Comparison of Properties of Granite Concrete and Washed Gravel Concrete (Varying mix

Proportions)

Uka, Uzoma Bright

Department of Civil and Environmental Engineering, University of Lagos, Nigeria.

Accepted: September, 2009

E-mail: onebrightslash@yahoo.com

Call: +234 08038317499

INTRODUCTION

All over the world the construction industry is rapidly developing based on the

invention of different materials and products in civil engineering field. Nigeria is

one of the many countries in the world that has the construction industry as one

of the most vibrant sectors. With building material being considered the

backbone of this industry, most construction materials are indispensable in any

form of construction work. There have been attempts by engineers to use various

types of materials for the sole purpose of making the task more efficient,

reducing time and cost, improving durability, quality, and performance of the

structures during their lifetime.

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The provision of shelter, clean environment and good road network, which is an

indication of National development, is taking place at a high pace in emerging

mega cities, like Lagos, Nigeria. Therefore, the need to use local available

material such as timber, clay, natural occurring aggregates (gravel, sand, shell

and pumice), pozzolana, mining wastes, bamboo natural fibers and various types

of laterite soil, has attracted the attention of many researchers in civil

engineering.

Over the years coarse aggregate such as granite and/or gravel has been major

aggregate used in structural concrete works, since it constitutes about 60 to 80

percent of concrete.

Natural aggregate are usually dug or dredged from rivers, lakes, seabed, or pit.

The dug or dredged material is washed to remove any associated mud or weed,

after which it is drained before delivery or use.

Sea-dredged aggregates may contain shells or shell-fragments of varying sizes.

These consist of calcium carbonate in a hard impermeable form rather resembling

good-quality limestone, and are chemically inert to most substances except acids.

The small fragments which may be present in the fine aggregate may thus be

unimportant, but the larger pieces, or even complete shells, which can occur in

the coarse aggregate, are possibly undesirable in certain types of works. In

exposed horizontal surfaces such as those of roads, the presence of hallow shell-

fragments may constitute voids in which water may collect and subsequently

freeze to cause frost spalling.

However, crushed aggregate (granites) is produced by crushing quarry rocks,

boulders, cobbles, or large-sized gravel. These aggregate processing consists of

crushing, screening and washing the aggregate to obtain proper cleanliness and

gradation. If necessary, a benefaction process such as jigging or heavy media

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separation can be used to upgrade the quality. Once processed, the aggregate are

handled and stored in a way that minimizes segregation and degradation and

prevents contamination [1].

Granite and gravel differ as regards the shape of the particles. The sea dredged

gravel consists of rounded and smooth particles, while the crushed granite

particles are angular and have a rough surface. The rounded aggregate facilitates

interparticle movement and thereby increase workability in concrete as compare

to the angular crushed granite aggregate. The rounded and smooth particle of sea

dredged gavel may result in lower adhesion between cement and aggregate as

compare to the rough surface of crushed granite. This would tend to reduce the

strength- especially the tensile strength.

Clearly it is important that the chosen aggregate should contain nothing which

might adversely affect the hardening of the cement or durability of the hardened

mass.

Some types of organic matter, for example, may reduce the hydraulic activity of

the cement to the detriment of normal setting and hardening, and any aggregates

must clearly be free from significant quantities of these. Dust or clayey matter on

the surface of the aggregate particles may reduce the bond between them and the

cement paste, and as a result should not be present in excessive quantities.

Aggregate must, of course, be free from constituents which decompose or change

significantly in volume on exposure to the atmosphere, or which react adversely

with the hardened cement paste.

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There is available nowadays a wide range of materials which, for practical

purposes, fulfill the requirements for aggregates. We may for convenience I shall

consider three classes: normal-density, lightweight and high-density aggregate.

Normal – Density Aggregate:- this normally taken to include aggregate having

a specific gravity between about 2.5 and 3.0 and a density in the range 1450 to

1750 kg/m3. it does include the most widely used of all aggregates, namely

gravels and crushed rocks. Together with blast furnace slag the latter is a by-

product from pig-iron manufacture. BS 882 lays down the requirements for

natural aggregate and embodies certain useful definitions which are worth

summarizing

1) Coarse aggregate is material substantially retained on a 5mm test sieve.

