Mechanical and microstructural properties of basalt fiber-reinforced concrete with coal gangue fine aggregate
Coal gangue fine aggregate (CGFA) can reduce the consumption of natural sand, but its high water absorption and heterogeneous pore structure may compromise concrete performance. This study investigates whether basalt fiber (BF) can improve the mechanical response and damage resistance of spontaneous-combustion CGFA concrete. Seventeen concrete mixtures were prepared by replacing natural fine aggregate with CGFA at 0, 10, 20, 40, and 50% and incorporating BF at 0, 0.10, 0.15, and 0.20 vol%. Cube compressive, axial compressive, splitting tensile, flexural, and dynamic elastic-modulus tests were conducted, and the microstructural mechanisms were examined using scanning electron microscopy. Strength and stiffness generally increased first and then decreased with increasing CGFA content, with the most favorable overall response at approximately 20% replacement. BF improved crack control and deformation capacity, and 0.15 vol% produced the highest strengthening efficiency, particularly for splitting tensile and axial compressive strength. Excessive BF reduced the reinforcing benefit because of poorer dispersion and fiber agglomeration. Moderate CGFA replacement and optimized BF dosage produce a synergistic enhancement through interfacial densification, crack bridging, and improved stress transfer. Empirical strength models are proposed for trend-level prediction within the investigated material system.