Influence of different aged and virgin asphalt fusion efficiency on fatigue performance, chemical structure and microscopic characteristics of recycled asphalt

To quantitatively analyze the fusion efficiency of aged and virgin asphalt and its influence on the performance and structure of recycled asphalt, 5 kinds of recycled asphalt, prepared with 5 distinct RAP (Reclaimed Asphalt Pavement) contents commonly used in engineering, were selected as research subjects. Gel permeation chromatography (GPC) test was utilized to examine the fusion efficiency of recycled asphalt with 5 common RAP material ratios in engineering (30 %, 40 % and 50 % RAP contents were used in the middle layer, and 70 % and 80 % RAP contents were used in the upper layer). The Large Molecular Size (LMS) content from GPC was introduced as a key indicator, providing a quantitative and molecular-level characterization method for fusion efficiency, which is more fundamental and precise than traditional empirical approaches. The effects of different fusion efficiencies on the fatigue performance, chemical structure and microscopic characteristics of recycled asphalt were investigated by Dynamic Shear Rheometer (DSR), Fourier transform infrared spectroscopy (FTIR) and Atomic Force Microscopy (AFM). The results showed that when the content of virgin asphalt and rejuvenator was constant, with the increase of RAP content from 30 % to 80 %, the fusion efficiency of recycled asphalt gradually decreased. When the RAP content was 30 %, the fusion efficiency of recycled base asphalt in the middle layer achieved an optimal fusion efficiency of 83.1 %. When the RAP content was 70 %, the fusion efficiency of recycled SBS modified asphalt in the upper layer reached its best fusion efficiency of 63.5 %. FTIR results showed that the carbonyl index (CI) and sulfoxide index (SI) of the recycled asphalt approached those of the virgin asphalt as fusion efficiency increased. DSR results revealed that higher fusion efficiency contributes to enhanced fatigue life of recycled asphalt. AFM results confirmed that improving fusion efficiency between aged and virgin asphalt leads to the recovery and improvement of micro-adhesion force. It is worth noting that the experimental results indicate a strong correlation between the microscopic properties of recycled asphalt and its fatigue life. Specifically, as the microscopic adhesion increases, the loss modulus decreases gradually, which provides a new perspective for analyzing the variations in the fatigue life of recycled asphalt.