Design and Performance Research on Soft BRA Modified Hot Recycled Asphalt Mixture

To analyze the feasibility of soft buton rock asphalt (BRA) as asphalt rejuvenating agent, and taking AC-20C asphalt mixture as the research object, the mix design and test of modified hot recycled asphalt mixture with five different soft BRA contents (1%–5%) and five different RAP contents (10%–50%) were carried out based on response surface optimization method, so the optimal soft BRA content was determined. Then the pavement performance tests of five kinds of modified hot recycled asphalt mixture with different RAP contents were carried out and compared with common asphalt mixture, so as to determine the suitable RAP content. The results show that the consistency, high-, and low-temperature performance of soft BRA are between those of A-70# matrix asphalt and hard BRA or RAP waste asphalt. The soft BRA has good viscoelasticity and more light components, which can be used as rejuvenating agent. With the increase of soft BRA and RAP content, the optimum oil–stone ratio of modified hot recycled asphalt mixture increases, while the optimum oil–stone ratio of matrix asphalt decreases. The optimal content of soft BRA is recommended to be 3%. Compared with the common asphalt mixture, when the RAP content does not exceed 30%, the mixing of soft BRA can comprehensively improve the high-temperature stability, water stability, low-temperature crack resistance, and impermeability of modified hot recycled asphalt mixture. It is suggested that the suitable content range of RAP is 10%–30%. Therefore, the soft BRA can provide a new economic and green rejuvenating agent for central plant hot-mix asphalt recycling technology.