Relationship Between Expansion Characteristics of Heat-Cured Mortars During Water Curing and Origins of Ettringite Formation

Delayed ettringite formation (DEF) is known as the deterioration phenomenon that occurs in mortar or concrete cured at high temperature. It has been proposed that DEF expansion is affected by calcium-silicate-hydrates (C-S-H), although the mechanism has not yet been clarified. The present study experimentally examined the relationship between the expansion characteristics of heat-cured mortar specimens used cement, anhydrite and supplementary cementitious materials (SCMs) during water curing and the origins of ettringite formation. The proportional change in length and the phase compositions of the heat-cured specimens were acquired. The respective amounts of ettringite generated from cement and SCMs were determined. The expansion of the mortar specimens using cement, anhydrite, silica fume and fly ash occurred continuously during water curing, while the continuous expansion did not occur in the mortar specimens using cement, anhydrite and blast furnace slag. These expansion characteristics could not be explained solely by the change in the amounts of ettringite. There was a certain correlation between the amount of ettringite generated from cement and the expansion characteristics of the specimens. It is one of the evident that origins of ettringite formation or coexisting materials such as C-S-H phase can affect expansion characteristics due to DEF.