Study on Influence of Concrete Protective Layer on Mechanical Properties of Sleeve Grouting Connections After High-Temperature Exposure

Sleeve grouting connections are one of the primary connection methods for reinforcing steel in prefabricated concrete structures. To investigate the effect of concrete cover on the mechanical properties of sleeve grout connections after exposure to high temperatures from fire， 12 sleeve grout connection components with a 30 mm concrete cover and 12 specimens without a concrete cover were subjected to uniaxial tensile and high-stress repeated tensile tests after high temperatures exposure. The study explored the influence of the concrete cover on the failure mode， load-bearing capacity， and ductility of sleeve grout connection components under different loading conditions. The test results indicated that the concrete cover had a significant impact on the failure mode of sleeve grouting connections after exposure to high temperature. After 60 minutes of exposure， the specimens with concrete covers exhibited reinforcement breakage failure under both uniaxial tensile and high-stress repeated tensile test， whereas the specimens without concrete covers exhibited bond failure. After high-temperature exposure， the concrete protective layer enhanced the ultimate load and ductility of the sleeve grout connection under both loading conditions， but the ultimate load and ductility of specimens with a protective layer under high-stress repeated tensile loading were slightly lower than those under uniaxial tensile loading. Based on the experiments， a numerical model was established using the finite element software ABAQUS， with concrete protective layer thickness and fire exposure time as the parameters. Finite element results indicated that the thickness of the concrete protective layer and exposure time significantly affected the ultimate load and bond strength of the specimens. Both the ultimate load and bond strength increased with increasing protective layer thickness and decreased with prolonged exposure time. Based on the experimental and finite element analysis results， a calculation method for the ultimate bond stress of sleeve grouting connections， considering the combined effects of protective layer thickness and exposure time， was proposed.