Long-term stability of ultra-high-performance concrete with steel fibers in various environments

Ultra-high-performance concrete (UHPC) is renowned for its exceptional strength, durability, and structural integrity, offering sustainable solutions for construction. However, concerns persist regarding its long-term performance under various environments due to unhydrated cementitious particles. In this study, the effect of steel fiber content on the long-term stability of UHPC in tap water, outdoor, and seawater environments over 720 days was investigated. In these three environments, adding 1–3% steel fiber increased the compressive strength of the UHPC by 4.5–11.5%, 9.5–18.5%, and 0.4–3.5%, respectively. The steel fibers also effectively reduced length changes, decreasing the rate by 26.3%, 57.0%, and 26.3%, respectively. Microstructural analysis confirmed the formation of calcite and brucite under seawater curing, indicating chemical interactions between seawater components and cement-based materials. After 720 days in seawater, the surface fibers exhibited corrosion, but the internal fibers were intact. The results of this work provide insights into UHPC’s long-term stability in diverse environments, which is critical for the durability and safety of infrastructure.