The synergistic strengthening effect of silane coupling agent on the interface between PVA/EPS and cement: experiment and molecular simulation

Expanded polystyrene (EPS) concrete is a new type of green building material. To make it more widely used, in this work, polyvinyl alcohol (PVA) fiber and silane coupling agent (SCA) were used to toughen it. The synergistic enhancement mechanism of SCA on PVA/cement and EPS/cement interfaces was systematically investigated from macro mechanical properties, microstructure characteristics, and nano interface interaction. Firstly, based on the mechanical property test, it was found that the introduction of SCA and PVA fibers can significantly improve the flexural strength of EPS composite concrete at 7 and 28 days, followed by the compressive strength. Secondly, the cut pieces of corresponding composite concrete were observed by electron microscope. It was found that SCA made the two interfaces more closely, and its bonding effect at the micro interface was described. Finally, molecular dynamics (MD) was used to model PVA/C-S-H and EPS/C-S-H with or without SCA. Then, the local structure, dynamic performance, and binding energy of the interface were calculated and analyzed. The analysis results showed that SCA reduced the interface effect and enhanced the interface hydrogen bonding, van der Waals interaction, Ca-H coordination bond and stability. Thus, the interfacial adhesion energy was improved, and the weak interfacial bonding between organic polymers (PVA, EPS) and inorganic silicates (C-S-H) was enhanced.