When should an asphalt mixture be compacted?

Compacting an asphalt mixture while it is still hot and workable is crucial for achieving the desired density and strength in the finished pavement. Asphalt mixtures need to be compacted before they cool down significantly, as the workability of the mix decreases as it cools. When the mixture is hot, the asphalt binder is more fluid, allowing for better manipulation of the aggregates, which helps eliminate air voids and achieves required compaction.

Compaction at the correct temperature ensures that the aggregates interlock properly, creating a stable and durable pavement structure. If compaction occurs after the mixture has cooled, the asphalt binder becomes too stiff to adequately bond the aggregates, potentially leading to a weaker pavement that's susceptible to cracking and deterioration over time.

Other options suggest compaction should occur when the mixture is either cooling down, before mixing, or at room temperature, which are all not ideal for achieving effective density and strength in the asphalt. Thus, the most effective timing for compaction is indeed while the asphalt mixture is still hot and workable.