A Dual-Permeability Approach to Study Anomalous Moisture Transport Properties of Cement-Based Materials

Anomalous moisture transport in cement-based materials is often reported in the literature, but the conventional single-porosity moisture transport models generally fail to provide accurate simulation results. Previous studies suggested that the anomalous moisture transport could be caused by different moisture transport velocity in large and small pores. Based on this concept, the present study proposes a continuous dual-permeability model for cement-based material. The proposed model includes the transport contribution of both liquid water and water vapor, which are governed by liquid advection and vapor diffusion, respectively. We explicitly consider that moisture transport in the large pore region is faster than the small pore region. The volumetric fraction of each region is determined when fitting the measured sorption isotherms by using a bimodal equation. The validation with experimental data shows that the dual-permeability model can well simulate both the normal and the anomalous moisture transport. The applicability of the proposed model implies that the dual-porosity property could be one of reasons that cause anomalous moisture transport in cementitious materials. In addition, results show that vapor diffusion can be neglected for moisture transport in both porosities at high relative humidity (RH), while at low RH, vapor diffusion must be considered.