Tension Stiffening and Cracking of Hybrid Fiber-Reinforced Concrete

An experimental program has been carried out to study the effect of hybrid fibers on the tension stiffening and cracking characteristics of high-performance concrete (HPC). A total of 24 axially reinforced concrete tension members were cast and tested, under uniaxial tension. The main variables considered were the volume fraction of: 1) crimped steel fibers (0.5 and 1.0%); and 2) polypropylene fibers (0.1, 0.15, and 0.2%). Load-deformation response was recorded and analyzed. Crack width and crack spacing were also measured at all stages of loading. Test results indicate that the addition of fibers in hybrid form significantly improves the tension stiffening effect and resistance to cracking. The combination of 1% steel fiber and 0.1% polypropylene fiber showed better performance than the other combinations considered in this study. A method is proposed to predict the crack width of hybrid fiber reinforced, high-performance concrete tension members, and the computed values compared satisfactorily with the test results.