Effect and mechanism of accelerated carbonization on the adhesion property of asphalt mixture containing recycled concrete aggregate

Abstract

Weak interfacial adhesion between asphalt and recycled concrete aggregate (RCA) poses a significant engineering challenge in asphalt pavements. Accelerated carbonization treatment effectively enhances the performance of RCA by filling microcracks and pores in the mortar on its surface. This study investigated the optimal carbonization time, balancing economic feasibility, using boiling water experiments, pull-off tests, X-ray diffraction, and thermogravimetric analysis. Changes in the micro-morphology of the RCA surface at various carbonization times were observed using scanning electron microscopy. Molecular dynamics simulation was then employed to analyze the mechanism by which accelerated carbonization affects the adhesion properties of asphalt mixtures containing RCA. The results indicate that interfacial adhesion between RCA and asphalt gradually improves with increasing carbonization time. After 48 hours of carbonization, the asphalt adhesion rate increased from 52.7 % to 92.2 %, and the tensile strength rose from 1.13 MPa to 2.85 MPa. As the carbonization reaction progresses, spherical vaterite, acicular aragonite and massive calcite in lump form gradually appear on the RCA surface. Eventually, a calcium carbonate film forms and adheres to the RCA surface, enhancing adhesion properties at the RCA-asphalt interface. At the molecular level, carbonization significantly increased the concentrations of asphaltenes, aromatics, and saturates near the interface. The interaction energies between RCA and asphaltenes, aromatics, saturates, and resins increased by 97.5 %, 51.4 %, 35.7 %, and 6.0 %, respectively. Accelerated carbonization offers a viable solution for incorporating RCA in hot-mix asphalt, contributing to the sustainability of pavement infrastructure.