Question

5.5 The shape and surface texture of aggregate particles are important for both portland cement concrete and asphalt concrete. a. For preparing PCC, would you prefer round and smooth aggregate or rough and angular aggregate? Briefly explain why (no more than two lines). b. For preparing HMA, would you prefer round and smooth aggregate or rough and angular aggregate? Briefly explain why (no more than two lines).

Answer 1

5.5 a) For portland cement concrete, if the round shaped aggregate are used the workability of the concrete will increase but the load bearing strength of the concrete will decrease drastically, as the friction between the round shaped aggregate will be minimum. But in angular aggregate there will be friction and will increase the load bearing capacity. Thus it is preferred to use angular shaped aggregate in a portland cement concrete.

5.5 b) For hot mix asphalt (HMA), if we use round shaped aggregate again there will be least friction between the aggregates and the binding of the aggregates will be loose and the road may wear off easily. Also, when a vehicle is moving over the asphalt the angular aggregate will provide greater friction to the wheels where as the round aggregate will offer no friction, as a result it will be difficult o drive on a round aggregate asphalt. Thus, angular aggregate should be used in hot mix asphalt (HMA).