Influence of Fibres on the Rebar - Concrete Bond: Further Evidence of Toughness Enhancement

Abstract

The bond between the rebar and the surrounding concrete plays a substantial role in the mechanical performance of a reinforced concrete member due to the stress transfer that occurs at the aforementioned interface. In this study direct rebar pull out tests were performed at different concrete maturities, fibre contents and fibre materials. PET fibres that have a lower energy requirement during production and improved properties in comparison to polypropylene were used and their performance compared to steel fibres. The addition of fibres leads to a more ductile failure during pull-out. The improved energy absorption capacity is particularly important under seismic loading. Interestingly, a small amount of fibres is enough to notably improve the post-failure behaviour by reducing the softening slope of the stress-slip curve. An increase in fibre content beyond 0.1% for PET fibres does not improve the post-failure behaviour any further. However, steel fibres continue to improve the post-peak behaviour. Thus, the effect of steel fibres is more significant compared to PET fibres and the most pronounced at a high concrete maturity. An analytical model describing the bond stress slip response is proposed and matches the experimental observations well.