Modelling of water vapour sorption hysteresis of cement-based materials based on pore size distribution

The purpose of this paper is to develop a model for predicting water vapour sorption hysteresis of cement-based materials. The sorption hysteresis was modelled based on the pore size distribution (PSD) and the pore network. The PSD of gel and capillary pores was predicted from the adsorption isotherm. The results indicated that the distribution had two peaks at 3.8 nm and 11 nm of the pore diameters, referring to gel and small capillary pores, respectively. The predicted ratio of gel water to evaporable interlayer water was not a constant, but decreased with an increasing hydration degree. When RH was below 0.25, the predicted sorption hysteresis was solely influenced by the hysteresis of water in interlayer spaces and minor hydrates. The hysteresis in gel pores, small and large capillary pores influenced the shape of desorption isotherms within the RH ranges of 0.25-0.85, 0.35-0.98 and 0.4-1, respectively.