No abstract

No abstract

Ultra-high performance fiber-reinforced concrete (UHPFRC) is a new class of concrete that has been developed in recent years. UHPFRC results from the addition of either short discrete fibers or continuous long fibers to the cement based matrix. When UHPFRC compared with high performance concrete (HPC), UHPFRC exhibits superior properties in terms of compressive behavior, tensile behavior, workability, toughness, ductility and durability. UHPFRC has exceptional mechanical and transport properties including a very high tensile strength, strain hardening, and a density leading to a very low permeability. In this research, tests were carried out on twelve ultra high performance reinforced concrete beams with 100 mm × 200 mm cross section, 1600 mm total length to study the effects of adding steel fibers on flexural behavior of UHPC beams. The major parameters included in this research were the amount of internal steel reinforcement and the volume fraction of fibers. The test results showed that adding steel fibers to UHPC beams led to an increase in both load-carrying capacity and flexural ductility, also the concrete strain reaches to high percentage of its ultimate value that taking full advantage of the improved properties of UHPFRC, Furthermore adding steel fiber to UHPC beams can change the crack patterns, delay the crack appearance and restrain the crack expansion in concrete specimen.

The addition of carbon fiber reinforced polymer (CFRP) composites, which is another form of tension reinforcement, affects the ductility of UHPFRC beams strengthened with CFRP sheets. However, the flexural ductility of beams with respect to amount and and yield strength of existing ordinary steel bars has not been investigated in depth. In addition, delamination of CFRP sheets dominates the ultimate mode of failure of flexural members strengthened with CFRP sheets, which limits the ductility of strengthened members. There is a need to investigate the effect of CFRP anchorage system on the overall ductility of strengthened UHPFRC concrete beams. In this research, tests were carried out on thirty two ultra high performance fiber reinforced concrete (UHPFRC) beams to study the effects of some parameters on the flexural strength and ductility of UHPFRC beams with externally strengthening with CFRP sheets. The major parameters included in this research were the amount of internal steel reinforcement, the volume fraction of the fiber and the configurations of placement of transverse anchorages along the external longitudinal CFRP. The test results showed that externally bonding CFRP sheets on the bottom flange of UHPFRC beams led to increase load-carrying capacity but reduce flexural ductility. Also the results showed that the CFRP anchorages could significantly increase the flexural ductility, Furthermore the transverse anchorages were sufficient to eliminate debonding, and the UHPFRC beams failed when the longitudinal CFRP materials fractured, in other cases, the transverse anchorages simply delayed debonding, and the longitudinal CFRP materials debonded after the transverse anchorages fractured.