A STUDY ON COMPRESSIVE STRENGTH CHARACTERISTICS OF CONCRETE ON

DIFFERENT DATES

BY

EZENWEKE ANASTESIA CHINENYE

NAU/CVE/2016224044

SUBMITTED TO

THE DEPARTMENT OF CIVIL ENGINEERING

FACULTY OF ENGINEERING

IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF

BACHELOR OF ENGINEERING DEGREE (B.ENG) IN

CIVIL ENGINEERING

NNAMDI AZIKIWE UNIVERSITY

AWKA

FEBRUARY 2022

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 CERTIFICATION

This is to certify that this research study carried out by Ezenweke Anastesia C hinenye

(Registration Number 2016224044) from the department of civil Engineering Nnamdi Azikiwe

University, Awka, Anambra State.

…………………………………….. …………………….

Ezenweke Anastesia Chinenye Date

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 APPROVALS PAGE

This project has been read and approved by the undersigned as meeting the requirement of the

Department of Civil Engineering, Faculty of Engineering, Nnamdi Azikiwe University, Awka

for Award of B.ENG in Civil Engineering.

…………………………………….. ……………………

Engr. I. Omaliko Date

………………………………………. …...…………………

Engr.Dr.C.A.Ezeagu

(Head of Department)

……………………………………… ………………………

External Examiner Date

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 DEDICATION

This project is most importantly dedicated to Almighty God, who through his ceaseless love,

protection and mercies brought me this far in the cause of my academic pursuit.

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 ACKNOWLEDGEMENT

First of all and most importantly, I give thanks to almighty God for his favor, grace, guidance,

strength and mercies upon by life and his abundant wisdom to push through my academic

sessions.

My unending gratitude goes to my supervisor, Engr. I. Omaliko for his patience, guidance,

encouragement and wonderful aid he gave me in getting this project research done. Thank you

sir

I thank profusely all my lecturers in the department of civil engineering for their guidance,

support, endurance and love

I owe a deep sense of gratitude to also Engr. B. Joseph of M.I.O. Construction Company for his

love, care and guidance towards the success of my research work.

My heartfelt appreciation and deepest sense of gratitude goes to my family, my parents Mr and

Mrs Arinze Ezenweke for their love, prayers, caring and sacrifices for educating and preparing

me for my future. I am very much thankful to my siblings for their love, understanding, prayers,

and continuing support to complete this research work.

I an extremely thankful to my friends Ruth, Vivian, Precious, Stanly and Anthony, this would

have been a much difficult feast without you. Thank you all for your unwavering support and for

reminding me to take breaks when I have been stressed out.

I thank profusely all my lecturers in the department of civil engineering for their guida nce,

support, endurance and love

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 ABSTRACT

This research investigation was based on the variation in the compressive strength of concrete

cast on different dates. Thus, this experiment showcased the investigative results of concrete cast

on different dates using different size of aggregates. This test was cured and crushed with

different number of days, 7, 14, 21 and 28 days to test its compressive strength. The test was

conducted under constant environmental conditions with the mix ratio 1.2.4 of cement, fine

aggregate and coarse aggregate. Hand compaction was used and curing was by immersion i.e.

deeping the cubes inside the curing tank and crushed after 7, 14, 21, and 28 days respectively.

The variation in strength on curing age from the graph shows that there was rapid increase of

strength gain for the first 7 days after which it reduced from the 14 th day and then increases from

21 to 28 days. The result of analysis carried out from the crushing strength showed that concrete

strength increases with curing age of 7 to 28 days. It also show that the strength of concrete

increases progressively with the age of curing and there is rapid strength gain in the first 7 days

of curing and concrete gains its maximum strength at 28 days of curing. In this research,

different sizes of coarse aggregates ranging from 10mm, 16mm and 25mm were used to cast

Concrete. Compressive strength test and slump consisting for different sizes were measured. The

result shows that the compressive strength of concrete made with 16mm at 28days of curing

period was much higher followed by 25mm and 10mm. The factors affecting the compressive

strength of concrete were also discussed, while aggregate parts were buttressed extensively.

Also, particle size distribution analysis was conducted in the course of this project for proper

grading and classification. The entire test was done with the British standard (BS) specifications.

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Table of Contents
CERTIFICATION .................................................................................................................................. ii
APPROVALS PAGE ............................................................................................................................. iii
ACKNOWLEDGEMENT .........................................................................................................................v
ABSTRACT .........................................................................................................................................vi
LIST OF TABLES ..................................................................................................................................ix
LIST OF FIGURES .................................................................................................................................x
CAPTER ONE.......................................................................................................................................1
INTRODUCTION ..............................................................................................................................1
1.5 Scope of this Report ..................................................................................................................5
1.6 SIGNIFICANCE OF STUDY............................................................................................................6
CHAPTER TWO ...................................................................................................................................7
2.7.2 Compaction of concrete .................................................................................................... 23
2.8 Curing of Concrete................................................................................................................... 23
2.8.1 Shrinkage of Concrete ....................................................................................................... 24
2.8.2 Creep in Concrete ............................................................................................................. 25
2.8.3 Bleeding ........................................................................................................................... 26
2.10 Crushing Strength.................................................................................................................. 29
2.11 Citations of Previous Works ................................................................................................... 30
CHAPTER THREE ............................................................................................................................... 32
3.0 MATERIALS AND METHOD ....................................................................................................... 32
3.1 MATERIALS ............................................................................................................................. 32
3.3.1 Sieve Analysis ................................................................................................................... 34
3.4 PRODUCTION OF CONCRETE .................................................................................................... 36
3.4.1 Mix Design........................................................................................................................ 37
3.4.2 Mixing of concrete ............................................................................................................ 37
3.4.3 Casting of Concrete ........................................................................................................... 38
3.5 Workability of Concrete ........................................................................................................... 38
3.5 Slump Test.............................................................................................................................. 39
3.6 Curing of Concrete................................................................................................................... 40
3.7 Compressive Strength Test....................................................................................................... 41
CHAPTER FOUR................................................................................................................................. 43
4.0 RESULTS AND ANALYSIS OF ALL TESTS ...................................................................................... 43

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CHAPTER FIVE .................................................................................................................................. 50
5.1 CONCLUSION .......................................................................................................................... 50
5.2 RECOMMENDATIONS .............................................................................................................. 51
REFERENCE ...................................................................................................................................... 53

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 LIST OF TABLES

Table 4.1 Sieve analysis result for fine aggregate

Table 4.2 Sieve analysis result for coarse aggregate

Table 4.3 Slump test result

4.4 Compressive strength test result for 7 days

4.5 Compressive strength test result for 14 days

4.6 Compressive strength test result for 21 days

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 LIST OF FIGURES

Fig 4.1 fine aggregate sieve analysis graph

Fig 4.2 Coarse aggregate sieve analysis graph

Fig 4.3 Graph of slump test

Fig 4.3 Graph of coarse aggregate size for 10mm, 16mm and 25mm

Fig 4.4 Comparison of compressive strength for 10mm, 16mm and 25mm

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 CAPTER ONE

INTRODUCTION

Concrete is a composite material produced by mixing homogeneously selected proportions of

water, cement, aggregates (fine and coarse). Concrete is said to be the second substance most

used in the world after water, and is one of the most frequently used building materials.

Approximately, three quarter of the volume of concrete are occupied by aggregates (Gumede and

Franklin, 2004.The most dominant construction material is Concrete and the most collapse

structure is Concrete structure. A number of researches (Ayininuola and Olalusi,2011) have

identified the use of substandard materials, particularly Concrete as the leading cause of building

collapse in Nigeria. Concrete failure still occurs despite adequate design and mix ratio. This

advocates the existence of a breach in requirement for production of quality Concrete. Previous

works confirm the use of inferior concrete aggregates materials as among the causative elements

of structural Concrete failure in building. Gollu et al.(2016)mentioned unsuitable materials,

unsound aggregate, reactive aggregate, and contaminated aggregate as part of the sources of

concrete failure in buildings.Akineleyeand Tijani(2017) stated that the use of low quality

aggregates also affect the performance of asphalt Concrete in southwest Nigeria. Concrete will

only become a quality material for construction when their constituents are properly sourced.

The quality of aggregate can vary significantly due to the geographical location and

environmental condition (Ajagbe et al., 2018).

