Coarse Aggregate

GS.Mohan
1011210335
1
COARSE
AGGREGATE

INTRODUCTION:-
Aggregate are the important constituent in
concrete. Aggregate are granular material, derived
from the most part from the natural rocks,
crushed stones, or natural gravels and sands.
Aggregate generally occupy about 70% to 80% of
the volume of concrete and can therefore be
expected to have an important influence on it
properties.
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CLASSIFICATION OF AGGREGATE:-
a)CLASSIFICATION BASED ON SIZE:
>Coarse aggregate:
Aggregate which retained on the No.4 (4.75mm) sieve.
The function of the coarse aggregate is to act as the main load-
bearing component of the concrete.
>Fine aggregate:
Aggregate passing No.4(4.75mm) sieve and
predominately retained on the No.200 (75µ) sieve. The fine
aggregate serve the purpose of filling all the open space in
between the coarse particles.
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b)CLASSIFICATION BASED ON SOURCE:
>Natural aggregates:
This kind of aggregate is taken from natural deposits
without changing their nature during the process production
such as crushing and grinding.
>Manufactured (synthetics) aggregates:
This is a kind of man-made materials produced as a main
product or an industrial by-product. Some example are blast
furnace slag, air cooled slag and broken bricks. Synthetics
aggregates are produced by thermally processed materials such
as expanded clay and shale used for making light weight
concrete.
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c)CLASSIFICATION BASED ON UNIT WEIGHT:
Aggregates are classified as Light-weight, Heavy-weight
and Normal-weight aggregate depending on weight and specific
gravity.
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AGGREGATE SPECIFIC
GRAVITY
UNIT WEIGHT
(kN/m3)
BULK DENSITY
(kN/m3)
EXAMPLE
normal-weight 2.5-2.7 23-26 15.20-16.80 sand
heavy-weight 2.8-2.9 25-29 >20.80 Scrap iron
light-weight 12 <11.20 dolomite

d)CLASSIFICATION BASED ON SHAPE:
The shape of aggregates is an important characteristic,
since it affect the workability of concrete.
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CLASSIFICATION EXAMPLE
Rounded River or seashore gravels
Partly rounded Pit sands & Gravels
Angular Crushed Rocks
Flaky Laminated rocks

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FLAT ELONGATED
ROUND
ANGULAR

e)CLASSIFICATION BASED ON SUFACE TEXTURE:
Surface texture is a measure of the smoothness and
roughness of aggregate. The grouping of aggregate is broad and
is based on visual examination of the specimen. As per IS:383-
1970 the aggregates are classified into five groups, namely,
Glassy, Smooth, Granular, Crystalline, Honeycombed and Porous.
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CLASSIFICATION EXAMPLES
Glassy Black flint
Smooth Gravel, Marble
Granular Sandstone
Rough Basalt
Crystalline Granite
Honeycombed & Porous Brick, slag

GOOD QUALITYIES OF AN IDEAL AGGREGATE:
An ideal aggregate used for the manufacturing of
concrete and mortar, should meet the following
requirements.
• (1) It should consist of natural stones, gravels and sand or
in various combinations of these materials.
• (2) It should be hard, strong and durable.
• (3) It should be dense, clear and free from any coating.
• (4) It should be free from injurious vegetable matters.
• (5) It should not contain flaky (angular) and elongated
pieces.
• (6) It should not contain any material liable to attack
steel reinforcement in case of reinforced concrete.
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TESTS ON AGGREGATE:-
The test usually conducted on coarse aggregates are
>PARTICLE SIZE
>FLAKINESS &ELONGATION INDEX
>MOISTURE CONTENT
>SPECIFIC GRAVITY AND WATER ABSORPTION
>TEN PERCENT FINE VALUE
>AGGREGATE CRUSHING VALUE
>AGGREGATE IMPACT VALUE
> AGGREGATE ABRASION VALUE
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IMPACT VALUE TEST
The aggregate impact value gives a relative measure of the
resistance of an aggregate to sudden shock or impact. The
impact value is some times used as an alternative to its
crushing value.
Material passing 12.5mm and retained on 10mm sieve is
taken.
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AGGREGATE CRUSHING VALUE:-
The aggregate crushing value gives a relative measure of
resistance of an aggregate to crushing under a gradually
applied compressive load. The aggregate crushing strength
value is useful factor to know the behavior of aggregates
when subjected to wear.
CRUSHING VALUE=weight of fraction passing the sieve
total weight of sample
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AGGREGATE ABRASION VALUE:-
The aggregate abrasion value gives a relative measure of
resistance of an aggregate to wear when it is rotated in a
cylinder along with some abrasive charge
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SIEVE ANALYSIS
Sieve analysis is also called as Particle size value.
In determination of the proportions of the
particles with in certain ranges in an aggregate
by separation on various sieves of different size
openings, may be defined as sieve analysis.
FINENESS MODULUS= cumulative % of agg retained on each sieve
100
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SPECIFIC GRAVITY OF AGG.
Sp.Gr. is used in certain computations for concrete mix design or
control work, such as, absolute volume of aggregate in concrete. It
is not a measure of the quality of aggregate.
Sp.Gr.=
Weight of Agg. (WA)
Weight of an equal volume of water (VA*ρw)
=
WA
VA*ρw
=
ρA
ρw
Density of Agg.
Density of Water

FLAKINESS & ELONGATION INDEX
FLAKINESS INDEX= weight of particle passing through the gauge
weight of sample
ELONGATION INDEX=weight of particle retained on length gauge
weight of sample
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Coarse Aggregate

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