High-Temperature Behaviour of Concrete in Tension

The mechanical properties of concrete at high temperature and in fire conditions have been the subject of a number of investigations over the past 50 years. Nonetheless, the wide range of materials at hand, especially after the advent of high-performance and high-strength concretes, makes these results difficult to be generalized. This is particularly true of tensile response, due to the challenging experimental conditions and to the still not standardized test methods: “hot” vs. residual test conditions, direct vs. indirect tensile loading, restrained vs. free strain localization, notched vs. unnotched specimens are only some of the possible options that make the comparison between tests from different sources a really difficult task. In this paper, the results collected by the authors on several different concrete mixes are illustrated, with the twofold objective of clarifying the relations among the most common direct and indirect testing techniques and to sketch any possible general trend in the tensile properties of ordinary and special concretes exposed to high temperature. Among the conclusions are the variable influence of the restraint exerted on the specimen ends in direct tension, the relatively good reliability of the splitting tests, the strong influence of specimen size and increasing material deformability in the bending tests, and the good agreement between the thermally induced decays of tensile strength and modulus of elasticity.