Which mineral resource is commonly used as the coarse aggregate in concrete?

• A. Limestone
• B. Clay
• C. Sand
• D. Gravel

Answer: (C)

Coarse aggregate is the larger-particle portion of concrete that provides the load-bearing skeleton and helps transfer stresses efficiently. In most mixes, coarse aggregate is gravel or crushed stone because their size and angular shape create a stable, interlocking framework that resists cracking and improves strength. Sand, by contrast, is the fine aggregate: its small particles fill the voids between the larger pieces and help with workability and density. Clay isn’t suitable as coarse aggregate because its fine particles and high plasticity can lead to poor strength and dimensional instability. Limestone can be used as coarse aggregate if crushed to appropriate sizes, but among common choices, gravel best fits the role of coarse aggregate.