Test on Aggregates.ppt

Mr. S. Vinoth
Assistant Professor in Department of civil Engineering at KPR Institute of Engineering and
Technology
Education
U.G : B.E Civil Engineering
KPR Institute of Engineering and Technology
P.G : M.E Structural Engineering
Sri Shakthi Institute of Engineering and Technology
Experience
1.Technical Assistant in Town Planning Section at Singanallur Corporation office, Coimbatore
Areas of Interest
- Structural Engineering
- Infrastructure Engineering and Management
- Earth System Science and Engineering

Topics Covered
Aggregates classification– gradation of aggregates – properties of aggregates (physical
and mechanical) – test on aggregates

Aggregate
 The aggregate is a relatively inert material and it imparts volume stability.
 The aggregate provide about 75% of the body of the concrete
and hence its influence is extremely important (70 to 80 %)
 An aggregate should be of proper shape and size, clean,
hard and well graded.
 It must possess chemical stability and it must exhibit
abrasion resistance.

Classification of Aggregate
I. Classification Based on Size
a. Fine aggregates:
It is the aggregate, which is passes through a 4.75mm IS sieve and retained
on 0.7 mm. The fine aggregate may be natural sand, crushed stone sand or crushed gravel sand. According to IS
383-1970, there are four grading zones of the fine sand, Zone I, Zone II, Zone III and Zone IV.
b. Coarse aggregates:
The aggregates, most of which are retained on 4.75mm IS sieve are termed as coarse aggregates. The coarse
aggregates may be Crushed stone, Uncrushed gravel and Partially crushed stone or gravel.
[*Sometimes combined aggregates are available in nature consisting of different fractions of fine and coarse
aggregates, which are known as all in aggregate.]

II. Classification Based on Shape
a. Rounded aggregate:
The aggregate with rounded particles (river or sea
shore gravel) has
minimum voids ranging from 32 to 33%.
It gives minimum ratio of surface area to
the volume, thus requiring minimum cement paste to make
good concrete.
The only disadvantage is that the interlocking between its particles is less, and
hence the development of the bond is poor, making it unsuitable for high
strength concrete and pavement.

b. Irregular aggregates:
The aggregate having partly round particles (pit sand and gravel) has
higher percentage of voids ranging from 35 to 38 %.
It requires more paste for a given workability.
The interlocking between particles, though better than that obtained
with the rounded aggregate, is inadequate for high strength concrete.

c. Angular aggregates:
The aggregate with sharp angular and rough particles (crushed
rock) has a maximum percentage of voids ranging from 38 to 40%.
The interlocking between particles is good, providing a good
bond.
The aggregate requires more paste to make workable concrete of
high strength.
The angular aggregate is suitable for high strength concrete and
pavements subjected to tension.

d. Flaky and elongated aggregates:
An aggregate is termed flaky when the ratio of least dimension
(thickness)
to the mean dimension is less than three-fifth (0.6).
The particle is said to be elongated when the ratio of greatest
dimension (length) to the mean dimension is more than nine-fifth
(1.8 times).

III. Classification based on unit weight
a. Normal weight aggregates:
 The commonly used aggregates i.e. sand, gravel, crushed rocks such as granite, basalt, sandstone
(sedimentary) and limestone.
 It has specific gravities between 2.5 and 2.7 produce concrete with
unit weight ranging from 23 to 26 kN/m3
 The compressive strength at 28 days between 15 to 40
MPa are termed Normal weight aggregate.
b. Heavy weight aggregates:
 Heavy weight concrete is produced from heavy weight aggregate, which is more effective as a radiation
shield.
 The unit weight of concrete varies from 30 to 57 kN /m3.
 The specific gravity is varies from 4 – 6.8
 Example: Baryte (Gs = 4 to 4.6), Ferrophosphorus (Gs = 5.8 to 6.8), Haematite (Gs = 4.9 to 5.3) and
Magnetite (Gs= 4.2 to 5.2)

c. Light weight aggregates:
The light weight aggregates have unit weight up to 12 kN /m3.
These aggregates are obtained from pumice, volcanic cinder, Diatomite, blast furnace slag, fly ash etc,.
The weight of concrete (structure) is reduced to a great extent
and it provides better thermal insulation and improved fire resistance.

Physical Properties of Aggregates
The physical properties of aggregates are;
1. Shape
2. Size
3. Color
4. Texture
5. Gradation
6. Fineness modulus

Effect of aggregate properties on
concrete
i. Particle Size, Grading and Dust Content
Well-graded sands tend to have lower water requirements than single-sized sands and increasing dust contents
tend to increase the water requirement of sands.
ii.Particle Shape
It is fact that sands with well-rounded particles will be less water and make more workable concrete than
sands with flaky, elongated particles. However, the strength is undesirable. Aggregate with angular shape,
will give moderate water and high strength to concrete by good interlocking characteristics.

