In the context of aggregate testing, what does the term 'gradation' refer to?

Gradation refers to the size distribution of the particles within an aggregate sample. It is a crucial factor in determining the suitability of the aggregate for various construction applications. Proper gradation ensures that the mixture of different size particles can fill voids effectively, providing strength and stability to the final product, whether it be concrete, asphalt, or other materials.

Assessing the gradation allows engineers and inspectors to evaluate how well an aggregate can achieve compaction and its overall performance characteristics, such as workability and durability. A well-graded aggregate promotes better interlock and can lead to optimized material performance, which is essential in construction practices.

In contrast, the other options pertain to different aspects of aggregate characteristics. The chemical composition refers to the minerals and elements present in the aggregate, which affects properties like reactivity and strength. The moisture content relates to the amount of water present in the aggregate sample, influencing its weight and overall behavior in mixtures. The shape of aggregate particles can impact the workability and stability of mixtures but does not define gradation. Thus, the correct understanding of gradation is fundamentally about the size distribution of the particles present in the aggregate.