Monday, February 22, 2010

AND FLEXURAL STRENGTH OF CONCRETE MADE FROM COMPARISON OF COMPRESSIVE DIFFERENT COARSE AGGREGATES

ABSTRACT
This research, comparison of compressive and flexural strength of concrete made from different coarse aggregates written in accordance to British standard. The different sizes of coarse aggregates used are; 10mm, 12 mm and 20mm.

These aggregates were used to produce concrete cubes (150mm x 150mm x 150mm) and beans (150 x 150mm x 150mm). The beans and cubes were compacted in three layers and cured for 7 days, 1 day and 28 days, after which they were crushed to determine their compressive and flexural strength and also comparing them. Slump test was also carried out.

The compressive strength of the 10mm aggregate ranges from 15.63 to 29.03 N/mm2, 3.97 t0 5.57N/mm2. The compressive strength of the 12mm aggregate ranges from 19.7 26.10N/mm2 while its flexural strength is from 4.05 to 5.63N/mm2 of 20mm aggregate ranges from 4.15 to 2.3.74N/mm2. The slump of the beans ranges from 1.8 to 2.05am for the different sizes of the aggregates.

TABLE OF CONTENTS
Title page- - - - -- - - - -- i
Approval page - - - - - - - -- ii
Dedication - - - - - - - - - iii
Certification - - - - - - -- - - iv
Acknowledgement - - - - -- - - - v
Abstract - - - - -- - - - -- - vi
Table of contents - - - - - - -- - vii
CHAPTER ONE
1.0 Introduction - - - - - - -
1.1 Statement of the study - - - - - -
1.2 Aims and objective of the study - - - -
1.3 Scope of the study - - - - - -- -
1.4 Limitations - - - - - - - -
CHAPTER TWO
2.0 Literature Review - - - - -- - -
2.1 Use of concrete - - - - -- - -
2.2 Concrete properties - - - - - - -
2.3 Properties of Aggregate - - - - - -
2.4 Types of Aggregates - - - - - -
2.5 Water - - - - - - - - -
2.6 Cement - - - - - - -- - -
2.7 Properties of cement - - - - - -
2.8 Concrete mix design - - - - - - -
2.9 Compaction of concrete - - - - - -
2.10 Curing of concrete - - - - - - -
CHAPTER THREE
3.0 Methodology - - - - - - - -
3.1 Concrete mix design - - - - - -
3.2 Raw materials to be used - - - - - -
3.3 Measuring and mixing of concrete - - - -
3.4 Compressive Test - - - - - - -
3.5 Flexural Test - - - - - - - -
3.6 Slump Test - - - - - - -- -
CHAPTER FOUR
Presentation of Results - - - - - - -
CHAPTER FIVE
Analysis of Results - - - - - - - -
6.0 Conclusion and Recommendation - - - -
6.1 Conclusion - - - - - - - -
6.2 Recommendation - - - - - - -
Reference - - - - - - - -- -
Appendix - - - - - - - -- -

CHAPTER ONE
1.0 INTRODUCTION
One of the characteristics of concrete that has made it to be widely used is due to its high compressibility in with standing burden.

Compressive strength of concrete can be defined as the maximum compressive load it can carry per unit area. The concrete performance test has always been referred to as the compressibility in withstanding concrete cube load with dimension of 150 x 150 x 150mm at the age of 28 days.

The flexural strength of a concrete can be defined as the maximum compressive load it can carry per unit areas. The concrete performance test has always been referred to as the compressibility in withstanding concrete cube load with dimension of 150 x 150 x 150mm at the age of 28 days.

The flexural of a concrete cab be defined as the ability of a beam to withstand a particular force before it shears. It gives a measure of tensile strength in bending. There are many techniques known to be applied order to obtain compressive and flexural strength of concrete, whether directly or indirectly non destructive test etc. In this research, the method applies shall be non destructive.

