Research on the effects of gradation composition on skeletal contact characteristics and homogeneity of asphalt mixtures

Abstract Conventional asphalt mixture gradation design is based on macroscopic volumetric and mechanical properties, without adequate microstructural evaluation frameworks. Therefore, an image-based analytical approach for characterizing the aggregate skeleton in asphalt mixtures was proposed. The coarse aggregate phase was first isolated using threshold-based image segmentation algorithms, generating binary representations of particle distribution patterns. Then contact analysis was performed across a range of thresholds (0.5–2.0 mm), with 1 mm identified as the critical value for defining effective inter-aggregate contacts in the mixture. Subsequently, skeletal parameter analysis was conducted across varying specimen heights, with evaluation parameters standardized to the 6–14 cm zone to ensure representative characterization. Comparative analysis of three distinct gradations (coarse, intermediate, fine) revealed that the intermediate gradation not only developed the most favorable skeletal microstructure. And the dynamic stability of Type-B graded asphalt mixture is 38% higher than that of Type-A and 23% higher than that of Type-C. Morever, a significant correlation was observed between high-temperature performance (dynamic stability and penetration strength) and skeleton parameters, with a correlation coefficient greater than 0.9. This study proposes an innovative evaluation framework that enhances the current mix design process of asphalt mixtures by integrating performance-based parameters.