Investigation on the properties of aggregate-mastic interfacial transition zones (ITZs) in asphalt mixture containing recycled concrete aggregate

Understanding and characterizing the properties of recycled concrete aggregate asphalt mixture (RCAM) is a challenge because there are more complicated aggregate-asphalt mastic interfacial transition zones (ITZs) in RCAM than that in conventional asphalt mixture. In this study, the nanoindentation test, backscattered electron image-analysis (BSE), and energy dispersive spectroscopy (EDS) were selected to identify and investigate the various ITZs in RCAM. According to the nanoindentation analysis, the thickness and elastic modulus of the ITZs change with the different components in recycled concrete aggregate (RCA), and ITZs adjacent to the porous components (i.e., cement mortar and brick) have a greater thickness and a lower elastic modulus. Based on the analysis of BSE images, ITZs of recycled granite and natural limestone are found to have a denser structure and more aggregate particles when compared with cement mortar and brick. The count variations along the EDS scanning line reveals that the element amount of interfacial transition zone is between the coarse aggregate and asphalt mastic. In addition, the increase in the elastic modulus of ITZ indicates a reduced exfoliation degree of asphalt. The aggregate compositions and aggregate morphology can have effects on the ITZ and adhesion between RCA and asphalt. The test results obtained in this study could support a better understanding of ITZs in RCAM and further mechanical modeling research. (C) 2020 Elsevier Ltd. All rights reserved.