Category: Aggregate

Importance of Different Testing on Road Aggregates

The importance of different testing on road aggregates are as follows:

1. Abrasion test

This test is performed to find out the hardness i.e. resistance to abrasion of the stone aggregate. It is very important to know the aggregate hardness value before it is used in road construction.

2. Impact test

This test is carried out to find the toughness i.e resistance to hammering effect of the stone aggregate.

3. Soundness or Durability test

This test is done to find durability, that is the resistance to weathering action.

4. Crushing test

This test is done to find out the strength of coarse aggregate.

5. Shape test

This test is done to find out the percentage of flaky and elongated particles contained in aggregate.

6. Specific gravity test

This test is done to find out the specific gravity of aggregate and the unit weight of aggregate.

7. Water absorption test

This test is done to know whether the aggregates are porous or not.

8. Bitumen adhesion test

This test is carried out to assess the adhesive property of aggregate.

9. Cementation test

This test is performed to assess the cementation property of aggregate.

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Different Types of Aggregates

Different Sizes of Aggregates Used For Different Purposes

Different Size of Aggregates Used For Different Purposes

For the same workability and strength, concrete having large size aggregate requires less amount of cement than in concrete having smaller size aggregate. Hence, in large bulk works large-sized aggregates are preferred.

Leaser cement reduces the heat of hydration and thereby the shrinkage cracks. Use of large-sized aggregates also increases the workability of concrete. The maximum size of aggregate is also governed by the following factors:

1. It should not be more than 3/4 of the clear spacing between reinforcing bars.

2. It should not be more than 1/4 of the minimum thickness of the member.

3. For heavily reinforced concrete members, the nominal maximum size of the aggregates should usually be restricted to 5mm less than the minimum clear distance between the main bars or 5mm less than the minimum cover to the reinforcement whichever is smaller.

5. For structures like abutments, piers, retaining walls, 40mm size aggregates should be used.

6. For flooring works normally 10mm size aggregate is used.

7. For normal RCC works 20 mm sized aggregate is used.

What is Grading And Proportioning of Aggregates

Grading of Aggregates

The art of doing gradation (particle size distribution) of an aggregate as determined by sieve analysis is called grading of aggregate.

The grading of aggregate has a considerable effect on workability, uniformity & finishing qualities of plastic concrete which ultimately affec& other properties of hardened concrete.

Proportioning of Aggregates

The art of determining the quantities of the various ingredient so as to obtain densest and most economical concrete mix is called proportioning of aggregate.

The principle of proportioning of aggregates is that the smaller particles will fill up the voids between large particles. A well proportioned concrete mix requires a minimum amount of cement per unit volume.

Purpose of Different Testing of Aggregates

Bulk Density of Aggregate

The bulk density of an aggregate may be defined as the mass of the material in a given volume. It depends on how densely the aggregate is packed.

The other factors affecting the bulk density are the particle size & shape, the grading of the aggregate and moisture content.

Bulk density of aggregate is generally expressed as kg/litre.

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Types of Aggregates

What is Grading And Proportioning of Aggregates

13 Types of Aggregates – According to Size, Shape, Weight and Geological Origin

13 Types of Aggregates

The following 13 types of aggregates are classified according to their size, shape, unit weight and geological origin:

A. According To Geological Origin

According to the geological origin, aggregates are the following two types:

1. Natural Aggregate

Examples of natural aggregate – Crushed Stone, Gravel etc.

2. Artificial Aggregate

Examples of artificial aggregate – Broken brick, Blust furnace slag etc.

B. According To Size

According to size, aggregates are the following 4 types:

1. Fine Aggregate

It is the aggregate most of which passes through 4.75mm I.S sieve.

Examples of fine aggregate- Natural sand, Crushed stone sand, Crushed gravel sand.

2. Coarse Aggregate

It is the aggregate most of which retained on the 4.75mm I.S sieve.

Example of coarse aggregate – Crushed stone or gravel.

3. All-in-aggregate

Combination of coarse & fine aggregates available in nature.

4. Single Size Aggregate

Comprising particles falling within a narrow limit of size.

