Optimizing high-performance lightweight concrete with hybrid fiber: Enhancing mechanical and thermal properties

High-Performance Concrete (HPC) is characterized by its densely structured microstructure, providing superior strength and impermeability compared to conventional concretes, but it remains susceptible to spalling when exposed to high temperatures. To address this limitation, the present study focuses on the formulation of High-Performance Lightweight Concrete (HPLC) by incorporating sisal fiber and steel fiber, aiming to mitigate the tendency for spalling under elevated thermal conditions commonly observed in HPC. The present research employed the Modified Andreasen & Andersen particle packing model to optimize the initial mixture proportions for HPLC. This study comprehensively examined the effects of varying sisal fiber concentrations on the workability, mechanical properties, durability, microstructure, and thermal spalling of HPLC. Key findings from the experimental investigation indicate that HPLC developed in this study exhibits high compressive strength, with the most notable performance observed at a sisal fiber volume of 2.0 %, resulting in an apparent density of 1876 kg/m³ and a compressive strength of 110.1 MPa. Incorporation of sisal fiber at a volume of 1.0 % significantly enhances the mechanical properties of HPLC, as evidenced by increases of 11.6 % in flexural strength, 11.9 % in compressive strength, 6.5 % in elastic modulus, and 25.8 % in impact resistance. Additionally, at the same fiber inclusion rate, improvements are noted in the material’s resistance to chloride ion penetration and drying shrinkage, with reductions of 4.9 % and 7.3 %, respectively. Adequate amounts of sisal fiber also improve the gel pore structure of HPLC matrix. The thermal degradation of sisal fibers at high temperatures creates channels for steam egress, reducing vapor pressure within HPLC and thereby enhancing its resistance to thermal spalling. A holistic examination of the influence of sisal fibers on the mechanical performance, micromorphology, and thermal endurance of HPLC indicates that the optimal sisal fiber content is established at 1.0 % by volume. Future research could concentrate on optimizing fiber types and compositions, exploring hybrid fiber options, and evaluating long-term durability under diverse environmental stresses to broaden the scope of applications.