Application of Imaging Technology to Improve the Laboratory and Field Compaction of HMA (0-5261-1)

Field compaction of asphalt mixtures is an important process that influences performance of asphalt pavements. This study evaluates the relationship between different field compaction patterns and the uniformity of air void distribution in asphalt pavements. A number of projects with different hot mix asphalt (HMA) types were compacted, and cores were taken at different locations from these projects. The X-ray Computed Tomography (X-ray CT) system was used to capture the air void distributions in these cores. The analysis results have revealed that the uniformity of air void distribution is highly related to the compaction pattern and the sequence of using different compaction equipment. More importantly, the efficiency of compaction (reducing air voids) at a point was found to be a function of the location of this point with respect to the roller compactor width. The results in this paper have supported the development of the "Compaction Index (CI)," which quantifies the degree of field compaction. The CI is a function of the number of passes at a point and the position of the point with respect to the compaction roller width. This index was found to correlate reasonably well with percent air voids in the pavement. The CI calculated from field compaction had a good relationship with the slope of the compaction curve obtained from the Superpave gyratory compactor. This relationship offers the opportunity to predict field compactability based on laboratory measurements. The compaction of longitudinal joints was investigated, and recommendations were put forward to improve joint compaction. The air void distributions in gyratory specimens were related to the mixture mechanical properties measured using the Overlay and Hamburg tests.