Fowler and Quiroga (2003) reported that aggregates are expected to have important effects on

the properties of concrete since they occupy 70-80% of it. Concrete aggregates and paste are the

major factors that affect the strength of concrete (shetty, 2005), the properties of aggregate

greatly affect the durability and structural performance of concrete as aggregate with undesirable

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propertiescannot produce strong Concrete (Neville,2001).According to Mehta and Menterio

(2001), the aggregates exercise a significant influence on strength, dimensional stability, and

durability of concrete. Ajagbeand Tijani (2016) stated the assessment of concrete aggregate is

vital to overcome the problem of structural collapse due to Concrete failure in a certain

environment. De Larrard (1999) and Dewar (1999) agreed that the aggregate source has an

impact on concrete strength. Concrete strength is govern by aggregate size, type, and source

(Hassan, 2014: Aginam et al., 2013; Jimoh and Awe, 2017; Abdullahi, 2012).

Comprehensive strength is the most significant mechanical property of concrete. It is obtained by

measuring Concrete specimen after curing for days. Some of the factors that influence the

Concrete strength include aggregate quality, cement strength, water content and water/ cement

ratio (Noorzaei ET el., 2007).

Concrete should be strong enough, when it has harden, to resist the various stresses which it will

be subjected to. Hardened Concrete has a number of properties, including:

1. Mechanical strength, in particular compressive strength.

2. Durability
3. Porosity and density
4. Thermal and acoustic insulation properties.
5. Impact resistance.

When freshly mixed, it must be of such mixed it must be of such a consistency that it can
readily be handled with segregation and easily compacted in the formwork leading to the
homogeneity of the finished work. The strength of concrete is governed by several factors
such as ratio of cement to water, ratio of cement to aggregates, maximum size of aggregates,
grading, surface texture, shape, strength and stiffness of aggregate particles. Fresh concrete
has many applications and can be cast into circle, rectangle, squares and more. It can also be
used for staircases, columns, doors, beams, lintels and other familiar structures.

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 BACKGROUND

The role of aggregate in concrete is central to this report. While the topic has been under
study for many years, an understanding of the effect of coarse aggregate has become
increasingly more important with the introduction of high strength concrete, since coarse
aggregate plays a progressively more important role in concrete behavior as strength
increases.

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

cement paste from the aggregate particle at what, for the purpose of this report, will be called
matrix aggregate interface. In contrast, in high strength concrete, the aggregate particle as
well as the interface undergoes 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 normally stiffer and stronger coarse aggregate and the
surrounding mortar. Thus, micro cracks tend s to propagate through the aggregate particle
since, not only is the matrix aggregate bond stronger than in concrete 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.

This report describes work that is aimed at improving the understanding of the role of aggregate

in concrete. The variables considered are aggregate type, aggregate size and aggregate

contenting normal and high strength concrete. Compression, flexural, and fracture test are used

to better understand the effects aggregates have in concrete

1.1 THE BENEFITS OF CONCRETE

There is numerous positive aspect of concrete:

1. It is relatively cheap material and has a relatively long life with few maintenance
requirements.
2. It is strong in compression.
3. Before it hardens, it is a very pliable substance that can easily be shaped.
4. It is not combustible.

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1.2 THE LIMITATIONS OF CONCRETE INCLUDE:

1. Relatively low tensile strength when compared to other building materials.

2. Low Durability
3. Low strength to weight ratio.
4. It is susceptible to cracking

1.3 THE TYPES OF CONCRETE

Concrete is made in different grades, including normal, standard and high- strength grades. This

grades indicate how strong the Concrete is and how it will be used in construction. They are

three grades or classes of cement in Nigeria, namely grades 32.5,45.5,and 52.5.These grades

corresponds to the minimum 28 day compressive strength of cement mortar after

curing(COREN,2017). It is important to note that the most common type of cement in Nigeria is

the Portland limestone cement (PLC)and not Ordinary Portland cement (OPC). The cement

available in the open Market of Nigeria is the Portland limestone cement designated as CEM II

in NIS 444-1(2003). PLC is a modified OPC which is produced by adding 6-35% of limestone

to OPC. It has a lower clinker content rage of 65-94% compared with OPC’s range of 95-100

(Joeland and Mbapuun, 2016). It has lower carbon footprint than the OPC and is deemed more

environmental friendly. The types of concrete include:

1. Normal strength Concrete

2. Plain or ordinary Concrete
3. Reinforced concrete
4. Pre-stressed Concrete
5. Lightweight Concrete
6. High density Concrete
7. Air-Entrained Concrete
8. Ready-mixed Concrete
9. Volumetric Concrete

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 10. Decorative concrete
11. Rapid set Concrete
12. Smart Concrete
13. Previous Concrete
14. Pumped Concrete
15. Limecrete
16. Glass Concrete
17. Asphalt Concrete
18. Shortcrete Concrete.

1.4 AIMS AND OBJECTIVES

The aim of this project is to investigate the compressive strength of concrete casted on different

dates.

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.

1.5 Scope of this Report

The purpose of this research work is to compare the compressive strength of concrete cast on

different dates and also to compare the strength exhibited by the concrete cubes after different

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dates of curing. Because of the nature of this project, the investigations conducted were limited

to particle size distribution, slump test and compressive strength test for 7days, 14 days, 21days

and 28days of curing. This test provides an idea about the characteristics of concrete. By this

single test one judge that whether concreting has been done properly. The mould size for the

practical used is 150mm by 150mm and the water cement ratio used was 0.5 liter and the mix

ratio is 1:2:4.

1.6 SIGNIFICANCE OF STUDY

Concrete being the major consumable material after water makes it quite inquisitive in its nature.

The compressive strength of concrete is the strength of hardened concrete measured by the

compression test to determine the concrete ability to resist loads which tends to compress it

where as other stresses such as axial stresses are catered by reinforcements and other means. The

significant/ important of conducting this test is to have an idea about the characteristics of

concrete. By this single test one judges whether concrete has been done properly or not. The

compressive strength of concrete depends on different factors such as water cement ratio, its

constituents, cement strength, air entrainment, mix proportion, curing method, temperature effect

quality of concrete material and quality control during the production of concrete. The aim of

this project is to determine the strength of a concrete cube cast on different dates, to determine its

strength after 28days curing period and also know the correct mix proportion to use for casting of

concrete.

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 CHAPTER TWO

2.0 LITERATURE REVIEW

INTRODUCTION

In building construction, concrete is used for the construction of foundations, columns, beams,

slabs and other load bearing elements. Various types of cements are used for concrete works

which have different properties and applications. Some of the type of cement are Portland

Pozzolana Cement (PPC), rapid hardening cement, Sulphate resistant cement e.t.c. Materials are

mixed in specific proportions to obtain the required strength. Strength of mix is specified as M5,

M10, M15, M20, M25 andM30. Where M signifies Mix and 5, 10, 15 etc. as their strength in

KN/m2.Water cement ratio plays an important role which influences various properties such as

workability, strength and durability.

Adequate water cement ratio is required for production of workable concrete. When water is

mixed with materials, cement reacts with water and hydration reaction starts. This reac tion helps

ingredients to form a hard matrix that binds the materials together into a durable stone- like

material. Concrete can be casted in any shape. Since it is a plastic material in fresh state, various

shapes and sizes of forms or formworks are used to provide different shapes such as rectangular,

circular etc. Various structural members such as beams, slabs, footings, columns and lintels are

constructed with concrete.(ACI 318 Building code requirements for structural concrete).

There are different types of admixtures which are used to provide certain properties. Admixtures

or additives such as pozzolans or superplasticizers are included in the mixture to improve the

physical properties of the wet mix or the finished material. Various types of concrete are

7
manufactured these days for construction of buildings and structures. These have special

properties and features which improve quality of construction as per requirement.

2.1 COMPONENTS OF CONCRETE

Components of concrete are cement, sand, aggregates and water. Mixture of Portland cement and

water is called as paste. So, concrete can be called as a mixture of paste, sand and aggregates.

Sometimes rocks are used instead of aggregates. The cement paste coat the surface of the fine

and coarse aggregates when mixed thoroughly and binds them. Soon after mixing the

components, hydration reaction starts which provides strength and a rock solid concrete is

obtained. Grade of concrete denotes its strength required for construction.

