Which type of aggregate is typically used in a concrete mix?

The use of natural sand and gravel or crushed stone in a concrete mix is essential because these materials serve as the primary aggregates that provide concrete with its strength, durability, and volume. Natural aggregates are commonly sourced from quarries, rivers, or lakes and are integral in creating a stable matrix that supports the cement paste once it hydrates and hardens.

Natural sand and gravel or crushed stone ensure that the concrete mix has the right balance of fine and coarse materials, which is crucial for achieving the desired workability and performance characteristics. The variations in size and shape of these aggregates also influence the density and mechanical properties of the hardened concrete.

Other options, like using only synthetic materials or focusing solely on fine aggregates, do not provide the robust framework necessary for concrete, while suggesting that aggregates are not required contradicts the fundamental composition of concrete itself, which relies on these materials for structural integrity.