Investigation on high-temperature stability of recycled aggregate asphalt mixture based on microstructural characteristics

Construction and demolition wastes (CDW) are a complex mixture containing cement mortar and mineral aggregate. Recycled aggregate (RA) is a production of CDW after the crushing process. The presented study efforts mainly focus on the influence of RA content on the high-temperature stability of RAAM, but the analysis of the RA morphology effect is still lacking. Giving microstructural insight into the impacts of RA on the high-temperature failure of RAAM is beneficial in promoting the utilization of CDW in pavement engineering. In this paper, RAAM with different RA contents was firstly designed by the Marshall method, and the mechanical properties of RAAM at high temperatures were investigated using a uniaxial penetration test (UPT). Then, high-precision spatial models of RA particles were reconstructed based on CT images, and four indicators were introduced to quantify the RA macro shape and micro-morphology through spatial model data. Furthermore, the relationships between shear resistance of RAAM and RA morphology were established according to UPT test results and spatial model indicators. Finally, an X-ray CT saner was employed to track the evolution of microstructure damage before and after compressive deformation. Results show that the attached cement mortar is the primary resource of pores in RA particles, and pores volume and number in RA particles are random. Compared with natural aggregate, RA particle has more complicated morphological characteristics due to its porous cement mortar. The complex morphology and attached porous cement mortar of RA particles significantly affect the asphalt mixture high-temperature stability. Using RA particles causes more structural failures in RAAM during high-temperature deformation, and the damage inside cement mortar and interface with asphalt mortar are the primary resources of failure. This study shows that RA with content less than 50% can be an effective alternative for natural aggregate when considering the high-temperature stability of RAAM.