Based on various lab tests, grade of concrete is presented in Mix Proportions. For example, for

M30 grade, the mix proportion can be 1:1:2, where 1 is the ratio of cement, 1 is the ratio of sand

and 2 is the ratio of coarse aggregate based on volume or weight of materials. The strength is

measured with concrete cube or cylinders by civil engineers at construction site. Cube or

cylinders are made during casting of structural member and after hardening it is cured for 28

days. Then compressive strength test is conducted to find the strength. Regular grades of

concrete are M15, M20, and M25 etc. For plain cement concrete works, generally M15 is used.

For reinforced concrete construction minimum M20 grade of concrete are used.

Concrete is manufactured or mixed in proportions with respect to cement quantity. There are two

types of concrete mixes, i.e. nominal mix and design mix. Nominal mix is used for normal

construction works such as small residential buildings. Most popular nominal mix are in the

proportion of 1:2:4.Design mixed concrete are those for which mix proportions are finalized

based on various lab tests on cylinder or cube for its compressive strength. This process is also

8
called as mix design. These tests are conducted to find suitable mix based on loca lly available

material to obtain strength required as per structural design. A design mixed offers economy on

use of ingredients. Once suitable mix proportions are known, and then its ingredients are mixed

in the ratio as selected. Two methods are used for mixing, i.e. Hand mixing or Machine Mixing.

Based on quantity and quality required, the suitable method of mixing is selected. In the hand

mixing, each ingredient is placed on a flat surface and water is added and mixed with hand tools.

In machine mixing, different types of machines are used.

In this case, the ingredients are added in required quantity to mix and produce fresh concrete.

Once it is mixed adequately it is transported to casting location and poured in formworks.

Various types of formworks are available which as selected based on usage. Poured concrete is

allowed to set in formworks for specified time based on type of structural member to gain

sufficient strength. After removal of formwork, curing is done by various methods to make up

the moisture loss due to evaporation. Hydration reaction requires moisture which is responsible

for setting and strength gain. So, curing is generally continued for minimum 7 days after removal

of formwork.

2.2 TYPES OF CONCRETE CONSTRUCTION

Concrete is generally used in two types of construction, i.e. plain concrete construction and

reinforced concrete construction. In PCC, it is poured and casted without use of any

reinforcement. This is used when the structural member is subjected only to the compressive

forces and not bending. When a structural member is subjected to bending, reinforcements are

required to withstand tension forces structural member as it is very weak in tension compared to

compression. Generally, strength of concrete in tension is only 10% of its strength in

9
compression. It is used as a construction material for almost all types of structures such as

residential concrete buildings, industrial structures, dams, roads, tunnels, multi storey buildings,

skyscrapers, bridges, sidewalks and superhighways etc. Example of famous and large structures

made with concrete are Hoover Dam, Panama Canal and Roman Pantheon. It is the largest

human made building materials used for construction.

2.2.1Steps of Concrete Construction

1. Selecting quantities of materials for selected mix proportion

2. Mixing
3. Checking of workability
4. Transportation
5. Pouring in formwork for casting
6. Vibrating for proper compaction
7. Removal of formwork after suitable time
8. Curing member with suitable methods and required time.

The variations on the compressive strength of concretes made with respect to tropical climate as

patterning to Nigeria in particular has not been fully worked on by many researchers. As a result,

it became difficult to lay hands on such information.

Originally, aggregates according to Neville, were viewed as an inert material dispersed through-

out the cement paste, largely for economic reasons. He went further to state the fact that

aggregates are not truly inert and its physical properties influence performance of concrete. The

strength requirement is generally specified in terms of characteristic strength ( BS 8110: Part 1)

coupled with a requirement that the probability of the strength falling below this shall not exceed

certain value. Neville stated that the shape of aggregate, its surface texture and cleanliness

influence the bond strength of concrete.

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He also stressed that in experimental concrete, entirely smooth coarse aggregates led to lower

compressive strength, typically by 10% than when roughened. Also on the effect of sizes,

Aggregates with maximum size of coarse aggregates has lower compressive strength. Also,

according to the University of Technology Malaysia, on the effect of aggregate shape, surface

texture and cleanliness; “a smooth rounded aggregate will result in a weaker bond between the

aggregates and the matrix than an irregular aggregate with rough surface texture”.

Explaining further, “a fine coating of impurities such as silt and c lay on aggregate surface

hinders the development of a good bond. The aggregate size can also affect strength. For a given

matrix proportion, the concrete strength decreases as the maximum size of aggregates increases.

Concrete of a given strength can be produced with well graded aggregates. I. This just mentioned

case, segregation does not occur”. According to national ready mixed concrete association, they

carried out a research work on coarse aggregate and in their conclusion, at a given water ratio,

within the range employed in most structural concrete, smaller maximum size of aggregate will

tend to produced higher concrete strengths than larger ones. Secondly, the larger sizes will

require less mixing water and hence for a given cement factor, will produce of lower water ratio

than the smaller sizes.

Bloem and Gaynor (1963) jointly studied the effects of aggregate properties on the strength of

concrete and they reported' that, tests were made with 546 combinations of fine and coarse

aggregate to study the effect of shape, surface texture, fine coatings, strength, and maximum s ize

other properties on water requirement and strength of concrete. The results showed that at equal

water-cement ratio, irregular shaped smaller sized aggregates without coatings, and those of

higher concrete strength. Also according to the same report, depending on circumstances such as

11
richness of concrete mix, individual properties of the particular aggregates and the magnitude of

the size difference, and increase or decrease in concrete strength at a fixed cement content.

Stantom and Bloem(1960) reported that at different water-cement ratio, strength levels prevail

for the maximum sizes. Without exception, the level increased with reduction in maximum size.

This implies that at same water-cement ratio, there is always a reduction of strength of concrete

as the maximum size of aggregate increases. The presence of clay or crush dust, or silt or rather

generalizing; presence of over coatings of aggregates is not surprising because it interferes with

the bond between the aggregates and cement paste. Another fine material which may be present

on a coating on aggregates is silt. Silt possesses some tendencies similar to that of clay and it

may undergo like clay, considerable shrinkage and expansion when exposed to changes in

moisture content. Clay, silt, crush and dust should not be in excess on aggregates so as not

increase the amount of water necessary to wet all particles in the mix.

The IPRF (Innovative Pavement Research Foundation) report on the effect of micro fine coatings

hinders the development of a good bond thereby reduces the compressive strength of concrete

and at the same time increases the shrinkage of the concrete. Aggregates are also to be seen as

anti-crackers in concrete because of its great function in bonding. They can be as the skeleton of

concrete. Consequently, an excess amount of organic materials in or on the aggregates prevents

cement paste from forming and adequate bond with aggregates particles. According to an online

article in press, the effect of coarse aggregate size on concrete under compression shows that

the concrete strength slightly increases when at low confinement. At high confinement, the

coarse aggregates size has a slight influence on concrete deviatory behavior and a significant

influence on concrete strain limit state.

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In conclusion, the higher the coarse aggregates size, the lower is the mean stress level

corresponding to concrete strain limit state. Cement paste volume also has effect on concrete

behavior. Otherwise decreasing cement paste volume increases concrete deformation capacity.

Since this work deals mostly with the determination of variations that exists on compressive

strength of concrete casted on different days, it then becomes necessary to analyze some factors

which generally affect the strength of concrete as well as some properties of concrete, and also

the effects of size of coarse aggregates on concrete.

2.2.3 LIMITATIONS OF CONCRETE

1. Concrete is quasi-brittle
2. Concrete has low toughness
3. Concrete has low specific strength
4. Formwork is required
5. Long curing time
6. Demands strict quality control
7. Relatively low tensile strength when compared to other building materials
8. Low Duct ability
9. Low strength to weight ratio
10. It is susceptible to cracking

2.3 CLASSIFICATION OF CONCRETE

Based on unit weight:

3
1. Ultra-light concrete < 1,200 kg/m
3
2. Lightweight concrete 1200- 1,800 kg/m
3
3. Normal-weight concrete 2,400 kg/m
3
4. Heavyweight concrete > 3,200 kg/m

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 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

2.4 PROPERTIES OF CONCRETE

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

rules.