In this work also, the non destructive test which is the cube compressive strength test with a dimension 150 x 150 x 150mm for three different aggregate sizes of 10mm, 12mm and 20mm and the flexural strength test with a beam of 150 x 150 x 600mm for the same sizes of aggregates were investigated. The cubes and beams were tested at the age of 7, 14 and 28 days respectively and the compressive and flexural strength compared.
1.1 STATEMENT OF PROBLEM
When concrete is stressed, failure may originate within the concrete, or the aggregate matrix interface (the bond).The aggregates are stringer that the concrete itself. Therefore a concrete cast without an aggregate does not develop the special properties required such as weather resistant and the strength characteristics. A smooth rounded aggregate result in a weaker bond between the aggregate than an irregular or angular aggregate.

The use of poor quality material in construction works due to its affinity is wearing and abrasion.
1.2 AIMS AND OBJECTIVE OF THE PROJECT.
The aims and objectives of this project are as follows;
1. Determination of workability of concrete.
2. Determination and comparison of both flexural and compression strength.
1.3 SCOPE OF THE STUDY
The concrete strength test to be carried out will be bases on the following;
i. Concrete cube test with the dimension 150mmx 150 mmx 150mm
ii. Flexural test with beam of dimension 150mm x 150mmx 600mm.
iii. Comparison of the results
obtained in (i) and (ii) above
1.4 LIMITATION OF THE STUDY
This project is handicapped by a number of factors such as:
i. Insufficient Equipment: Most of the equipment used were borrowed from labourers working within the Engineering block. There are also limited number of beam moulds for the practical.

ii. Safety: No personal protective equipment was used during the experiment and which is very dangerous. Concrete splash for instance is vulnerable to skin corrosion.
iii. Time: The writing of this project could have been to a large extent enhanced if the researcher did have sufficient time to do the work, since it was carried, alongside with pressure of other academic commitment.
iv. Finance: The project was obviously limited by inadequate or insufficient finance.

CHAPTER TWO
LITERATURE REVIEW
2.0 DEFINITION OF CONCRETE
Concrete may be defined as mixture of cement or binder, water, and aggregates, where the water and cement or binder form the paste and the aggregate forms inert fillers. In the absolute volume, the aggregate amounts in 60-80% of the volume of concrete and is therefore the major constituent.

Concrete can also be defined as a man made composite, the major constituents of which is natural aggregate such as gravel, and sand or crushed rock. Alternatively, artificial aggregates for example, blast furnace slag, expanded clay broken bricks and steel may used where appropriate. The other principal constituent of concrete is the binding medium used to bind the aggregate together to form a hard composite. The most commonly used binding medium is the product formed by a chemical reaction between cement and water. Other binding medium is used on a much smaller scale for certain project in which the cement and water are replaced either wholly or partial by polyester resins.

In the hardened state, concrete is a rock like material with a high compressive strength.

Normally concrete is good in compression, but poor in tension. For structural applications, it is normal practice either to incorporate steel to resist any tensile forces (reinforced concrete) or to apply compressive forces to counteract these tensile forces.
2.1 USES OF CONCRETE
Concrete may be used for the following purposes:
* For decorative purpose:
Special surface finished for example exposed aggregates can be used to great effect.
* Concrete is used structurally in buildings for foundation, columns, beams and slabs, in shell structures bridges, sewages treatment work, rail way sleepers, roads, cooling to were, dams, chimneys, harbors, off shore structures, coastal production work and so on.
* It is used for a wild range of pre cast concrete products which includes concrete blocks, cladding panels, pipes and lamp standards.

