Creep of Calcium Hydroxide from Stress-induced Dissolution: Kinetic Monte Carlo Simulations

Mechanical stress can promote dissolution of calcium hydroxide in concrete; combined with carbonation, this may accelerate creep, damage, and corrosion. The existing microstructural simulators struggle with stress-induced dissolution processes, because of their strong chemo-mechanical coupling. This article presents results from recent Kinetic Monte Carlo simulations of dissolution and precipitation of solid phases, described as mechanically interacting particles. Chemo-mechanical coupling is embedded in the chemical reaction rates, featuring both chemical potentials of ions in solution and mechanical stress in the solid. The simulations are applied to a calcium hydroxide crystal, at chemical equilibrium in a solution of its ions but compressed between two stiff platens. Depending on the applied stress, the crystal partially dissolves and recrystallizes, producing an apparent viscoplastic deformation process. The simulation results inform mathematical creep laws with a size effect, as the strain rate depends on the crystal size. Upper-bound creep moduli for typical calcium hydroxide crystals in concrete are estimated as 237 to 2370 GPa, and carbonation would likely reduce them. This indicates that stress-induced dissolution of calcium hydroxide may underpin the nonlinear acceleration of concrete creep during carbonation. An experimental strategy to assess this mechanism is finally proposed, leveraging the size effect argument.