Investigating mechanical performance and interface characteristics of cold recycled mixture: Promoting sustainable utilization of reclaimed asphalt pavement

The recycling and sustainable utilization of reclaimed asphalt pavement (RAP) are the key method to improve resource conservation and reduce energy consumption in roadway construction. The cold-recycled technology has been regarded as a promising recycling one because it can achieve mixing at room temperature and high utilization of RAP. Investigating the mechanical mechanism of cold-recycled asphalt mixture (CRAM) is the basis for large-scale application. Thus the splitting tests were carried out to study the influencing law of the material components on the strength performance of CRAM by varying RAP, cement and asphalt content. Then the effects of material component on the strength mechanism were further revealed by the interface characteristics analysis, including void and filler parameters, binder and interface transition zone (ITZ) thickness. The results show that the CRAM with more RAP has a higher splitting strength and the aged asphalt contributes to the reduction of void number around the aggregate interface, indicating a stronger bonding effect with binder. The asphalt mixture has lower void size, void number and porosity than cement mixture, and shows more uniform distribution of binder thickness and lower void distribution difference between the ITZ and the mortar phase, which is conducive to force uniformly and prevent stress concentration within mixture. The above outcomes confirm the effects of strength improvement from RAP and the void increment from cement, and the contents could be reasonably increased for RAP and strictly controlled for cement to ensure strength performance of CRAM while promoting saving energy and environmental protection.