Experimental study on mechanical properties of bundled basalt fiber reinforced concrete

In order to study the mechanical properties of bundled basalt fiber (BBF) reinforced concrete, cube compressive strength, splitting tensile strength and fracture toughness experiments of fiber reinforced concrete with different fiber lengths (12 mm, 18 mm, 24 mm), volume fraction (0.1vol%, 0.2vol%, 0.3vol%) and types (bundled basalt, chopped basalt and polypropylene) were carried out. And the microstructure was observed by scanning electron microscopy. Results show that the effect of BBF on compressive strength of concrete is not obvious; When the fiber length is 24 mm and the dosage is 0.2vol%, the maximum increase of tensile strength is 26.65%. With the reinforcement index (RI) increases, the tension-compression ratio of BBF concrete tends to increase, and when RI gets to 24, the tension-compression ratio is 1.39 times that of normal concrete (NC). The incorporation of BBF significantly enhanced the peak load, initial cracking toughness, and unstable fracture toughness of concrete in three-point bending tests. Moreover, at the optimal dosage of 0.3vol% and fiber length of 12 mm, the maximum improvements in these three properties compared to the NC were 53.66%, 47.06% and 151.03%, respectively. Scanning electron microscopy shows that a large number of hydration products are attached to surface of BBF, which are closely bonded to cement paste and have no obvious interface transition zone with matrix, effectively inhibiting propagation of micro-cracks.