Expansion of Alite Paste Caused by Gypsum Formation during Sulfate Attack Factors Affecting Resistance of Concrete to Freezing and Thawing Damage

This paper introduces a study carried out to investigate sulfate attack caused by gypsum formation. The aim, specifically, was to study whether gypsum formation can be a factor leading to expansion in concrete exposed to solutions containing sulfate ions. It was found from the laboratory study that alite paste specimens (0.48 water-to-alite ratio) expanded and cracked significantly in 5% Na2SO4 solution after a "dormant" period of about 1 year. X-ray diffraction confirmed that gypsum was the main product—ettringite does not form in the system, because of the lack of aluminate. The detailed study of the mechanism for expansion and cracking is continuing. These findings confirm the longterm understanding that sulfate attack mechanism is a complicated process. A highlight of the study, therefore, reveals that expansion and cracking of portland cement concrete may not be attributed solely to ettringite formation. Gypsum formation may be a cause leading to expansion and subsequent cracking. More research is needed in this area. The variation in cement type affects the performance of concrete in terms of durability and strength. Concretes made with different cement types are known to behave differently under similar conditions such as environmental conditions, mixture proportions, etc. In 1940, the Portland Cement Association initiated a long-time durability study to investigate the effects of the variation in cement type on different durability aspects. The United States Bureau of Reclamation agreed to place 28 different cement types on the parapet wall panels of the Green Mountain Dam. Each of the 28 cement types was used in 3 or 4 of the 104 panels of the parapet wall. The Green Mountain Dam is located on the Blue River, a tributary of the Colorado River, 13 mi southeast of Kremling, Colo. The dam itself is an earthfill structure. This particular paper investigates the influence of cement type, air-entrainment, and method of airentrainment on the freezing and thawing resistance of concrete.