Developing Ultra-High-Performance Fiber-Reinforced Concrete for Large-Scale Structural Applications

Recent advances in the next generation of fiber-reinforced concrete (FRC) have led to a new class of concrete known as ultra-high-performance FRC (UHP-FRC), which exhibits very high compressive strength (22 to 30 ksi [152 to 207 MPa]) and tensile ductility (with strain-hardening behavior after first cracking). Its casting and mechanical properties, however, have been mainly reported based on small batch mixing and small-scale specimens. Therefore, this research first focused on developing UHP-FRC using commercially available constituent materials in the United States, utilizing dense particle packing concepts without any special materials or treatments. Major parameters, including the effects of varying mixture components, water-cementitious materials ratios (w/cm), fiber volume fractions, and sand ratios were studied. As part of this study, fly ash was introduced as a supplemental cementitious material to enhance flow ability of the mixture during the mixing stage and large-scale casting. Both compressive and tensile tests with smaller- and larger-scale material specimens were performed. This study shows that the specimen size and tension-stiffening effects have appreciable influence on UHP-FRC s mechanical properties. Finally, to verify the large-scale cast-in-place ability of the developed UHP-FRC mixture, 22 f[t.sup.3] (0.62 [m.sup.3]) of UHP-FRC was produced and cast in a full-scale moment frame column at the plastic hinge region. Keywords: flow diameter; liquefaction time; ultra-high-performance concrete (UHPC); ultra-high-performance fiber-reinforced concrete (UHP-FRC).