Determination of relevant parameters influencing gas permeability of mortars

This paper is devoted to the study of the influence of the microstructure of cementitious materials on their gas permeability. For that purpose, cement pastes with four water to cement ratios W/C and mortar specimens with two aggregate volume contents have been cast. On the one hand gas permeability tests with a low pressure device have been carried out on desaturated materials and on the other hand porosity features have been determined by mercury porosimetry measurements. Gas permeability depends upon the mixture parameters (W/C, aggregate volume content, aggregate size) and the moisture content. Correlation between gas permeability and pore size distribution has been discussed from Katz–Thompson equation too. Our results showed that permeability predicted from the threshold radius of the capillary porosity for cement pastes and mortars whatever the aggregate volume content corresponds to permeability measured after drying at relative humidity, RH equal to 90%. For preconditioning with lower RH, the measured permeability is influenced by microcracking generated by drying shrinkage.