Properties in Fresh State Include

1. Workability
2. Segregation
3. Bleeding
4. Hardness
The properties in hardened state include

1. Strength
2. Durability
3. Impermeability
4. Dimensional change

2.5 Workability of Concrete

Workability of concrete is a broad and subjective term describing how easily freshly mixed

Concrete can be mixed, placed, consolidated and finished with minimal loss of homogeneity

.ASTMC 125-93. Workability is a property that directly to impact strength, quality, appearance,

and even the cost of labor for placement and finishing operation.

Types of workability of concrete

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According to the American Concrete institute (ACI) standard 116R-90(ACI 1990), Workability

of concrete can be classified into three types

1. Unworkable Concrete: An unworkable Concrete also known as harsh Concrete, is a

concrete with a very little amount of water. The hand mixing of such Concrete Is difficult,

such type of concrete had high segregation of aggregates and it is very difficult to maintain

the homogeneity of Concrete mix.

2. Medium workable Concrete: Medium workable Concrete is used in most of the

construction works. This Concrete is relatively easy to mix, transport, place and compact

without much segregation and loss of homogeneity.

3. Highly workable Concrete: This type of concrete is very easy to mix, transport, place and

compact. It is used where effective compaction of concrete is not possible. The problem is

that they are high chances of segregation and loss of homogeneity in highly workable

Concrete.

The desirable Workability depends on two factors which are the section sizes, amount and

spacing of reinforcement and the method of compaction.

2.6 Strength of Concrete

The strength of concrete is the most important property for us. It depends on density ratio or

compaction and compaction depend on sufficient Workability BSI (1983), part 108. The

different types of concrete strength are;

1. Compressive strength: It is widely accepted measure to access the performance of a

given concrete mixture. It accurately tells you whether or not a particular mix is suitable to

meet the requirements of a specific project.

15
 2. Tensile strength of concrete: The tensile strength of concrete is its capacity to resist

cracking or breaking under tension. Although Concrete is rarely loaded under pure pressure

in a structure, determining the tensile strength is necessary to understand the extent of the

possible damage. Breaking and cracking arise when tensile forces surpass the tensile

strength.

3. Flexural strength of concrete: Flexural strength establishes the ability of concrete to

withstand bending. It is an indirect measure of tensile strength. The Flexural strength of

concrete is usually determined by testing a simple beam where the concentrated load is

applied at each of the third points. The numbers are expressed in a modulus of rupture (MR)

in psi.

2.6.1 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

The influence of cement on concrete strength, for a given mix proportion is determined by its

fineness and chemical composition through the process of hydration. Generally, cement can be

described as a material with adhesive and cohesive properties which make it capable of bonding

mineral fragments into a compact whole. For construction purposes, which are the case in this

project work, the term cement is restricted to the bonding material used with stones, sand, bricks

and building blocks. The gain in strength as the fineness of its cement particles increases cannot

be underestimated. The gain in strength is most marked at early ages and after 28days the

relative gain in strength is much reduced.

16
The role of the chemical composition of cement in the development of concrete strength can

always be appreciated. It is apparent that cement which contain a high percentage of tricalcium

silicate (Ca3S) gain much more strength rapidly than those rich in dicalcium silicate (Ca2S). The

sulphate resistance of concrete can be improved by the use of sulphate resisting cement which

has low tricalcium Aluminates content.

However, there is a tendency for concretes made with low- heat cements eventually to develop

slightly higher strengths. This is possible due to the formation of a better quality gel structure in

the course of hydration. Because we are in the tropics, low heat cements best advisable to use in

concreting. This is because the heat evolved during the cement hydration process needs to be

reduced. The use of low heat cement can minimize this effect. However, most (OPC) ordinary

Portland cements we use are (LH) i.e. Low heat cement. The specification for Portland cement is

the BS 12:1991 of the British standard.

Water

A concrete mix containing the minimum amount of water required complete hydration of its

cement, if it could be fully compacted, would develop the maximum attainable strength at any

given age. Water plays a critical role, particularly the amount used. The strength of concrete

increases when less volume of water is used to make it. The hydration reaction itself consumes a

specific amount of water. A water-cement ratio of approximately 0.25 (by weight) is required for

full hydration of the cement but with this water content normal concrete mix would be extremely

dry and virtually impossible to compact. Concrete is actually mixed with more water than is

needed for the hydration reaction.

17
This extra water is added to give concrete sufficient workability. Flowing concrete is desired to

achieve proper filling and composition of the forms. The water not consumed in the hydration

reaction will remain in the micro- structure pore space. Adequate compaction will then be

introduced to reduce the pore space. A partially compacted mix will contain a lot of voids and

subsequently or rather consequently the concrete stre ngth will drop. On the other hand, while

placing and compacting, water in its excess for full hydration would consequently produce some

porous structure resulting from loss of excess water. Consequently, in practice if the ratio of

water to cement increases the strength of that particularly concrete decreases. (BS EN 1008:2002

specifies-Mixing specification for water in concreting).

Aggregate

Aggregate is an important ingredient in concrete, which can be regarded as the skeleton of the

concrete. The aggregate must have a minimum inherent strength requirement for structural

concrete; the coarse aggregate must not be weaker than the concrete paste. Therefore, the bond

between aggregate and cement paste is an important factor in the strength of concrete. The

discussion of the aggregate as a factor that affects the strength of concrete will be based here on

shape, surface texture, grading, size and strength of the aggregates. When a concrete mass is

stressed, failure may originate within the aggregate, the matrix or at the aggregate- matrix

interface; or any combination of these may occur.

The aggregate- matrix interface is an important factor determining concrete strength. Bond

strength is influenced by the shape of the aggregate, its surface texture and c leanliness. Surface

texture is generally only considered in relation to concrete flexural strengths, which are

frequently found to reduce with increasing particle smoothness. However, inadequate surface

18
texture can similarly adversely affect compressive strength in high strength concrete (say

50N/mm^2) when the bond with the cement matrix may not be sufficiently strong to enable the

maximum strength of the concrete can be realized. Bonding mostly is due, in part, to the

interlocking of aggregates and the paste owing to the roughness of the surface of the

former.Coating of impurities, such as silt, clay and oil, on the aggregate surface hinders the

development of a good bond. Aggregates with micro fine coatings hinder the development of a

good bond thereby reducing the compressive strength of concrete and at the same time increasing

the shrinkage of concrete.The size of aggregate also affects the strength of concrete. As the

maximum size of aggregate is increased, the concrete strength decreases for a particular mix

proportion. But invariably, in concrete works, the bigger or larger the aggregate size for a

particular size of project the stronger the concrete required for the project.

The optimum maximum aggregate size varies with the richness of the mix, being smaller for the

less rich mixes. Generally aggregate sizes lies between 10mm and 50mm in accordance with BS

812: part 1/1975.Good concrete can be made by using different types of aggregates (considering

shapes) like rounded and irregular gravel and crushed rock which is mostly angular in shape. The

grading of aggregates is a major factor, influencing the workability of a concrete mix. The

grading should be such as to ensure that the voids between the larger aggregates are filled with

smaller fractions and mortar so as to achieve maximum density and strength. The coarser and

finer fractions of aggregates available at site can be suitably combined to obtain the desired

standard grading. Aggregates which react with alkali content of cement adversely affect concrete

strength.

Aggregates containing some forms of silica will react with alkali hydroxide in concrete to form a

gel that swells as it absorbs water from the surrounding cement paste or the environment. These

19
gels can swell and induce enough expansive pressure to damage concrete. Typical indicators of

Alkali- silica Reaction (ASR) are random map cracking and, in advanced cases, closed joints and

attendants spalled concrete. Cracking due to ASR usually appears in areas with a frequent supply

of moisture, such as close to waterline in piers, near the ground behind retaining walls, near

joints and free edges in pavements, or in piers or columns subject to wicking action. Petro

graphic examination can conclusively identify ASR. ASR can be controlled using certain

supplementary cementitious materials like silica fume, fly ash, and ground granulated blast-

furnace slag in proper proportions. There also exists Alkali Carbonate Reactions (ACR), but is

relatively rare.

It is common practice in Nigeria for construction to be carried out using locally founded

aggregates of different sizes i.e. 8mm, 12mm and 14mm. This project engulfs the attainment of

the functionality of locally found coarse aggregates of different sizes cas ted on different dates.

