Compressive stress–strain responses of concretes containing raw coal gangue aggregates exposed to elevated temperatures

Abstract This study experimentally examined the residual compressive performance of concrete incorporating raw coal gangue aggregates (RCGA) as partial replacements for natural coarse aggregates (NA) after being exposed to elevated temperatures ranging from 20°C to 800°C. A total of 90 cube specimens and 90 prism specimens were fabricated to assess the residual mechanical characteristics of RCGA concretes, including failure mode, compressive strength, peak stress, elastic modulus, and stress–strain responses. The experimental study considered three replacement ratios of RCGA (0%, 30%, and 50%) and two water‐cement ( w/c ) ratios (0.36 and 0.47). In addition, crack evolution and microstructural characteristics after thermal exposure were examined. Test results showed that increasing temperature led to reductions in both compressive strength and elastic modulus of RCGA concrete. Compared with the specimens at 20°C, the residual peak strength decreased by approximately 80%–90%, while the elastic modulus by nearly 99% after exposure to 800°C. In contrast, the peak strain exhibited a pronounced increase, particularly between 600 and 800°C. The influence of the RCGA replacement ratio on the relative peak stress, relative elastic modulus and relative peak strain was limited after thermal exposure. Furthermore, a normalized stress–strain model was proposed to predict the residual compressive response of RCGA concrete after thermal exposure.