The splitting tensile strength and impact resistance of concrete reinforced with hybrid BFRP minibars and micro fibers

Basalt fiber reinforced polymer (BFRP) minibar is a novel kind of macro fiber, which is high-performed, green and durable. This study aimed to use hybrid BFRP minibars and micro fibers to control cracks of concrete from micro size to macro size, ultimately improving the mechanical properties of concrete. The compressive strength, splitting tensile strength and impact resistance of concrete reinforced with hybrid BFRP minibars and various micro fibers were tested and evaluated. The micro fibers contained micro basalt fibers, polyvinyl alcohol (PVA) fibers and steel fibers. Test results showed that the hybrid fibers provided significantly positive synergistic effects on the impact resistance, compressive and splitting tensile strength of concrete. Micro fibers improved the microcrack resistance capacity of concrete that increased with micro fiber content and modulus, but most of fractured during the development process of microcracks owing to their tiny size, showing little contribution to macrocrack resistance. BFRP minibar showed the pull-out failure, and the force preventing BFRP minibar from pullout bridged macrocracks, improving the macrocrack resistance capacity of concrete., but they seldom improved the microcrack resistance capacity of concrete because of its large size. Hybrid fibers improve the sustained resistance to crack during the whole crack development process owing to the synergistic contribution of hybrid fibers. Thereby, the concrete reinforced with hybrid 1.5% BFRP minibars and 0.75% micro steel fibers showed the highest compressive strength, splitting tensile strength and final-fracturing impact life under the failure probability of 30%, which were 22% 29% and 415% higher than those of concrete with mono 1.5% BFRP minibars. The method, which is that using hybrid macro fibers and micro fibers with high modulus and proper content to reinforce concrete, supports for further improving the mechanical properties of concrete in practice.