What is the optimal moisture condition for aggregates before mixing?

The optimal moisture condition for aggregates before mixing is the surface-dry condition. This state is ideal because it strikes a balance between having enough moisture to aid in the proper mixing and hydration of the binder, while also ensuring that the aggregates themselves do not hold excess water that would interfere with achieving the desired mix properties.

When aggregates are in a surface-dry condition, the moisture is present primarily on the surface, which allows for effective bonding with the asphalt or cementitious materials used in the mixture. This condition helps prevent issues such as segregation and ensures that the aggregates can effectively contribute to the overall strength and durability of the final product.

In contrast, aggregates that are in a completely saturated condition can lead to difficulties in mixing, as excess water can displace the binder and create inconsistencies in the mixture. If the aggregates are wet with excess water, it can promote segregation and reduce the cohesion needed for an effective mix. Finally, a dry condition with fine dust can compromise the bond between the aggregates and the binder, leading to weaker mixtures and increased susceptibility to damage. Thus, the surface-dry condition is preferred for achieving optimal performance in mixed materials.