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 con taining silica fume (W/B = 0,25 and 0,38) was studied by soaking small paste disks in three different pH-controlled solutions, with or witho ut sodium chloride, for periods of up to three years. The three soluti ons 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. Aft er three years of exposure, the results confirm that the pH level of t he aggressive solution is the most important factor controlling the du rability of cement pastes subjected to chemical attack. The total poro sity and the depth of decalcification were found to increase with a re duction of the pH level. The results further show that the presence of chloride ions tends to increase the leaching of calcium and the openi ng of the porosity. The reduction of the water/binder ratio does not i nfluence the degradation processes but affects the kinetics of these p rocesses. Chloroaluminate formation was observed only in the 0,38 mixt ure and is related to the presence of C(3)A. The results obtained afte r 3 years of exposure confirm those previously obtained after three mo nths of exposure [1].