2.2 PROPERTIES OF CEMENT (FRESH)
Fresh concrete is a mixture of water, cement, and aggregate. After mixing of these constituents materials, to produce a uniform blended operation such as transporting, placing compacting and finishing of fresh concrete can also affect the properties of hardened concrete. It is important that the constituent materials remain uniformly distributed within the concrete mass during the various stages of its handling in order to achieve full compaction.
2.3 WORKABILITY
Workability can be defined as the ease with which a concrete mix can be handled from the mixer to its final compacted shape. The three main characteristics of the property are consistency, ability and compatibility. In this context, the required workability of a mix depends not only on the characteristics and relative proportions of the constituent material but also on the:
* Method employed for conveyance and compaction
* Size formwork or mould.
2.4 MEASUREMENT OF WORKABILITY
Four tests widely used for measuring workability are the slump, compacting factor, and vibe time and flow tests. These are standard tests in the United Kingdom (UK). The British standard 5328 (BS 5328) requires the measurement of workability of concrete to be writing certain limited of the required value as given in table 1 below.
TABLE 1
Suitability and allowable to levance of workability test for concrete.
METHOD WORKABILITY RANGE ALLOWABLE TO LEVANCE
Slump Medium high Greater of 1mm of required value
Compacting factor Low- high -+0.03 for values > 0.90
+ 0.04 for values >0.8 &<0.8
+0.05 for values < 0.8

Vibe time Very low- low greater of + 3 req. value

Flows Very low + 50mm about the req.

2.5 SLUMP TEST
This test was developed by chap man Adams in the United States (US) in 191, and has been adopted as a check of the consistency of concrete in the construction works. A 300mm high concrete cone with the bottom and top diameter of 200mm and 100mm respectively was used for the test. It is suitable for detecting changes in workability. For example, an increase in the water content or deficiency in the proportion of fine aggregate results in an increase in slump. Although the test is suitable for quality control purposes, it should be remembered that it is generally considered to be unsuitable for mix design since concrete requiring varying amount of work for compaction can have similar numerical values of slump. The test is not suitable for very dry or wet mixes. For very dry mixes, with zero or nearly zero slump, moderate variations in workability do not result in measurable changes in slump. For very wet mixes, complete collapse of the concrete produces unreliable values of slump.

The three types of slump shear slump and collapse slump. The true slump gives the correct slump. The true slump is up to 125mm, shear slump up to 150mm while the collapse slump is between 150-250mm. a true slump is observed with cohesive and rich mixes for which the slump is usually associated with very wet mixes and is generally in dilative of poor quality concrete and most frequently results in segregation of its constituent materials. Shear slump occurs more often learner mixes than in rich ones and indicates a lack of cohesion which is generally associated with harsh mixes ( low mortar contents). Wherever a shear slump is obtained, the test should be repeated and if persistence, this fact should be recorded together with test results, because widely different values of slump can be obtained depending on whether is of true or shear form.

The standard slump apparatus only suitable for concrete in which the maximum aggregate size does not exceed 0mm. It should be noted that the value of slump, changes with mal hydration process and evaporation of some of the free water, and it is desirable therefore that tests are performed within a fixed period of time. It is advisable delay testing for around 10 minutes after the addition of water to allow for the absorption of water by dry aggregates.
2.6 FACTORS AFFECTING WORKABILITY
Various factors known to influence the workability of a freshly mixed concrete are shown in fig 1 from the following discussions, it will be apparent that a change in workability associated with the constituent materials is mainly affected by water content and specific surface of cement and aggregates.


CEMENT
FACTORS AFFECTING WORKABILITY
Constituent materials
Ambient condition
TIME
WATER
Admixtures
Aggregates
Temp.
Wind & velocity
Max. size
Shape
Grading
Absorption
Coarse & fine aggre
Surface Texture






Fig 1: Factors affecting workability of concrete.

2.6.1. CEMENT AND WATER
Typical relationship between the water/ cement ratio by (volume) and the volume fraction of cement for different workability are shown in fig 2.

