An experimental clarification of the association of delayed ettringite formation with alkali-aggregate reaction

Abstract

The issue of determining the primary cause of damage to concrete elements in the presence of a combination of delayed ettringite formation (DEF) and alkali-aggregate reaction (AAR) is very controversial. Some authors believe that DEF has been the cause of serious damage (cracking) to concrete elements cured at elevated temperatures, and some others attribute the damage to AAR, with a minor role for DEF. To assist in clarifying the issue, experimental mortar specimens were devised in which either of these chemical processes could occur separately or in combination. The specimens were subjected to either continuous curing at 40 °C or initial steam curing at 75 °C for 8 h followed by storage at 40 °C, 100% RH. The results of length change measurements on these specimens favour the conclusion that AAR is the primary cause of damage, but under certain conditions DEF may contribute to it. However, in the absence of AAR cracking no DEF was observed in the systems examined here, emphasising the primary role of the AAR in causing damage in the form of cracking in concrete.