Tensile fatigue endurance in UHPC reinforced with steel and carbon fibers using advanced monitoring techniques

This study examines the tensile fatigue behavior of Ultra-High Performance Concrete (UHPC) reinforced with steel and carbon fibers under cyclic loading.Three specimen types -unreinforced matrix (BM), steel fiber-reinforced (SF), and carbon fiber-reinforced (CF)-were tested using indirect tensile static and fatigue methods with a modified Brazilian test setup.A hinge-based T-shaped loading mechanism ensured stable crack propagation, while strain monitoring combined localized strain gauges with full-field digital image correlation (DIC) for detailed crack behavior analysis.Results indicate tensile strength enhancements of 40% for CF and nearly 3 times for SF over BM.Crack initiation stresses were 7.5 MPa (BM), 6.8 MPa (CF), and 8.6 MPa (SF), with SF specimens demonstrating superior fatigue resistance, sustaining one order of magnitude more cycles than BM.Conversely, CF specimens showed reduced fatigue life due to fiber brittleness and matrix porosity.These findings highlight the influence of fiber type on the fatigue durability and mechanical performance of UHPC under cyclic loading.