Long term strength of internal GFRP reinforcement by alkaline, temperature and cyclic loading

Abstract

The article deals with the two current problems of determining long-term strength of non-metallic reinforcement in concrete structures: degradation of GFRP reinforcement caused by alkaline environment and cyclic loading.The alkaline environment of concrete with a pH higher than 12.0 affects the glass fibres degradative, whereas this degradation presents by reduction of their mechanical characteristics, resulting in a decrease in the tensile strength of the whole composite.An experimental results of cyclic loading on fatigue life of GFRP bars are presented. The specimens of bare bars and bars encased in concrete were tested. At the tested stress levels, the concrete has a positive effect on the fatigue life of FRP due to confinement, which prevents the fibers from a broom-like failure mode. Two different S-N curves for bare and encased bars are described. At the tested stress levels, considerable matrix or matrix/fiber interface damage occurs at the beginning of the cyclic loading, whereas the fibres are likely to remain intact.Obtained results will allow to define the reliability coefficients for long term behavior of GFRP reinforcement more precisely. It will help to optimal design of GFRP reinforced concrete structures.