Shape of Aggregate:

Based on the shape, the aggregates are classified as Rounded, Angular, Flaky and Elongated aggregates. The rounded aggregates are without edges or corners and are smooth as compared to angular aggregates, which can be identified by their well-defined edges and corners. The surface area of rounded aggregates is comparatively smaller. Flaky aggregate is that whose least dimension (i.e. thickness) is reasonably small relative to its other two dimensions (i.e. width and/or length), whereas elongated aggregate is that whose greatest dimension (i.e. length) is reasonably large relative to its mean dimension. Flaky and elongated aggregates are elaborates in detail later.

Comments

Rounded aggregates provide good workability, as they require less amount of cement for the same w/c ratio but they lead to weak bond with the cement paste as compared to angular aggregates. Angular aggregates give better durability, better bond and higher strength but to achieve desired workability these aggregates require more cement paste. The presence or use of flaky and elongated aggregates should be discouraged as they adversely effect the workability, cement requirement, strength and durability, which finally lead to poor quality concrete.