Effects of temperature and temperature gradient on concrete performance at elevated temperatures

To assure adequate fire performance of concrete structures, appropriate knowledge of and models for performance of concrete at elevated temperatures are crucial yet currently lacking, prompting further research. This paper first highlights the limitations of inconsistent thermal boundary conditions in conventional fire testing; and of using constitutive models developed based on empirical data obtained through testing concrete under minimised temperature gradients in modelling of concrete structures with significant temperature gradients. On that basis, the paper outlines key features of a new test setup using radiant panels to ensure well-defined and reproducible thermal and mechanical loadings on concrete specimens. The good repeatability, consistency and uniformity of the thermal boundary conditions are demonstrated using measurements of heat flux and in-depth temperature of test specimens. The initial collected data appear to indicate that the compressive strength and failure mode of test specimens are influenced by both temperature and temperature gradient. More research is thus required to further quantify such effect and also to effectively account for it in rational performance-based fire design and analysis of concrete structures. The new test setup reported in this paper, which enables reliable thermal/mechanical loadings and deformation capturing of concrete surface at elevated temperatures using digital image correlation, would be highly beneficial for such further research.