Influence of Steel Fiber Content on the Long-Term Stability of Slag-Containing UHPC Under Different Environments

Ultra-high-performance concrete (UHPC) is an advanced material known for its high strength and durability. This study investigates the long-term stability of slag-containing UHPC exposed to outdoor, tap water, and seawater environments over 720 days, focusing on the impact of steel fiber content. The results show that UHPC in tap water exhibits higher compressive strength compared to seawater and outdoor environments. Without fibers, compressive strengths at 1 day, 28 days, and 720 days are 99.7 MPa, 104.7 MPa, and 148.0 MPa, respectively. With 3% steel fiber, these values increase to 132.9 MPa, 143.6 MPa, and 166.6 MPa, representing increases of 33.3%, 37.2%, and 12.6%. Steel fibers also reduce the expansion rate of UHPC, with the expansion decreasing from 525 × 10^-6 (no fibers) to 345 × 10^-6 (3% fibers), a reduction of 34.3%. Additionally, differential thermogravimetry (DTG) analysis further confirms the formation of C-S-H, ettringite, calcium hydroxide, and calcite under different environments.