Study on the properties of EPS composite concrete enhanced by silane coupling agent: Experiment and molecular simulation

Due to the organic porous nature of expanded polystyrene (EPS) foam concrete, the bond strength between it and cement is weak, leading to a weakened interface transition zone and low strength. However, most studies on this issue have been limited to phenomenological approaches, neglecting the role of atomic-level mechanisms. Therefore, this study combines macroscopic and microscopic experiments, as well as molecular dynamics, to investigate the mechanisms of a silane coupling agent (SCA) enhancing the interface performance of EPS-concrete. Macroscopic mechanical tests demonstrate that SCA can improve the compressive and flexural strength of EPS concrete. Combined with the test and analysis of variance, the addition of 9% SCA has the best enhancement effect on the mechanical properties of EPS composite concrete. The compressive strength increased by 24% and 17% on day 7 and day 28, respectively, and the flexural strength increased by 39% and 16% on day 7 and day 28, respectively. At the microscopic scale, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are used to analyze the effects of SCA on the microstructure and functional groups of the EPS-cement interface. Microscopic analysis shows that SCA optimizes the composition of cementitious products, effectively repairing and improving the defects of the EPS-cement interface. Ultimately, molecular dynamics simulations and analysis are conducted on two interface models, one including and one excluding SCA, at the nanoscale. The results indicate that SCA enhances the hydrogen bonding, H-Ca ion bonding, and interface interactions between EPS-C-S-H, resulting in a tighter and more stable bond between the two phases, effectively enhancing the mechanical properties of EPS composite concrete. This study provides valuable insights into the strengthening mechanisms of EPS composite concrete and proposes a promising improvement method.