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Sunday 23 December 2012

Road aggregate forms the princpal material in the construction of road pavements. Therefore, it should be of good quality. A good road aggregate should fulfill the following requirements:-

1. Hardness :- A good road aggregate should be sufficiently hard i.e. it should offer maximum possible resistance to abrasion.
This requirement of the road aggregate is particularly needed when it is to be used in flexible pavements. Since flexible road pavements go on distorting under heavy traffic  load,  the road metal is constantly but slightly disturbed. This causes pieces of stones to rub and grind against each other. Therefore, the road aggregate should be hard enough to resist abraison due to grinding of pieces of  stones against each other.

2. Toughness :- A good road aggregate should be quite tough i.e. it should offer the maximum possible resistance to the hammering effect of wheel loads.
This requirement is essential so that the road aggregate used in the construction of flexible pavements can resist the impact caused due to movements of heavy traffic loads without breaking into smaller pieces.

3. Durability :- A good road aggregate should be sufficiently durable i.e. it should be sufficiently resistant to weathering agencies.
This requirement of the road aggregate is essential so that it can resist the effects of weathering agencies like rain, variation of temperature, frost, etc. in order to achieve long life of the road pavement.

4. Strength :- a good road aggregate should have high crushing strength.
This requirement of the road aggregate is essential so that it can withstand safely the stresses developed in the road pavement due to traffic wheel loads.

5. Cementation :- a good road aggregate should have sufficient cementation property i.e. it should have sufficient binding property within itself.
This requirement is essential for road aggregate used in the water bound macadam road surfaces. in such roads, the road aggregate should form its own binding material under the load of road roller and bind itself so that  the road pavements may remain serviceable for a longer period.

6. Adhesiveness :- A good road aggregate should have adhesive property i.e. it should have sufficient binding capacity with the binders.
This requirement is essential of road aggregate used in the bituminous roads. In such roads, the road aggregate should have adequate binding capacity with the binders like bitumen, asphalt. coaltar, etc. so as to ensure stability of the road surface.

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