Silane coupling agent enhances recycle aggregate/asphalt interfacial properties: an experimental and molecular dynamics study

Incorporating recycled concrete aggregate (RCA) into hot mix asphalt mixtures is an effective means of reducing natural sand and gravel extraction and consuming construction solid waste. The surface cement mortar and micro-cracks are the essential differences between RCA and natural aggregates. Therefore, it reduces the adhesion energy between RCA and asphalt interface, resulting in the performance decline of RCA asphalt mixture. To address this issue, this study used a silane coupling agent (SCA) to enhance the adhesion performance at the RCA/asphalt interface. The enhancing mechanism of SCA on the interface was systematically explored in terms of macroscopic performance, micro-interface structure, and nano-interfacial interactions. The macro-experimental results indicated that the performance of RCA asphalt mixes was significantly improved after modification of RCA with SCA solution at 10% concentration. The microscopic test results showed that the hydrolysis products of SCA could chemically adsorb on the surface of RCA to form a dense coupling layer, thereby fixing the interface structural defects. The molecular dynamics results show that SCA can form strong binding energy with the RCA surface mortar through interaction such as Si-O-Si bonds, stable ionic bonds, and hydrogen bonds, and it also has good compatibility with the asphalt layer. In conclusion, SCA can effectively enhance the performance of RCA asphalt mixtures, especially addressing the issue of poor adhesion between RCA surface mortar and asphalt. This study provides theoretical and experimental support for the application of SCA in RCA asphalt mixtures.