It may be described as:

a) uncrushed gravel, if it results from the natural disintegration of

rock;

b) Crushed stone, if it is produced by crushing hard stone.

2) Fine aggregate is material mainly passing the 5 mm sieve. It may be

described as;

a) Natural sand, if it results from the natural disintegration of rock;

b) Crushed stone sand, if it is produced by crushing hard stone or

gravel.

The term ‘mixed sand’ may be used to describe a blend of natural

sand

with crushed stone sand.

Lightweight Aggregates:- a variety of porous solid, both natural and man- made,

are available for use as lightweight aggregate. As a general rule, the higher the

porosity of the aggregate, the lower the thermal conductivity, density and

strength of the lightweight concrete made with it. Aggregates having high

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porosity, such as vermiculite, make low-weight concrete of excellent thermal

insulating value but little resistance to stress. The less porous lightweight

aggregates can produce concrete which are strong enough to resist structural

stresses, but which are dense and less efficient thermal insulators than those made

with the high-porosity aggregates.

High-density aggregate:- aggregates of high specific gravity are used to make

high-density concrete for such applications as screening radioactive sources.

Example are Barytes (barium sulphate rock), and ferrous metal granules such as

shot and punching, and ferrous ores such as magnetite, haematite and limonite.

Concrete densities up to 4800kg/m3—i.e. about twice the density of conventional

concretes—have been obtained.

Cement:- cement suitable for reinforced concrete is ordinary Portland cement,

rapid- hardening Portland cements, Portland blast-furnace cement, low-heat

Portland cement, sulphate-resistance, super-sulphate cement and high alumina

cement. Cement of different types should not be used together; they all have

specific conditions under which they are used. Super sulphate cement concrete is

used for very corrosive soils while low heat cement is better for massive

concreting e.g. dam construction. High alumina cement is used for emergency

work where very high early strength concrete is desire. The quality of cement is

governed by BS12, which specifies some test tests like fineness test chemical

composition test, strength test, soundness test, setting time test and heat of

hydration test. 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. The role of cement paste is to fill the void between the

aggregates to give certain workability (like the grease in ball bearing) and to bind

aggregate when the paste hardens. A reduction in the cement paste (and the

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concrete mix price) is thus mainly possible through a reduction of the void

volume between the aggregates to achieve this a better packing of the aggregate

mix is required [2].

Grading:- the ‘grading’ of an aggregate means the relative proportions of the

different sizes of particles. It is important, because, as will be seen in the section

on ‘mix design’, it influences the selection of the mix proportions required to

give a concrete of the desired workability.

The grading of an aggregate is found by process called ‘sieve analyses’. For

consistent results a standard method should be used; one such appears in BS12.

Sizes of apertures in test sieves are given in BS410; the sizes most commonly

used in aggregate analysis are as follows; 75mm, 37.5mm, 20mm, 10mm, 5mm,

2.36mm, 1.18mm, est.

In engineering firms, designs of concrete is usually based on specified

characteristic strength of concrete, which is the strength expected to be achieved

on construction sites to ensure that the structures do not reach their limit states in

service.

Compressive strength remains the most important properties of structural

concrete, from an engineering point of view. The relationship between concrete

composition and compressive strength has been a matter to researchers. It could

be said that the four most important potential properties of concrete are

workability, durability, resistance to compressive stress, and ability to protect

steel against rusting. The first enables the material to be compacted into forms

having any reasonable shape, while the second ensures a long life for the

hardened mass; the third and fourth forms the basis of modern design techniques

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which use the compressive strength of concrete in partnership with the tensile

strength of steel.

Nevertheless, to develop these potential properties fully requires concretes to be

proportioned appropriately. The freshly mixed concrete must have a consistence

which enables it to be transported from the mixer and readily compacted into the

necessary forms or moulds. The hardened material must not only resist the

stresses imposed upon it, including those caused by climatic and other

environmental conditions, but also the effects of any aggressive substances likely

to come into contact with it. If steel is to be embedded in the mass to resist tensile

stresses, the concrete must be impermeable to the agents which rust steel.

