Modeling of concrete under external sulfate attack considering the effect of multiple chemical reactions

Once sulfate ions enter a concrete structure, they can react with multiple aluminate phases within the concrete to form ettringite, which eventually leads to swelling and cracking of the structure. To reveal the mechanism of external sulfate attack (ESA), a fully coupled nonlinear constitutive model is developed for transient diffusion-reaction-deformation response of concrete exposed to sulfate environment, by introducing the concentration of sulfate diffusion and the extents of multiple sulfate reactions as independent variables to characterize their respective contributions to free energy and volume expansion. In addition, a structural damage function is incorporated to measure the effect of ESA on elastic constants and diffusion coefficient of concrete. Specially, multiple reaction kinetics equations are established to satisfy the dissipation inequality, which depend not only on the concentrations of the species involved, but also on the stress. The model is then validated by comparing with the experimental results of one-dimensional sulfate attack, and numerical examples are used to illustrate the competing mechanisms between multiple reaction pathways and the interaction between chemical reactions and mechanical loading.