What material most impacts the strength of concrete?

The strength of concrete is significantly influenced by the aggregate used in the mix. Aggregates are the granular components, typically comprised of sand, gravel, or crushed stone, which make up a substantial portion of the concrete's volume. The size, shape, texture, and grading of the aggregate can greatly affect the final strength and durability of the concrete.

Large and well-graded aggregates provide better interlock, enhancing strength, while the quality of the aggregates—such as their cleanliness and hardness—affects the bond with the cement paste. A proper balance of coarse and fine aggregates ensures optimal packing and minimizes voids, leading to a denser and stronger concrete mix.

While cement is crucial for binding the aggregates together, and water is necessary for the hydration process, the characteristics of the aggregates often have the most direct impact on the structural integrity of the final product. Additives can modify certain properties of the concrete, but they are typically used to enhance performance rather than to serve as the primary contributor to strength. Thus, the role of aggregate is central to achieving the desired strength in concrete.