree
39
of accuracy. All the concrete constituents were weighed out, from calculations of required mix

quantities using the bulk densities of the constituents as well as the volume of mix required to

obtain the weights required. The mixing was performed on the floor of the laboratory premises

by hand mixing using a shovel and a trowel.

The mixing process was done with measured amount of water, measured amount of fine

aggregate, and a well measured amount of coarse aggregate (which could be of 20mm, 16mm,

12mm size) and was mixed together with a mix design ratio of 1:2:4 before it was poured into a

concrete cube of 150mm by 150mm.

The coarse aggregates used were of approximately uniform grading at each size and

water/cement ratio was also constant throughout the mixing as effectively calculated. This is

because it is a well- known fact that concrete strengths vary with aggregate (coarse) grade or

sizes as well as water/cement ratio. These were all done to provide for a uniform basis for clearly

distinguishing the effects of the coarse aggregate sizes on the compressive strength of concrete.

Mixing Procedure

As obtained from the mix calculations by weight, 1.2727kg of cement, 2.5454kg of sand

and5.0919kg of coarse aggregate was the quantity of components adequate for one concrete

cube. Subsequently for 8 cubes 10.1816kg was weigh out and mixed with20.3632kg of fine

aggregate (sand) until an even mix was obtained. Thereafter, 40.7352kg of gravel was weighed

out and added to the cement and sand mixture and water of 5.5992kg in conformity with a 0.55

water-cement ratio was gradually added to the mixture. The mixture was gradually stirred with a

shovel as the water was added to bring about an even concrete paste.

40
 Plate 3.3: Hand mixing of concrete

Details of the testing of cubes, beams and cones as stated before are given in part 4 of BS

1881.The testing procedure is as follows. Cube is removed from the curing tank and dimensions

and weight of then cube duly noted. The Bearing surface of the testing machine is wiped clean

and the cube placed in the compression machine in such a way that the load is applied to the

surface of the cube. The axis of the cube must be carefully aligned with the center thrust of the

machine. The load from the machine is applied to the cube by pulling on the machine lever

handle repeatedly until such a point when the concrete cube show signs of failure or crushing.

The compressive strength is then recorded.

41
 CHAPTER FOUR

RESULTS AND

DISCUSSIONS

4.1 Sieve Analysis For Fine Aggregates

Weight of container used for measurements – 110.42

grams Weight of sample plus the container - 410.42 grams

Weight of test sample used - 300 grams

Table 4.1: Sieve analysis results for fine aggregates

Sieve Size Weight % Weight Cumulative % Cumulative %

(mm) Retained (g) Retained Retained (g) Passing (g)

2.00 6.03 2.01 2.00 97.99

1.60 1.61 0.54 2.50 97.45

1.40 49.03 16.34 18.90 81.11

0.80 140.03 45.67 65.60 34.44

0.40 77.52 25.84 91.40 8.60

0.25 23.23 7.74 99.00 0.86

Sieve Pan 2.55 0.85 100 0.00

Total 300 100

42
 120

Cumulative % passing
100

80

60

40

20

0
0.1 1 10
Sieve Sizes
(mm)
Figure 4.1: Sieve analysis for fine aggregate

4.2 Sieve Analysis for Coarse Aggregates

Table 4.2: Sieve analysis results for coarse aggregate (20mm)

Sieve Size Weight % Weight Cumulative % Cumulative %

(mm) Retained (g) Retained Retained (g) Passing (g)

31.50 0.0 0.00 0.00 100.00

26.50 175.0 8.75 8.75 91.25

20.00 561.5 28.08 36.83 63.17

14.00 112.3 56.15 92.98 7.02

10.00 140.5 7.02 100.00 0.00

4.75 0.0 0.00 100.00 0.00

Tray 0.0 0.00 0.00 0.00

Total 2000.00 100.00

43
 120

100
Cumulative % Passing

80

60

40

20

0
1 10 100
Sieve Sizes (mm)

Figure 4.2: Sieve analysis graph for 20mm coarse aggregates

Table 4.3: Sieve analysis results for coarse aggregate (16mm)

Sieve Size Weight % Weight Cumulative % Cumulative %

(mm) Retained (g) Retained Retained (g) Passing (g)