Hughes (1971) has shown that similar linear relationship exist, irrespective of the properties of the constituent materials. Workability is relatively insensitive to changes in only the cement content and for practical purposes may be considered dependent only the cement content and for practical up to 10- 22%. For a given mix, the workability of the concrete decreases as the fineness of the cement increases as a result of the increased specific surface. The effect being more marked in reach mixtures. It should be noted that finer cement improves cohesiveness of a mix.
Very low



1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
6 7 8 9 10 11 12 13 14 15

0.5

Basic volume fraction of cement (Percentage) for different workability Fig 2: Graph showing typical relationship between the water/ cement ratio and volume fraction of cement for different workability.
2.6.2 ADMIXTURES
The principal admixtures affecting the improvement in the workability of concrete are water reducing and air entraining agents. The extent of the increase in workability is dependent on the type and amount of admixture used and the general characteristics of the fresh concrete. Water reducing admixture is used to increase workability while mix proportion are kept constant or to reduce the water content while maintaining constant workability.
2.6.3 AGGREGATES
For a given cement, water and aggregate contents, the workability of concrete is mainly influenced by the total surface area of the aggregate. The surface area is governed by the maximum size, grading and shape of the aggregate. Workability decreases as the specific surface increases, since this required a greater proportion of cement paste to wet the aggregate particles, thus leaving a smaller amount of paste for lubrication.

It therefore follows the, all other conditions being equal, the workability will be increased when the maximum size of aggregate increases.


2.6.4 AMBIENT CONDITION
The environmental factor that may cause a reduction in workability are temperature, humidity and wind velocity. For a given concrete changes in workability are government by the rate of hydration of the cement and the rate of evaporation of water. Therefore, both the time interval from the commencement of mixing to compaction and the condition of exposure influences the reduction in workability. An increase in the temperature speeds up the rate of which water is used for hydration as well as its loss through evaporation.
2.6.5 TIME
The time that elapse between mixing of concrete and its final compaction depends on the general conditions of work such as the distance between the mixer and the point of placing, site procedures and general management. The associated reduction in the workability is a direct result of loss of free water with time through evaporation, aggregate absorption and initial hydration of the cement. The rate of loss of workability is affected by certain characteristics of the constituent materials, for example, hydration and heat development characteristics of the cement, initial moisture content and porosity of the aggregate as well as the ambient conditions.
2.7 STABILITY
Apart from being workable, fresh concrete should have a composition such that its constituent material remain uniformly distributed in the concrete during both the period between mixing and compaction and the period following compaction before the concrete stiffens. Because of the differences on the particle size and specific gravity of the constituent materials, there exist a natural tendency for them to separate, concrete capable of maintain the required uniformity is said to be stable and most cohesive mixes belong to the to this category. For an unstable mix, the extent to which the constituent materials will separate depends on the methods of transportation, placing, and unstable concrete are segregation and bleeding.
2.8 PROPERTIES OF HARDENED CONCRETE
The properties of fresh concrete are important only in the first few hours of its history, whereas the properties of hardened concrete assume an important which is retained for the remainder of the life of the concrete. The important properties of hardened concrete are strength, deformation under load, durability, permeability and shrinkage.
The general strength is considered to be the most important property and the quality of concrete is often judged by strength.

There are however many occasion when other properties are more important for example, low permeability and low shrinkage are required for water retaining structures.

Although in most cases, an improvement of the other properties of concrete. For example, increase in the cement content of a mix improves strength but results in higher shrinkage, which in extreme cases can adversely affect durability and permeability.
2.8.1 STRENGTH
The strength of a concrete is defined as the maximum load (stress) it can only carry. As the strength of concrete increases, its other properties usually improved and since the tests particularly in compression are relatively simple to perform concrete compressive strength are commonly used in the construction industry for the purpose of quality control, concrete is a comparatively brittle material which is relatively weak in tension.
2.8.2 COMPRESIVE STRENGHT
The compressive strength of a concrete is taken as the maximum compressive load it can carry per unit area. Compressive strength of up to 80Nm-2 or more can be achieved dependent mainly on the relative proportion of water to cement that is water / cement ratio, and the degree of compaction.

Concrete structure except for road pavements are designed on the basis that concrete is capable of resisting on compression, the tension being carried by steel reinforcement. A cube of 150mm is used to determine compressive strength and the test specimen should be cured in water at 20_+20C and crushed by loading it at a constant rate of street increase of between 12 and 24N/mm2 Immediately after it has been removed from curing tank.