Effect of aggregate properties
on concrete
iii. Particle Surface Texture
In general, aggregate with a rough surface texture will have a higher water requirement than aggregate with
smooth particle surfaces.
iv. Water Absorption
All aggregates absorb water to a greater or lesser degree. The higher the water absorption the higher the
water requirement will be, but the water absorbed into the aggregate will not affect the effective water:
binder ratio or the strength. It will however lead to rapid slump loss if absorption is excessive, say >1%
by mass. In general it is preferable to avoid concrete aggregate properties with water absorptions of
more than 1 or 1.5% by mass

FINENESS MODULUS (FM)
 The fineness modulus (FM) is a numerical index of fineness, giving some idea of the mean
size of the particles present in the entire body of the aggregate.
The fineness modulus =
 According to IS 2386-1963, the sieves that are to be used for the sieve analysis of the
aggregate for concrete are 80mm, 40mm, 20mm, 10mm, 4.75mm, 2.36mm, 1.18mm, 600m,
300m and 150m.

FINENESS MODULUS
 For example, a fineness modulus of 6 can be interpreted to mean that the sixth sieve, i.e. 4.75 mm is
the average size.
 The value of fineness modulus is higher for coarser aggregate and lower for
fine aggregate.
Limitations:
The FM for fine sand = 2 - 3.5
The FM for coarse aggregate = 5.5 - 8
[Note: higher FM, the mix will be harsh and if on the other hand gives a lower FM, it produces an
uneconomical mix]

FINENESS MODULUS
Aggregates Sieve size Weight retained(g)
Cumulative weight
retained (g)
Cumulative %
retained (g)
Coarse aggregates
80mm 0 0 0
40mm 250 250 5
20mm 1750 2000 40
10mm 1600 3600 72
Fine aggregates
4.75mm 1400 5000 100
2.36mm 0 5000 100
1.18mm 0 5000 100
0.6mm 0 5000 100
0.3mm 0 5000 100
0.15mm 0 5000 100
Sum = 717
Worked Example: (Take 5000 g sample)

FINENESS MODULUS
 Therefore, fineness modulus of coarse aggregates = sum (cumulative % retained) / 100
= (717/100) = 7.17
 Fineness modulus of 7.17 means, the average size of particle of given coarse aggregate sample is
in between 7th and 8th sieves, that is between 10mm to 20mm.

Gradation of aggregates
 Gradation refers to the particle size distribution of aggregates.
 The gradation of coarse aggregate plays an important role in workability and paste requirements.
 The gradation of fine aggregate affects the workability and finishing ability of concrete.
Types of gradation:
1. Well graded
2. Poor / Uniform graded
3. Gap graded

1. Well graded
Incorporates a combination of particles of many sizes. Hence, it has Low void content, Low permeability
and High stability but increases the particle surface area. This is the preferred gradation for making a
good concrete.

2. Poor / Uniform graded
All particles are of same size. It produces a large volume of voids irrespective of particle size. Hence the
paste requirement for this concrete is high.

3. Gap graded
This involves grading in which one or more sizes are omitted. It has low stability, moderate voids content
and permeability than well graded aggregate. This type of concrete is generally used for architectural or
aesthetic purposes.

Mechanical Properties
The following are the properties to be analyzed for aggregates, they are
1. Toughness
2. Hardness
3. Specific gravity
4. Bulk Density
5. Porosity and absorption of aggregates
6. Moisture content of aggregate

1. Toughness
 Toughness of the aggregate is the resistance to the failure by load (impact or crushing)
 The impact and crushing load value should not exceed 45% for the aggregate in concrete and 30% for
the concrete for wearing surfaces such as runways, roads and pavements. (IS: 2386 (part – 4) - 1963)
2. Hardness
 Wear and tear property of aggregate is checked (concrete used in roads and in floor surfaces subjected to
heavy traffic).
 For determining the hardness or resistance to wear property - abrasion test is carried out. (IS: 2386 (part
– 4) - 1963)

 Deval machine and Los Angeles machine are used to perform the abrasion test.
 For a good stone the aggregate abrasion value shall not exceed 16%.
3. Specific gravity
 The specific gravity is defined as the ratio of weight of the solid(aggregate), referred to vacuum, to the
weight of an equal volume of gas-free distilled water, both taken at standard temperature.
 The quantity of aggregate required for given volume of concrete is calculated using specific gravity.
(IS: 2386 (part – 3) - 1963)
 The majority of aggregates have specific gravity value between 2.6 – 2.7

4. Bulk density
 The bulk density is the weight of the material in a given volume and expressed in terms of kg/lit or
cubic cm.
 It is affected by several factors including the Fineness modulus, shape of particles and the amount of
moisture present in the material.
 When aggregate is to be actually batched by volume it is essential to know the weight of the aggregate
that would the fill the container unit volume is known as bulk density of aggregate.
 The bulk density of the aggregate is depends on how densely is packed.
 (IS: 2386 (part – 3) - 1963) used for bulk density test.

