8. Compaction

8.1 Introduction

The final step in the construction of asphalt pavement is the compaction process. Compaction is the process by which the freshly placed asphalt mat is compressed (or densified) to reduce the in-place air voids in the mat. Compaction is accomplished while the mat is still at elevated temperature directly behind the paver. The initial compaction forces are applied by the paver screed during placement, and the final compaction is achieved by rollers of various types. During the compaction process, aggregate particles in the mat are reoriented closer and closer together and locked into place to provide a strong skeleton for the asphalt mixture.

Compaction is the most important factor in the performance of a flexible pavement. Adequate compaction of the mix increases fatigue life, decreases permanent deformation (rutting), reduces oxidation or aging, decreases moisture damage, increases strength and stability, and decreases low-temperature cracking. Research and experience have consistently shown that asphalt mixtures that are constructed with marginal materials but well compacted have a good opportunity to perform acceptably. However, mixtures that use top-quality materials and have great volumetric designs but are poorly compacted are more prone to poor performance. Therefore, it is important for an agency to include a density requirement in their specifications that results in a consistent, optimum air void content after compaction.

Compaction is the most important factor in the performance of a flexible pavement.