What is the primary reason for using different sizes of aggregates in concrete?

Using different sizes of aggregates in concrete primarily serves to achieve the desired strength and finish of the final product. Aggregates play a crucial role in the concrete mix as they significantly influence the mechanical properties and durability of the concrete.

When various sizes are combined, they can fill the voids between larger particles with smaller ones, resulting in a denser and more compact mixture. This combination allows for better packing efficiency, reducing the amount of air voids and enhancing the overall mechanical properties such as compressive strength and tensile strength. Furthermore, different aggregate sizes also contribute to the workability of the mix, making it easier to place and finish.

Ultimately, the correct choice highlights how the selection of aggregate sizes is fundamentally linked to achieving an optimal balance of strength, durability, and aesthetic attributes in the finished concrete product.