Analysis of Concrete Transient Thermal Deformation in the Context of Structures Submitted to Various Levels of Temperature and Mechanical Loading

During their service life, concrete structures are submitted to various types of boundary conditions among which thermal and mechanical loads are the most common. Thermal variations can be non-negligible in case of specific service conditions of the structures such as the storage of exothermic nuclear waste, or during some accidental conditions. Mechanical loading or moderate temperature can, independently from each other, induce high concrete deformations and cracking leading to a loss of serviceability of the structure. In the case of a simultaneous mechanical loading and heating or a heating of a previously loaded concrete structure, an additional deformation, called Transient Thermal Deformation (TTD), occurs. This phenomenon should be monitored because its kinetics and amplitude are significant. Since many concrete structures may be affected by TTD, investigations are needed to assess the coupled effects of different levels of mechanical loadings and heating on this additional deformation. This study presents a part of a wide experimental program dealing with the containment vessel behaviour of a nuclear power plant in case of a severe accident characterized by an increase in internal pressure and temperature. Concrete specimens were submitted to two levels of sustained stress, 30% and 60% of the compressive strength, using uniaxial compressive creep devices, and heated to various temperatures, 20, 40 and 70 ℃ under autogenous conditions representative of the core of the structure. TTD and the thermo-mechanical effects were analyzed through the strain evolutions of loaded and unloaded specimens.