An experimental study on damage and failure modes in a high-performance concrete at elevated temperature loaded in compression and tension

The brittle, composite nature of concrete makes stress-induced damage a multi-faceted phenomenon at the microscale, particularly in the transition zones between the cement matrix and the aggregate, influencing micro-cracking development and propagation. Factors like high temperature, pre-loading (stressed / unstressed) during the heating process and test modalities (in either hot or residual conditions) significantly affect concrete’s damage evolution and toughness. Despite the many studies on concrete at high temperature, the influence of different heating and loading conditions on the post-peak behaviour in compression and direct tension at elevated temperatures is still an open question. The current study presents an extensive experimental investigation into the mechanical behaviour of high-performance concrete exposed to elevated temperatures by analysing the post-peak failure and damage evolution under different loading and heating conditions. Observations indicate enhanced strength retention and toughness for concrete in the ‘hot’ state. The results also confirm better stiffness retention of concrete when heated and / or cooled under sustained compression. Stressed specimens, however, exhibit a more significant evolution of the damage in the post-peak phase followed by a sudden failure compared to unstressed specimens. Findings indicate that hot and residual strengths and ultimate strains are not sufficient indicators of concrete response and solely relying on these properties may lead to incorrect assessments of concrete failure behaviour. Input parameters are recommended in this manuscript for numerical modelling, facilitating the development of advanced nonlinear material’s models, which are essential for the numerical analysis of concrete structures under fire, and for a more accurate prediction of failure modes. • Compressive and direct tensile strength of concrete is studied at high temperature. • Post-peak failure and damage evolution is observed in concrete at high temperature. • The residual state of stressed concrete is a critical loading environment. • Peak strengths are incomplete indicators of material performance. • Usability of experimental data for numerical model development is verified.