Describe the concept of "aggregate grading."

Aggregate grading refers to the distribution of particle sizes within an aggregate sample. This concept is crucial in mixture design because the gradation affects the performance and workability of the final concrete or asphalt mixture. An optimal grading ensures that there are appropriately sized particles to fill voids, reduce the amount of cement or binder needed, and achieve the desired strength and durability of the final product.

Good aggregate grading can lead to improved compaction and reduced segregation, which are vital for the stability and longevity of pavement and concrete structures. It involves not just the sizes of the particles present but also the proportions of those sizes, which can influence properties such as water demand, workability, and the void content of the mix. Proper understanding and control of aggregate grading are essential for achieving quality in construction materials.