Application of fiber-reinforced concrete in the end zones of precast prestressed bridge girders

The secondary spiral and skin reinforcement in the anchorage zone of prestressed post-tensioned girders cause congestion and poses difficulty in the placement of concrete. It is also labor intensive to produce and place the secondary anchorage reinforcement. The objective of this study was to determine the feasibility of reducing the secondary reinforcement with fibers for post-tensioned anchor zones, because of the expected improvement in mechanical properties of fiber reinforced concrete (FRC) over non-fibrous concrete. The first phase of the test program involved the determination of split tensile strength, compressive strength and flexural toughness of FRC and non-fibrous concrete. Two steel fibers and one synthetic fiber with varying amounts were utilized. Steel fibers enhanced the properties of concrete, whereas the role of synthetic fiber was not encouraging. As a result, further testing involved only steel fibers. In the second phase, AASHTO Special Anchorage Device Acceptance Test was performed. Variations of spiral and skin reinforcement, with two levels of concrete strengths, were utilized to investigate the performance of the two types and various amounts of steel fibers. The experimental results indicated that 1% ZP305 steel fiber could be used to replace all the secondary reinforcement for a minimum concrete strength of 5900 psi (40.7 MPa), and could reduce a maximum of 79% of the secondary reinforcement for a minimum concrete strength of 4710 psi (32.5 MPa). Lower volumes of steel fibers may also result in reduction of secondary reinforcements. A finite element model of the AASHTO test block was also developed to validate the experimental results. Good agreement was found between theoretical and experimental strain values. Usage of steel fiber reinforced concrete in the anchorage zones will result in negligible change in the girder costs.