Expansion of Alite Paste Caused by Gypsum Formation during Sulfate Attack

Abstract

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 long-term 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.