Answer:

Introduction:
In order to obtain the best workability of concrete, the shape of the aggregate plays a significant role. The shape of the aggregate affects the workability, strength, and durability of the concrete. The preferred shape of the aggregate is round.

Explanation:
The shape of the aggregate refers to the geometry of the individual particles that make up the aggregate. The shape can vary from round to angular, flaky, or elongated. Each shape has its own characteristics and impact on the properties of concrete.

Round Aggregate:
Round aggregates are preferred for achieving the best workability of concrete due to the following reasons:

1. Improved Workability: Round aggregates have a smooth surface and are free from sharp edges. This smoothness allows the concrete mix to flow more easily, resulting in better workability. The rounded shape reduces friction between the particles, making it easier for them to slide past each other.

2. Better Cohesion: The round shape of the aggregate promotes better cohesion between the particles and the cement paste. This cohesion contributes to the overall strength and durability of the concrete.

3. Reduced Water Demand: Round aggregates require less water for the same workability compared to angular or flaky aggregates. This is because the smooth surface of round aggregates reduces the internal friction within the concrete mix, resulting in lower water demand.

4. Improved Pumpability: Round aggregates are more pumpable compared to angular or flaky aggregates. The smooth shape allows the concrete mix to flow easily through pipelines without clogging or segregation.

5. Reduced Bleeding and Segregation: The round shape of the aggregate helps to reduce bleeding and segregation in the concrete mix. Bleeding is the migration of water to the surface of freshly placed concrete, while segregation is the separation of coarse aggregates from the rest of the mix. Round aggregates minimize the chances of both these issues.

6. Improved Finish: Round aggregates contribute to a smoother and more aesthetically pleasing finish of the concrete surface. The absence of sharp edges reduces the risk of surface defects or roughness.

Conclusion:
In conclusion, the preferred shape of the aggregate for obtaining the best workability of concrete is round. Round aggregates offer improved workability, better cohesion, reduced water demand, improved pumpability, reduced bleeding and segregation, and an improved finish. However, it is important to note that the selection of aggregate shape should also consider other factors such as grading, size, and availability to ensure the overall quality and performance of the concrete.