Which factor is critical in determining the compressive strength of concrete?

The compressive strength of concrete is largely influenced by the proportion and quality of aggregate used in the mix. Aggregates are critical components that contribute to the overall density, strength, and durability of concrete. The quality of the aggregates—including their size, gradation, and cleanliness—can directly affect the bonding characteristics with cement paste and influence how effectively the concrete can withstand compressive loads.

When the right proportions of coarse and fine aggregates are used, it helps to achieve an optimal packing density, which can significantly enhance the mechanical properties of concrete. High-quality aggregates that are free from impurities or excessive moisture also allow for better adhesion and a stronger final product.

Other factors, while essential in their own right, do not have the same level of impact on compressive strength as aggregate characteristics. For instance, the type of formwork can affect the shape and finish of the concrete but does not influence the strength the way aggregate quality does. The color of the cement might have aesthetic implications but is not related to compressive strength. Curing time is important for the hydration process of concrete, but without the right aggregate characteristics, even optimal curing can’t compensate for poor strength. Therefore, the proportion and quality of aggregate is a critical factor in determining compressive strength.