Temperature-adaptive mechanism of bamboo fibers for regulating elevated temperature performance of UHPC

Ultra-high performance concrete (UHPC) is known for its exceptional mechanical properties due to its high density; however, this also makes it prone to explosive spalling at elevated temperatures. This study investigates the effects of bamboo fibers on UHPC under elevated temperatures, focusing on the synergistic impact of mixed bamboo and steel fibers on the material's performance. UHPC specimens were prepared with varying fiber contents (0–2.0 % steel fibers, 0–1.5 % bamboo fibers) and tested at temperatures of 200℃, 400℃, 600℃, and 800℃. The study evaluates macroscopic mechanical properties, microstructural void evolution, and thermal performance. The results reveal that bamboo fibers significantly enhance crack resistance and anti-spalling behavior. At 200℃, UHPC showed a reduction in macro-voids and an increase in micro-voids, improving mechanical performance. Between 400℃ and 600℃, bamboo fiber carbonization created channels that alleviated thermal stress and steam pressure, suppressing crack propagation and spalling. Compared with steel fiber-only UHPC, the hybrid fiber system exhibited reduced porosity, less crack propagation, and maintained compressive strength. The synergistic effect of bamboo fibers enhances material stability under elevated temperatures, with improvements in both mechanical strength and crack resistance. The presence of bamboo fibers also improves the material's overall thermal stability by mitigating the internal stresses caused by differential thermal expansion. This study provides an effective optimization strategy for UHPC in high-temperature environments.