Study on the optimal compaction effort of asphalt mixture based on the distribution of contact points of coarse aggregates

Compaction effort significantly influences the skeleton characteristics of asphalt mixture, and mixtures of different skeletons show widely varying demands for compaction effort. Based on a digital image processing technique, this study characterises the skeleton characteristics of asphalt mixture under various cycles of compaction repetitions by introducing coarse aggregate contact points, aggregate inclination and some other indexes. A meso-macro perspective is taken to analyse the variation in the aggregate skeleton of asphalt mixtures during compaction. Furthermore, this study conducts a non-standard rutting test to verify the high-temperature stability of the material, and establishes a correlation between the compaction effort and the stability parameter of the skeleton of an asphalt mixture. As indicated by the test results, gradation can determine the value of asphalt mixture’s CEP25 (compaction energy parameters under 25 compaction repetitions) and the growth trend of CEP (compaction energy parameters). When compaction effort exceeds the bearing capacity limit of the skeleton, the reduction of coarse aggregate particles, the decrease in the number of contact points and the fluctuation in aggregate inclination are observed. With an increase in compaction repetitions, average coordination number n¯ and contact points Na first increase and then decrease, but the compaction repetitions to the peak values are different. According to the results of a non-standard rutting test, an increase in compactness can strengthen the rutting resistance of asphalt mixture, but this conclusion does not suitable for skeleton void-type mixtures. The established CEP calculation model can reflect the influence of gradation on compaction effort, and the compaction effort calculated from contact point number Na has a fairly good correlation with the test results.