Chloride Ion Transport Experiment And Theoretical Study In The Anchoring Area Of Prestressed Concrete T Beam Under Wet And Dry Cycles

Chloride erosion of unsaturated concrete under alternating wet and dry and load is one of the main topics in the study of durability of concrete structures.Most of the studies are based on chloride ion erosion of concrete under single tensile stress or single compressive stress,while the study of chloride transport mechanism in concrete in the dry and wet alternating area under the complex stress state of pull-pressure-shear is relatively weak,and it is difficult to reflect the service status of the anchorage area of prestressed concrete.Aiming at the above problems,under the joint funding of the National Natural Science Foundation of China project"Mechanism and Model of Chloride Ion Transport in the Anchoring Zone of Posterior TENSION PC Structure under Alternating Wet and Dry Interaction(52078056)" and the Open Project of the Key Laboratory of Bridge Structural Health and National Security(BHSKL2007-GF),experimental research and numerical simulation of chloride ion transport characteristics in the anchoring zone of posterior PC structure under alternating wet and dry action were carried out.The main contents of this article are as follows:(1)Three pieces of post-tensioning prestressed concrete T beam were designed and produced,and the mid-span load value that generated the crack bending moment and the span load value reaching the ultimate bearing capacity were calculated according to the specification,the key strain point test of the anchoring area under the concentrated load of the span,the deflection test of the T beam 1/2 and 1/4 section were carried out,and the three-dimensional geometric model of the prestressed concrete T beam was established using Abaqus finite element software,and the complex stress distribution of the overall bending performance,load deflection curve and anchoring area of the T beam was carried out.The model calculation results and test results were compared and analyzed,and the analysis results had small errors and high coincidences.(2)The chloride ion transport test in the anchoring area under the alternating action of dry and wet was carried out,and the dry and wet time ratio was set to 3:1,the wet state was 5%NaCl salt mist environment,and the dry state was 20%constant indoor humidity,the mass fractions of chloride ions under impermeability,one-dimensional osmosis and two-dimensional osmosis in the anchoring zone were compared and analyzed by chloride concentration determination,the mass fractions of chloride ions under three different dry and wet cycle cycles,and the mass fractions of chloride ions corresponding to the characteristic points of different principal tensile stresses were compared and analyzed.(3)A computational model of chloride ion transport in unsaturated concrete under the coupling of stress and wetness and dryness was constructed,a finite element model of a T beam of prestressed concrete was established by Comsol software,and the rationality of the model was verified by comparing the measured mass fraction of chloride ions and the calculated mass fraction of chloride ions,and finally the sensitivity of four important parameters in the model was analyzed.