Corrosion Characteristics Of Reinforcement In Interfacial Zone Of Precast And Post-cast Concrete Under Chloride Erosion And Constant Compressive Stress

Full-span precast box girder bridge is gradually applied in bridge engineering all over the world due to its fast construction and high quality.Many bridges are built in coastal environment or deicing salt environment in the north,so they have been eroded by chloride salts for a long time which causing serious durability problems.Chloride is an important factor causing problems such as corrosion of reinforcements and peeling of the concrete protective layer.The precast and post-cast interfacial zone of the precast bridge section in full-span precast box girder bridge is a weak part to resist chloride penetration.It is important and significant in engineering background to research the chloride transport,corrosion and mechanical properties degradation of the reinforcement.Therefore,the corrosion problem of reinforcement in the precast and post-cast concrete interfacial zone is taken as the research object in this paper.Through the long-term experimental simulation of single-sided chloride salt dry-wet cycle erosion and constant compressive stress,the chloride transport behavior in the interfacial zone and the influence on the reinforcement corrosion are obtained.Chloride salt dry-wet cycle erosion and constant compressive stress long-term interaction experiments show that there is a special chloride transport behavior in the interfacial zone between precast and post-cast concrete.That is,the chloride transport speed in the interfacial zone is faster than that of the concrete bodies on both sides under no stress and small compressive stress,which is called the “funnel effect”.As the compressive stress increases,the “funnel effect” of the chloride concentration distribution in the interfacial zone decreases.When the compressive stress increases to a certain degree,the rate of chloride transport in the interface decreases and gradually begins to exhibit the “inverse funnel effect”.Based on the experimental results,the distribution model of chloride diffusion coefficient in the interfacial zone under nostress and constant compressive stress was established by the Fick's second law.Due to the “funnel effect”,chloride first enter the concrete to form accumulation on the boundary steel surface in the interface,resulting in the first corrosion of the reinforcement at this location,thereby accelerating the corrosion of the reinforcement near the interface which resulting in local corrosion pits and significant degradation of the mechanical properties of reinforcements.A digital model of corroded rebar was obtained by 3D laser scanning technology,and further analysis of its corrosive characteristics and corrosion rate,and a finite element static tensile simulation of the digital model was conducted,comparing the maximum cross-sectional area corroded rate and rebar correlation between the degree of degradation of mechanical properties.The physical tensile test of corroded reinforcement verified the rationality of the numerical simulation results.