Thaumasite form of sulfate attack (TSA) in limestone cement pastes

摘要

The thaumasite form of sulphate attack (TSA) concerns cements and concretes containing limestone and is attributed to the formation of thaumasite (CaSiO_3 centre dot CaCO_3 centre dot CaSO_4 centre dot 15H_2O). During the last 10 years, the TSA has been found in field structures and buildings in many countries worldwide. In the present work the behavior of Portland limestone cements was studied in the presence of sulfate ions at low temperatures. Cement paste specimens were constructed using Portland cement, Portland cement with 15 percent (w/w) limestone content and Portland cement with 30 percent (w/w) limestone content. Twenty-eight days paste specimens were cured in 1.8 percent (w/w) magnesium sulfate solution of temperature 5 deg C. Visual inspection, mass measurements and ultrasonic pulse velocity measurements were carried out for 1 year. Pastes containing limestone are susceptible to the thaumasite formation of sulfate attack and the deterioration is severer, the higher the limestone content.