C. According To Shape

Round Aggregate.
Irregular Aggregate.
Angular Aggregate.
Flaky & Elongated Aggregate.

D. According To Unit Weight

1. Normal-Weight Aggregate

Sp. Gravity 2.5 to 2.7

Examples of normal-weight aggregate – Sand, Gravels, Crushed rocks etc.

2. Heavy-Weight Aggregate

Sp. Gravity 2.8 to 2.9

Examples of heavy-weight aggregate – Magnetite(Fe3O4), Barytes(BaSO4).

3. Light-Weight Aggregate

Sp. Gravity 1.0 to 1.2

Examples of light-weight aggregate – Sintered fly ash aggregate, expanded shale etc.

Requirements or Characteristics Of A Good Fine & Coarse Aggregates

Deleterious Material in Aggregates

Purpose of Different Testing of Aggregates

Purpose of Different Testing of Aggregates

The following tests are generally performed to find out the standard aggregate:

Test for determination of Flakiness Index.
Test for determination of Elongation Index.
Test for determination of Clay, fine silt & fine dust.
Test for determination of Organic Impurities.
Test for determination of Specific Gravity.
Test for determination of Bulk Density & Voids.
Test for determination of Aggregate crushing value.
Test for determination of Aggregate Impact Value.
Test for determination of Aggregate abrasion value.

Requirements or Characteristics Of A Good Fine & Coarse Aggregates

Functions Of Fine and Coarse Aggregate in Concrete

Functions Of Fine Aggregate in Concrete

Fine aggregates perform the following functions:

Functions Of Fine and Coarse Aggregate in Concrete

1. It assists in producing workability and uniformity in the mixture.

2. It assists the cement paste to hard the coarse aggregate particles.

3. It helps to prevent possible segregation of paste and coarse aggregate, particularly during the transport operation of concrete for a long distance.

4. Fine aggregate reduces the shrinkage of binding material.

5. It prevents the development of a crack in the concrete.

6. It fills the voids existing in the coarse aggregate. Thus, it helps in increasing the density of concrete.

7. It assists in the hardening of cement by allowing the penetration of water through its voids.

Functions Of Coarse Aggregate in Concrete

Coarse aggregate is used in concrete to achieve the following functions:

1. It makes a solid & hard mass of concrete with cement and sand.

2. It provides bulk to the concrete.

3. It increases the crushing strength of concrete.

4. It reduces the cost of concrete by using cheaper materials.

Bulking Of Sand

Different Grading Zone Value of Fine Aggregates(sand) As Per IS: 383

Requirements or Characteristics Of A Good Fine and Coarse Aggregates

Requirements or Characteristics Of A Good Fine Aggregates

The following are the requirements of good fine aggregate:

It should consist of coarse, angular, sharp & hard grains.
A Good Fine Aggregates must be clean & free from coatings of clay and silt.
It should not contain any organic matter.
It should be free from hygroscopic salt.
It should be chemically inert.
It must be strong and durable.
The size of its grains should be such that the pass-through 4.75mm I.S sieve & retained entirely on 75 µ I.S sieve.

Requirements Or Characteristics Of A Good Coarse Aggregate

A good coarse aggregate should fulfil the following requirements:

It should be angular or cubical in shape.
It must be sound & durable.
A Good Coarse Aggregate should be absolutely clean and free from any organic matter, chemicals and coating of clay.
It should be hard and tough.

Deleterious Material in Aggregates

Functions Of Fine & Coarse Aggregate in Concrete

Sizes Of Coarse Aggregates For Mass Concrete as Per IS:383

The sizes of coarse aggregates are four types, they are small, medium, large, and very large. Below, the aggregate sizes, and, IS sieve designation and percentage of passing are presented in the form of a table.

Different Grading Zone Value of Fine Aggregates(sand) As Per IS: 383

There are 4 types of grading zones for fine aggregates(sand) namely Grading zone I, II, III, IV. All grading zones and their recommended value for different sieve size are given below:

Recommended Gradient as Per I.R.C

Recommended Design Speed on Urban Roads