Influence of chloride ions and pH level on the durability of high performance cement pastes .2.

The resistance to chemical attack of low water/binder ratio pastes containing silica fume (W/B = 0,25 and 0,38) was studied by soaking small paste disks in three different pH-controlled solutions, with or without sodium chloride, for periods of up to three years. The three solutions in which the paste disks were soaked were the following: 3% NaCl (by mass) at a pH level of 8,5, 0% NaCl at 8,5, and 0% NaCl at 4,5. After three years of exposure, the results confirm that the pH level of the aggressive solution is the most important factor controlling the durability of cement pastes subjected to chemical attack. The total porosity and the depth of decalcification were found to increase with a reduction of the pH level. The results further show that the presence of chloride ions tends to increase the leaching of calcium and the opening of the porosity. The reduction of the water/binder ratio does not influence the degradation processes but affects the kinetics of these processes. Chloroaluminate formation was observed only in the 0,38 mixture and is related to the presence of C(3)A. The results obtained after 3 years of exposure confirm those previously obtained after three months of exposure [1].