Failure to consider all these factors before selecting mix proportions may later

entail expensive remedial measures which would otherwise have been

unnecessary. Once the underlying principles are understood, however, it will be

found that there is considerable flexibility in the choosing materials and in

combining them into different concrete mixes suitable for many differing

applications.

The aim of this project is therefore to reach a clear understanding of the role and

effect of coarse aggregates (gravel and/or granite) in the characteristic strength of

structural concrete using constant water cement ratio (say 0.55) on different, mix

proportions by volume such as 1:1.5:3, 1:2:4, 1:2.5:5, 1:3:6 (cement : sand :

washed gravel / granite)

The first set of experiment will be, to use washed gravel as the coarse aggregate

along with other mix proportions for the preparation of the concrete. The

concrete strength test will be based on crushed cube test, using a cube dimension

of 150 x 150 x 150mm. the test to be carried out will be for curing ages of 7, 14,

21, and 28 days respectively. While the second set will be to use granite as the

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coarse aggregate and the process repeated. After these experiments, a comparison

will then be drawn based on workability and compressive strength of the concrete

produced by washed gravel as coarse aggregate and granite as coarse aggregate.

CHAPTER TWO

LITERATURE REVIEW

Iravani3, carried out a research on mechanical properties of high performance

concrete, which was defined as concrete that meets special performance and

uniformity requirements that cannot always be achieved routinely by using

conventional materials and normal mixing, placing and curing practices. Based

on the results, the following conclusions was drawn

1) For high-performance concrete without silica fume, the ratio of

compressive strength gain before 28 days increases and the ratio of

compressive gain after 28 days, decrease as the 28-day compressive

strength increases. For high performance concretes with silica fume, the

ratio of compressive strength gain before 7 days increases and the ratio of

compressive strength gain after 28days decrease as the 28day

compressive strength increases.

2) The ratios of 7 to 28 day compressive strength in the test reported herein

suggest that a significant strength gain occurs between 7 and 28 days for

the ultra-high-strength silica fume high-performance concrete.

3) Drying after moist-curing increases the 147-day compressive strength of

high- performance concrete relative to moist-cured concrete tested moist.

It can be concluded that 3 weeks is a sufficient moist curing period

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4) The composition of the coarse aggregate has a major effect on the static

modulus of elasticity of high- performance concrete.

Lassa Frolic4 and Vigil V. Sorensen5, conducted a study on the use of Sea

Dredged Gravel versus Crushed Granite as Coarse Aggregate for Self

Compacting Concrete (SCC) in aggressive environment. According to them, the

sea gravel allowed a higher aggregate proportion in the concrete leading to higher

modulus of elasticity. They further concluded that,

1) At equal flow properties SCC with sea gravel had an aggregate

content of 67 % by volume as compared to 64 % with crushed granite.

This contributed to the modulus of elasticity of the concretes being

systematically 20-30 % higher with the higher content of sea gravel

aggregate.

2) Tensile, flexural and compressive strength were found to depend

both on aggregate type and on the Properties of the interfacial zone close

to the aggregate surface that is at the highest W/B (0.40) the SCC with

sea gravel exhibited significantly lower values, than the SCC with

crushed granite, whereas the opposite was the case at the lowest W/B

(0.28).

This is believed to be due to the characteristics of the interfacial zone between the

hardened paste and the aggregate particle surfaces: At high W/B the paste phase

is more porous and the undulations of the rough granite surface acts as shear keys

resisting propagation of cracks along the aggregate surface, much more so than is

the case for the smoother sea gravel particles. At low W/B, however, the

interfacial zone is denser and has a finer microstructure which is able to provide a

strong connection to the surface of the smooth sea gravel particles which in turn

are stronger and than the crushed granite particles.

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Freeze-thaw scaling resistance was good with crushed granite, whereas sea gravel

led to more severe scaling caused by porphyry and iron-bearing sandstone

particles – but not by porous flint particles.

Punkki, golaszewski and odd6, carried out a research on workability loss of high-

strength concrete. The experiment program includes three different test series

based on ten (10) concrete mixes with basically the same mix proportions. In the

first test series, five different mixing procedures were included. In the second test

series, the amount of super-plasticizer was varied from 1.9 to 2.5 and 3.1 percent

by weight of cement, while the water content was adjusted to give the same

initial slump. Based on the result achieved, the following conclusions can be

drawn.

