Chloride-Ion Attack on Low Water-Cement Ratio Pastes Containing Silica Fume

The chloride ion attack on low-water cement ratio pastes containing silica fume was studied by soaking small paste disks in 4 different pH controlled sodium chloride solutions for periods of up to 12 months. The chloride ion attack on these low water-cementitious material ratio pastes was always very small even after 12 months of exposure to 3% NaCl solutions at pH values of 13.0 and 11.5. After several months of exposure at a pH of 13, only very small amounts of chloride ions were detected and only minor changes to microstructure were noted. The major parameter controlling chloride ion penetration in low water-cementitious material ratio pastes is the pH of the NaCl solutions. For this relatively low pH, it was found that the use of lower water-cementitious material ratios and silica fume can reduce the amount of chloride ions that can penetrate the cement paste.