Predicting water permeability and relative gas permeability of unsaturated cement-based material from hydraulic diffusivity

In this paper, unsaturated water permeability and relative gas permeability of cement-based materials are predicted indirectly. First, the theoretical relationship between water permeability and hydraulic diffusivity is thoroughly analyzed, which leads to a new restriction on capacity function, the first derivative of water retention curve (WRC) model. To comply with this restriction, a new WRC model is then proposed, based on which unsaturated water permeability can be easily estimated from hydraulic diffusivity. Furthermore, the relative gas permeability is evaluated from relative water permeability through their relationship. The proposed WRC model is validated with measured water retention data of various cement-based materials. Moreover, predicted relative gas permeability agrees with reported testing results very well. Additionally, the influence of fitting parameters of the WRC model and shape parameter, which determines the shape of hydraulic diffusivity, is investigated. It is found that they have rather limited effects on relative water and gas permeability.