Which factor is crucial for the compaction of HMA?

The temperature of the material is a crucial factor in the compaction of Hot Mix Asphalt (HMA) because it directly affects the workability of the mix. When the HMA is placed at the proper temperature, the asphalt binder remains sufficiently fluid, allowing the aggregate particles to shift and orient themselves during the compaction process. This fluidity is essential to achieve adequate densification and to minimize the porosity of the finished pavement.

If the temperature is too low, the binder becomes too stiff, leading to inadequate compaction, which can result in increased air voids within the mix. Conversely, if the temperature is too high, the binder can become overly fluid, compromising the performance of the mix once it cools and hardens. The right temperature range not only assists in achieving optimal density but also enhances the overall durability and longevity of the asphalt pavement.

The type of asphalt binder, percentage of voids, and duration of rolling are also significant factors in the compaction process but without the right temperature, achieving ideal conditions for those factors is nearly impossible. Proper temperature management ensures that the mix is both workable and capable of achieving the desired density.