Bond Between Steel and Steel Fiber-Reinforced Concrete Under Normal and Elevated Temperature

Presented by Akanshu Sharma, University of Stuttgart This presentation summarizes the results of an experimental study carried out to investigate the bond behavior between steel reinforcement and steel fiber reinforced concrete under ambient conditions and after exposure to elevated temperature in residual state. Square prismatic pullout specimens were used in which three different reinforcement locations were studied namely (i) rebar in the center, (ii) rebar at the edge and (iii) rebar in the corner. The specimens were prepared using normal concrete (NC) and steel fiber reinforced concrete (SFRC) having a steel fiber content of 50 kg/m3. The average concrete cubic compressive strength was around 73 MPa. In order to prevent explosive spalling of concrete at elevated temperatures, 0.5kg/m3 of polypropylene (PP) fibers were added to the mix. Each case was tested at room temperature and after exposure to an elevated temperature of 300°C, 500°C and 700°C. The target temperature was reached at a relatively slow heating rate of 2°C/min followed by a retention time of 3 hours and further followed by a gradual cooling phase. The pullout tests were then carried out in residual state. All the tests with rebar in the center of the specimen resulted in pure bond failure (pullout) for the complete temperature range, whereas a splitting failure was observed for the cases of rebar at the edge and rebar in the corner. For concrete without steel fibers, in the case of bond failure, the thermal degradation is gradual and approximately corresponds to thermal degradation of compressive strength. In case of the splitting failure, however, there is a more pronounced degradation with temperature. For concrete with steel fibers, the degradation of bond is more gradual for both pullout and splitting failure modes compared to that in normal concrete. The results indicate that the inclusion of steel fibers have a potential to increase the bond performance even at relatively high temperatures.