Development of Hybrid Fiber Reinforced Cementitious Composites and their Structural Application

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New type of fiber reinforced cementitious composites were developed, in which not only high performance polymeric fibers but also steel cord were mixed together. That is Hybrid Fiber Reinforced Cementitious Composites (HFRCC). These new materials achieve multiple cracking of so thin width that the composites are possessed of high strength, strain hardening and high ductility. The summary of the results are as follows :1). Mix proportion of HFRCC was studied to produce the highly ductile composites. Examined parameters were the length and volume contents of fibers, and the combination. Not only the mechanical performance but also the workability was investigated.2) A series of a uniaxial tension test was carried out on a deformed bar embedded in the newly developed HFRCC. Microcracking around the deformed bar was carefully observed by means of a unique method of X-ray technique. Macroscopic bond behavior was also studied to find a much more obvious tension stiffening effect than that observed in plain concrete. Even after yielding of the steel bar, HFRCC still resisted the load so that the total strength capacity is much higher than the yield strength.3) HFRCC beams reinforced with deformed bars were tested under a type of shear loading. Influences of type of fibers and also stirrups ware examined. Cracking process was carefully observed by means of the X-ray technique to discuss the fracture mechanism.4) Column-type members made with reinforced HFRCC were tested under cyclic loading to examine the energy absorption capacity and also numerically analyzed by means of a nonlinear FEM. Tapered members with X-shaped reinforcement showed very good results from the view point of the ductility and the damage level of cracking even after a large deformation. It proved that the tapered members with X-shaped reinforcement can be practically applied as energy absorbers.