The core functions which will aid this work are strength and economy. The specified standard

and requirements available in recent times are based on materials which are from different

sources and bearing in the fact that no two materials which are from different sources behave

like, it is mostly likely they share the same properties but differs.

2.6.2 Classification of Aggregates

1. Artificial aggregates: They are manufactured industrial products. They are generally

lighter than ordinary aggregates. The uses of these artificial aggregates arise not just from

its light weight properties but because in many countries, there is a shortage of naturally

occurring aggregates.

20
 2. Natural aggregates: They are naturally occurring i.e. they are fond naturally. Distinction

can be between aggregates reduced by natural agents to its present size and crushed

aggregates obtained by deliberate rock fragmentation.

Fine aggregates either occur naturally in deposit distribution to some privileged locations over

the earth surface or could be delivered by the reduction of some larger gravel to smaller sizes in

quarry plants. Locally found fine aggregates are:

1. River sand: Sand deposits in river beds obtained by dredging or by locally divers scooping

from the river beds up to the collection boats. River sand in Awka locality is often gotten

from Amansea River. River sand is used in making concrete works, sandcrete and concre te

blocks.

2. Fine sand: This is often used in rendering or plastering and mortar making. When these

aggregates pass through sieve, they are usually of 0.06 - 0.6mm.

3. Laterites: This is used as filling sand or backfill for foundations and road basement

COARSE AGGREGATE

Coarse aggregates are irregular broken stone or naturally occurring gravel used in construction.

The aggregate which will get retained on a 4.75mm sieve or the aggregate which have size more

than 4.75mm are known as Coarse aggregate. They are commonly obtained by crushing the

naturally occurring rocks. Aggregates are mainly classified into two types which are fine

aggregates and coarse aggregates. The aggregates which are used in the construction must be

durable, hard and strong, should not be soft and porous, must be free from the dust and organic

materials and should be chemically inert. Aggregates are use in construction for even distribution

of load and to increase the volume of concrete. Coarse aggregates are classified based on the

nature or source of formation, according to size and according to shape.

21
Naturally occurring aggregates are obtained from the stone quarries and the stone crushers.

Natural aggregate materials originate from bedrock. Artificially manufactured aggregates are

gotten from the broken brisk or blast furnace slag. The air cooled slag is also used as a coarse

aggregate. Coarse aggregate can come in different shapes which include rounded aggregates,

angular aggregates, flaky aggregates and irregular aggregates. The properties of the coarse

aggregate include size, shape, surface texture, water absorption, soundness, specific gravity and

bulk modulus.

2.7 Wate r/Cement Ratio

The water-cement ratio is the ratio of the weight of water to the weight of cement used in a

concrete mix. (Abrams, (1918) A lower ratio leads to higher strength and durability but may

make the mix difficult to work with and form. Workability can be resolved with the use of

plasticizer or super plasticizer. Often, the ratio refers to the ratio of water to cementitious

materials, W/cm. Cementitious materials include cement and supplementary cementitious

materials such as fly ash, ground granulated blast furnace slag, silica fume, rice husk ash and

natural pozzolans (Duff, 1997).

Coarse and fine aggregates ratio

The maximal fine to coarse aggregate ratio described in ACI544.3R-2008is 0.6. Coarse and fine

aggregate comprises almost 75%of total concrete volume, therefore, balancing the usage of fine

aggregate and coarse aggregate plays vital role in determining the performance and quality of the

concrete.

Aggregate/ cement ratio

22
Aggregate cement ratio is the ratio of weight of aggregate to the weight of cement. When the

weight of cement is less, i.e. aggregate cement ratio is more, and then there will be very less

cement paste to coat aggregate surfaces and fill the voids, thus mixing, placing and compacting

of concrete will be higher than previous case.

2.7.1 Age of Concrete

Concrete increase in strength with age when moisture is available. This is initially greatest but

progressively decreasing over time. The rate will be affected by cement type, cement content and

internal concrete temperature. Moisture content of concrete also affec t the age of concrete where

by dried concrete immediately exhibits high strength due to the drying process but will not gain

strength thereafter unless returned to and maintained in a moist condition.

2.7.2 Compaction of concrete

Compaction is the process which expels entrapped air from freshly placed Concrete. Compaction

also allows the fresh Concrete to reach its potential design strength, density and low

permeability. The different methods of Compaction of concrete are Manual compaction,

Concrete compaction by pressure and jolting, concrete compaction by spinning and mechanical

compaction by vibration. The four types of vibrators commonly used for Concrete compaction

are

1. Internal vibrators
2. Form vibrators
3. Surface vibrators
4. Vibrating Tables

2.8 Curing of Concrete

23
Curing of concrete is a method by which the concrete is protected against loss of moisture

required for hydration and kept within the recommended temperature range. (Agbede and

Manasseh, 2008; Wazin, et al, 2011).Generally speaking, the longer concrete is kept under

curing condition the greater its strength. The gain of strength during curing depends on a number

of factors such as relative humidity, wind velocity and size of structural member or test

specimen. The temperature at which concrete is cured is also an important factor in the

development of its strength with time. It has been suggested that the strength of concrete can be

related to product of age and curing temperature, commonly known as maturity. Curing will

increase the strength and decrease the permeability of hardened Concrete. Curing also helps in

mitigating thermal and plastic cracks

2.8.1 Shrinkage of Concrete

Shrinkage is the phenomenon which occurs in wet concrete when it loses moisture and

invariably loses volume. It can be of two kinds: plastic shrinkage and drying shrinkage. Drying

shrinkage in concrete is caused by loss of moisture in the paste. It is influenced by a variety of

factors, which includes: environmental conditions (temperature and relat ive humidity), size of

member (surface area to volume ratio), and etc. On the other hand plastic shrinkages result from

surface evaporation due to environmental conditions such as humidity, wind speed or ambient

temperature and restrained stresses.

In reinforced concrete structures, the restrains may be caused by the reinforcement bars or by

supports. Shrinkages show as miniature cracks on the concrete surface. Concrete swells under

moist conditions, but shrinks when there is change in volume by shrinkage or restrained

stresses, as the case may be.

24
2.8.2 Creep in Concrete

Compressive strength is set up in concrete because of development of the menisci in the

capillaries as drying of concrete progresses. These stresses transform to stresses we can see on

the concrete surface as cracks. Creep of concrete develops gently and slowly. Creep of concrete

results from the action of sustained stress which graduates into gradual increase to strain in

time; it can be of the same magnitude as drying shrinkage. Creep does not include immediate

elastic strains caused by loading or shrinkage or swelling caused by moisture changes. When a

concrete structural element is dried under load that which occurs is one to two times as large as

it would be under constant moisture conditions. Adding normal drying shrinkage to this and

considering the fact that creep can be several times as large as the elastic strain on loading, it

may be seen that these factors can cause considerable deflection and that they are of great

importance in structural mechanics.

If a sustained load is removed, the strain decreases immediately by an amount equal to the elastic

strain at given age; this is generally than the elastic strain on loading since the elastic modulus

has increased in an intervening period. This instantaneous recovery is followed by a gradual

decrease in strain, called creep recovery.There are numerous factors that affect creep in concrete

as well as shrinkage. Relative humidity is first; when hydrated cement is completely dried, litt le

or no creep occurs; for a given concrete the lower the relative humidity the higher the creep.

Second factor is the strength of concrete.

It has a considerable influence on creep within a wide range creep is inversely proportional to

the strength of concrete at the time of load application. From this it follows that creep is closely

related to water-cement ratio Modulus of elasticity of aggregates is the fourth factor that affect or

influence creep in concrete. It is realized that concretes made with different aggregates exhibit

25
creep in varying magnitudes. The fifth factor is age. Experiments have shown that creep for a

very long time; detectable changes have been found after as long as 30years.The rate decreases

continuously, however, and it generally assumed that creep tends to a limiting value.

The effects of creep on concrete cannot be underestimated .Creep hastens the approach of

limiting strain at which failure takes place.

