Experimental Research On Mechanical Performance Of Large-scale Reinforced RPC Columns At High Temperature And After High Temperature

This study focused on the blank areas of the fire resistance of reactive powder concrete（RPC）structural columns and finished the elevated temperature tests on seven large-scale reinforced RPC columns.The cross-sectional temperature field of the specimen and the axial deformation curve at elevated temperature condition were measured.The influence of temperature,axial compression ratio,thickness of RPC cover and concrete types were investigated through compression test on the specimens after high temperature.Based on the existing relationship between RPC strength and high temperature,a calculation method was proposed to predict the residual load carrying capacity of the reinforced RPC columns after exposure to high temperatures,and it was also validated with experimental results.The current study provided basic outcomes for the fire resistance design and the residual load carrying capacity evaluation of RPC columns after elevated temperature.The main research results can be drawn as follows.（1）The appearance of the RPC columns are obviously changed after high temperature,in which the surface of the specimen exhibits white colour and gray-white colour after subjected to 600°C and 800°C,respectively.For the RPC columns without axial loading,visiable transverse cracks appear on the surface after high temperature and the number and width of the cracks increase significantly as increasing of the test temperature.On the other hand,the number and width of the cracks on the surface of the RPC columns with axial loading obviously decrease after elevated temperature test.Compared with ordinary reinforced concrete column,the cracking phenomenon caused by high temperature of RPC columns has been significantly suppressed.（2）Heating time of the reinforced RPC column increases significantly with the target temperature increases,while it is obviously shorter than the ordinary concrete column.The test results show that pre-loading on RPC column decreases the temperature expansion at elevated temperature and reduces the shrink cracking after high temperature.Increasing the thickness of RPC cover can reduce the residual axial deformation of the RPC column after high temperature.Compared with the ordinary concrete column,the expansion deformation of reinforced RPC column at elevating temperature significantly decreases and its residual deformation also reduces after elevated temperature test.（3）The failure modes of the reinforced RPC columns after elevated temperature are influenced by different factors.For the RPC columns exposure to 600 ℃,the existing temperature cracks extended along the circumferential direction and gradually penetrated.Eventually,the specimens were destroyed due to rupture of the stirrups.However,obvious peeling phenomenon of RPC cover was not be observed in the compression test,which was significantly different from the failure mode of the ordinary reinforced concrete column.The stirrup failure of RPC column exposure to800℃ did not occur after compression test.（4）The mechanical properties of the reinforced RPC column show significantly degradation after high temperature test.The peak load and corresponding axial deformation gradually decrease as increasing of the control temperature.So shape of the load-deformation curve gradually becomes gentle.Compared with the control RPC column,the residual load carrying capacity decrease by 39% and 68%,and the axial stiffness decreased by 68% and 83% after the reinforced RPC column exposure to 600℃and 800℃,respectively.The coupling of temperature and load exhibits significant effect on the residual compressive performance of RPC columns after high temperature.Generally,pre-loading on RPC column can increase the axial stiffness after high temperature.On the other hand,the pre-loading decreases the residual deformation capacity of the specimen.Compared with ordinary concrete columns and high-strength concrete columns,The RPC column exhibits relatively more severe reduction in the load carrying capacity after exposure to high temperature compared with the existing test results from NC columns,while the former has much higher residual strength.（5）Based on the existing relationship between RPC strength and high temperature,a calculation method was proposed to predict the residual load carrying capacity of the reinforced RPC columns after exposure to high temperatures,and it was also validated with experimental results.This method can be used to evaluate the residual loading carrying capacity of RPC column after high temperature.It is also found that the influence from the coupling of high temperature and axial load needs further investigations.