Étude de la cinétique de séchage des bétons : Application à l'atteinte d'un gradient hydrique représentatif dans le cadre des essais au feu

Spalling of concrete is one form of the thermal instability induced by fire exposure. It needs to be investigated when the fire behaviour of structures is to be assessed.Fire behaviour is commonly assessed by reference to the requirements of NF EN 1363-1 "Fire resistance tests - Part 1: General requirements". According to this standard, conditioning at 23 °C, 50 %RH for at least 3 months should be used on concrete elements and should allow the tested element to reach a hydric and mechanical state representative of its normal service state on the day of the fire testing, whatever the type of concrete and the geometry of the structure. In this context, the main objective of the thesis is to study the impact of drying time and conditions on (i) the spalling profiles of different concretes and (ii) the associated water profiles. Accelerated drying protocols are proposed on the basis of experimental and numerical study.The drying protocols aim either (i) to reduce the conditioning time usually used in standard conditions (3 months) while maintaining acceptable representativity or (ii) to propose a protocol allowing to reproduce the hydric state of concrete structures in service condition (2 years) while ensuring the reproducibility of the spalling facies. An extensive experimental campaign and a numerical study of the drying kinetics are carried out on two high-performance concretes and two ordinary concretes. The fire behaviour of loaded and non-mechanically loaded slabs was evaluated at the various times and studied conditioning modes. The importance of the water gradient and the water content in relation to spalling was highlighted. A good representativity of the proposed accelerated drying protocols was also observed.