Geometry, material properties and bond performance of prototype titanium reinforcing bars

Abstract

The use of titanium as a concrete reinforcing bar material has been proposed. This study summarizes measured geometric and experimentally determined material properties of 6Al-4V titanium reinforcing bars and comparable properties of ASTM A615 steel. All bars are nominally #5 bars. Bond characteristics of the titanium bars were assessed through ASTM D7913 pull-out tests, ASTM A944 beam-end tests and four concrete prism tension tests. The nature of reinforcing bar bond to concrete is such that deformed bars exhibit very similar patterns of bond stress-slip behaviour. Provided adequate deformations are provided, the bond-slip relationship is dominated by concrete behaviour. The bond performance of the 6Al-4V titanium bars was similar to that of A615 steel bars and, as expected, clearly affected by the rib ratio. The results presented reinforce the ASTM A615-implied lower limit for the rib ratio, Rr > 0.05. The implication of a similar bond-stress behaviour is that existing bond relationships for steel-reinforced concrete likely apply to titanium bars provided they meet the deformation requirements of ASTM A615 – the standard for which steel reinforcing bars, and therefore their bond characterisation – is calibrated. Both the pull-out and beam-end test results reinforce the conclusion that bond behaviour of titanium bars is essentially the same as that steel bars. The bond stresses, normalised to account for variation in concrete strength, are similar and the calculated development lengths are essentially in the ratio of yield strengths of the materials. The prism tension tests demonstrated that concrete crack width is proportional to modular ratio of the reinforcing material, while spacing is inversely proportional to the stiffness of the initial bond-slip response.