Abstract
The mortar expansion by delayed ettringite formation (DEF) in high slag cement (ECM) in accordance with blast furnace cement class C was examined. The effects of cement composition, SO3 content, type of sand, water to binder ratio (W/B), pre-curing time, curing conditions, and the addition of an air entrained (AE) agent were studied through experimental approaches. SO3 was added in the form of anhydrite and potassium sulfate at 0.92 to 3.0mass%. Type of sand was selected from ISO standard or limestone. The W/B was varied from 22% to 60%. Pre-curing times before high temperatures varied from 1.0 to 13.5 hours. After pre-curing, three curing conditions were studied; sealing, moisture curing, and water curing. Expansion was measured by JIS A 1146. Morphological observation of expanded mortar was conducted by scanning electron microscopy (SEM). As a result, the expansion by DEF increased at high SO3 content, lower pre-curing time, greater water supply by curing condition, and non-AE condition in high early strength cement. Microcracks were observed in only high early strength cement. Expansion was not observed at any experimental condition on ECM.
