Porosity development in a thermo-hygral finite element model for cementitious materials

A numerical model for the thermo-hygral (TH) behaviour of cementitious materials is presented. The model includes a new approach to the evaluation of porosity during hydration in which a colloid model and stoichiometry are used to evaluate the volume of bound and unbound water forms. The advantage of the proposed porosity function is that it accounts for different cement types and concrete mixes and it gives a porosity evolution consistent with the moisture mass balance equation. Sink/source terms are introduced for the capillary water that account for the moisture entering/exiting the gel pores and the aggregate, whilst the standard capillary curve is modified to account for temperature and changing porosity with hydration. The numerical model considers as the primary variables the water degree of saturation of capillary pores and the temperature and is validated using several drying experiments. The results are generally in good agreement with experimental measurements.