Investigations on stress corrosion of hardened cement pastes

Test specimens made from "white" Portland cement (WPC), "sulfate resistant" Portland cement (SRPC) and tricalcium silicate were exposed to solutions of ammonium nitrate, sodium sulfate and ammonium sulfate. The interaction between the paste and the dissolved corrosive agents was studied by optical microscopy, back scatter electron imaging, electron microprobe analysis and X-ray diffraction. It was found that a simultaneous exposure of the test specimens to a flexural load accelerated the progress of the corrosion process in the zone under tension and reduced it in the zone under compression in samples that were in contact with ammonium sulfate, whereas it had no noticeable effect on the action of the two other agents. Specimens exposed to ammonium nitrate and ammonium sulfate failed spontaneously if exposed to a simultaneous mechanical loading that was lower than the load needed to produce fracturing of samples not exposed to the corrosive agent, apparently due to a reduced strength of the corroded surface regions. (C) 2000 Elsevier Science Ltd. All rights reserved.