What does the term "gradation" refer to in aggregate analysis?

Gradation refers specifically to the particle size distribution of aggregates, which indicates the range and proportions of different sized particles within a sample. Understanding gradation is crucial since it affects the strength, workability, and stability of concrete and asphalt mixtures. A well-graded aggregate will have a range of sizes that helps fill the voids between larger particles with smaller ones, ensuring a denser and more robust mixture. This concept is essential in construction, as proper gradation can lead to improved performance characteristics in the final product.

The other options, while related to aggregate properties, do not directly address the specific meaning of gradation: uniformity of color pertains more to aesthetic properties, moisture content relates to how much water is present in the aggregates affecting workability, and hardness refers to the strength and durability of the material rather than the size distribution. Therefore, recognizing gradation as the primary focus for aggregate analysis underlines its significance in materials engineering and construction practices.