Study on test of free and total SO42- in cement-based materials subjected to sulfate attack by conductivity titration

It is necessary to accurately, efficiently, and economically test SO42- in cementitious materials subjected to sulfate attack for the calculation of diffusion coefficient, estimating damage degree and analysis of corrosion mechanism. In this study, the test of free and total SO42- in cementitious materials was investigated by conductivity titration. The results show that the key to test SO42- by conductivity titration is removement of the influential ions such as H+ and OH- with higher molar conductivity. In the test of free SO42-, HCl or CO2 can be used to eliminate the effect of OH- or OH- and Ca2+. In the test of total SO42-, the combination of Ag2O with Ag2CO3 or the combination of Ag2O with CO2 can be used to eliminate the effect of H+, Cl-, and Ca2+ where Ag2O and CO2 is more applicable to eliminate influential ions because CO2 is easily controlled by CO2 generator. The ultrasonic can be used to clean the AgCl attached to the surface of Ag2O to increase the hydrolysis reaction of Ag2O. To eliminate the effect of reaction between Ag+ from hydrolysis reaction of Ag2O and Cl- from the conventional titrant of BaCl2 on titration endpoint, the Ba(NO3)2 is chosen as a new titrant.