Optimizing hybrid fiber content for enhanced thermo-mechanical performance of high-strength concrete

Fiber-reinforced concrete (FRC) is an innovative category of construction materials known for their enhanced mechanical strength and durability. However, there is limited information regarding the synergistic effects on concrete strength in hybrid configurations. This study utilizes steel and basalt fibers (BF) in the concrete matrix to make high-strength concrete (HSC) specimens. Moreover, varying proportions ranging from 0.25% to 1% are employed by volume of concrete to assess its mechanical properties, mass degradation, and surface cracking after exposure to escalating temperatures of 300°C, 600°C, and 800°C at a rate of 5 °C/min. The findings revealed that hybrid fiber-reinforced concrete (HFRC) exhibited superior mechanical properties relative to the control specimen. This improvement is due to the basalt fibers' filler properties and the hybrid fiber's ability to bridge cracks. In addition, 0.5% HFRC demonstrates superior mechanical properties as compared to the control specimen. The inclusion of Hybrid fibers prevented crack growth through fiber bridging, resulting in delayed crack propagation and significant enhancement in the toughness and crack energy of HFRC. The toughness and crack energy was increased with the rising content of hybrid fibers (HF) in concrete. The compressive failure mode of HSC with low fiber content changes from a single, brittle crack to a more durable multiple crack-resistant mode. It was noted that too many hybrid fibers in concrete can have adverse effects, resulting in clumping. This not only causes voids but also diminishes the amount of cement present, which in turn minimizes the strength of the concrete. Ultimate and peak strain is positively associated with the content of HF in concrete. Furthermore, concrete specimens with 1% hybrid fiber exhibited the most minor mass degradation.