This Article Covers Various Test On Aggregates Used Before Selection For Pavement Construction.
Test On Aggregates
In order to decide the suitability of the aggregate for use in pavement construction, following tests carried out :-
- Crushing test
- Abrasion test
- Impact test
- Soundness test
- Shape test
- Specific gravity and water absorption test
- Bitumen adhesion test
One of the model in which pavement material can fail is by crushing under compressive stress. A test standardized by IS:2386 part-IV and used to determine the crushing strength of aggregates.
The aggregate crushing value provides a relative measure of resistance to crushing under gradually applied crushing load.
Abrasion test carried out to test the hardness property of aggregates and to decide whether they are suitable for different pavement construction works. Los Angeles abrasion test is a preferred one for carrying out the hardness property and has standardized in India (IS:2386 part-IV)
The aggregate impact test carried out to evaluate the resistance to impact of aggregates.
Aggregates passing 12.5 mm sieve and retained on 10 mm sieve filled in a cylindrical steel cup of internal diameter 10.2 mm and depth 5 cm which attached to a metal base of impact testing machine.
The material filled in 3 layers where each layer tamped for 25 number of blows.
Soundness test intended to study the resistance of aggregates to weathering action, by conducting accelerated weathering test cycles. The Porous aggregates subjected to freezing and thawing are likely to disintegrate prematurely.
To ascertain the durability of such aggregates, they subjected to an accelerated soundness test as specified in IS:2386 part-V.
The particle shape of the aggregate mass determined by the percentage of flaky and elongated particles in it. Aggregates which are flaky or elongated are detrimental to higher workability and stability of mixes.
The flakiness index defined as the percentage by weight of aggregate particles whose least dimension is less than 0.6 times their mean size. Test procedure had been standardized in India (IS:2386 part-I).
Specific Gravity and water absorption
The Specific gravity and water absorption of aggregates are important properties that required for the design of concrete and bituminous mixes.
The Specific gravity of a solid is the ratio of its mass to that of an equal volume of distilled water at a specified temperature.
- Apparent Specific Gravity
- Bulk Specific Gravity
Water absorption, The difference between the apparent and bulk specific gravities is nothing but the water- permeable voids of the aggregates.
The specific gravity of aggregates normally used in road construction ranges from about 2.5 to 2.9. Water absorption values ranges from 0.1 to about 2.0 percent for aggregates normally used in road surfacing.
Bitumen Adhesion Test
Bitumen adheres well to all normal types of road aggregates provided they are dry and free from dust.
In the absence of water there is practically no adhesion problem of bituminous construction.
Adhesion problem occurs when the aggregate is wet and cold.
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