Concrete workability at constant water content — influence of aggregate shape For the same water content and grading, which aggregate shape generally gives the best workability (highest slump/flow) in concrete?

Introduction / Context:
Workability is the ease with which concrete can be mixed, placed, consolidated, and finished without segregation. Aggregate characteristics strongly influence workability at a given water content because they affect internal friction, paste demand, and packing density.

Given Data / Assumptions:

• Water content and grading are held constant.
• Only particle shape/texture varies among options.
• No chemical admixtures are considered.

Concept / Approach:
Rounded aggregates have lower specific surface area and smoother textures than angular, flaky, or elongated particles. This reduces paste demand and internal interlocking, resulting in reduced friction during movement. Consequently, for the same water and cement content, rounded particles produce higher slump (better workability). Flaky/elongated or angular aggregates increase interlock, raise surface area, and therefore demand more paste or water for the same workability.

Step-by-Step Solution:

Verification / Alternative check:
Empirical slump tests demonstrate higher slump for river gravels at equal water content compared to crushed stone mixes; finishing effort is also reduced due to smoother textures.

Why Other Options Are Wrong:

• Irregular/angular: higher interlock and surface area, lower workability.
• Flaky: worst for workability; may cause segregation and poor finish.
• None: incorrect because rounded is clearly best under stated conditions.

Common Pitfalls:
Ignoring grading and fines content, which also affect workability; assuming better workability always means better strength (not necessarily true).

Final Answer:
Rounded aggregates (river gravel)