| With the renewal of design codes and the progress of society,it is particularly necessary to reinforce old buildings and buildings with defects.Among them,CFRP reinforcement systems are widely used.However,considering its poor heat resistance,it is difficult to be used in projects with strict fire resistance requirements.In this paper,a series of experimental studies have been conducted on how CFRP-reinforced concrete can maintain its performance after fire and the law of performance degradation.The main conclusions are as follows:(1)Experimental study on CFRP reinforced concrete subjected to fire.Test through the hot cone of the FTT0007 cone calorimeter: the test piece without fire protection measures will quickly carbonize or even burn and lose its mechanical properties when the hot cone is above600 ℃.When the heat cone is 800 ℃ and exposed to fire for more than 2 h(first-class fire resistance limit),increasing the thickness of thick fireproof coating can reduce the temperature of the glue layer,and the thickness of more than 20 mm can keep the temperature of the glue layer below 200 ℃.On the basis of 15 mm thick fireproof paint,3 layers(0.8mm)and 6 layers(1.6mm)of thin fireproof paint are applied.Compared with 15 mm thick paint,the temperature of the adhesive layer is lower by 13.7% and 20.1%,and the temperature of the adhesive layer is both It can be lowered to less than 200 ℃;fire-proof coating can effectively reduce the fire hazard of structural adhesive and CFRP-reinforced concrete specimens.(2)Research on the mechanical properties of CFRP-reinforced concrete after fire.The single-shear ultimate bearing capacity of the CFRP-concrete bonding interface does not change much before the temperature of the adhesive layer reaches 200 ℃,but decreases rapidly after reaching 200 ℃,and basically loses its bearing capacity when it exceeds 250 ℃.Through curve fitting,the temperature-ultimate bearing capacity formula of the CFRPreinforced concrete interface can be obtained.This formula fits well during the rapid deterioration of the bearing capacity;the failure mode of the bonding interface is related to the maximum temperature reached by the adhesive layer during the fire process.The higher the temperature of the glue layer,the more glue remains on the concrete,and when the temperature of the glue layer is greater than 200 ℃,the specimen is basically peeled off from the CFRP and the glue layer.(3)Scanning electron microscope microscopic experimental research.When the fire temperature of the sample is greater than 200 ℃,the higher the temperature,the smoother the peeling interface,otherwise,the rougher,the carbon fiber layer will remain on the adhesive layer if the sample does not reach 200 ℃.Observing the section of the adhesive layer,it is found that when the fire temperature is greater than 200 ℃,the higher the temperature,the worse the toughness of the adhesive layer,and the more obvious the plastic deformation of the section.When the temperature does not reach 200 ℃,the adhesive layer has good toughness,no stress whitening zone,and plastic deformation.Smaller,the result of the microscopic test can correspond to the result of the simple shear test.(4)Through the Fourier Transform Infrared Spectroscopy test.In the fire test,samples with a temperature greater than 200 ℃ exhibit carbon-oxygen double bond absorption peak positions,and the carbon-oxygen single bond absorption peak positions of all fired samples are shifted.The changes in these molecular bonds cause the intermolecular force of the structural glue.It becomes weaker,which leads to the deterioration of the toughness of the adhesive layer.The test results can correspond to the phenomena and results of the scanning electron microscopy test and the simple shear test.In summary,when the CFRP-reinforced concrete specimen is subjected to a fire test under no load,as long as the temperature of the glue layer does not exceed 200 ℃,it can maintain good performance after cooling,and its physical and chemical properties will not change significantly. |
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