## 1 Introduction
Therefore, when BF and PF with different mechanical properties are mixed into concrete, they can play the role of crack bridging on different structural scales. The hybrid basalt-polypropylene fibre can not only enhance the strength of concrete but also effectively restrain the expansion of concrete cracks and improve the toughness of concrete. [PERSON] and colleagues [35] utilizing scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), demonstrated that incorporating BF into blast-furnace slag concrete greatly enhances tensile strength, flexural strength, and toughness without notably increasing compressive strength. Similarly, [PERSON] et al. [36] conducted impact strength and fracture performance tests on basalt fibre (BF)-reinforced self-compacting concrete. The findings showed that BF combinations demonstrate superior impact resistance and fracture energy values to alternative fibre combinations. [PERSON] et al. [37] examined the dynamic shear behaviour of basalt-fibre-reinforced concrete (BFRC) in blast furnaces by utilizing samples containing various fibre lengths and fibre contents, totalling four variations each. Researchers have carried out comprehensive tests on the dynamic performance of direct shear, taking into account the impact of the seismic strain rate. The findings indicated that BFRC demonstrates a distinct impact on the strain rate, as an escalation in the strain rate considerably augments the shear stress. [PERSON] et al. [38] found through experiments that the reinforcement effects of polypropylene fibre (PF) on the toughness and crack resistance of plain concrete are more pronounced than those on high-strength concrete. [PERSON] [39] demonstrated through experiments that basalt fibre (BF) and polyvinyl alcohol fibre (PF) can enhance and fortify rubber concrete, impacting the mechanical properties, pore structure, and microstructure. According to experiments conducted by [PERSON] and his team [40], inclusions of BF and PF in concrete can boost its flexural strength and enhance the tortuosity of crack propagation,ultimately improving its ductility. Additionally, it was discovered that a blend of fibres with a concentration of 0.1% is highly favourable for enhancing flexural durability. The aforementioned studies highlight the potential of basalt fibre (BF) and polypropylene fibre (PF) to act as crack-bridging agents on different structural scales. Therefore, incorporations of BF and PF with varying sizes and mechanical properties into concrete can effectively mitigate the propagation of concrete cracks, thereby enhancing the strength and toughness of the material. However, as of now, the related research is primarily concentrated on the influences of hybrid BF's effects and PF's effects on the compressive strength, flexural strength, splitting tensile strength, and impact resistance of ordinary concrete. Compared with ordinary concrete, coal-gangue concrete has lower strength but higher brittleness, which greatly limits the application range of coal-gangue concrete. Enhancing the strength and ductility of coal-gangue concrete, characterized by higher brittleness, lower toughness, and inferior carbonation resistance to ordinary concrete, holds significant practical relevance. However, there are few investigations into the application of hybrid basalt-polypropylene fibre in coal-gangue concrete. Therefore, the primary focus of this study is on experimental analysis to explore the mechanical and deformation properties of mixed basalt-polypropylene fibre in coal-gangue concrete. The aim of this paper is to find the optimum hybrid-fibre content to enhance the strength and ductility of coal-gangue concrete, and it provides a reference for improving the mechanical properties of coal-gangue concrete by adding fibre.