Resistance of High Strength Concrete to Sulfate Attack: Soaking and Drying Test

The sulfate resistance of concretes with compressive strengths between 60 and 110 MPa was evaluated. The test comprises several soaking/drying cycles of samples in a Na sub 2 SO sub 4. 10H sub 2 O solution, followed by measurement of mass variation and residual compressive strength. Visual inspection and sulfate recovery by distilled water immersion increased the accuracy of test results. Results reveal significant differences compared to those test normally used, involving prolonged immersion. The resistance to sulfate attack depends on concrete porosity and capillary absorption, and not on permeability, because pozzolanic reactions seem to interrupt pore continuity. The reduced w/c ratio obtained with the aid of the super-plasticizer was much more effective than the chemical characteristics related to the presence of mineral admixtures in concrete, as regards its resistance to sulfates.