Compressive strength of high-strength concrete modified with synthetic fibers at elevated temperatures

High-strength concrete (HSC) demonstrates exceptional performance at room temperature, including high compressive and flexural strengths, coupled with remarkable durability. However, it exhibits poor performance under high temperatures due to its dense microstructure that leads to increased risk of explosive spalling. Studies also showed that HSC has higher degradation in its mechanical properties under elevated temperatures compared to normal-strength concrete. Therefore, synthetic fibers, such as polypropylene (PP) fibers are added to the concrete mix to reduce the extent of spalling and increase its fire resistance. This study aims to investigate the degradation in compressive strength properties of HSC, made of local materials in the UAE, with variable composition of PP fibers and steel fibers. Two mix designs were developed in this study. The first mix had 1% steel fibers only, and the second mix consisted of 1% steel fibers with 0.1% PP fiber. Results showed that specimens with steel fibers only exhibited the highest compressive strength at room temperature with the lowest residual The second mix provided comparable strengths to the first mix and acceptable strength degradation. Thus, it can be concluded that the design of the HSC mix can be utilized with the inclusion of synthetic fibers to enhance its fire resistance whilst maintaining its strength. Finally, material models for the degradation in the compressive strength of HSC are developed for the two mixes, respectively.