5. Porosity and Absorption
 The bond between aggregate and cement paste is get affected by the permeability and water absorption.
(thus causes strength decrease)
 Even the smallest aggregate pores are generally larger than the gel pores in the cement paste.
 But there is no theoretical relation between the concrete strength and aggregate water absorption.
 (IS: 2386 (part – 3) - 1963) describes the test for finding the water absorption.

6. Moisture content of aggregate
 The surface moisture is expressed as a percentage of weight saturated an surface dry aggregate (termed
as moisture content).
 The moisture content of aggregate changes with weather condition, if aggregate exposed to rain, then
they will absorb some water (especially for fine aggregate) and also from one stockpile to another.
 (IS: 2386 (part – 3) - 1963) describes the test to determine the moisture content.

1. Crushing strength Test
 Ascertained by aggregate crushing value
 It gives a relative measure of the resistance of an aggregate to crushing under a gradually applied
compressive load
 For this test, 12.5 mm passed and 10 mm retained aggregates are used
 Surface dry condition aggregates are filled into the standard cylinder with three layer of 25 blows
 Compressive force is gradually applied up to 40 tons in 10 minutes time
 The crushed aggregates are sieved in 2.36 mm sieve
 Then aggregate crushing value = B/A x 100
where, A- Weight of sample and B- weight of retained aggregate in 2.36mm sieve.
 [Crushing value should not higher than 45%]

2. Impact strength Test
 Ascertained by aggregate impact value
 It gives a relative measure of the resistance of an aggregate to sudden shock or
impact. For this test, 12.5 mm passed and 10 mm retained aggregates are used
 Surface dry condition aggregates are filled into the test cylinder with three layer of 25 blows
 Filled cylinder is placed in impact testing machine
 Then, 15 blows are given to the cylinder using 14 kg weight hammer.
 The crushed aggregates are sieved in 2.36 mm sieve
 Then aggregate impact value = B/A x 100
where, A- Weight of sample and B- weight of retained aggregate in
 2.36 mm sieve. [Crushing value should not higher than 45%]

3. Abrasion Test (Los Angeles Test)
 Select the grading to be used in the test such that it conforms to the grading to be used in construction
 Choose the abrasive charge balls depending on grading of aggregates.
 Place the aggregates and abrasive charge on the cylinder and fix the cover.
 Rotate the machine at a speed of 30 to 33 revolutions per minute with uniform speed.
 The machine is stopped after the desired number of revolutions and material is discharged to a tray.
 The entire stone dust is sieved on 1.70 mm IS sieve.
 The material coarser than 1.7mm size is weighed correct to one gram.

Abrasion Test (Los Angeles Test)
 Abrasion Value = (W1 – W2 ) / W1 X 100
Where,
 Original weight of aggregate sample = W1 g
 Weight of aggregate sample retained = W2 g
 Weight passing 1.7mm IS sieve = W1 – W2 g
 [Note: Abrasion value should not more than 16%]

Water (for concrete)
Water is the most important material for construction, especially
for making concrete.
The purpose of water in concrete are
 It distributes the cement evenly.
 It reacts with cement chemically and produces calcium silicate hydrate (C-S-H) gel which gives the
strength to concrete.
 It provides for workability, i.e., it lubricates the mix.
 Hence, for construction, quantity and quality of water is as important as cement.

As water quantity goes up in a mix (ill effect), the following are the effects:
 Strength decreases
 Durability decreases
 Workability increases
 Cohesion decreases
 Economy may increase at the expense of quality and reliability.

Quality of water for concrete (IS10500:2012)
 Water used for mixing and curing should be free from oil, acid and alkali, salts and organic material.
 It should be potable and concreting generally requires a value purer than that of drinking
 Whenever there is uncertainty in quality, water should be tested before use.
 Even chlorine added for city water supply will affect concrete if used carelessly without proper testing
and treatment.
 If well water is used for construction, it must be tested for
 impurities.

Chlorides: They can cause corrosion of steel reinforcement, can accelerate setting. The water used
may be contaminated with chlorides because of seawater, some admixtures, salts or deliberate
chlorination for disinfections.
Sulphates: They reduce long-term strength levels.
Organic matter: Their effects on concrete are variable. If an alga is present, water should not be used.
It will affect the setting and strength development.
Sugar: It will retard setting time. Too much may ‘kill' the concrete (the concrete will never set).
Wastewater: It should never be used in construction. Water for curing should be as pure as water for
mixing concrete.
Quality of water for concrete (IS10500:2012)

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