Optimization of gradation design of recycled asphalt mixtures based on fractal and Mohr-Coulomb theories

Abstract

Pavement deteriorations of recycled asphalt mixture (RAM) are mainly caused by the variability of reclaimed asphalt pavement (RAP). Moreover, with the increasing amount of RAP, the pavement damages tend to be more serious. Therefore, this research aims to explore an optimized gradation design method to reduce the influence of RAP gradation variability on the performance of RAM. Before that, the RAM gradation segregation with high RAP contents in transportation and construction were evaluated first. For the variability analysis, in accordance with the fractal dimension (FD) in fractal theory, a FD-based gradation segregation model was established to evaluate the variability of RAP gradation. RAP content of 20%, 35% and 50% was analyzed, respectively. It was found that the FD is applicable to evaluate the degree of RAM gradation segregation. The results reveal that the higher the amount of RAP in RAM, the more serious the degree of gradation segregation. To ensure the performance of RAM with high RAP contents, it is necessary to reduce the variability of RAP gradation. Therefore, an optimized gradation design method by increasing the 4.75 mm passing rate of RAM was proposed based on the Mohr-Coulomb theory. After the calibration and validation, the optimized gradation design method was applicable to weakening the influence of RAP variability on RAM. Through performance tests, it was confirmed that the optimized gradation design method of RAM with high RAP contents established in this paper is reasonable and effective.