Recent research development on gas permeability of cement-based materials

The involved flow mechanisms, the experimental methods and the prediction models for the gas permeability of cement-based materials were reviewed. The gas flow mechanisms in pores include the viscous flow, boundary slip and Knudsen diffusion. The experimental methods include the constant pressure flow method, variable pressure flow method and variable pressure method. The microstructure of materials has impact on the gas permeability through the pore structure and pore saturation. On the basis of available literature research, it is found that the contribution of Knudsen diffusion to the global gas flow is not clear in pores on nano-scale so that the prediction models of permeability has not enough basis. The constant pressure flow method is proved to be the most reliable experimental method and the validity of other methods should be tested against this method. The key parameters of pore structure for gas permeability are porosity and characteristic size of gas flow, and the relevant prediction models apply better to cement pastes than to mortars and concretes. The impact of pore saturation on gas permeability can be described by Van-Genuchten-Mualem model but the regressed parameters from literature are scattered. © 2015, Chinese Ceramic Society. All right reserved.