Theoretical and experimental validation of a simple method to reproduce representative DEF-prone conditions in laboratory

Delayed Ettringite Formation (DEF) is a possible autogenous expansive reaction of concrete. It can affect materials that have experienced temperatures higher than about 65°C at early age. This temperature increase can be the result of the cement heat of hydration in massive structures where the heat transfers are particularly low. To understand the effects of DEF, it is necessary to be able to reproduce thermal DEF-prone conditions in laboratory. This paper proposes a method developed during an extensive experimental programme that aimed at studying the mechanical effects of DEF on structures built with different concretes. The objective was to design a single heat treatment profile to generate homogeneous and similar temperature fields in specimens of various geometries, concrete constituents and mix proportions. It has been demonstrated that quasi-adiabatic conditions were to be realized at early age, whatever the samples size, to simulate the curing conditions in massive structures. The experimental method developed is described in details: the design of the temperature profile, the experimental device and its operation are presented. Both a numeric and an experimental validation are proposed. They emphasize the good accuracy of the process and demonstrate the possibility to trigger similar DEF potential expansions due to the thermal history for all the specimens of the programme.