Multiscale Enhancement Mechanisms of EVA on EPS-Cement Composites

Ethylene-vinyl acetate (EVA) lotion can significantly improve the interface problems caused by the physical and chemical differences between expanded polystyrene (EPS) beads and cement, which is one of the reasons why EPS cement composites are widely used in the construction field. However, the research on its problems is often limited to phenomenological engineering methods, ignoring the potential interaction mechanism in atomic structure. Therefore, in this study, the strengthening mechanism of EVA on EPS particle–cement slurry interface was systematically studied from the aspects of macromechanical properties, microstructure characteristics, chemical composition, and molecular structure. In terms of physical test, it was found that the compressive strength and flexural strength of EPS-cement-based materials containing EVA are increased by 19% and 31%, respectively, at 28 days when the content of EPS particles is the same. It was observed through an electron microscope snapshot that EVA makes a uniform and dense interface structure between EPS particles and cement. For chemical tests, EPS particle surface hardening cement was ground into powder and tested by X-ray diffraction and Fourier transform infrared spectrometer. It was comprehensively analyzed that EVA reduced the hydration product Ca(OH)2 and increased calcium silicate hydrate (C-S-H) at the interface. In terms of numerical simulation, through molecular simulation modeling and calculation, it was found that the introduction of EVA can produce more stable hydrogen and ion bonds at the EPS–C-S-H interface, which plays a vital role in reducing the interface effect and increasing the interface binding energy.Practical ApplicationsCement-based materials containing expanded polystyrene beads are considered environmentally friendly, lightweight, and high-strength green building materials widely used in construction projects, such as load-bearing concrete blocks, insulation boards or walls, cladding or structural insulation panels, composite floors, structural insulated panel, pavement base material, geogrid, road barrier, and floating offshore structure. These structures have the advantages of good durability, good thermal insulation, high fire rating, low water absorption, low price, and convenient construction. In order to promote its application in practical engineering, it is necessary to solve the problems of poor adhesion of EPS/cement-based interface and uneven separation and dispersion of EPS particles in EPS cement-based composites. As an effective method, the surface modification of EPS is worth studying. This study discussed the strengthening mechanism of EPS/cement-based interface modified by ethylene-vinyl acetate lotion from multiscale by experiment and numerical simulation. It can provide a reference for preparing more stable, uniform and excellent EPS concrete.