Multiphysics meshless method for mesoscopic concrete cracking under frost action

Abstract

Frost cracking in the interior part of concrete in the cold region has a great influence in the concrete durability and the safety of hydraulic structure. In this paper, mesoscopic concrete is investigated taking into consideration the effect of pore water phase change resulting from heat exchange under frost action in the framework of Material Point Method (MPM). For meso-structure in the real concrete consisting of mortar, interfacial transition zones (ITZ) and aggregates, ITZ-embedded method is proposed to reproduce the discontinuity of heat exchange and mechanical simulations in MPM. The relationships between phase transition and stress evolution is incorporated into the constitutive model in MPM by introducing the parameter, liquid phase fraction, to realize the simulations of concrete behavior under frost action. Firstly, the verifications of thermo-mechanical coupling and the phase transition of pore water considering evolution of pore pressure are presented respectively in two homogeneous examples compared to the literature results. A simple concrete model with a polygon aggregate is used to present the rationality of ITZ-embedded method in reproducing the heat exchange discontinuity role of ITZ in the internal part of concrete. The following investigation is conducted in a square concrete model, and the effect of different influencing factors on frost cracking morphologies is systematically discussed for studying the comprehensive mechanism of concrete damage and phase transition under frost action. The aggregate percentage Pagg, heat convective coefficient of ITZ Qh and ice plugging point αp obviously influence length, depth and density of frost cracks in the interior part of the concrete. The results demonstrate the numerical feasibility of multi-field coupling MPM method in the mesoscopic research of concrete initiation and propagation under frost action.