Definition of aggregates | Desirable properties of aggregates

Aggregates

Aggregates are the fraction of rock which are inert or non-reactive. These are obtained from rocks by means of crushing.

Main constituents of the wearing surface are bitumen and aggregates. Mostly 90 % of the road consists of aggregates.

There are two problems to use non-inert materials.

1. Cost will increase. As non-inert materials are expensive than inert materials.
2. Non-inert materials will form weak bond with bitumen.

Desirable properties of aggregates

1. Strength is a measure of resistance to crushing. Crushing value depends on strength.
2. Soundness is another property of aggregates. It is the measure of resistance to weathering. Weathering includes variation of temperature, rainfall, and wind forces etc.
3. Their Shape must be angular for roads. They should not be rounded, flaky or elongated.
4. Toughness should be more. Toughness is the measure of resistance of aggregates to fracture. Fracture is the splitting of aggregates into pieces.
5. Hardness should be more. Hardness is the measure of resistance of aggregates to abrasion. Abrasion is the rubbing action between road and tire.
6. They must be non-porous. They should absorb minimum water as much as possible.
7. They should have more affinity for bitumen. Hydrophobic have less affinity with water and more affinity for bitumen. Whereas Hydrophilic having more affinity for water and less affinity for bitumen.
8. They must be economical.