Aggregates for Concrete

Gurukul Education SociEty’S inStitutE of
EnGinEErinG & tEchnoloGy
Subject : Concrete Technology (CTE) Semester : Third
Subject Code : 22305 Year : 2nd (2020-21)
Subject Teacher: Prof. K. S. Somase Scheme : I
Department of Civil Engineering
Concrete Technology
Unit 2-Aggregates
By
Prof. K. S. Somase
(BE-Civil Engg)

Unit : 2 (Topics and Subtopics)
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civil EnGinEErinG dEpartmEnt
Gurukul Education Society’s Institute of Engineering & Technology
by : prof: k.s.somase

Unit : 2 Aggregates
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Introduction
➢Aggregate-
• Granular materials produced from crushed rock, gravel, sand, or reclaimed
material, used to make concrete and more generally in construction work.
• Aggregates provide the concrete with its body and strength and act as filler
material to give the homogeneous mass of concrete along with cement paste.

Requirement of Aggregates
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1. It must be clean
2. It should be strong.
3. It must be hard.
4. It must be durable.
5. It should not react with cement after mixing.
6. It should have rough surface.
7. It should not absorb water more than 5%.
8. It should not be soft and porous.
9. It should be of limited porosity.
10. It should preferably be cubical or spherical in shape.

Types of Aggregates
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➢Mainly two types of aggregates are used in concrete:
1. Fine Aggregates
2. Coarse Aggregates
➢ Fine Aggregates:
The aggregate having size less than
4.75mm is called as fine aggregate.
Example- Sand, Surkhi, fly ash, etc.
➢ Coarse Aggregates:
The aggregate having size More than
4.75mm is called as Coarse aggregate.
Example- crushed stone, river gravel,

Classification of Aggregates
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➢Classification of Aggregates:
I. Classification According to source:
1. Naturally Occurring Aggregates.
2. Artificial Aggregates.
II. Classification According to size:
1. Fine aggregates.
2. Coarse aggregates
3. All-in-aggregates
III. Classification According to shape:
1. Irregular
2. flaky.
3. Rounded
4. Angular

Properties of Fine Aggregates
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Following are the properties of fine aggregates.
1. Size
2. Specific gravity
3. Bulk density
4. Water absorption
5. Bulking
6. Impurities
7. Specific surface
1. Size:
The largest size which comes under the range of fine aggregates is 4.75 mm. Using
the largest size will give a more dense concrete, but a mixture of all sizes is more
desirable and more economical. If cement mortar is prepared for purpose of
masonry work then very fine sand of uniform size is used.

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2. Specific gravity:
Specific gravity of aggregate is the ratio of its density to the density of water.
This is used for concrete mix design and if not specified the specific gravity is taken
as 2.7 as the specific gravity of majority of aggregates obtained from
different sources falls between 2.6 and 2.8.
Procedure:
(1) Take pycnometer and weight it say (W1)
(2) Take about 300 gm of oven dried sand and cool it an it is then placed in
pycnometer and again weigh it say (W2)
(3) The remaining is filled with water and weight is noted (W3)
(4) Empty the Pycnometer and fill it with water Upto cap
and weigh it say (W4).

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Procedure:
(5) Wt. of dry soil = (Ws) = W2 - W1
(6) Wt. of equal volume of water = (W2-W1)-(W3-W4)]
(7) Specific gravity (G) = [(W2- W1)]/ [(W2-W1)-(W3-W4)]
3. 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.
4. Water absorption :
• Generally, for sand, water absorption is negligible. It is desirable that
water absorption should be kept minimum.

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5. Bulking
• Bulking is a phenomenon due to which the aggregate swells by absorbing
moisture from humid air.
•Due to bulking, the concrete mix design may go wrong and sufficient extra sand is
always added to compensate for this swelling when this bulked sand will come to the
normal state.
6. Impurities
Four types of impurities in sand/which are as follow:
a) Organic Impurities – Decayed vegetables matter /Animal matter.
b) Inorganic Impurities – silt and clay.
c) Presence of salt
d) Mica

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7. Specific surface
The surface area per unit weight of material is called as
specific surface.

Test on Fine Aggregates
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1. Fineness Modulus
• The proportion of different particle sizes present in an aggregate
determine its grading. If all the sizes of the range are present in
appreciable proportions then the aggregate is termed as well
graded.
• If the size of all particles is almost the same, the aggregate is poorly
graded.
• If the aggregate shows total absence of a particular size or a
particular range of sizes, it is called gap graded.
• Sand or fine aggregate is graded depending. on a parameter known
as Fineness Modulus.