The influence of creep on the ultimate strength of a simply supported, reinforced concrete beam

subjected to a sustained load is insignificant, but deflection increases considerably and in many

cases may be a critical consideration in design. Another instance of the adverse effects of creep

is its influence on the stability of the structure through increase in deformation and consequent of

loads to other components. The loss of pre-stress concrete due to creep is well known and

accounted for the failure of early attempts at pre-stressing. Only with the introduction of tensile

steel did pre-stressing become a successful operation. The effects of creep may thus be harmful.

On the whole, however, creep unlike shrinkage is beneficial in relieving stress concentrations

and has to the success of concrete as a structural material.

2.8.3 Bleeding

In concrete, bleeding is a phenomenon in which free water in the mix rises up to the surface and

forms a paste of cement on the surface known as laitance. Bleeding occurs in concrete when

coarse aggregates tend to settle down and free water rises up to the surface. This upward

movement of water while traversing from bottom to top makes continuous channels. These

continuous bleeding channels are often responsible for permeability in structure. In the process

of upward movement, the water gets accumulated below the aggregate and creates water void

and reduces the bond between the aggregates and the paste.

26
Bleeding is a type of segregation, in which water comes of concrete. Segregation is the cause of

bleeding in the concrete mix. Bleeding will be more frequent on the surface of concrete, when

water to cement ratio is higher. The type of cement used, quality of fine aggregate also plays a

key role in rate of bleeding. The effect of bleeding is that concrete losses its homogeneity and it

is also responsible for causing permeability in concrete. Bleeding in concrete can be reduced by

adding a minimum water content in the concrete, use chemical admixture to reduce demand to

water for a required workability. Also the use of a proper design mix and fly ash or

supplementary cementitious materials can reduce bleeding in concrete.

Influence of test conditions

The condition under which tests to determine the strength of concrete are carried out can have a

considerable influence on the strength obtained and it is important that these effects are

understood if test results are to be correctly interpreted.

Specimen shape and size

These are commonly used shapes for the compressive strength of concrete determination namely

cubes cylinder and prism. Each shape gives different strength results. Also for a give shape, it

varies in size. From the test conducted by Neville A. M.1963, based on specimen shape and size

influence, it was found out that as size increases, the apparent strength increases. Also

pertaining to their findings, height diameter ratio [for cylinder test] affects compressive strength.

The specimens with lesser height diameter ratio came out with higher compressive strengths

compared with the specimen with higher height diameter ratio. BS 1881 Part 116 specified the

use of concrete cubes for determining compressive strength and quality control purposes, while

27
BS 1881 part 120 specifies cored cylindrical specimens for measuring the compressive strength

in-situ and pre-cast members.

Method of loading

The compressive strength of concrete increases as the lateral pressure in concrete increases. The

rate at which concrete is loaded affects the apparent strength of the Concrete. Generally, for

static loading, the faster the loading rate the higher the indicated strength. High strength matured

concrete cured in water are most sensitive to loading rate and particularly so for loading rates

greater than 600N/mm^2/min.BS 1881: Part 4 requires concrete in compression test to be loaded

at 15N/mm2/min while for flexural strength is 18N/mm2/min.

Placing and compacting of concrete

The operations of placing and of compacting of concrete are independent and are carried out

almost simultaneously as they are most important for purpose of ensuring the requirements of

strength, impermeability and durability of hardened concrete in the actual structure. The placing

of concrete has to do with the direct introduction of concrete mix in the formwork. A good

workable concrete with target class S3 (>100mm<150mm) is desirable for placing concrete in

the formwork and around reinforcement, whether by skip or by pump.

Stiff mixes are difficult to place and compacting and most times consequently result in honey

combing on concrete. In small scaled concrete works, concretes are normally placed with head

pans and wheelbarrows. But in large scaled concrete works, concrete is often placed with skips

from cranes and concrete pumps. Although some concrete are self-compacting, compacting is

highly essential in concreting. It is used to eliminate the major air voids between aggregates in

wet concrete. Compaction aids in achieving concrete with strong outcome. With adequate

28
water-cement ratio administered in concreting, definitely a strong concrete will be result after

compaction, devoid of honey combs, sand scouring, etc.

2.10 Crushing Strength

The crushing strength of concrete is influenced by a number of factors in addition to water

cement-cement ratio and degree of compaction. The more important ones are:

1. Cement type and quality: The rate of strength gain and the ultimate strength may be

affected. OPC cement concretes when prepared well and cured adequately can poss ess

more compressive strength than RPC (Rapid Hardening Portland Cement).On the other

hand, concretes whose qualities have been upgraded, that is, added admixtures like

plasticizers or Retarders can bear more strength than ordinary concrete without

admixture.

2. Temperature : Initial rate of hardening concrete is generally induced/ increased by an

increase in Temperature but may lead to lower ultimate strength. At low temperature, the

crushing strength may remain low for some time, particularly when cements of lower

strength gain are used, but invariably may lead to higher ultimate strength.

3. Efficiency of Curing: A loss of strength of up to 40% may result from premature drying

out. The method of curing concrete test cubes given in BS 1881: Part 3, 1983 should be

strictly adhered to. Concrete properly cured is stronger and less susceptible to chemical

attack, water tight and traffic wear.

4. Type and Surface Texture of Aggregates: This is considerable- to suggest that some

aggregates produce concrete of greater compressive strength and tensile strength than

others. This is as a result or consequence of type, surface texture, chemical properties,

e.t.c.

29
 5. Moisture Content: Concrete dried immediately exhibits high strength due to the drying

process but will not gain strength thereafter unless returned to and maintained in a moist

condition. Notably, dry concrete will exhibit a reduced strength when moistened

thereafter.

2.11 Citations of Previous Works

Walker and Bloem (1960) studied the effect of coarse aggregates on the compressive strength of

concrete. This work demonstrates that an increase in aggregate in a concrete mix increases the

strength of the concrete. The study also shows that the flexural to compressive strength ratio

remain at approximately 12 percent for concrete with compressive strength between 35 MPa

(5100 psi) and 46 MPa (6700psi).

Ruiz (1966) in research on the effect of aggregate on the behaviour of concrete found out that the

compressive strength of concrete increases along with an increase in coarse aggregate content.

The increase is due to the reduction in the voids with the addition of aggregates.

Giaccio, Rocco, Violini, Zappitelli, and Zerbino (1992) studied the effect of coarse aggregate on

the mechanical properties of high strength concrete.

Maher and Darwin (1976,1977) observed that the bond strength between the interfacial region

and aggregate plays a less dominant role in the compressive strength of concrete than generally

believed. Finite element model were used to evaluate the effect of matrix aggregate bond strength

on the strength of concrete

2.12 Summary

The need for conducting the compressive test on concrete is to determine the strength of concrete

cast on different dates and also to determine the necessary steps and from aggregate to avoid the

30
use of substandard aggregate materials that might contribute to failure of structures and also to

determine whether a given concrete mixture will meet the needs of a specific job. Compressive

strength test also gives an idea of the overall strength of concrete and quality of a concrete

produced.

31
 CHAPTER THREE

3.0 MATERIALS AND METHOD

The objective of the preliminary test was to determine some physical properties of the concrete

constituents and materials used in this work. These include the particle size distribution of fine

3.1 MATERIALS

The following concrete constituent materials and equipment were used during the process of

carrying out this project. Since the investigation was on coarse aggregate, 3 different coarse

aggregates were used while that of fine was one only.

Coarse aggregate

Aggregates used in this project (coarse) were made of three different sizes. The coarse

aggregates were washed thoroughly with water to remove any impurity or dirt therein and then it

was sun-dried to obtain saturated dry surface condition to ensure that the water-cement ratio is

not affected. Some properties of coarse aggregates which affect the workability and bond

between concrete matrixes are shape, texture, gradation and moisture content. The coarse

aggregate size used was 10mm, 16mm and 25mm.

32
Fine aggregate

The fine aggregate used was dry river sand from Amansea River. The soil sample was

thoroughly washed with clean water to remove any debris, organic matter and impurities present

in the sand and then sun dried to obtain a dry surface condition and ensure that the water cement

33
ratio is not in any way affected.

Cement

Ordinary Portland cement (Dangote Brand) was used for this work.

Water

The water for all the purpose in this work is fresh clean water gotten from the civil engineering

laboratory water tank, which was clear, clean in appearance and without damaging amounts of

oil, acid, salt, organic material and other substances that may impact the resistance of the

concrete.