1) Loss of workability is often expressed in terms of slump loss, which does

not necessarily reflect the change workability properties. Even for a small

slump loss of workability. Therefore changed workability should be

expressed in terms of more basic rhological parameters such as yield

stress and plastic viscosity.

2) While a short delay in the addition of super-plasticizer (1 to 2) both

increased the yield stress and the plastic viscosity over a period of 60

minutes, a longer delay mainly increase the plastic viscosity.

3) While a small dosage of super-plasticizer (1.9 percent) mainly

increase the yield stress over a period of 60 minutes, a higher dosage of

up to 1.3 percent caused a smaller change in yield stress but a distinct

increase of plastic viscosity.

Chris Erlangsen7, investigated the suitability of using decomposed

granite in concrete. The results of the preliminary testing on the

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decomposed granite indicate that the fine particle content was a major influence

in the high percentage of water absorption.

The proportion of decomposed granite used in the concrete mix is equal to

approximately 30% of the total aggregate.

Results from tests of both workability and compressive strength show that both

concrete mix designs appear to be suitable for use in concrete with a

characteristic strength of 25MPa.

The results of this study suggest that the naturally occurring quarry bi-product

appears to be suitable for use in non-structural concrete applications when the

portion of material passing the 0.15mm sieve is removed.

Alexander and Milde8, carried out an experiment on the influence of cement

blend and aggregate type on strain behavior and elastic modulus of concrete in

which four aggregate types- granite, dolomite, andesite and quartzite were used

in concretes made with four cement types- ordinary Portland cement(OPC) and

blends of OPC with silica fume, slag, and fly ash. The influence of these mix

variables on short-term stress –strain behavior and concrete elastic modulus E

was assessed. The result shown clearly the E was markedly dependent on

aggregate and cement type and that age played an important role. The following

conclusions were drawn;

1) Stiffer concretes are likely to be produced using dolomite or andesite

aggregates in combination with ordinary Portland cement (OPC) or an

OPC / silica fume blend.

2) Granite and quartzite concretes, particularly at early ages, tend to produce

concretes with low E values.

3) Mature concretes (90 to 180 days) of all aggregate types experience

substantial increases in E that are not solely strength-related.

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4) It is a reasonable hypothesis that different aggregates and cement blends

affect the nature of the transition zone, and that this strongly influences

the concrete properties measure. This influence is also markedly age-

dependent.

5) For practical design purposes, it is useful to group together OPC and

silica fume concretes and slag and fly ash concretes.

I.G. Akpokodje and P. Hudec9, the compressive strength and the expansion of

concrete made with both highly and slightly/moderately indurate concretionary

laterite gravels were studied. The compressive strength (19–42 N/mm2) of most

of the laterite concrete is comparable with the average strength (45 N/mm2) of

concrete made with the usual granite crushed rock aggregates from the region.

The strength of the laterite concrete is mainly dependent on the aggregate-cement

bond whereas the physical properties of the aggregates are only of secondary

importance.

The laterite concrete showed a net contraction when immersed in hot NaOH

solution (i.e. rapid alkali reactivity test). This behavior is attributed to the

low/very low contents of silica, clay and lime in the aggregates. The results of the

study reveal that concretionary laterite gravels are potential alternative cheap

sources of aggregates for structural concrete.

Tavakoli and Soroushian10, investigated on Strength of Recycled Aggregate

Concrete Made Using field-Demolished Concrete as Aggregate, the experimental

work was performed to determine the compressive, splitting tensile, and flexural

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strengths of recycled coarse aggregate concrete and to compare them with those

of concrete made using natural crushed stone. The properties of the aggregate

were also compared. The fine aggregate for recycled and convectional concrete

was 100 percent natural sand. The following conclusions were drawn;

1) If the compressive strength of the original concrete that is being recycled

is higher than that of the control concrete, then the recycled aggregate

concrete can also be made to have higher compressive strength than the

control concrete.

2) Increase L.A. abrasion loss and water absorption capacity of recycled

aggregates, which partly reflect the increase amount of mortal adhered to

original stone aggregate, generally lead to reduced compressive strength

of recycled aggregate concrete.