2.8.3 TENSILE STRENGTH
The tensile strength of concrete various from one eight of the compressive strength at early ages to about one-twentieth later, and it is not usually taken into account in the design of reinforced concrete structures. The tensile strength is however of considerable important in resisting cracking due to changes in moisture content or temperature. The test is used for concreter roads and airfields.

The measurement of the strength of concrete in direct tension is difficult and is rarely attempted. Two more practical methods of accessing tensile strength are available, the split cylinder tests and the flexural test.

The flexural strength gives a measure of tensile strength in bending. The standard size of specimen used is a beam of 150mm x 150mm x 600mm for aggregate of maximum size 40mm and 100mm x 100mm x 400mm long for 20mm size of aggregate.

After curing, the specimen is crushed by applying a load at the third point of the span until the specimen breaks and the modulus of rupture calculated. The two half of the specimen may then be crushed to determine the approximate compressive strength. The flexural strength can be calculated using the formula,

Mo.R = PL
Bd 2

Where P = maximum applied loan
L = Length of the beam
b = Beam breath
d = Beam depth

2.8.4 SHEAR STRENGTH
In practice, shearing of concrete is always accompanied by compression and tension caused by bending and even in testing, it is impossible to eliminate an element of bending.
2.8.5 FACTORS AFFRECTING STRENGTH
In practice, shearing of concrete is always accompanied by compression and tension caused by bending and even in testing, it is impossible to eliminate an element of bending.

2.8.5 FACTORS AFFECTING STRENGTH OF CONCRETE
Several factors which affect the strength of concrete are listed below; their influence is discussed with particular references to compressive strength. In general, tensile strength is affected in a similar manner.
2.8.5.1 TYPE AND QUALITY OF CONCRETE
The rate of strength gain and the ultimate strength may be affected. The influence of cement on concrete strength for a given its fineness and chemical composition through the process of hydration, the increases the strength of concrete. The gain in strength is most marked at the early stage and after 28 days, the relative gain in strength is much reduced. It is apparent that cement containing a relatively high parentage of Tricalcium silicate (C3S) gains strength much more rapidly than those rich in Dicalcium silicate (C2S).
2.8.5.2 TYPES AND TEXTURE OF AGGREGATE
The bond strength is influenced by the shape, surface texture and cleanliness of the aggregate. A smooth rounded aggregate will result in a weaker bond than an irregular or angular aggregate or an aggregate with a rough surface texture. Aggregate shape and strength. A fine coating of impurities, such as silt and clay on the aggregate surface hinders the development of a good bond. A weathered and decomposed layer on the aggregate can also result in poor bond as this layer can readily become detached from the sound aggregate beneath. The aggregate size also affects the strength. For given mix proportion, the concrete strength decreases as the maximum size of aggregate increases.
2.8.5.3 INFLUENCE OF CURING
Curing of concrete us a pre- requisite for the hydration of the cement content. For a given concrete, the amount and rate of hydration and furthermore, the physical make up of the hydrate products are dependent on the time- moisture temperature history. The greater its final strength. It is normally accepted that a concrete made with or denary Portland cement and kept in normal curing conditions will develop about 75% of its final strength in the first 28 days. This value various with the normal strength of concrete however, it increases as the nominal strength of the concrete increases.
2.8.5.4 INFLUENCE ON THE METHOD OF PREPARATION
When concrete materials are not adequately mixed into a constant homogenous mass, some poor quality concrete is inevitably the result. Even when a concrete is adequately mixed care must be taken during placing and compaction to moralize the probability of occurrence of bleeding, segregation and honey comb, all of which can result in poor quality concrete.
2.8.5.5 INFLUENCE OF WATER
A concrete mix containing a minimum amount of water required for complete hydration of its cement, if fully compact would develop the maximum attainable. Strength at any given age. A water cement ratio of approximately 0.25 (by weight) is required for fully hydration of the cement but with thus water content a normal mix would be extremely dry and virtually impossible to be compaction. A partially compacted strength will drop.
2.9 DEFINITION OF AGGREGATE
Aggregates may be defined as a naturally occurring gravel, crush rock, slag, sand and other similar material, which helps to improve the volume, stability and durability of concrete. The geological process by which a deposit was formed are responsible for it size, shape and location, the type and condition at the rock, the grading, rounding and degree of uniformity. Aggregate is cheaper then cement and maximum economy is obtained by using as much aggregate as possible in concrete.
2.9.1 PROPERTIES OF AGGREGATES
The criterion for a good aggregate is that it should produce the desired properties in both the fresh and hardened state. The most important properties of aggregate are the crushing strength and the resistance to impact, other important properties are: the size and shape of the particles, which can affect the bond with cement paste. The porosity and water absorption characteristics affects the resistance to chemical attach and forest attach and the immunity from shrinkage.
2.9.2 BULK DENSITY AND VOLD
The bulk density of a material is the weight of the material held by a container of unit volume when filled on compacted under defined conditions. It is expressed in Kg/m3. The bulk density of an aggregate is affected by several factors, including to amount of comp active effort used in filling the container.
2.9.3 BULKING
When sand is moistened, films of water form on the particles and the surface tension tends to hold them apart, causing an increase in volume or bulking. Fine sand bulks more than coarse sand, aggregate retained on a 5mm sieve is scarcely affected. As the moisture content of sand increases to about 4-6% the sand rapidly bulks to the extent of 20- 30%. Further increase in moisture content results in a decrease in bulking until when the sand is completely saturated, its volume practically the same as it was in a dry condition.

