EFFECTS OF MIXING AMOUNT OF MONOCARBONATE AND CURING TEMPERATURE ON THAUMASITE AND ETTRINGITE FORMATION

Abstract

Sulfate attack is known as one of the deterioration phenomena of concrete structures. According to previous researches, it has been suggested that the presence of carbonate ion may promote secondary ettringite formation and expansion；however, the details of this hypothesis have not been confirmed by experiments. The purpose of this research is to examine the effects of mixing amount of monocarbonate and curing temperature on thaumasite and ettringite formation. Synthesized monocarbonate and the materials required for thaumasite formation were mixed with deionized water in order to hydrate in the suspension, after which the solid phases after hydration were analyzed. As a result, when a mixture of portlandite, calcium carbonate, amorphous silica, gypsum and a large amount of monocarbonate was mixed and hydrated at 5, 20, 40℃, the amount of secondary ettringite formation was increased with the rise of curing temperature. In particular, the amount of secondary ettringite formation was increased significantly when a large amount of monocarbonate was mixed. It was suggested that the secondary ettringite formation from monocarbonate is strongly affected by the dissolution of CH and the formation of C-A-S-H in the suspensions.