Fineness Modulus Test
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➢ Procedure
1. For finding FM (fineness modulus) of sand, the sieves 4.75 mm, 2.36
mm, 1.18 mm, 600 micron, 300 micron, 150 micron and 75 micron are
used.
2. The sieves are arranged in descending order i.e. sieve with the largest
opening on top, and the aggregate, i.e. the sand is placed in the top
sieve.
3. A pan is provided below the bottom most sieve and the top sieve is
closed by a lid.
4. This entire assembly is then shaken vigorously for such time that no
particle is passing through. The sieving is done either by hand or by a
mechanical device known as sieve shaker.

Fineness Modulus Test
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➢Procedure
5. The weight retained on each sieve are measured. From this cumulative
weight retained is calculated for each sieve. The cumulative percentage
retained is calculated.
Σ Cumulative percentage retained
Fineness Modulus = 100
FM is graded as,
Fine Sand – FM 2.2 – 2.6
Medium Sand – FM 2.6 – 2.9
Coarse Sand – FM 2.9 – 3.2
• A sand having fineness modulus less than 2.2 or more than 3.2 is
considered unsuitable for use in concrete.

Silt Content in Sand Test
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➢Excessive silt content in sand also makes it unsuitable for use in
concrete. Silt means very fine particles of size less than 75
microns.
➢The quantity of silt, fine silt, clay and fine dust is determined by
sedimentation method.
Procedure:
1. First of all fill the jar up to 50 ml with water (containing 1%
common salt added in water).
2. Add sand in the jar which is to be tested till it reaches
100 ml mark in jar.
3. The jar with the liquid is vigorously shaken and then kept in
undisturbed condition for at least 3 hours.

Silt Content in Sand Test
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4. The reading of settled silt and clean sand should be taken and
percentage of silt can be calculated.
volume of silt after 3 hours
% of silt content by volume = volume of sample X 100
%silt = [V2/V1] X 100
V1 = volume of sample
V2 = volume of silt after three hour
The impurities thus measured should not exceed 5% according to
IS-383.

Bulking of Sand
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➢Definition
▪ The free moisture content in F.A. or sand results. In increasing
volume of sand called as bulking or swelling of sand.
▪ This happens especially in rainy seasons and the Quantity of
sand may be taken enormously due to rainy seasons.
➢Procedure:
1. Filling the gauge box or other container of known volume V with Sand then
this sand is dried in an oven at 110°+ 5° C till surface moisture disappear
completely.
2. It is then refilled in same container the new depth (V1) gives
unbulked volume. The unbulked volume can also be determine by filling
container having wet sand by water till it becomes saturated completely and
settle down.
Percentage bulking of sand = [(V – V1)/ V] X 100

Phenomenon Bulking
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➢Bulking is due to adsorption of moisture on individual sand
grains in the form of a thin film. The film of moisture produces
surface tension which keeps the sand grains away from each other.

Phenomenon Bulking
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➢Field test
• A sample of moist fine aggregate is filled in measuring cylinder in
normal manner. The level h1 is noted down. Water is added to
drown the sand completely and the cylinder is shaken vigorously.
The level h2 is noted down. Then the percentage of bulking is
given as,
Percentage of bulking = [h1 – h2/ h2 ] X 100
➢ Effects of bulking on concrete:
• This will affect the properties of concrete as it will contain less
sand than the mix design.
• This leads to harsher concrete wit less workability. It also
decreases the yield of concrete per bag of cement.

Typical Curves represent the Effect of Moisture Content
on the Bulking of Fine, Medium and Coarse Sand:
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Properties of Coarse Aggregates
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➢ Following are the properties of Coarse aggregates.
1. Size
2. Shape
3. Surface Texture
4. Water absorption
5. Soundness
6. Specific gravity
7. Bulk density

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➢ Following are the properties of Coarse aggregates.
1. Size
• For mass concreting works without complicated reinforcement,
larger aggregates of 80 mm, 40 mm, 20 mm size are used.
For ordinary construction of residential or other buildings,
20 mm is the maximum size that will be used.
2. Shape
• Rounded, irregular, Angular , Flaky.
• Angular aggregate shows better interlocking effect, which gives a
superior concrete .
• The total. surface area of rough angular aggregate, is more than smooth
rounded aggregate hence bond formation is enhanced giving greater ence
bond strength

Classification of Aggregates according
to shape
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3. Surface Texture :
• It is the property of coarse aggregate deals with roughness and
smoothness of aggregate. As far as possible for coarse aggregate
rough texture aggregates are preferred.
• Classify aggregates on the basis of surface texture
1. Smooth – Marble
2. Glassy
3. Crystalline- lime stone
4. Granular – sandstone
5. Honey Combed and porous

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4. Water Absorption:
The water absorption of coarse aggregate is measured by the percent
increase in weight of an oven dry sample after immersion in water
for 24 hours.
5. Soundness
This is expansion and contraction of the aggregate when subjected to
temperature variation.
6. Specific Gravity
It is the ratio of dry weight of aggregate to the weight of equal
volume of water.

