An experimental assessment of ultra high performance concrete beam reinforced with negative Poisson's ratio (NPR) steel rebar

An innovative meta steel rebar with negative Poisson's ratio effect (termed as NPR steel rebar), which possesses both high strength (ultimate tensile strength is approximately 1100 MPa) and high uniform elongation (approximately 40%), is developed. This paper experimentally investigated the implications of NPR steel rebar on flexural behavior of ultra high performance concrete (UHPC) beams. Four UHPC beams reinforced with varying reinforcement ratio and longitudinal reinforcement type were prepared and tested. Traditional mono-tonic four-point bending test was performed. The test results showed that UHPC beams reinforced with NPR steel rebar could effectively improve the flexural strength by 47.8%-55.2%, and upgrade the deformability and ductility by 13.6%-180.9% respectively compared with UHPC beams reinforced with HRB 400 steel rebar under same reinforcement ratio, and the crack pattern of which exhibited multiple (6-8) uniformly main cracks located in pure bending region. Discussion included crack pattern, load-midspan deflection curve, ductility and load--strain response. The crack clustering mechanism of beams reinforced with NPR steel rebar was selectively emphasized in the discussion.