Evolution of the bond strength between reinforcing steel and fibre reinforced concrete after high temperature exposure

Abstract

Reinforced concrete structural strength depends on the bond between steel rebars and concrete. This mechanism can be compromised during a fire, but may be one of the least investigated phenomena in concrete research, and is not addressed in concrete design codes. This paper is focused on the characterization of the bond strength after exposure to temperatures up to 825 °C, by means of pull-out tests carried out in normal and high strength concrete, with polypropylene and steel fibres. Compressive and pull-out tests were performed after exposure to high temperature and cooling down to room temperature. Hybrid fibre addition including steel fibres with a high aspect ratio proved beneficial to the peak bond strength at the highest temperatures tested. However, high strength concretes exposed to 450 °C presented higher bond strength losses if steel fibres were added. Finally, equations are proposed for predicting the bond strength after high temperature exposure.