Compressive stress-strain relationship for fly ash concrete under thermal steady state

The paper presents an experimental study on the mechanical properties of fly ash concrete during thermal exposure. The tests were carried out on an apparatus specially designed for studying “hot” mechanical properties of concrete materials. The results presented include the compressive strength, strain at peak stress point, Young's modulus, and stress-strain relation at temperature ranging from ambient to 900 °C. It was found that 25% replacement of ordinary Portland cement with fly ash in concrete would yield less decrease of compressive strength and more linear stress-strain response at high temperatures due to the further reaction between the reactive silica in fly ash and calcium hydroxide under hydrothermal conditions. Based on the experimental results, an advanced temperature-dependent stress-strain model for fly ash concrete under thermal steady state is proposed. Compared with previous models, the present model has the advantage of considering the variation of the curvature of stress-strain relationship with the increase in temperature. The results are not only a supplement to existing experimental data but also provide the basis for the continuous research on the fly ash concrete under thermal transient state.