A concrete performance test for delayed ettringite formation: Part I optimisation

Abstract

Delayed ettringite formation (DEF) is a rare internal swelling reaction of concrete that, in a wet environment, may considerably reduce the durability of a structure or a member that has been prefabricated in a factory. As a result of a large number of studies, the main causes of this problem have been established and this paper proposes a test method to predict the susceptibility of a concrete to DEF and provide long-term protection against this hazard. After an examination of the feasibility of a test based on wetting and drying cycles, the results of an optimisation study based on a factorial experimental plan are presented. The test is in four stages: concrete manufacture, a heat treatment that simulates steam curing in a factory or the heating that occurs in mass cast in-situ concrete, wetting and drying cycles and the monitoring of the longitudinal expansion of specimens that are immersed in water. Optimisation essentially concerns the last two stages and resulted in the decision to apply two drying cycles (38 °C at a relative humidity of approximately 30%) and wetting cycles (in water at 20 °C) followed by permanent immersion in water (at 20 °C). This test is applied to concrete that has undergone early age heating. It provides a means of evaluating the potential reactivity of “mix design–heating cycle” pairs as realistically as possible within a reasonable period of time.