Relationship between delayed ettringite formation and delayed expansion in massive shrinkage-compensating concrete

The possibility of delayed expansion induced by delayed ettringite formation in massive shrinkage-compensating concrete was investigated. Mortars were prepared using ordinary Portland cement and a sulfoaluminate-based expansive agent. They were cured in three different moist conditions at elevated temperature in a temperature match conditioning process to simulate the temperature development in the interior of massive concrete, and then at ambient temperature. Changes in quantity and morphology of ettringite were examined using semi-quantitative X-ray diffraction and scanning electron microscopy. The time-dependent length change of restrained mortars was also measured. The results show that, in addition to the quantity of ettringite, the structure of mortar, morphology of ettringite and curing conditions also influenced expansion of mortars induced by delayed ettringite formation. The expansion mechanism of delayed ettringite formation and the relationship between curing conditions and length change, delayed expansion and damage to concrete structure are discussed. (C) 2003 Elsevier Ltd. All rights reserved.