31.50 0 0.00 0.00 100

26.50 250 12.50 12.50 87.50

20.00 450 22.50 35.00 65.00

14.00 1000 50.00 85.00 15.00

10.00 200 10.00 95.00 5.00

4.75 100 5.00 100.00 0.00

Tray 0 0.00 0.00 0.00

Total 2000 100.00

44
 Cumulative % Passing 120

100

80

60

40

20

0
1 10 100
Sieve Sizes (mm)

Figure 4.3: Sieve analysis results for 16mm coarse aggregate

Table 4.4: Sieve analysis results for coarse aggregate (12mm)

Sieve Size Weight % Weight Cumulative % Cumulative %

(mm) Retained (g) Retained Retained (g) Passing (g)

31.50 0 0 0 100

26.50 0 0 0 100

20.00 0 0 0 100

14.00 900 45 45 55

10.00 1000 50 95 5

4.75 100 5 100 0

Tray 0 0 0 0

Total 2000 100

45
 120

100
Cumulative % Passing

80

60

40

20

0
1 10 100
Sieve Sizes (mm)

Figure 4.4: Sieve analysis results for 12mm coarse aggregate

The results for sieve analysis test on the aggregates shown in tables 4.1 to 4.4. The grading curve

for the aggregates in fig 4.1 to 4.4 falls within the lower and upper limit of grading requirement

for aggregate from natural sources BS882 (1992). This implies that the aggregates are suitable

for construction work. The following results obtained from graphs for coefficient of uniformity

and curvature of each aggregate size

For fine aggregate

𝐷6 1.10
= = 2.74
0.40
0
𝐶𝑐 =
�10
�

𝐷30 0.602
𝐶𝑢 = = 1.10 × 0.40
= 0.82
𝐷 2

×
𝐷
60 10

46
For 20mm aggregate size;

𝐷6 10.99
0 = = 1.05
𝐶𝑐 = 10.50
� 10
�

𝐷30 10.652
𝐶𝑢 = = 10.99 × 10.50
= 0.98
𝐷 2

×
𝐷
60 10

For 16mm aggregate size;

𝐷6 10.99
= = 1.06
10.40
0
𝐶𝑐 =
� 10
�

𝐷30 10.802
𝐶𝑢 = = 10.99 × 10.40
= 1.02
𝐷 2

×
𝐷
60 10

For 12mm aggregate size

𝐷6 10.50
= = 1.04
10.10
0
𝐶𝑐 =
� 10
�

𝐷30 10.252
𝐶𝑢 = = 10.50 × 10.10
= 0.99
𝐷 2

×
𝐷
60 10

4.3 Slump

The results obtained for the slump test on the 12mm, 16mm and 20mm aggregate size are

97mm, 94mm and 92mm respectively as shown in table 4.5 and figure 4.5 below. Showing an

increase in workability as the aggregate size increases which in agreement with Bruce et al,

(2016).

47
Findings.

48
Table 4.5: Slump Test Results

Mix Size Mix Height of Cone Height of Slump Concrete Slump

(mm) Ratio (mm) (mm) Value

12 1:2:4 300 203 97

16 1:2:4 300 206 94

20 1:2:4 300 208 92

variation in slump value with different coarse aggregate sizes

97
96
Slump Value (mm)

95
94
93
92 12 mm Aggregate
91
16 mm Aggregate
90
89 20 mm Aggregate

12mm
16mm
Aggregate 20mm
Aggregate Aggregate

Aggregate Sizes

Figure 4.5: Variation in Slump with Different Coarse Aggregate

4.4 Compressive Strength

Table 4.6 to 4.8 and figure 4.6 and 4.7 shows the variation in the compressive strength of

concrete using aggregate sizes of 12mm, 16mm and 20mm for 7, 14, 21 and 28 curing days at a

water cement ratio of 0.55 and a mix ratio of 1:2:4 throughout the work.

49
For the 7 curing day been the first shows an increase in compressive strength as the aggregate

size increases. With compressive strength of 15.53, 17.55 and 19.34 N/mm 2 for 12mm, 16mm

and 20mm aggregate sizes respectively.

For the 28 curing day been the first shows an increase in compressive strength as the aggregate

size increases. With compressive strength of 22.03, 24.02 and 26.20 N/mm2 for 12mm, 16mm

and 20mm aggregate sizes respectively.

