04: Aggregates

Question 1

Definition of Aggregate

Answer 1

• The term “aggregates” generally refers to mineral particles which have rocks as their origin unless otherwise specified.
• Aggregate; the inert filler materials, such as sand or gravel, used in making concrete
• Aggregates make up 60-75% of total volume of concrete (normal/ordinary concrete) 90% of asphalt pavements.
• Sand, gravel, boulders, stones or rocks that can be crushed into particles.
• By-product or waste material from industrial process or mining operation.

Question 2

What are the Aggregate Sources

Answer 2

Natural Aggregate
• Sand and Gravel Mine (Pit)
• Quarry
Contrived Aggregate
• Recycled

Question 3

Aggregates that come from
unconsolidated sand and gravel
deposits. Typically deposited by
streams (alluvium) or glaciers.

Answer 3

Sand and Gravel Mine (Pit) Aggregates

Question 4

Aggregates that come from bedrock deposits. Bedrock, which is a consolidated rock includes: granite,
basalt, quartzite, gabbro, etc.

Answer 4

Quarry Aggregates

Question 5

Products that include crushed concrete, bituminous or demolition debris and in some instances taconite tailings.

Answer 5

Recycled Aggregates

Question 6

Methods of Extraction and Processing

Answer 6

Underwater Sources
• Dragline Extraction
• Dredging
Land Sources
• Track Drills
• Blasting Bedrock
• Crushers and Screens

Question 7

Classification of Aggregates

Answer 7

Based on Shape
• Rounded aggregates
• Irregular or partly rounded aggregates
• Angular aggregates
• Flaky aggregates
• Elongated aggregate
• Flaky and elongated aggregates

Question 8

These are completely shaped by attrition and available in the form of seashore gravel. These aggregates result the minimum percentage of voids (32-33%) hence gives more workability.

Answer 8

Rounded Aggregates

Question 9

They require lesser amount of water-cement ratio. They are not considered for high strength concrete because of poor interlocking behavior and weak bond strength.

Answer 9

Rounded Aggregates

Question 10

When the length of aggregate is larger than the other two dimensions then it is called _______ aggregate or the length of aggregate is greater than 180% of its mean dimension.

Answer 10

Elongated Aggregate

Question 11

When the aggregate thickness is small when compared with width and
length of that aggregate, it is said to be?

Answer 11

Flaky Aggregate

Question 12

When the least dimension of aggregate is less than the 60% of its mean dimension then it is
said to be?

Answer 12

Flaky Aggregate

Question 13

This aggregates are partly shaped by attrition and these are available in the form of pit sands and gravel.

Answer 13

Irregular Aggregate

Question 14

It may result 35-37% of voids. These will give lesser workability when compared to rounded aggregates. The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete.

Answer 14

Irregular Aggregate

Question 15

It consist well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks.

Answer 15

Angular Aggregate

Question 16

It result maximum percentage of voids (38-45%) hence gives less workability. They give 10-20% more compressive strength due to development of stronger aggregate-mortar bond. So, these are useful in high strength concrete manufacturing.

Answer 16

Angular Aggregate

Question 17

Classification of Aggregates

Answer 17

Fine Aggregates
Coarse Aggregates

Question 18

Define Fine Aggregates

Answer 18

• Sand and/or crushed stone
• <5 mm (0.2 in.)
• F.A. content usually 35% to 45% by
mass or volume of total aggregate

Question 19

Define Course Aggregate

Answer 19

• Gravel and crushed stone
• ≥ 5 mm (0.2 in.)
• typically between 9.5 and 37.5 mm

Question 20

Enumerate Aggregate Properties

Answer 20

• Strength
• Hardness
• Impact Value
• Resistance against Weathering (Weathering Resistance)
• Shape of Aggregate
• Bitumen Adhesion
• Specific Gravity/Relative Density
• Water Absorption

Question 21

Aggregate crushing value gives the crushing strength of aggregate up to which it can bear the load without fail.

Answer 21

Crushing Strength Test

Question 22

Hardness property of aggregate is determined by conducting what kind of test?

Answer 22

Abrasion Test
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Los Angeles abrasion testing machine is used to conduct this test.

Question 23

Shape of aggregate is also important consideration for the construction of pavement. Aggregate should not contain flaky and elongated particles in it. If they contain this type of particles, they will affect the stability of mix.

Answer 23

Shape Test

Question 24

This test will give the stripping of bitumen from the aggregate.
In case of bitumen pavement, the bitumen should be in pure contact with aggregate. To attain this aggregate should be clean and dry.

Answer 24

Bitumen Adhesion Test

Question 25

To determine the stripping value of bitumen what kind of test is conducted on aggregates?

Answer 25

Static Immersion Test

Question 26

Impact value of aggregate will give aggregate capability against sudden loads or forces.

Answer 26

Impact Test

Question 27

To determine the weathering resistance of aggregate, this kind of test is conducted. If the resistance against weathering is good for aggregate, then it will have high durability.

Answer 27

Soundness Test

Question 28

This property of an aggregate is the ratio of its mass to that of an equal volume of distilled water at specific temperature.

Answer 28

Specific Gravity (Test)

Question 29

The specific gravity of aggregate is of two types, these are?

Answer 29

• Bulk specific gravity, in which total volume of aggregates along with their void space is considered.
• Apparent specific gravity, in which the volume of aggregates without considering void spaces is taken into account

Question 30

This test helps to determine the water absorption value of aggregate.

Answer 30

Water Absorption Test

Question 31

Kinds of Testing of Sand Quality in Construction Sites

Answer 31

• Organic Impurities Test
• Silt Content Test
• Particle Size Distribution
• Bulking of Sand

Question 32

Sand shall not contain any harmful impurities such as iron, pyrites, alkalis, salts, coal or other organic impurities, mica, shale or similar laminated materials, soft fragments, sea shale in such form or in such quantities as to affect adversely the hardening, strength or durability of the mortar.

This test is conducted at the field, for every 20 cu m or part thereof.

Answer 32

Organic Impurities Test
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The maximum quantities of clay, fine silt, fine dust and organic impurities in the sand/marble dust shall not exceed the following limit:
• Clay, fine silt and fine dust when determined in accordance within not more than 5% by mass in IS 2386 . natural sand or crushed gravel sand and crushed stone sand.
• Organic impurities when determined in color of the liquid shall be lighter in accordance with IS 2386

Question 33

The maximum quantity of silt in sand shall not exceed 8%. Fine aggregate containing more than the allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.

This is also a field test and to be conducted for every 20 cu m.

Answer 33

Silt Content Test

Question 34

On the basis of particle size, fine aggregate is graded into four zones Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.

This test can be conducted at site or in laboratory for every 40 cum of sand

Answer 34

Particle Size Distribution

Question 35

Fine aggregate, when dry or saturated, has almost the same volume but dampness causes increase in volume. In case fine aggregate is damp at the time of proportioning the ingredients for mortar or concrete, its quantity shall be increased suitably to allow for bulkage.

This test is conducted at site for every 20 cu m of sand. Based on bulking of sand, suitable water cement ratio is calculated for
concrete at site

Answer 35

Bulking of Sand