Effect and mechanism of coal gangue concrete modification by basalt fiber

Coal gangue is a waste that is largely produced during coal mining. Its massive accumulation has caused great damage to the environment. In order to promote the resource utilization of coal gangue, coal gangue with a constant replacement rate of 40% is used to replace coarse aggregate and make coal gangue concrete (CGC). In this study, basalt fiber (BF) with different volume content and length was mixed into CGC, and the modification effect and mechanism of BF on CGC performance and mechanical properties were revealed. Macroscopically, the compressive strength, splitting tensile strength, and flexural strength were tested by using a pressure tester. Nuclear magnetic resonance technology was used to analyze the pore structure of CGC. Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy were used to characterize the bonding mechanism of BF on cement matrix and the microstructure of the interfacial transition zone of CGC. Results show that BF can reduce the performance of CGC to a certain extent. However, adding the proper amount and length of BF can significantly improve the mechanical properties of concrete. The addition of BF improves the aperture structure of CGC. At the same time, BF plays a "crack-blocking effect" in CGC, forming a grid structure and hindering the extension and development of microcracks. Chemically, BF undergoes complex chemical reactions in the alkaline environment of CGC and generates a dense gel layer on the surface. Thus, the adhesion between BF and matrix is increased.