type of aggregate

Guidance by:
MS. Payal Gahukar Mam

CONTENTS:
 Introduction of aggregate.
 Definition of aggregate
Requirement of aggregate
Classification of aggregate
Classification based on unit weight
Properties of fine aggregate
Properties of coarse aggregate
Grading of aggregate
Thermal properties of aggregate
Tests on aggregate

INTRODUCTION
 Aggregate are generally cheaper than cement and impact
greater volume stability and durability to concrete. The aggregate is
used primarily for the purpose of providing bulk to the concrete. To
increase the density of the resulting mix, the aggregate is frequently
used in two or more sizes. The most important function of the fine
aggregate is to assist in producing the workability and uniformity in
mixture.
 The aggregates provide about 75% of the body of the
concrete and hence its influence is extremely important. The must be
of proper shape ( either rounded or approximately cubical), clean hard
strong and well graded.
Fig. Aggregate

What is aggregate ?
• The materials used for manufacture of mortar and concrete such as
sand, gravel etc. are called as aggregate.

REQUIREMENT OF GOOD AGGREGATE
It must be clean i.e. it should be free from lumps, organic materials etc.
It should be strong.
It should be durable.
It should not react with cement after mixing.
It should have rough surface.
It should not absorb water more than 5%.
It should not be soft and porous.
It should be chemically inert.
It should be of limiting porosity.
It should preferably be cubical or spherical in shape.

CLASSIFICATION OF AGGREGATE
According to geological origin
• Natural Aggregate: These aggregates are generally obtained from
natural deposits of sand and gravels, or from quarries by cutting rocks.
The cheapest among them are the natural sand and gravel. Which have
been reduced to their present size by natural agents, such as water, wind
and snow, etc. The river deposits are the most common and are good
quality.
Fig. Natural Aggregate

• Artificial Aggregate:
The most widely used artificial aggregate are clean broken bricks and
air cooled fresh blast- furnace- slag. The broken bricks of good quality
provide a satisfactory aggregate for the mass concrete and are not
suitable for reinforced concrete work if the crushing strength of brick is
less than 30 to 35 Map. The bricks should be free from lime mortar and
lime sulfate plaster. The bricks aggregate is not suitable for waterproof
construction. It has poor resistance to wear and hence is not used in
concrete for the road work.
Fig. Artificial Aggregate

Classification according to size:
1. Fine aggregate: The aggregate which passes through 4.75 mm
sieve and retained on 75 micron sieve are known as fine aggregate.
Fig. Fine Aggregate

2. Coarse Aggregate:
The aggregate retained on 4.75 mm IS sieve are Known as
coarse aggregate.
Fig. Coarse Aggregate

3. All-in-aggregate:
It is the combination of both coarse and fine aggregate.
Fig. All-In-Aggregate

CLASSIFICATION ACCORDING TO SHAPE:
The aggregate may be classified as rounded, irregular, angular and flaky.
1. Rounded Shape: The aggregate with rounded particles ( river or seashore
gravel) has minimum voids ranging 32 to33 %. The only disadvantage is that
interlocking between its particles is less and hence the development of bond is
poor, making it unsuitable for high strength concrete and pavement
Fig. Rounded Aggregate

2. Irregular Aggregate:
The aggregate having partly rounded particles (pit sand and gravel)
has higher of voids ranging from 35 to 38% . It required more cement
paste for a given workability.
Fig. Irregular Aggregate

3. Angular Aggregate:
The aggregate with sharp, angular and rough particles (crushed rocks)
has a maximum of voids ranging from 38 to 40%.The interlocking between
the particles is good.
Fig. Angular Aggregate

4. Flaky Aggregate:
An aggregate is termed flaky when its least dimension (thickness)
is less than three-fifth of its mean dimension. The presence of these
particles should be restricted to 10 to 15%.
Fig. Flaky Aggregate

CLASSIFICATION BASED ON UNIT WEIGHT
1. Normal Weight Aggregate: The commonly used aggregate, i. e,
sands and gravels; crushed rocks such as granite, basalt quartz,
sandstone and limestone; and brick ballast, etc., which have specific
gravities between 2.5 and 2.7 produce concrete with unit weight
ranging 23 to 26 KN/m3 and crushing strength at 28 days between
15 to 40 Map are termed normal- weight concrete.
2. Heavyweight Or High-Density Aggregate: concrete having unit
weight of about 30, 31, 35, 38, 40, 47 and 57KN/m3 can be
produced by using typical goethite, limonite, baryte, magnetite,
hematite, ferrophosphorus and scrap iron, respectively.
3. Light Weight Aggregate: The light weight aggregate having unit
weight up to12KN/m3 are used to manufacture the structural
concrete masonry blocks for reduction of the self weight of the
structure.

PROPERTIES OF FINE AGGREGATE:
1. Size: The largest size which may under the range of fine aggregate is
4.75mm. Using the largest size will give a more dense concrete, but a
mixture of all sizes is more desirable and more economical.
2. Shape: Shape of aggregate plays an important role in coarse aggregate
rather than fine aggregate.
3. Strength: The strength of aggregate alone cannot ensure strength of
concrete. Strength of coarse aggregate is more important.
4. surface Texture: Generally rough surfaced aggregate is preferable to
smooth aggregates. This property is also related with coarse aggregate.

5. Specific Gravity: Specific gravity of aggregate is the ratio of its
density to the density of water.
6. Bulk Density: This refers to the density of aggregate considered
along with volume of voids or empty spaces between the particles.
The density of sand falls between 17 to 25 KN/m3.
7. Water Absorption: Generally, for sand, water absorption is
negligible, It is desirable that water absorption should be kept
minimum.
8. Soundness: This refers to expansion and contraction of the
aggregate when subjected to temperature variation.