3) Splitting tensile and flexural strengths of recycled aggregate concrete can

be higher or lower than those of the natural aggregate concrete,

depending on water-cement ratio and dry mixing period.

4) Effects of dry mixing and recycled aggregate top size on the strength of

recycled aggregate concrete depend on the ratio of the top size of the

original stone particles in the original concrete to the top size of the

recycled aggregate, the coarse to-fine aggregate ratio in the original

concrete, the cement content of the original concrete, and the water-

cement ratio of the recycled aggregate concrete.

5) Convectional relationships established between splitting tensile and

flexural strengths and the compressive strength of natural aggregate

concrete are generally unconservative in application to recycled

aggregate concrete.

6) The qualities of original concrete seem to restrict the qualities achievable

in recycled aggregate concrete. However, the complex effects and

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interactions of various variables make it difficult to come up with

specific predictions regarding the behavior of recycle aggregate in

concrete without conducting tests under applicable circumstances.

7) As far as strength is concerned, the basic trends in behavior of field-

demolished concrete aggregate are not significantly different from those

of the laboratory-made recycled concrete aggregate. The major difference

between the two cases is that many different variables such as the mix

proportions and the aggregate gradation in the original concrete are

involved in the field-demolished concrete that cannot be changed during

the recycling process. In demolishing the laboratory-made concrete, the

properties of the original concrete can be controlled.

Isioma11, carried out a research on the effect of varying water cement ratio on

the compressive strength of fibre-reinforced laterized concrete. A slump test was

carried out with the water cement ratio varied and fibre content varied too. Also,

a crush test was carried out on cubes and cylinders with water-cement ratio

varied. And the following conclusions were made,

1) For all the water-cement ratios used (0.55, 0.65, 0.75, & 0.85), increase

of fibre in the laterized concrete specimens increased their compressive

strength. The optimum value is 2% fibre content.

2) For each water cement ratio, the increase of fibre lowered the workability

of concrete. At 1.5% fibre content, the workability of the concrete is most

suitable

3) The compressive strength of fibre reinforced laterized concrete reduced

with an increase in the water cement ratio. At 0.65 w/c ratio the

compressive strength was a maximum.

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4) The workability of the fibre laterized concrete increased with an increase

in the water cement ratio. At 0.65 w/c ratio, the workability of the

concrete was optimum. Any further increase in the w/c ratio above this

optimum value would lead segregation of the concrete constituents.

5) The results show that the optimum w/c ratio for a mix of 1:1.5:3 should

not be greater than 0.65 if segregation is to be avoided 0.55 w/c is

suitable for this mix as the mix is not stiff and can still be vibrated. Any

w/c ratio lower than this would lead to a very stiff mix.

Maharjan and Naresh12, conducted a study to evaluate quality of river gravel to

know its suitability for aggregates (raw material for concrete and road). The

samples of river gravel were analyzed for petrographic, physical, mechanical and

chemical properties sample were categorized as quartzite group, carbonate group

and granite group. According to the British Standard Institute (BSI). Among

these, sample of quartzite group were found dominant. Image analysis of gravel

showed that clasts were well graded. The majority of the sample had rounded

high Shericity and oblate triaxial clasts. The surface texture of clast was rough to

smooth. In terms of shape, workability of gravel was satisfactory. Gravel samples

possess low water absorption value (0.69 to 1.12%) and low effective porosity.

Dry density of sample ranged from 2460 to 2680 kg/m3. Aggregate impact values

of sample (14.2 to 16.1%) showed good soundness. Los Angeles abrasion test

also showed consistent hardness of each of the sample as uniformity factor did

not exceed 0.2 magnesium sulphates ranged between 4.46% and 7.29%

suggesting good resistance against chemical weathering and frosting comparing

with the existing Napel standard, B.S and American standard of testing materials,

the studies sample were suitable for concrete and road aggregate.

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Oyekak13, carried out a study to examine the effect of crushed waste glass,

(CWG) when used as partial substitute for cement in laterized concrete. One mix

(1:2:4) of cement plus CWG, sand, laterized and granite coarse aggregate was

used with a constant water cement ratio of 0.65, the effect of crushed waste glass

on 2 properties of laterized concrete, namely, compressive strength and

workability was investigated. the result shows that

1) The CWG did not enhance the compressive strength of laterized concrete

2) The compressive strength of the laterized concrete actually decreased as

the percentage CWG content increased.