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Specific Gravity
Procedure-
1. Take aggregate not less than 2 kg in a wire basket.
2. Dip the basket in water and immerse to the bottom.
3. Lift it and drop it 25 times to release entrapped air and adhering
particles. The basket is kept in water till 24 ± 1/2 hours.
4. Lift and weigh aggregate plus basket when still immersed in water
(weight A1).
5. Remove the basket, take out aggregate and weigh empty basket in
water (weight A2).
6. Expose the aggregate to air but not to direct sunlight for 10
minutes or more until it appears surface dry.

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Specific Gravity
Procedure-
7. Weight the aggregate in air (Weight B)
8. Keep the aggregate in oven at 100 to 110°C for 24 ± 1/2 h Weigh the aggregate
in air (weight B).
9.Cool it weigh it (weight C)
Specific Gravity= C/ (B-A)
Apparent Specific Gravity = C/ (C-A)
Water Absorption = 100 X (B-C) / C
where A = weight in gm of saturated aggregate in water (A1-A2)
B = weight in gm of saturated surface dry aggregate in air
C = weight in gm of oven dry aggregate in air

Apparent Specific Gravity and
Absolute Specific Gravity:
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➢Apparent Specific Gravity
It is defined as the weight of the oven dry aggregate (maintained
for [24+1/2] hours as temperature of 100° C to 110 °C) divided by its
absolute volume excluding the natural pores in the aggregate
particles.
➢ Absolute Specific Gravity
It is the weight of oven dry aggregate divided by it volume
including the natural pores in the aggregate particles.

Bulk Density
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➢Definition
The ratio of net weight of aggregate to the volume of aggregate gives
bulk density.
Bulk density = ɣ = Net wt of aggregate(Kg)
capacity of container(litre)
% of voids is also calculated from this test as,
percentage of voids = G - ɣ
G
where, G = Specific gravity
ɣ = Bulk Density

Bulk Density
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➢Procedure
1. Fill the aggregate in a cylindrical measure of known internal
dimensions in three layers, tamping each layer 25 times by a
standard tamping rod.
2. Using Tamping rod itself as straight edge, level the cylinder.
3. Measure weight of cylinder with aggregate and empty
cylinder and find net weight of aggregate in Kg.
4. Measure inner dimensions of the cylinder and find its volume
in liters.
5. The ratio of net weight of aggregate to the volume of
aggregate gives the bulk density in Kg/liter.

Bulk Density
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➢Factor affecting bulk density
1. Degree of compaction : Greater Compaction gives greater bulk
density.
2. Grading : Bulk Density increases with improvement in grading
as graded aggregate has less voids
3. Shape: Rounded Particles has greater bulk density, due to less
voids.

Strength
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➢Various test are required to determine strength of coarse aggregate.
1. Crushing Value
• The aggregate crushing value
should not more than 45% for
ordinary concrete.
• For wearing surfaces such as
runways, roads, and pavement
it should not be more than 30%.

Crushing Value
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Procedure:
The test sample: It consists of aggregates sized 12.5 mm - 10.0 mm
(minimum 3kg). The aggregates should be dried by heating at 100-110o C
for a period of 4 hours and cooled.
1. Sieve the material through 12.5 mm and 10.0 mm IS sieve. The aggregates
passing through 12.5 mm sieve and retained on 10.0 mm sieve comprises
the test material.
2. The cylinder of the test shall be put in position on the base-plate and the
test sample added in thirds, each third being subjected to 25 strokes with
the tamping rod.
3. The surface of the aggregate shall be carefully levelled.
4. The plunger is inserted so that it rests horizontally on this surface, care
being taken to ensure that the plunger does not jam in the cylinder

Crushing Value
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Crushing Value
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Procedure:
5. The apparatus, with the test sample and plunger in position,
shall then be placed between the plates of the testing machine.
6. The load is applied at a uniform rate as possible so that the
total load is reached in 10 minutes. The total load shall be 40
tonnes.
7. The load shall be released and the whole of the material is
removed from the cylinder and sieved on 2.36mm IS Sieve.
8. The fraction passing the sieve shall be weighed and recorded.

