| Reactive powder concrete(RPC)is a type of ultra-high performance concrete(UHPC),characterized by super-high compressive strength,extreme durability and high toughness.Through eliminating the coarse aggregates and reducing the water-to-cementitious material ratio,RPC realizes the ultra-high performance.Nowadays,RPC is regarded as a promising material applied to extreme environmental conditions,such as in nuclear power,marine and military facilities.The fire spalling of RPC at elevated temperature and the residual mechanical performance after exposure to high temperature exhibit significant influence on the safety of RPC structure subjected to fire.However,relative test data of fire resistance of RPC elements are scarce till now.This study focuses on the fire resistance of relatively larger-scale of reinforced RPC beams at elevated temperatures and after high temperature.Five large-scale reinforced reactive powder concrete(RPC)beams and a reinforced normal concrete(NC)beam were performed the elevated temperature test by using an electric furnace in this study.The cross-sectional temperature filed and the axial deformation development of the specimens were measured under elevated temperature.The influence of the control temperature,load level and protection layer on the flexural performance were also analyzed through bending test on the specimens after high temperature.Based on the experimental results and discussions,the following conclusions can be obtained:(1)Explosive spall phenomenon was not observed during elevating temperatures of the large-scale RPC beams,meaning that mixing 2% steel fiber and 0.3%Polypropylene fiber(volume dosage)in RPC mixture can suppress the fire spalling of RPC after exposure to 800℃ high temperature.This result indicates that the fire resistance test results of RPC materials can guide the fire resistance design of h RPC elements.(2)The flexural performance of reinforced RPC beams at high temperature and after high temperature is closely related to the control temperature.The deflection of the specimen at high temperature significantly increases with the control temperature increases,while the flexural stiffness and residual load carrying capacity after high temperature decreases with the control temperature increases.Under the test conditions,the degradation range of flexural capacity of reinforced RPC beams are close to 13% and 24% after exposure to high temperatures of 600℃ and 800℃,respectively.(3)The reinforced RPC beam wrapped by the mortar coat can effectively reduce the high-temperature damage at elevated temperature,showing an obviously protective effect.Relatively,the fire resistance of RPC beam is slightly improved by increasing the thickness of RPC cover from 25 mm to 35 mm.(4)The load level exhibits significantly effect on the deflection of RPC beam at elevated temperature,corresponding that the deflection development and the residual deflection of specimen increase as increasing of the load level at high temperature and after high temperature,respectively.However,the load level has only slightly influence on the residual flexural performance of RPC beam after exposure to high temperature.(5)Based on the existing research results of material strength-temperature relationship and equivalent section method,a strength model was proposed for predicting the residual bending capacity of reinforced RPC beams after high temperature.This model was verified by the test data and showed an acceptable accuracy,suggesting that it may be used to evaluate the safety of the reinforced RPC beams exposed to high temperature.Based on the proposed model,parametric analysis was performed on the residual flexural performance of reinforced RPC beam.The results showed that the degradation of tensile strength of RPC after high temperature has the greatest impact on the residual flexural capacity of reinforced RPC beams,while the degradation of tensile strength of longitudinal bars shows the least influence on the residual flexural capacity.The research results of this study provide basic data for the high temperature fire resistance evaluation and retrofitting design of reinforced RPC beams subjected t o high temperature. |
