EVA/KH560 synergistically modified recycled concrete mechanical properties - Experiment and molecular dynamics simulations

Abstract

Considering the long-term working performance of recycled concrete (RC) members, there is a need to compensate for the performance deficiencies of RC. In this study, the mechanical properties of RC were improved by two different modification methods, and the reinforcement effects of RC modified by Silane Coupling Agent (KH560)/Ethylene vinyl acetate copolymer (EVA) and RC modified by EVA alone were compared and analyzed. The effects of separate modification and co-modification on RC were analyzed through multi-scale methods in terms of macro-mechanical properties, microstructure, chemical composition and molecular mechanism, respectively. The results of macroscopic mechanical experiments showed that the compressive and shear strength of EVA/KH560 synergistic modification is higher than that of EVA alone. Scanning Electron Microscope (SEM) data showed that the surface density of the old and new concrete interfaces was higher under EVA/KH560 co-modification. X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) data showed that more cement gel will be produced under EVA/KH560 synergistic modification. Molecular dynamics (MD) simulations show that EVA single modification can produce hydrogen and ionic bonds at the interface of old and new concrete, while EVA/KH560 synergistic modification not only produces them, but also forms a stable Si-O-Si chemical bond.