METHODOLOGY

3.3.1 Sieve Analysis

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

fractions (groups), each consisting of particles of the same size. In practices, each fraction

contains between specific limits, these being openings of standard test sieves. I t is also shown

34
graphically on particle size distribution curve for the purpose of obtaining the grade of the

aggregate. The main aim is to determine the various sizes of particles present in aggregates.

Apparatus

In the analysis, the following apparatus were used:

1. B.S test sieves of different sizes complying with the requirements of B.S 410, full
tolerance
2. A weighing balance
3. Metal brush
4. Stop watch
5. Plate

Procedure

1. The fine aggregate samples were collected in a suitable quantity. Note: the larger the

particle size, the quantity required.

35
 2. The aggregate were dried and kept free from moisture and was also protected from

containing any lumps.

3. The sample is sieved through a 5mm sieve; the portion retained on the sieve was

discarded while those passing through were used for the particle size analysis.

4. The sample gotten from the 5mm sieve is placed in the top sieve and the set of sieves

is kept on a mechanical shaker and the machine is started.

5. The machine is allowed for 10 minutes of shaking for sufficie nt particles to pass.

6. The mass of the samples retained on each sieve and on pan is obtained to the nearest

0.1gm.

7. The mass of the retained aggregate is checked against the original mass.

8. A graph is plotted to ascertain the grade of samples.

3.4 PRODUCTION OF CONCRETE

Batching

Batching is the process measuring ingredients or materials to prepare concrete mix. Batching can

be done of two methods, volume batching and weight batching. Batching should be done

properly to get quality concrete mix. Batching by Weight is considered to be more accurate than

volume batching hence; batching was done by weight for the Purpose of this work. As much as

possible, there would always be variation in the proportion of voids in the aggregates; volume

batching therefore is considered as not being very reliable and accurate for the test. Method of

batching adopted in this work was based on the calculation of the necessary number of specimen

to be cast for each of the coarse aggregate. The moulds used were of each of the dimens ions and

so their volume could be calculated.

36
3.4.1 Mix Design

The concrete mix design adopted for this research is as stated below; the design was adopted

based on the availability of the material and also the aim of the experiment.

Density of concrete = 2400Kg/m3

Volume of cube sample = 150mmx150mmx150mm =3375cm³ =3375cm³/100³ =3.375x10-³m³

Density =mass/volume

Where mass =2400kg/ m³ x0.003375 m³ = 8.1Kg

Using mix ratio = 1: 2: 4 =1+2+4+0.45 = 7.45

W/C= W/1.16 =0.45 = W=1.16 x 0.45= 0.522kg =522ml.

Cement =10x 1.16Kg =11.6kg

Fine aggregate=10 x 2.3Kg =23kg

Coarse aggregate=10x 4.6Kg=46kg.

Concrete characteristic Strength, Fcu at 28 days = 30 MPa

3.4.2 Mixing of concrete

The process of mixing was performed on the floor of the concrete technology laboratory by hand

using trowel. After weighing out the various quantities of materials, the cement and the fine

aggregate were first mixed under dry condition until the mixture became thoroughly blended,

then the coarse aggregate was introduced, mixed with the already mixed cement and sand until

the mix becomes uniformly distributed throughout the batch. As the mixing process continued

37
the quantity of water calculated for was carefully and gradually added. The mixing proceeded

until a homogeneous concrete mix appears and the desired consistency emerged.

3.4.3 Casting of Concrete

The moulds used for the casting was 150mmx 50mmx150mm. Before the casting operation was

carried out, the moulds were properly cleaned and inside oiled with used engine oil (as releasing

agent) to ensure easy de- molding operation. The concrete in the mould were filled in three layers

approximately 50mm thick with the Concrete (that is, about 50mm depth). Adequate compaction

by hand was done using a standard steel tamping rod; each layer was compacted with at least 25

strokes per layer using the tamping rod before the cube mold is fully filled up with concrete and

then compact completed. The trowel was used to give smooth finish on the surface after casting.

3.5 Workability of Concrete

Workability of concrete has never been precisely defined. Practical purpose it generally implies

the case with which concrete mix can be handled from the mixer to its final compacted shape.

The three main characteristics of the property are consistency, mobility and compatibility.

38
Consistency is a measure of wetness or fluidity .Mobility defines the ease with which a mix can

flow into and completely fill the mould or formwork. Compatibility is the ease with which all

trapped a given mix can be fully compacted to remove all air. Four tests are widely used for

ensuring workability such as slump tests, compacting factor, and time and flow test. But for the

purpose of this research, slump test was used.

3.5 Slump Test

Slump test is used for the measurement of a property of fresh concrete. The test is an empirical

test that measures the Workability or flow of fresh concrete. ASTM C143 More specifically, it

measures Consistency between batches. The slump test is used to ensure uniformity for different

batches of similar concrete under field conditions.

Apparatus

1. A truncated slump cone: height =300mm Tamping Rod

2. Measuring Tape

39
 3. Trowel
4. Base plate
5. Brush

Procedure

A freshly mixed concrete with water-cement ratio of 0.5 was made. The following steps were

undertaken to carry out the slump test:

1. The cone was placed on the flat form tray in a position such that the wider surface is

on the form.

2. The cone was filled in 3 layers of equal height with trowel giving each layer 25 stokes

or taps.

3. After leveling and smoothing the top of the concrete and clearing around the cone of

any dropping, the cone was lifted upright with two hands.

4. After pulling the cone, it was placed close to the concre te without applying any

vibration or jointing round plat form.

5. The sprit level was trace on top of the cone to span across the concrete.

6. The measuring tape was then place perpendicular to the straight edge and lowered to

the top of the slump concrete.

7. The difference in height between the top of the cone and the top of the slumped

concrete was then measured and recorded.

3.6 Curing of Concrete

After the casting, proper identification marks were given showing time interval and the type of

coarse aggregate used. Then the concrete moulds were left in the laboratory for 24 hours. It was

left uncovered because the relative humidity of the period was fairly high since it was done

40
during the rainy season. The cube were demoulded after 24 hours and then transferred into the

curing tank.

3.7 Compressive Strength Test

The compressive strength test was carried out using the compressive strength test machine as

find in the test method BS 1881 part 116, 1983. An increasing compressive strength was

introduced to the cube specimen until failure occurred to obtain the maximum compressive load.

The specimen dimension was taken before testing. The testing was carried out for 7, 14, 21 and

28 days after curing.

𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝐿𝑜𝑎𝑑,𝑃 (𝐾𝑁)

Compressive strength = (1)
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 ,𝐴 (𝑚𝑚2 )

41
Procedure

1. Remove the specimen from water after specified curing time and wipe out excess water

from the surface.

2. Take the dimension of the specimen to the nearest 0.2m.

3. Clean the bearing surface of the testing machine.

4. Place the smoothest side of the specimen in the machine in such a way that the loads

shall be applied to the opposite sides of the cube.

5. Align the specimen centrally on the base plate of the machine.

6. Rotate the movable portion gently by hand so that it touches the top surface of the

specimen.

7. Apply the loads gradually without shock and continuously at the rate of

140Kg/cm/minute till the specimen fails.

Record the maximum load and note any unusual features in the type of the failure.

