Fatigue flexural properties of graphite tailings concrete modified with basalt fiber

Graphite tailings were solid wastes which were large and difficult to deal with. In order to promote the utilization of graphite tailings and reduce the consumption of natural river sand, this paper replaced part of the natural river sand with graphite tailings and added environmentally friendly green fibers for modification to jointly prepare basalt fiber modification graphite tailings concrete. In order to encourage the adoption of graphite tailings concrete during the construction of roads, it was crucial to fully understand the fatigue and flexural properties of concrete. Through experimental research, this paper analyzed the effects of graphite tailings and basalt fiber mixing on the flexural mechanical properties and fatigue life of concrete, and used solidstate 29Si nuclear magnetic resonance, back scattered electron microscope, and nanoindentation to investigate the interface transition zone. The results indicated that the most effective combination was concrete with a 20 % graphite tailings substitution rate and 0.1 % basalt fiber by volume, whose flexural strength could be increased by up to 19.10 % compared with PC, and when the stress level was 0.6, the fatigue life characteristic value of it was 3.94 times than that of PC. Combined with the results of the microscopic testing, it could be demonstrated that an appropriate amount of graphite tailings could promote the absorption of the Al element, increase the chain length and strength of C-S-H gel, and thereby increase the total content of C-SH gel. Compared with PC, when the graphite tailings substitution rate was 20 %, the hydration degree increased by up to 37.00 %, and the total C-S-H gel content also rose by 12.01 %. In addition, the admixture of an appropriate amount of graphite tailings would reduce the pores and micro-cracks in the interface transition zone, make the interface transition zone denser, increase its elastic modulus, and reduce the width. At 20 percent of the graphite tailings substitution rate, compared with PC, the minimum width could be reduced by 33.33 %, and the elasticity modulus improvement range could reach 33 %-40 %. These further proved that basalt fiber-modified graphite tailings concrete could strengthen its flexural properties and fatigue life, as well as its feasibility in road engineering applications.