Modelling non-isothermal chloride ingress in unsaturated cement-based materials

Abstract

The realistic environments for engineering practices are diverse, where the temperature, relative humidity, and surface ionic concentrations often experience seasonal variations. The accurate evaluation of the multi-species transportation is crucial in terms of durability assessment of cement-based materials. In this work, an improved moisture transportation model is developed, which takes the influences of the changes in relative humidity, temperature and microstructure into account. The moisture transportation model is coupled with the Poisson-Nernst-Planck model to study the chloride ingress problems. To model the chloride binding effect, both the pre-designed chloride binding isotherm and the thermodynamic modelling method are implemented. In the thermodynamic method, the physical and chemical binding of chloride are modelled in details, and coupled with other simultaneous reactions so as to model the variations of the microstructure. The proposed method is validated against a variety of reported experiments and a long-term field study. The Numerical modelling demonstrates the effectiveness of the improved moisture transportation model and the significance of using the thermodynamic modelling method for long-term durability assessments.