3) Laterized concrete (at 25, 50 and 75% laterite content)shows an initial

increase in workability with decrease in percentage CWG content in the

cement matrix with the maximum slump being obtained at 25% CWG

content

4) Further increase in CWG content results in decrease workability.

5) The result shows that laterized concrete containing 50% laterite and 15%

cement replacement with CWG can be used for low medium cost

housing.

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CHAPTER THREE

METHODOLOGY

This chapter gives the descriptions and discussions of the materials, equipments,

composition of concrete, and testing procedure, I intend to use. All material

ranging from coarse aggregate, sand (fine aggregate), to the cement used for the

production of the concrete will be obtained locally.

MATERIALS USED FOR THE STUDY

C OARSE AGGREGATE

The coarse aggregate used are crushed granite of igneous origin and thoroughly

washed river dredged gravel. The particle size range used for both aggregate was

5-19mm. Analysis was carried out on the aggregate and their respective grain

size distribution obtained The compressive concrete strength testing was

conducted on the concrete cube of 150 X 150 X 150mm dimension for granite

concrete and gravel concrete respectively. The test carried out was for curing

days of 7, 14, 21 and 28 days respectively.

FINE AGGREGATE

The sand used was dry clean, sharp river sand that is free clay, loam, dirt and

organic or chemical matter of any description and was passing through 5 and

4.75mm zone of British standard sieve.

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CEMENT

Ordinary Portland Cement (OPC) Burham brand type with properties conforming

to those specified in the British Standard document (BS 12, 1971) was used..

WATER

The water used was portable water, which was fresh, colourless, odourless and

tasteless water that was free from organic matter of any type. The amount of

water used in the various mixes was based on the water-cement ratio.

EQUIPMENT TO BE USED FOR THE STUDY

The equipment intended to be used are those available in the structures and

concrete laboratory of the civil and environmental engineering of University of

Lagos. A brief description of the equipment to be used in the course of the

investigation is given below.

WEIGHING MACHINE

A weighing machine of 50kg capacity (Avery type) is to used to weigh the

individual material constituents and the resulting cubes. It consists of a

measurement gauge vertically standing, and attached to the back of a loading

platform. It also has a knob to adjust the gauge to zero before being used for

weighing.

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COMPRESSION TESTING MACHINE

This is hydraulically operated mechanical equipment. Load is applied to the test

specimen placed between two steel platforms (a fixed upper platform and an

upward moving lower platform). The machine consists of two dial gauges, one

calibrated in KiloNewtons and the other in newtons. Both have two pointers (red

and black) used for determining readings. Before testing, these pointers are set at

zero. As testing commences, the lower platform moves upwards towards the

fixed upper platform until failure of the specimen is reached, the black pointer

which moves along with the red during loading returns to zero, while the red

remains in position to allow for the reading of the compressive strength value.

The Avery compression test machine has maximum load capacity of 300kN.

MOULDS

I will use two different types of mould (mould A and B) in the course of the

investigation. Mould A, is in form of a frustum of a cone, this mould is provided

with suitable foot pieces as well as handles to facilitate placing the concrete, and

lifting the molded concrete test specimen in a vertical position. Mould B is a cube

of 150 X 150 X 150mm dimension with screw and nut to ease de-molding.

OTHER EQUIPMENT

Tamping rod (i.e. 16mm diameter, 600mm long and rounded at one end), Steel

rule, Trowel, Scoop, Vibrator, Curing tank Tray, etc.

COMPOSITION OF CONCRETE

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A single water-cement ratio (i.e.0.55) will be used. And the mix proportion by

weight will be in four different batches forms i.e.

1:1.5:3

1:2:4

1:2.5:5

1:3:6 (cement: sand: coarse aggregate).

The concrete batches will be mix in a tray. The surface of the tray will be wetted

before mixing to avoid water absorption and to ensure the same mixing

conditions for all mixes.

