Maximum Size of Aggregate:

The effect of size of aggregate is not straightforward but it depends upon the grade of concrete (i.e. whether the concrete is high strength or low strength). The size of aggregate does not affect much the strength of low strength concrete but for high strength concrete the strength increases with decrease in size of aggregate. This is due to the fact that in high strength concrete the failure is more likely to take place due to the loss of bond between the aggregate and the cement paste whereas in the low strength concrete the failure of cement paste it take place. The bond strength between the aggregate and cement paste depends upon the surface area provided by the aggregates. The surface area provided by the aggregates will be large for smaller size aggregates as compared to the large size aggregates.