Strength and ductility of ultra-high-performance fiber-reinforced concrete beams strengthened with carbon-fiber sheets

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 tothe cement based matrix. When UHPFRC compared with high performanceconcrete (HPC), UHPFRC exhibits superior properties in terms ofcompressive behaviors, workability, toughness, ductility and durability.UHPFRC has exceptional mechanical and transport properties including avery high tensile strength, strain hardening, and a density leading to a very low permeability.On the other hand, the addition of carbon fiber reinforced polymer(CFRP) composites, which is another form of tension reinforcement, affectsthe ductility of UHPFRC beams strengthened with CFRP sheets forincreasing the flexural strength. However, the flexural ductility of beams with respect to amount and yield strength of existing ordinary steel bars has not been investigated in depth. Moreover, delamination of CFRP sheets dominates the ultimate mode of failure of flexural members strengthened withCFRP sheets, which limits the ductility of strengthened members. Hence thereis a need to investigate the effect of CFRP anchorage system on the overallductility of strengthened UHPFRC concrete beams.In this research, tests were carried out on thirty SlX ultra-high-performance fiber-reinforced concrete (UHPFRC) beams with 100 mm x 200mm cross section, 1600 mm total length to study the effects of someparameters on the flexural strength and ductility ofUHPFRC beams with andwithout externally flexural strengthening with carbon-fiber reinforced polymers (CFRP). The major parameters included in this research were as follows:1. The amount of internal steel reinforcement.