REQUIREMENTS OF A GOOD AGGREGATE

Following are the desirable properties and requirement of a good aggregate-

1. Adhesion 
2. Cementation
3. Durability
4. Hardness
5. Shape
6. Strength
7. Toughness

SHAPE:

The shape of aggregates may be rounded, cubical, angular, flaky or elongated. The flaky and elongated aggregates possess less strength and durability and they are not used in construction work as far as possible. The rounded aggregates are preferred in cement concrete construction. They are unsuitable in W.B.M construction, bituminous construction, and in granular base course because their stability due to interlocking is less. The angular aggregates are used for such types of construction work.

  

HARDNESS:

A good aggregate  should be sufficiently hard, it should offer maximum possible resistance to abrasion and attrition. The road aggregate should be hard enough to resist abrasion due to grinding of pieces of stones against each other.

  

ADHESION:

A good aggregate should have adhesive property, it should have sufficient binding capacity with binder. If this quality is absent in the aggregate, it will lead to the separation of bituminous and cement coating in the presence of water.   

CEMENTATION:

The binding quality of the aggregate depends on its ability to form its own binding material under different loading so as to make the rough broken stone pieces grip together to resist displacement 

DURABILITY:

A good aggregate should be sufficiently durable, it should be sufficiently resistant to weathering agencies and is largely dependent upon its petrological composition. This requirement of aggregate is essential so that it can resist the effect of weathering agencies like rain, frost, variation of temperature etc. in order to achieve long life of the structures.   

STRENGTH:

The good aggregates should be sufficiently strong to withstand the stresses developed due to the wheel load of traffic. This property is especially desirable for the road aggregates which are to be used in top layer of the pavements. Thus the wearing course of road should be composed of aggregates which posses enough strength in addition to enough resistance to crushing.

TOUGHNESS:

A good aggregate quite tough, it should offer the maximum possible resistance to the hammering effect of wheel load. This is essential so that the aggregate used in the construction of pavement can resist the impact caused due to movement of heavy traffic load without breaking into smaller pieces.