In order to obtain the best workability of concrete the prefect shape of aggregate is 

Explanation:

Workability of concrete is affected by the shape of aggregate.

Generally aggregates are found in variety of shapes, such as angular aggregate, flaky aggregate, elongated aggregate, rounded aggregate, sub-rounded aggregate, cubical aggregate etc.

Rounded or subrounded aggregate have following advantages:

• For a given volume or weight, it has less surface and less void, so the excess paste is available to give a better lubricating effect.
• Due to its rounded shape, it has less friction resistance.

Because of the above-mentioned reasons rounded aggregate shows high workability as compared to angular, flaky, or elongated aggregates.

Angular, flaky & elongated aggregates reduce the workability of concrete.