Multiscale Numerical Simulation of Expansion Response of Hardened Cement Paste at Dormant Period of External Sulfate Attack

Expansion of concrete caused by external sulfate attack (ESA) is a multiscale chemomechanical response, mainly including internal stress evolution at the dormant period and significant cracking expansion for a detrimental duration in hardened cement paste (HCP). The internal stress generated in the dormant period of ESA can result in the microcracking of HCP and further significant volume expansion of concrete, which can reduce the durability of concrete structures. Based on the ESA-induced expansion mechanism, a multiscale model is developed to describe the expansion response of HCP in the dormant period of ESA. In this model, a saturated and homogeneous HCP and a representative volume element (RVE), which is composed of a pore and nearby cement paste, are regarded as macroscopic and microscopic objects, respectively. By using Fick's law and reaction kinetics, a diffusion-reaction model is proposed to simulate the macroscopic sulfate diffusion in HCP and microscopic chemical reaction to produce ettringite in RVE. According to the crystallization pressure theory and continuum mechanics, some mechanical models are constructed to investigate the microscopic mechanical response caused by the supersaturation of ettringite in RVE and its induced macroscopic mechanical response in HCP. Taking a HCP cylinder under different sulfate exposures as an example, a numerical simulation is performed to investigate its expansion response in the dormant period of ESA.