Study on frost resistance of EPS concrete based on EPS beads wrapping modification

Expanded polystyrene (EPS) concrete is an ideal low carbon green building material, but the frost resistance is weak in natural environment, which hinders the popularization of EPS concrete. In this study, magnesium phosphate cement (MPC), ultra-high performance concrete (UHPC), and waterborne polyurethane (WPU) were used to wrap the surface of EPS beads and enhance its concrete performance. The frost resistance durability of four groups of EPS concrete was studied, the uniaxial compression tests of concrete after freezing and thawing were conducted, the results show that: the freeze thaw damage law of EPS concrete is different from ordinary concrete, the standard of freeze-thaw failure of EPS concrete is the sudden increase of dynamic elastic modulus but not continues decreasing, the mass of EPS concrete increases but not decreases; concrete with EPS beads wrapped by UHPC and WPU has good frost resistance, the frost resistance level has been increased by 100 levels and the service life increased by 60% than that of EPS beads unwrapped, the strength-degradation is much slower than that of concrete without wrapped; after freeze-thaw failure, the cracks and the interface transition zone (ITZ) gap of concrete with EPS beads wrapped is smaller than unwrapped, the macro phenomenon of freeze-thaw failure is explained from the micro level, based on macro and micro test results, the degradation mechanism of concrete with EPS wrapped and unwrapped under the action of freezing-thawing cycles are discussed. Beside, the stress-strain curves of EPS concrete after freeze-thaw attenuation were studied, the attenuation of concrete with EPS beads wrapped with WPU and UHPC is not serious as the concrete with EPS unwrapped, the proposed stress-strain model is in good agreement with the experimental results, which can provide a reference for evaluating the mechanical properties of EPS concrete after freeze-thaw. Finally, it is suggested to use linear segment and curve segment to describe the attenuation trend of relative dynamic elastic modulus, the fitted model is in good agreement with the experimental results, it can provides a reference for the study of freeze-thaw mechanical properties and the prediction of freeze-thaw cycle of this kind of concrete.