Why is cleanliness considered a property of aggregate?

• A. To increase color uniformity.
• B. To improve abrasion resistance.
• C. To measure moisture absorption only.
• D. To ensure free from deleterious materials that could reduce adhesion and performance.

Answer: (D)

Cleanliness of aggregate means removing contaminants that can interfere with how well the asphalt binder adheres to the rock and how the mix performs over time. When the aggregate carries deleterious materials such as clay, silt, shale, organic matter, coal, or lignite, these substances can weaken the bond between the binder and the aggregate, trap moisture, and promote stripping. That reduces durability and performance of the pavement, especially under traffic and weather cycles. Ensuring the aggregate is free from these contaminants helps maximize adhesion and long-term performance.

Color uniformity isn’t a factor in adhesion or durability, so it isn’t the goal of cleanliness. Abrasion resistance relates to the hardness and shape of the aggregate, not the presence of contaminants. Measuring moisture absorption is a separate property and isn’t what cleanliness is about.