Mechanical behaviour and model of polypropylene fibre-reinforced coal gangue concrete

Using raw coal gangue (RCG) as a coarse aggregate in concrete mitigates the environmental issues of RCG and reduces the demand for natural gravel, providing a sustainable alternative for the construction industry. However, the high crushing index and porosity of raw coal gangue aggregate (RCGA) lead to degraded mechanical properties of concrete. This study systematically investigates the enhancement of raw coal gangue aggregate concrete (RCGAC) using polypropylene fibres. The effects of water–binder ratio, RCGA replacement ratio, and polypropylene fibre content on mechanical properties are examined. By analysing both macroscopic failure patterns and microscopic structural characteristics, the enhancement mechanisms of the polypropylene fibres are clarified. Furthermore, existing prediction models are evaluated against experimental data, and modified models are proposed for predicting the splitting tensile strength and elastic modulus of polypropylene fibre-reinforced RCGAC, with the RCGA replacement ratio incorporated as a variable. The results indicate that EC 2, ACI 318, and GB/T 50010 standards are inadequate for predicting these properties for the developed material. The modified prediction models integrate the RCGA replacement ratio as a variable and offer high accuracy and reliability for assessing the mechanical properties of polypropylene fibre-reinforced RCGAC.