All through the test 20mm showed the highest compressive strength followed by 16mm then

12mm in this order for each of the curing days showing that the compressive strength of concrete

increases with increase in curing days and aggregate size as represented in figure 4.6 and 4.7. this

increase in strength as the curing age increases is in agreement with the findings of James et al,

(2011) and Joseph et al, (2012)

Table 4.6: Compressive strength of concrete test results for coarse aggregate of 12mm

Specimen Curing Area of Average Average Average

Age Specimen Weight of Crushing Compressive
(Days) (150mm×150mm) Specimen load Strength
(kg) (N/mm2) (N/mm2)
A12 7 22,500 8.30 349.38 15.53

A12 14 22,500 8.25 393.00 17.47

A12 21 22,500 8.40 426.68 18.17

A12 28 22,500 8.40 495.65 22.03

50
 Table 4.7: Compressive strength of concrete test results for coarse aggregate of 16mm

Specimen Curing Area of Specimen Average Average Average

Age (150mm×150mm) Weight of Crushing Compressive
(Days) Specimen load Strength
(kg) (N/mm2) (N/mm2)
A16 7 22,500 8.45 394.50 17.55

A16 14 22,500 8.55 450.67 20.03

A16 21 22,500 8.40 492.69 21.85

A16 28 22,500 8.45 540.54 24.02

Table 4.8: Compressive strength of concrete test results for coarse aggregate of 20mm

Specimen Curing Area of Average Average Average

Age Specimen Weight of Crushing Compressive
(Days) (150mm×150mm) Specimen Load Strength
(kg) (N/mm2) (N/mm2)
A20 7 22,500 8.70 435.84 19.34

A20 14 22,500 8.60 478.15 21.24

A20 21 22,500 8.65 530.86 23.23

A20 28 22,500 8.60 589.73 26.20

51
 30

25
Compressive Strength (N/mm2)

20

15 12mm Aggregate
16mm Aggregate
20mm Aggregate

10

0
0 7 14 21 28 35

Curing Age (Days)

Figure 4.6: Graph of compressive strength against curing age

52
 30

25
Compressive Strenght (N/mm2)

20

15
12 mm Aggregate
16 mm Aggregate
10
20 mm Aggregate

0
7 days
14 days
21 days
28 days
Curing Age (Days)

Figure 4.7: Effects of different coarse aggregate sizes on the compressive strength of concrete

53
 CHAPTER FIVE

CONCLUSION AND

RECOMMENDATION

5.1 Conclusion

Based on the results obtained and discussed, the following conclusions were drawn:

1. Concrete made with 20mm showed the highest workability for mix ratio of 1:2:4 and a

water cement ratio of 0.55 used throughout the research and therefore it is the bet in

terms of workability.

2. Concrete made with 12mm aggregate showed the less workability as compared to 16mm

and 20mm for the same condition all through.

3. Concretes made with 20mm aggregates performed best in compression than that of 16mm

and 16mm better than 12mm in this descending order.

4. Compressive strength of the different sizes of aggregates also increase as the curing days

increases.

5. Concrete with 12mm showed the least compressive strength value throughout the project

for each of the curing days.

6. 20mm aggregate showed the highest average compressive strength of 26.20N/mm 2 at 28

curing days as seen in figure 4.5 and 4.6. Which makes it more suitable and the best for

compressive structural element.

7. 20mm aggregate showed higher compressive strength on each of the curing days as

compared to 16mm and 12mm. shown in figure 4.5 and 4.6 graphically.

54
 8. Bigger sizes of aggregates should be used (notwithstanding the cost) in high rise

buildings and other massive structures in which high factors of safety for the strength of

concrete is required.

5.2 Recommendation

1. The investigation should be extended to the effect of different shape of coarse

aggregates on the compressive strength of concrete.

2. The flexural and tensile strength of concrete with aggregate size should be studied so

as to draw a general conclusion on the strength of concrete.

3. The effect of water cement ratio of each aggregate size should be studied to see the

effect on compressive strength.

4. More studies can be done on the effect different brands of cement produced in Nigeria

on compressive strength of concrete.

55
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61
 APPENDICE

Plate 1: Sieve Analysis on Coarse Aggregate.

Plate 2: Sieve Analysis on 20mm Coarse Aggregate.

62
 Plate 3: Batching of Concrete.

Plate 4: Removal of Cubes from Metallic Molds

63
Plate 5: Getting Cubes Ready for Curing.

64