Experimental Research On Durability And Mechanical Properties Of RC Structures Influenced By Adverse Factors In Cold Region

Reinforced concrete(RC)is one of the most widely used materials in constructions,especially used in road structures,bridge structures and their ancillary facilities.Nowadays,durability of RC structures is widely concerned by engineers,because it is related to structures' service life and structural carrying capacity,the cost of repair and rebuild,and the sustainability of environmental resources.Therefore,it is necessary to investigate the durability of RC structures.Exposed to aggressive environments in cold regions,RC structures often suffer from concrete crack and rebar corrosion due to environmental load and mechanical load,which will deteriorate the durability and structural carrying capacity of RC structures.From now on,many experimental researches have been conducted for investigating the effect of environmental factors such as freeze-thaw cycles,carbonation and loading crack on durability of RC structures,most of which only focus on a single factor that influence the durability.However,RC structures often suffer from a couple effects of multi-factor in natural environment,and the number of researches on the durability of RC structures under the effect of multi-factor is not very large.Besides,the methods applied in the researches on the mechanical properties under the effect of environmental factor influence results(such as concrete crack and rebar corrosion)are outdated.Therefore,in order to scientific analyze the durability and mechanical properties of RC structures under the effect of adverse factors in cold region,developed combined with the Project supported by National Natural Science Foundation of China(Nos.51378236)and The Science and Technology Project on Transportation Construction in the West Region(Nos.20113188011000),the major works carried out in this paper are as follows:1.Freeze-thaw cycles,carbonation and loading crack were chosen as the representative adverse factors in cold region.Experimental research on the durability under the effect of these adverse factors was conducted in this paper.RC samples were suffered pre-crack,cyclic freeze-thaw,carbonation and chloride-induced rebar corrosion.The concrete mass change ratio and compressive strength were used as the indicator for investigated the deterioration of concrete material properties.Besides,rebar corrosion ratio was used as the indicator for quantitatively analyze and compare the effects of crack,freeze-thaw cycles and carbonation on durability of RC structures by statistical analysis methods.The results reveal that crack presents the most significant effect on durability of RC structures.2.RC specimens with different crack number,width and spacing were prepared and the rebar corrosion was conducted through an accelerated chloride penetration method.Then,corrosion current densities of rebar were calculated from electrochemical test methods.Bases on the corrosion current densities of rebar,a more reasonable electrochemical test method was recommended used in RC corrosion system.Corrosion current densities of rebar were treated as the indicator for quantitatively analyze and compare the effects of crack number,spacing and width on rebar corrosion behavior by statistical analysis methods.3.Based on Non-Steady-State Chloride Migration test,a simulation study was conducted for analyze the migration behavior of chloride ions in cracked concrete under the effect of concrete saturation,crack number and width.Furthermore,a prediction model of chloride concentration on the simulated surface of rebar in concrete influenced by different crack states is established.This model is used to derive the corrosion current density and corrosion depth prediction models of rebar in this paper,which can be used by engineers to estimate the migration behaviors of chloride and rebar corrosion degree in RC structures in a short time and evaluate duration of RC structures after knowing the status of cracks and chloride diffusion sources.4.RC beams were prepared and the rebar corrosion was conducted through an electrochemical accelerated method.Vibration measurement was employed to obtain modal frequencies of RC beams under different rebar corrosion ratio for investigating the dynamic property under the effect of rebar corrosion.In this paper,the effect of rebar corrosion ratio and concrete crack area on modal frequencies was investigated.Besides,equivalent elastic modulus of RC beams were obtained by deflection test,and the relation between equivalent elastic modulus and rebar corrosion ratio were determined and used for establishing a prediction model to obtained projected RC structures' service life.5.RC beams were prepared and the rebar corrosion was conducted through an electrochemical accelerated method.Flexural capacities of RC beams were used to evaluate the static performance under the effect of rebar corrosion.Besides,acoustic emission testing technology was employed for monitoring the conditions of RC beams during their loading procedure.Moreover,basic parameters,statistical parameter and location signal of acoustic emission signal and crack conditions of RC beams were compared to analyze the flexural capacities and acoustic emission characteristics of RC structures under different rebar corrosion ratio.