Curing–dependent structural behavior of ultra-high-performance hybrid fiber-reinforced concrete beams

Abstract

The application of ultra-high-performance fiber-reinforced concrete (UHP-FRC) is exceptionally versatile. However, a comprehensive understanding of UHP-FRC beam structural performance characteristics is lacking. The majority of research has concentrated on the behavior of structural members following standard water curing. This study investigated the impact of the curing regime on the structural performance of UHPC beams. The four different curing regimes used were standard, simulated hot arid weather, steam curing at various ages, and 5% sodium sulfate curing. Experimentally measured mechanical properties of UHP-FRC have been determined following ASTM guidelines, and the investigated beams have been tested under displacement-controlled four-point loading. Additionally, ACI 318 and FHWA-HIF codified formulas were employed in this study to predict the moment capacity of the tested beams. As a result of the various steam systems of varying ages, the load-carrying capacities of the beams were improved. By accelerating cement hydration, steam curing produces a stronger bond between fibers and the cementitious matrix, improving flexural strength. The control beam (under standard curing) showed a smaller maximum deflection, while all other beams showed similar deflection capacity. By accelerating the drying shrinkage, the beams under the 28-day standard with hot air curing were negatively impacted, with an average deflection value around 5% lower than control beams. The cured beams under simulated hot, arid conditions had the lowest flexural rigidity. A steam-cured beam had the highest moment-curvature performance, while a beam cured under simulated arid conditions had the lowest. Additionally, the ACI 318 design equation significantly underestimated beam maximum moments, while the FHWA approach marginally overestimated beam maximum moments with a predicted-to-tested average of 0.82.