Strain-hardening UHP-FRC with low fiber contents

This research work focuses on the optimization of strength and ductility of ultra high performance fiber reinforced concretes (UHP-FRC) under direct tensile loading. An ultra high performance concrete (UHPC) with a compressive strength of 200 MPa (29 ksi) providing high bond strength between fiber and matrix was developed. In addition to the high strength smooth steel fibers, currently used for typical UHP-FRC, high strength deformed steel fibers were used in this study to enhance the mechanical bond and ductility. The study first shows that, with appropriate high strength steel fibers, a fiber volume fraction of 1% is sufficient to trigger strain hardening behavior accompanied by multiple cracking, a characteristic essential to achieve high ductility. By improving both the matrix and fiber parameters, an UHP-FRC with only 1.5% deformed steel fibers by volume resulted in an average tensile strength of 13 MPa (1.9 ksi) and a maximum post-cracking strain of 0.6%.