Bulding can be determined by filling gauge-box or other container of a known volume (A) filled with damp sand the sand is then dried and filled back into water and the damp sand poured into displace the water. The new depth of aggregate in the container gives the unbulked volumes (R). The percentage bulking can then be calculated thus:
A- B X 100
B 1

2.9.4 RELATIVE DENSITY
If a section is cut through any piece it will be seen that it is to some extent honey combed with capillarity’s and tiny air holes. The relative density of a material is therefore the ratio of its unit weight to that of water. Since aggregates in corporate pores, the value of relative density varies depending on the extent which the pores absorbed water when major constituent of concrete. Therefore its relative density is an important factor affecting the density of the resulting concrete.
2.9. 5 SHAPE AND SURFACE TEXTURE
Aggregate shape and surface texture can affect the properties of concrete in both its plastic and hardened state. These external characteristics may be assessed by observation of the aggregate particles and classification of the particle shape and texture. The particle shape can also be assessed by a direct measurement of the aggregate particles to determine the Flakiness, elongation and angularity.
2.9.6 GRADING
The grading of aggregate defines the proportions of particles of size of the aggregate particles normal used in concrete varies from 37.5 to 0.15 mm. Aggregates are placed in three categories name; fine aggregate, containing particles of which the majority are smaller than 5.0mm, Coarse aggregate containing particles the majority of which are larger than 5.0mm and all in aggregate comprising both fine and coarse aggregate. The grading of an aggregate can have a considerable effect in the workability and stability of a concrete mix design.
2. 9. 7 STRENGTH
The strength of an aggregate limits the attainable strength of concrete only when its compressive strength is less than or of the same order as the design strength of concrete. In practice the majority of rock aggregate used are usually considerably stronger than concrete. While the strength of concrete does not normally exceed 80N/mm2, the aggregate commonly used is in the range of 70-35N/mm2.
2.9.7 DEFORMATION
This is considered in assessing aggregate suitability for concrete work, although they can easily be determined from compression tests on specimens from the parent rock. The deformation characteristics of aggregate plays an important role in the creep and shrinkage properties of concrete.
2.9.8 TYPES OF AGGREGATES
The general classifications of aggregates are as follow
2.10 HEAVY WEIGHT AGGREGATE
This provides an effective and economical used of concrete for radiation shielding by given the necessary protection against X- ray, gamma rays and Neutrons. The effectiveness of heavy weight concrete with a density from 400 to 850kg/m3 depends on the type of aggregate, the dimensions and the degree of compaction. It is frequently difficult with heavy weight aggregates to obtain a mix which is both workable and not prone to segregation.

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