42
 CHAPTER FOUR

4.0 RESULTS AND ANALYSIS OF ALL TESTS

SIEVE ANALYSIS (PARTICLE SIZE DISTRIBUTION OF FINE AGGREGATE)

TABLE 4.1
Weight of sample=500gms
Sieve Weight % weight Cumulative Cumulative
size retained retained weight weight passing
(m) (g) retained (%) (%)
4.75 4.63 0.926 0.926 99.070
2.00 8.82 1.764 2.690 97.310
1.80 16.23 3.226 5.916 94.084
0.85 20.30 4.060 9.976 90.024
0.60 49.74 9.948 19.924 80.076
0.45 91.81 18.362 38.286 61.714
0.30 154.01 30.802 69.088 30.912
0.15 142.84 28.568 97.656 2.344
0.075 10.30 2.060 99.716 0.284
Plate 1.42 0.284 100.00 1.000
Total 500

PARTICLE SIZE DISTRIBUTION OF COARSE AGGREGATES

TABLE 4.2
Weight of test sample=1250gms
Sieve sizes (mm) Weight % weight Cumulative % Cumulative
retained (g) retained passing % retained
54.40 100.00
25.40 5.00 0.40 99.60 0.40
16.52 380.00 30.40 69.20 30.80
9.52 570.75 46.14 23.06 76.94
4.76 283.75 22.70 0.36 99.64
Plate 0.36 0.00 100.00
Total 1250

43
SLUMP TEST RESULTS
Table 4.3
Mix Mix Height Height Slump
size Ratio of cone of slump value
Concrete
10mm 1:2:4 300mm 203mm 92mm
16mm 1:2:4 300mm 205mm 93mm
25mm 1:2:4 300mm 207mm 95mm

DETERMINATION OF THE COMPRESSIVE STRENGTH OF CONCRETE TEST

RESULTS FOR COARSE AGGREGATE OF SIZE 25mm
Table 4.4
Specimen Age of Area of Weight Average Mean
Curing Specimen of Test compressive
(Days) (150mm Specimen load strength
by (kg) (KN) (N/mm2 )
150mm)
B11 7 150 8.4 582.5 17.43
C11 14 150 8.3 630.28 18.60
D11 21 150 8.4 690.35 20.99
E11 28 150 8.5 756.30 21.99

DETERMINATION OF THE COMPRESSIVE STRENGTH OF CONCRETE TEST

RESULTS FOR COARSE AGGREGATE OF SIZE 16mm
Table 4.5
Specimen Age Area of Weight Average Mean
of specimen of Test compressive
curing (150mm specimen Load strength
(Days) by (kg) (KN) (N/mm2 )
150mm)
B11 7 150 8.4 642.67 19.62
C11 14 150 8.5 666.90 20.03
D11 21 150 8.4 774.85 23.67
E11 28 150 8.3 801.00 24.02

44
DETERMINATION OF THE COMPRESSIVE STRENGTH OF CONCRETE TEST RESULTS
FOR COARSE AGGREGATE OF SIZE 10mm
Table 4.6
Specimen Age of Area of Weight Average Mean
curing specimen of test compressive
(days) (150mm specimen load( strength
by (kg) KN) (N/mm2 )
150mm)
B11 7 150 8.8 320.40 14.02
C11 14 150 8.7 356.76 15.20
D11 21 150 8.7 380.00 16.78
E11 28 150 8.9 426.06 18.05

Figure 1 fine aggregate sieve analysis graph

45
 Sieve graph for fine aggregate
120
Cumulative % weight passing

100
80
60
40
20
0
-20
0.01 0.1 1 10
Sieve size (mm)

Aggregate Analysis (Fine Aggregate)

The result of sieve analysis from figure 4.1 clearly show the grade distribution of fine aggregate from the

graph deduced from the table. It is seen that the aggregate is of uniform fine grading.

Figure 2 coarse aggregate sieve analysis graph

Sieve graph for coarse aggregate

120

100
Cumulative % passing

80

60

40

20

0
1 10 100
Sieve size (mm)

46
Aggregate Analysis (Coarse Aggregate)

The result of the test of the coarse aggregate from the graph shows that the coarse aggregate

were well and uniformly graded.

Figure 3 Slump test graph

Slump graph
95.5
95
94.5
Slump value (mm)

94
93.5
93
92.5
92
91.5
91
90.5
10 16 25
Aggregate size (mm)

Workability

The workability of a concrete mix is affected by the mix proportion. Figure 3 above shows that for a
given water cement ratio, workability decreases as the coarse aggregate size (proportion) increases in a
concrete mix, this is probable because there is insufficient paste to lubricate the aggregate. It is also
observed that the workability is decreased as the quality of fine aggregate is increased and this is likely
due to the increase in the surface area of the aggregate proportion and the dryness of the concrete mix.

This result indicates that adequate paste content and aggregate surface area is required to achieve a
certain degree of workability.
Figure 4 graph of coarse aggregate 10mm, 16mm and 25mm

47
 30
Compressive strength (N/mm2)
25

20

15 10mm
16mm
10
25mm

0
0 7 14 21 28
Curing (Days)

The result of the compressive strengths of concrete specimen using a constant water cement

ration are presented in the figure 4 above. It shows that the compressive strength increases

progressively with increase in curing age for the different aggregate proportion in the concrete.

Figure 4 also shows that the compressive strength of the concrete improved when the concrete

aggregate proportion was varied i.e. when the concrete was slightly sandy and stony. It was also

notice from the figure above that an early strength was obtained when the concrete was cured for

the first seven days/ from the figure 4 about, the concrete made with coarse aggregate size of

16mm gave the highest strength gain followed by aggregate size 25mm and aggregate size 10mm

Figure 5 comparison of 10mm, 16mm and 25mm aggregate

48
 30
Compressive strength (N/mm2 )
25

20
10mm
15
16mm
10
10mm
5

0
7 14 21 28
Curing (Days)

From the chart above, it shows that the strength of concrete is affected by the variation in the

aggregate size of the concrete. The compressive strength of the 16mm coarse aggregate size was

highest because there was sufficient paste to completely fill all the voids in the concrete mix.

This increase in strength as the curing age increases is in agreement with the finding of James

etal, 2011 and Joseph etal, 2012.

49
 CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

The compressive strength of the concrete has been measured at ages 7, 14, 21 and 28 days

respectively. The tests are summarized in the tables above. The results from the crushing test

shows in fig 4.3 shows that there is progressive increase in average compressive strength of

concrete from 7-28 days respectively. The variation in numbers of days of curing increases the

compressive strength of the concrete cube crushed. Observation shows that at 28 days, the

concrete has achieved its maximum strength.

5.1 CONCLUSION

a. There is rapid increase in strength again during the first seven (7) days of curing followed by

14 days, 21 days and 28 days.

b. Concrete strength increase progressively with the age of curing.

c. Concrete gain its maximum strength at 28 days of curing

d. From the study, it can be concluded that the compressive strength of a Concrete is affected by

the size, shape and surface texture of the aggregate.

e. It was observed that during the mixing of the concrete, the aggregate with the smallest surface

area tends to be covered with cement paste wholly while the one with large surface area is not

properly covered.

f. The curing days also affect the strength of the Concrete. As the curing days increases, the

compressive strength also increase.

50
g. No matter the aggregate sizes, the failure patterns of the test specimens were the same. The

failure patterns were pyramidal.

5.2 RECOMMENDATIONS

Based on the obtained results of the tests carried out and considering the importance of this

investigation, the following recommendations are made

1. In this study, varying ages were used to obtain the compressive strength of concrete with

different specimen of coarse aggregate (10mm, 16mm, and 25mm) and constant specimen of

cement, water and fine aggregate. The author wish to suggest that other aggregates types within

our area be used with the aim of determining the best aggregate size to be used in construction of

reinforced concrete and mass concrete which should equally be more cost effective.

2. Machine mixing and machine compaction could be used in future studies for more uniform

and adequate compaction to see if the compressive strength would be affected. The

aggregate/cement ratios as well as water/ cement Ratio for aggregate type should be varied. The

flexural and the tensile strength of the concrete with different aggregate sizes should also be

studied to be able to draw a general conclusion.

3. Since there is increase and decrease in variation strength of concrete, it is good to conduct

compressive strength of concrete without curing of the cubes to determine the compressive

strength of the cubes

4. In this project, ten specimens (concrete cubes) were produced per aggregate type, only two

samples were used for each of the 7, 14, 21, and 28 day tests. The author wishes to suggest that

for effective study a greater number specimens per age be used in order to plot the best diagram

51
and obtain best fit curves. It will then be possible to observe the abnormal specimen(s)

effectively at all water/ cement ratios and at all ages for each maximum size of aggregate.

5. from the test conducted for the compressive strength of concrete cast on different dates using

different coarse aggregate size ,It is equally recommended that 16mm be used for reinforced

concrete during construction since its compressive strengths are high while 25mm for mass

concrete because of its low compressive strength.

6. Also for workability, the use of 10mm is recommended for beams and columns so as to

achieve maximum compaction and less honey comb.

7. For the purpose of cost and economy in use of materials, the use of 25mm is recommended

because of its large surface area.

8. Other types of cement should be used to see if the compressive strengths will be affected. And

there should be awareness about the importance of recommending aggregate sizes for every

structural element during design stage

52
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