The effect of initial moisture content on water transport in concrete containing a hydrophobic admixture

Tests on initially saturated and dried concrete containing a hydrophobic admixture showed that initial moisture content had a significant effect on measured water transport properties. Concrete specimens containing the hydrophobic additive significantly reduced water penetration when the concrete had been initially dried, and had limited or no positive effect on water penetration into initially saturated specimens. The reduction in water transport compared with the control was generally more pronounced in hydrophobic concrete of higher w/c ratio, as well as under conditions of limited curing and greater drying. The hydrophobic admixture had no significant effect on water vapour diffusivity. These results suggest that the ingredients in the admixture only become effective where a clear wet-dry interface is present and tend to influence water transport through larger pores.