A diffusion-reaction model for sulfate ion corrosion in multi-phase concrete immersed in ionic solution

A diffusion-reaction model is developed in this paper to investigate the corrosion of sulfate (SO42-) ions to a concrete structure immersed in the surrounding solution with multi-ions, such as calcium (Ca2+), sodium (Na+), hydroxyl (OH-), SO42-, silicate (SiO(OH)(3)(-)) and aluminate (Al(OH)(4)(-)) ions. The described approach enables the complete consideration of the dissolution and precipitation reactions between the hydrated products and the mobile ions with three phases involved, such as cement paste, aggregates, and interfacial transition zone (ITZ). The governing equations are achieved by the conservation law of mass and the Maxwell equation, and the constitutive relations are achieved by the second law of thermodynamics. Moreover, the computational region covers both the concrete structure and its surrounding solution instead of the concrete structure only. After validation with the experimental results in the open literature, critical parameters of the numerical model developed are recognized and established. The results reveal that the spatial and temporal evolutions of the ion concentrations and the amounts of the hydrated products are significantly affected by the corrosion time, the external solution concentration, the aggregate fraction and the electric potential applied. However, the diffusion constant ratio between ITZ and cement paste DITZ/DCP contributes minimally to the ion concentration distribution when ranging from 1 to 4. Furthermore, an abrupt variation is found for the ion concentration at the concrete-solution interface, indicating the critical role of the surrounding solution domain. The present model will provide theoretical guidance in the design and optimization of the concrete structure's durability.