Effects of basalt fiber mini-bar and polypropylene fiber on the flexural behavior and crack self-monitoring capability of concrete beams

In high-salinity, high-humidity, and high-temperature environments of coastal regions, steel fibers in cracked concrete are susceptible to corrosion. To meet the demands for flexural toughening and crack self-monitoring of concrete beams in such areas, basalt fiber mini-bars and macro polypropylene fibers were selected to construct a non-metallic fiber reinforcement system. Based on Fib Model Code 2010, three-point bending tests were conducted to investigate the effects of different dosages of basalt fiber mini-bars and hybridization with polypropylene fibers on the flexural behavior of concrete beams. Nano carbon powder was incorporated into the concrete to reduce the electrical resistance of the matrix, and the fractional change in resistance (FCR) during the bending process was monitored by the four-probe method, thereby analyzing the crack self-monitoring capability of basalt fiber mini-bar and polypropylene fiber reinforced concrete beam. The results indicate that basalt fiber mini-bars can effectively improve the flexural toughness of concrete beams, and their hybridization with polypropylene fibers can further enhance the toughness. In particular, the combination of 20 kg/m³ basalt fiber mini-bars and 4 kg/m³ polypropylene fibers overall exhibited a positive synergistic effect on residual flexural tensile strengths. Effective monitoring of crack development in basalt fiber mini-bar and polypropylene fiber reinforced concrete beam can be achieved based on FCR, and a strong linear relationship exists between FCR and CMOD, with the coefficient of determination C_R² ranging from 0.913 to 0.966. Nano carbon powder can significantly improve the sensitivity of crack self-monitoring.