On the relevance of electrochemical diffusion for the modeling of degradation of cementitious materials

Reactive solute transport models have been broadly used over the last years to evaluate the durability of cementitious materials because they provide a mechanistic approach to cope with the complex diffusion–reaction phenomena involved in cement and concrete degradation processes. However, most of the numerical models published in the scientific literature use Fick’s law as the constitutive equation for the diffusive transport of dissolved ions, neglecting the electrochemical constraints imposed by the various ionic fluxes, which conspire against the local electroneutrality of the system. In this work, the relevance of electrochemical diffusion and its impact on the nonlinear coupled phenomena concerned by cement degradation were evaluated, on the basis of its influence on the simulation of deterioration of concrete exposed to weak sulfate solutions. Results obtained show that diffusive approaches based on Fick’s law may not be accurate enough for modeling the degradation of cementitious materials since, for the case considered, when ignored, electrochemical interactions in the diffusion process may lead to the inability of reactive transport models to reproduce key phenomena such as gypsum precipitation near the exposed cement surface.