Studies of pore size distribution in mortars

Abstract

Summary Pore size distributions of mortars cured by hydration, carbonation, and under atmospheric conditions were measured down to pore sizes of 0·01μ diameter by the method of mercury penetration. It was found that hydration decreased the volume of the larger pores and that carbonation decreased the volume of the intermediate size pores but increased the volume of pores exceeding 5μ in diameter. The main effect of curing in carbon dioxide was evident after 1 day, but equilibrium during hydration was reached in about 12 days. The pore size distribution was not greatly affected by curing under atmospheric conditions. The larger pore sizes (>5μ) appeared to be affected by the extent to which the samples were compacted in moulding. The volume of pores between ∞ and 0·01μ as determined by mercury penetration is, for mortars with low cement/water ratios, considerably less than the total porosity determined by saturation with water. This points to the existence of capillaries of diameters of 0·01μ and less, or of cavities with entrances of these diameters in set cement, as deduced by Powers, Copeland and Mann from permeability data.