TESTING

Sieve Analysis

The particle sizes distribution of aggregate (coarse and fine) affects the

workability of concrete, which in turn controls the water-cement ratio,

segregation and finishes of concrete, hence it is essential that aggregate of

suitable coefficient of uniformity is used. The coefficient of uniformity is

calculated from the particle size distribution drawn from sieve analysis tests.

Before conducting the test, the specimens are oven-dried for about 24 hours.

Then they are weighed and sieved by shaking through a set of standard B.S.

range from 5mm to 0.15mm while that of granite ranges from 1” to 1/8” with

receiver at the bottom of the sieve.

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Aggregate Crushing Value

The aggregate crushing value give a relative of the resistance of an aggregate to

sudden shock or impact, which usually differs from its resistance to a slowly

applied compressive load. The aggregate crushing value is usually not more than

40%.

Procedure

The material for this test consist of aggregate passing the 14mm BS test sieve and

retained on the 10mm BS test sieve and tested in a surface dry condition. The

apparatus required for this test consist of test of an open ended steel cylinder of

normal size 150mm internal diameter with plunger and base plate. The

approximate quantity may be found conventionally by filling the cylindrical

measure in three layers, each layers being tamped 25 times from a height of about

50mm above the surface of the aggregate with the rounded end of the rod and

finally leveled off. I recorded the mass (weight) of the sample (w1). I inserted the

plunger so that it rest horizontally on this surface.

I placed the apparatus between the plates of the testing machine and applied a

load of 399.5KN (40 tones). I then released the load and remove the crushing

material into a clean try sieve the whole of the sample on the 2.36mm BS sieve

size. Weigh the fraction passing the sieve (W2). The ratio of the mass of fine

formed to total mass of the sample expressed as percentage is the aggregate

crushing value.

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Percentage fine = (W2-W1) / W2 X 100%

Slump test

Slump test is the most commonly used method of measuring consistency of

concrete which can be employed either in laboratory or at site of work. It is not a

suitable method for very wet or very dry concrete. However, it is used

conveniently as a control test and gives an indication of the uniformity of

concrete from batch to batch.

Procedure

I thoroughly clean the surface of the mould and place on a smooth, horizontal,

rigid and non-absorbent surface. The place of the test must be free of vibration.

I then prepare the concrete mix ratio 1:1.5:3 (cement: sand: coarse aggregate),

19mm maximum aggregate using 0.65 water cement ratio. I sought for a support

to hold the mould firmly while I fill, in four layers with the concrete. Each layer,

about 1/4 of the height of the mould, was tamped with 25 blow of the rounded end

of the tamping rod. I ensured the blows are distributed uniformly over the cross-

section of the mould and second and subsequent layer is tamped throughout its

depth. After tamping the top layer, I filled the mould completely and concrete

struck off and the level finished with a trowel.

I repeat the above using, 1:2:4, 1:2.5:5 and 1:3:6 concrete mix respectively.

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Compressive strength test using concrete cube

Compressive strength remains the most important properties of structural

concrete, from an engineering point of view. In most structural applications

concrete is employed primarily to resist compressive stresses. I cases where

strength in tension or in shear is of primary importance, the compressive strength

is frequently used as a measure of these properties.

Procedure

I tighten and clean the moulds, for easy removal of the concrete cubes after

setting, after which, I will apply the mould oil on the internal surface of the

mould.

I then prepare a fresh concrete (mix 1:1.5:3, 20mm maximum aggregate), using

0.65 water cement ratio fill three concrete moulds with concrete and vibrate. I

finish the level of the compacted concrete with a trowel..

I remove the mould after 24 hours (from time of casting) and cure in clean water

until the time of testing. I will repeat the above using 1:2:4, 1:2.5:5 and 1:3:6

concrete mix respectively.

On the 7th days three (3) samples will be tested using compressive test machine

and the other 3 at 14, 21, and 28 day respectively. Each cube shall be centrally

placed on the machine such that cast surface will be on the side. The load will

then be applied at appropriate limit indicated on the testing machine.

I shall calculate the compressive strength of the each cube by dividing the

maximum load by the nominal cross-sectional area. The strength is expressed in

N/mm2 [13].

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CHAPTER FOUR

RESULTS AND DISCUSSIONS

Just contact me with the Email and phone number above.

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