Study On Time-varying Properties Of Load Bearing-corroded Reinforced Concrete Structures

Steel corrosion is one of the main reasons for the failure of the durability of reinforcement concrete structure in corrosive environment.After the corrosion of steel,on the one hand,the effective section area decreases and the mechanical property is reduced;On the other hand,the corrosion product expands in volume and produces the corrosion-induced,crack along the longitudinal direction of reinforcement,which causes the bond property between the reinforcement and the concrete to be reduced and the concrete protection layer peeling down,which eventually leads to the service performance and the bending bearing capacity of the reinforced concrete beam declining.Therefore,it is of great practical significance to study the time-varying rule of the corroded crack width expansion and the degradation of flexural properties of reinforced concrete members.In this paper,based on the support by the National Natural Science Fund Project "The research of whole-life time-varying properties and performance reliability based on the reinforced concrete structure under chlorine salt environment"(No.51278444),the mechanical properties of high strength steel bar after rust in concrete,the time-varying rule of the corrosion cracking width and the bending properties of the reinforced concrete beams are studied under the stress state.The main research work is listed as follows:(1)Accelerating rust on reinforced concrete beams under sustained load by accelerating method of electro-constant current-dry cycle,the different corrosion rates of high-strength steel are obtained.The corrosion of corroded high strength steel bars under stress state is analyzed.The fracture form of corroded high strength steel bar under stress state is studied by tensile test.The stress-strain curve,relative nominal strength,relative equivalent strength,modulus of elasticity and elongation with the mass corrosion rate of high strength reinforced bar under stress state are gived.(2)Considering the coupling effect of load and environment,the experimental study on single fly ash beam,single mixed fly ash beam,double doped fly ash and mineral powder beam is carried out.The accelerated rust method of electro-constant current-dry cycle is used to study the change law of rust corrosion-induced crack with time.The results show that the crack width of rust expands slowly and expands to the slow expansion process with time,showing a nonlinear growth.The effect of sustained load on the development and distribution of rust swelling cracks is studied.The results show that under the sustained load,the width of the rust bulging crack during initiation period fluctuates 0.2mm along the length of beam,and the width of the rust bulge crack during the later period shows the result that the width of the middle beam is larger and the two ends are lower.The relationship between the width of corrosion cracking and the corrosion rate of steel bars is studied.The results show that the average width and maximum width of the rust bulging cracks are increasing with the increase of the mass corrosion rate.(3)Considering the coupling effect of load and environment,the flexural capacity test of single fly ash beam,single fly ash beam,double doped fly ash and mineral powder beam is carried out,and the load deflection curve of the corroded beam is studied.The results show that the load-deflection curve of the corroded beam is similar to that of the unrusted beam when the mass corrosion rate is small.With the increase of corrosion rate,the ultimate load decreases faster,and the discrete type of load deflection curve increases.The strain distribution law of the normal section of corroded beam is studied.The results show that when the corrosion rate is small,the concrete strain along the beam height basically satisfies the plat section assumption.But when the corrosion rate is large,the concrete no longer conforms to the assumption of the flat section.The degradation rule of the relative bending strength with the mass rusting rate,the maximum crack width and the average width of the rust swelling crack of the corroded beam are studied.The results show that the degradation rules of bending performance of the reinforced concrete beams with different mineral admixtures are basically similar,and the ultimate bearing capacity of the concrete beams with different mineral admixtures shows a linear declining with the increase of the corrosion degree.