Combined effect of coarse aggregate and fiber on tensile behavior of ultra-high performance concrete

In this study, combined effect of coarse aggregate and fiber properties on tensile behavior of ultra-high performance concrete (UHPC) was investigated. Four replacement levels of coarse aggregates (0%, 15%, 25%, 35% by volume of mortar) and four types of steel fiber (three micro-fibers with a shape difference and one macro-fiber) were considered. Results showed that replacement level of coarse aggregate has a critical value of 25% and different fiber types act similarly in regard of compressive strength. Coarse aggregate brought impairment to bonding strength and utilization efficiency of fiber, especially for deformed ones. Furthermore, coarse aggregate could be successfully introduced into system of UHPC without impairing its tensile properties at a favorable replacement level (⩽25%). In addition, phenomenon of strain hardening behaviors of UHPC incorporating coarse aggregate could be triggered by further increasing fiber dosage to larger than 2.5%, however, it was independent of fiber type due to combined effect of coarse aggregate and fiber bridging.