Impact Value
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➢ This test gives relative measure of resistance of aggregate to
suddenly applied load or impact load.
➢ For ordinary concrete, it should not be more than 45% and for wearing
surface it should not be more than 30%
Procedure:
1. Sieve the material through 12.5 mm and 10.0 mm IS sieve. The aggregates
passing through 12.5 mm sieve and retained on 10.0 mm sieve comprises
the test material.
2. Pour the aggregates to fill about 1/3rd depth of measuring cylinder.
3. Compact the material by giving 25 gentle blows with the rounded end of
the tamping rod.
4. Add two more layers in similar manner, so that cylinder is full.
5. Strike off the surplus aggregates.
6. Determine the net weight of the aggregates to the nearest gram (W).

Impact Value
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Procedure:
7. Bring the impact machine to rest without wedging or packing up on the level plate,
block or floor, so that it is rigid and the hammer guide columns are vertical.
8. Fix the cup firmly in position on the base of machine and place whole of the test sample
in it and compact by giving 25 gentle strokes with tamping rod.
9. Raise the hammer until its lower face is 380 mm above the surface of the aggregate
sample in the cup and allow it to fall freely on the aggregate sample.
Give 15 such blows at an interval of not less than one second between successive falls.
10 Remove the crushed aggregate from the cup and sieve it through 2.36 mm IS sieves
until no further significant amount passes in one minute. Weigh the fraction passing the
sieve to an accuracy of 1 gm (W2). Also weigh the fraction retained in the sieve.
11 Note down the observations in the Performa and compute the aggregate impact value.
The mean of two observations, rounded to nearest whole number is reported as the
Aggregate Impact Value.
Impact Value
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Procedure:
1. Take aggregate of 5kg or 10kg depending on the size of aggregate is
taken and it is placed in cylinder of the loss angle machine along with
the abrasion charge.
2. The abrasion charge consists of a specific number of steel balls.
3. The cylinder is rotated at 20 to 33 r.p.m. for 500 or 1000 revolution,
depending on the Grading of the aggregate
4. The aggregate is removed from the cylinder and sieved on 1.7mm sieve,
5. The sample passing through 1.7mm sieve is expressed as percentage of
original weight gives the aggregate abrasion value.
Abrasion Value
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Los Angle Abrasion Testing Machine
Abrasion Value
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➢The Flakiness Index is the percentage by weight of particles whose least
dimension is less than 3/5th of their mean dimension.
Procedure:
1. A quantity of aggregate shall be taken sufficient to provide the minimum
number of 200 pieces of any fraction to be tested.(W1)
2. The sample shall be sieved with sieves specified in the chart.
3. Now the aggregate retained on different sieves should be separated.
4. Then each dry aggregate should pass through the corresponding slot of the
thickness gauge.
5. Now weight all The pieces which passes through respective slot.(W2)
6. Now calculate flakiness index
flakiness index = W2 X100
W1
Flakiness Index
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Flakiness Index
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Thickness Gauge

➢The Elongation Index is the percentage by weight of particles whose
Greatest dimension is greater than 1.8 times their mean dimension.
Procedure:l
1. Sieve the aggregate passing through IS sieve as specified chart
2. Pass each aggregate piece through the corresponding slot of length gauge.
3. Weight all material retained by length gauge say W3.
4. Now, calculate Elongation Index as,
Elongation index = W3 X100
W1
Elongation Index
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Elongation Index
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LENGTH GAUGE

Grading of coarse Aggregate
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➢Concrete may contain coarse aggregate from 4.75 mm to 150 mm
sizes.
➢The percentage of different sizes is taken for maximum density and
strength. This is done with the help of grading curves and standard
tables.
➢Good grading of aggregates will give very good quality and quantity.
The of aggregate ig normally done by following IS test sieves.
➢3.35 mm, 2.36 mm, 1.18 mm, 600μ, 300 μ, 150 μ, 75 μ, 80 mm,
63 mm, 50 mm,40 mm, 31.5 mm, 25 mm, 20 mm, 16 mm, 12.5 mm,
10 mm,6.3 mm and 4.75 mm.

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➢ In practice while concreting is done smaller particles will fill
the voids between large particles and thus economical use of
particles and cement paste is achieved. Thus proper use of fine
and aggregate will gives dense concrete with less quantity of
cement.
➢This art of doing particle size distribution of an aggregate is
known as grading of aggregate.
➢ The grading affects workability, strength, economy,
durability and hence in concrete mix fine and coarse aggregate
used should be well graded.

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thank you !!!

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