Delayed ettringite formation (DEF) can affect the long-term durability of concrete structures by causing cracking and expansion of the material. Consequently, mechanical properties decrease which may cause large structural disorders due to unexpected deformations and additional stresses in concrete and reinforcement. This reaction consists in ettringite crystallization within concrete after hardening is substantially complete, and in which no sulphates come from outside the cement paste. It may occur in materials that have been subjected to temperature above about 65 °C at early age and to high humidity. At this high temperature, the ettringite turns unstable while the concrete is still plastic and forms again after cooling in the hardened material, thus generating swelling due to crystallisation pressure.This article aims to present a new model for the calculation of structures affected by DEF and to study the effect of the prefabrication temperature on the development of this reaction. In this context, the elaborated model was applied to the 3D simulations of a real bridge affected by this phenomenon. The results highlight that the temperature reached in the precast beams of the studied bridge during prefabrication has a significant effect on the displacements and stresses. Therefore, more precise control of the prefabrication temperature has to be applied in order to prevent the swelling and damage to structures.