Steel fibers and self-consolidating concrete in prestressed concrete beams

Prestressed concrete I-beams are used extensively in highway bridges. A common problem in these beams is the appearance of end zone cracks due to the effects of prestressing forces, hydration, shrinkage, creep and temperature variation. In spite of providing large quantity of transverse steel reinforcement (4.2% by volume) in the end zones, cracks continue to occur. The present research was targeted to develop a workable steel fiber reinforced concrete that would be capable of partially or completely replacing the dense traditional transverse reinforcement and eliminating cracking in the end zones.; The research work was carried out in three phases: Phase-I consisted of developing Traditional Fiber Reinforced Concrete (TTFRC) and Self-Consolidating Fiber Reinforced Concrete (SCFRC) mixes with two different types and variable amounts of steel fibers. Based on their performances of workability and hardened properties, suitable TTFRC and SCFRC mixes with optimum fiber contents were selected to cast seven full-scale beams. A new Passing Ability Tester and test method was developed to provide more realistic passing ability values of SCFRC mixes in comparison to the conventional tests. Phase-II research dealt with casting of beams and early-age end zone monitoring of strains and concrete temperatures, to investigate the effect of steel fibers on early-age beam behavior. Phase-III research consisted of load testing the beams until failure to determine the influence of steel fibers on the structural performance of the beams.; On an average, steel fibers increased the tensile strength of concrete by about 50% and 25% in case of SCFRC and TTFRC mixes, respectively. All the optimized TTFRC and SCFRC mixes were deemed suitable to cast the beams. Load test of TTFRC beam with 1.5% by volume of short steel fibers (1.2 inch long), established its potential to completely eliminate the end zone cracking and transverse reinforcement along with 50% reduction in shear crack widths, in the beam. The use of steel fibers in normal slump concrete and self-consolidating concrete was structurally effective in partially or entirely replacing the traditional transverse reinforcement, to control end zone cracking, to augment the shear strength and to enhance the ductility.