What does 'gradation' refer to in relation to aggregates?

Gradation refers to the range of particle sizes present within a sample of aggregates. It essentially describes how the sizes of the particles are distributed across the spectrum, from the smallest to the largest. This distribution is critical as it affects various properties of the material, including its density, compaction ability, and overall performance in construction applications. A well-graded aggregate sample contains a variety of particle sizes that fit together closely, providing stability and strength to the material when used in mixtures such as concrete or asphalt.

Understanding gradation is vital for engineers and technicians because it influences factors like drainage, strength, and durability of the final structure. In contrast, other aspects like uniformity of aggregate shape, moisture content, and density, while important, do not directly define gradation. Hence, the emphasis on the range of particle sizes as the correct understanding of gradation is essential for aggregate testing and its implications in construction practices.