Numerical modelling of mechanical deterioration of cement mortar under external sulfate attack

- An analytical model to estimate the flexural strength of composite is developed.
- The proposed method is applied to investigate the external sulfate attack.
- Internal pressure is a critical factor for evaluating the flexural strength.
- An empirical model is proposed to estimate the degradation of flexural strength.

An integrated numerical method is developed to model the deterioration of mechanical properties of cement mortar under external sulfate attack (ESA). The proposed method is module-oriented, which includes three modules, i.e. an ionic diffusion module, a chemical reaction module and a mechanical module. In the mechanical module, an analytical model is developed for evaluating the variation of flexural strength under ESA. The development of internal pressure obtained from numerical computations and the degradation of elastic property estimated using the conventional Mori-Tanaka (MT) method are both considered in the proposed analytical model. Ionic diffusion and chemical reactions during the ESA are solved by the modified Poisson-Nernst-Planck (MPNP) model and chemical thermodynamics in the ionic transportation and the chemical reaction modules respectively. The developed method is validated against the reported ESA experiments in terms of the deterioration of both the elastic modulus and the flexural strength. Furthermore, the key factors governing the mechanical deterioration of cement mortars under ESA are discussed in details, and an estimation model is developed.