INFLUENCE OF CHLORIDE-IONS AND PH LEVEL ON THE DURABILITY OF HIGH-PERFORMANCE CEMENT PASTES

The resistance to chemical attack of low water to binder ratio pastes containing silica fume was studied by soaking small paste disks in thr ee different pH controlled solutions, with or without sodium chloride, for periods of up to three months. The pastes were made using water t o binder ratios of 0,25 and 0,38. The three solutions in which the pas te disks were soaked were the following: 3% NaCl (by weight) at a pH l evel of 8,5,0% NaCl at 8,5, and 0% NaCl at 4,5. After three months of exposure, the results show that the pH level of the aggressive solutio n is the most important factor controlling the durability of cement pa stes subjected to chemical attack. The total porosity and the depth of decalcification was found to increase with the decrease of the pH lev el. It was also found that the water to binder ratio does not signific antly affect the deterioration processes, but only influences the kine tics of these processes. The decrease of the water to binder ratio red uces significantly the rate of deterioration. Chloroaluminate crystals were observed only in the cement pastes having a water to binder rati o of 0,38.