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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 article 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, this article 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 article, 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.

Important coupled effects of stress and temperature change have long been recognised and taken into account in models assessing the performance of solid materials. However, due to incomplete understanding, existing models used for concrete are essentially empirical and lack rational basis. This limits their predictive capability and applicability range. In this paper, fundamental thermodynamics and continuum mechanics laws are used to obtain an expression quantitatively predicts the effects of stress on the coefficient of thermal expansion. The newly-defined thermal expansion coefficient is then used to develop a rational model, which is shown to be capable of reliably quantifying the coupling effects of stress and temperature change. Good agreement between the model predictions, available data and observations is obtained. Equally important, all parameters of the developed model can be determined using simple tests. This enables a wide adoption of the model in practical engineering applications. While this paper uses data for concrete, the proposed model is developed from first principles and using fundamental physical laws, therefore, it should be applicable to a wide range of solid materials.

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Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effective curing as well as timely and adequate saw-cutting.