Multiphysics and Multiscale Modeling of Coupled Transport of Chloride Ions in Concrete

Chloride ions (Cl )-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl from the surface of the concrete towards the reinforcing steel. The accumulation of Cl at the steel-concrete interface could initiate reinforcement corrosion once a threshold Cl concentration is achieved. An accurate numerical model of the Cl transport in concrete is required to predict the corrosion initiation in RC structures. However, existing numerical models lack a representation of the heterogenous concrete microstructure resulting from the varying environmental conditions and the indirect effect of time dependent temperature and relative humidity (RH) on the water adsorption and Cl binding isotherms. In this study, a numerical model is developed to study the coupled transport of Cl with heat, RH and oxygen (O ) into the concrete. The modeling of the concrete microstructure is performed using the Virtual Cement and Concrete Testing Laboratory (VCCTL) code developed by the U.S. National Institute of Standards and Technology (NIST). The concept of equivalent maturation time is utilized to eliminate the limitation of simulating concrete microstructure using VCCTL in specific environmental conditions such as adiabatic. Thus, a time-dependent concrete microstructure, which depends on the hydration reactions coupled with the temperature and RH of the environment, is achieved to study the Cl transport. Additionally, Cl binding isotherms, which are a function of the pH of the concrete pore solution, Cl concentration, and weight fraction of mono-sulfate aluminate (AFm) and calcium-silicate-hydrate (C-S-H), obtained from an experimental study by the same authors are utilized to account for the Cl binding of cement hydration products. The temperature dependent RH diffusion was considered to account for the transport of Cl with moisture transport. The temperature and RH diffusion in the concrete domain, composite theory, and Cl binding and water adsorption isotherms are used in combination, to estimate the ensuing Cl diffusion field within the concrete. The coupled transport process of heat, RH, Cl , and O is implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE) developed by the U.S. Idaho National Laboratory (INL). The model was verified and validated using data from multiple experimental studies with different concrete mixture proportions, curing d