PROPERTIES OF COARSE AGGREGATE:
1. Size: The size of coarse aggregate depends on the used to which the
concrete is to be put. For mass concreting works without complicated
reinforcement, larger aggregates of 80 mm, 40mm, 20mm sizes are
used.
2. Shape: The shape of aggregate is an important characteristic as it
affects the workability of concrete. It also affects the strength.
3. Surface Texture: It is the property of coarse aggregate deals with
roughness and smoothness of aggregate. Rounded aggregate with
smooth surface will require less cement paste and hence increase the
yield per bag.

4. Water Absorption: Some of the aggregate water absorb and porous. Hence, it
affect the water cement ratio and the workability of concrete. The porosity of
aggregate also the affect if durability of concrete.
5. Soundness: soundness refer to expansion and contraction of the aggregate.
When subjected to temperature various. A good aggregate is that which shows
minimum expansion and contraction.
6. Specific Gravity: It is the ratio of dry weight of aggregate to the weight of equal
volume of water.
7. Bulk Density: The ratio of net weight of aggregate to the volume of aggregate
gives bulk density.

GRADING OF AGGREGATE:
The particle size distribution of an aggregate as determined by sieve
analysis is termed grading of the aggregate.
The well graded aggregate containing minimum voids hence it
required minimum paste to fill the gap/ voids in the aggregate result in
increase economic, higher strength and greater durability.
The sieve analysis conducted for determine the particle size
distribution in a sample of aggregate is called gradation.
The aggregate used for making the concrete 80mm, 40mm, 20mm,
10mm, 4.75mm, 2.36mm, 600micron, 300micron and 150micron.
The aggregate from 80mm to 4.75 mm are coarse aggregate and
from 4.75mm to 150 micron are fine aggregate.

THERMAL PROPERTIES OF AGGREGATE
The thermal properties of aggregates affect the durability and
other qualities of concrete. The investigations reported to date do not
present a clear-cut picture of the effects that might be expected.
The principle thermal properties of aggregate are:
1. Coefficient of thermal expansion,
2. Specific heat,
3. Thermal conductivity.
The coefficient of thermal expansion of the concrete increase
with the coefficient of thermal expansion of aggregate. The coefficient
of expansion of the aggregate depends on the parent rock.
The specific heat of aggregate is a measure of its heat capacity,
whereas the thermal conductivity is the ability of the aggregate to
conduct the heat.

TESTS ON COARSE AGGREGATE:
1. DETERMINATION OF CRUSHING VALUE
(IS 2386 Part 4 – 1963):
Fig. Aggregate Crushing Value Apparatus

1. This test gives a relative measure of the resistance of
aggregate to compressive stress.
2. Crushing value of aggregate is a relative measure of resistance
of an aggregate to crushing under gradually applied crushing
load.
3. Aggregate passing through 12.5 mm sieve and retained on
10mm sieve is taken. About 6.5 kg of surface dry aggregate
filled in the standard cylinder in three layers, tamping each
layer 25 times by a standard tamping rod. It is levelled off. Its
weight found out(A).

4. The plunger is placed on the aggregate taking care that it does not jam the
cylinder by becoming tilted.
5. The assembly is then kept under compression testing machine and total
load of 40 tonnes is applied uniformly during 10 minutes.
6. The load is released, the aggregate is taken out and sieve on 2.36 mm
sieve. The friction passing through weight is (B).
7. The aggregate crushing value is given by,
Aggregate crushing value=B/A×100%.

2. DETERMINATION OF IMPACT VALUE
(IS 2386 4-1963):
Fig. Aggregate Impact Value Apparatus

1. This test gives relative measure of resistance of aggregate to
suddenly applied load or impact load.
2. The test sample consists of aggregate passing through 12.5
mm IS sieve and retained on 10 mm IS sieve. The aggregate is
oven dried at 110 degree C for 4 hours.
3. The aggregate is filled in the cup, (weight A). By lifting the
handle, hammer is allowed to fall freely as it is released by the
tripping mechanism, on to the aggregate in the cup.

4. 15 such blows are given and then the aggregate is taken out and sieved
on 2.36 mm sieve.
5. The fraction passing through is weighed (weight B).
6. The fraction retained is also weighed (weight C). If (B+C) is less than A
by more than 1 gram, the result is discarded and a fresh test is made.
7. The aggregate impact value is given by,
Aggregate impact value = BA×100

3. DETERMINATION OF ABRASION VALUE
(IS 2386 Part 4-1963):
Fig. Los Angles Abrasion Testing Machine

1. This test gives the relative resistance of aggregate to
wearing.
2. There are two methods prescribed in the IS code, Deval
Attrition Test and Los Angeles Abrasion Value.
3. But since LA test gives more realistic results, it is more
commonly used.
4. In this method, the specified weight, 5kg or 10 kg, depending
on the size of aggregate is taken and is placed in the cylinder
of the LA machine along with the abrasive charge.

5. The abrasion charge consists of specific number of steel
balls.
6. The cylinder is rotated at 20 to 33 r. p. m. for 500 or 1000
revolution, depending on the grading of the aggregate.
7. The aggregate is removed from the cylinder and sieved on
1.75 mm sieve.
8. The fraction passing through 1,7 mm sieve is expressed as
percentage of original weight give the aggregate abrasion
value.

type of aggregate

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