| The durability of concrete structures is becoming increasingly prominent in theworld at present, which draws worldwide attention of scientific and technical workersas well as industrial community. External load and environmental factors are the mainfactors affecting the durability of concrete structures. The permeability of the concreteto chloride ion and the variation law under the condition of the coupling of stress andwetting-drying cycles, and the life prediction of the concrete structures under thiscondition are valuable for practical projects. This paper investigates this area deeply.The research contents and the main results are as follows:The stress device were assessed and improved according to results of previousresearch, and it realizes the stress of concrete through the method of loading discspring, and realizes the timely regulate and control and dead load by virtue of stresssensor. It also combines the NEL method and the Electric Quantity method effectivelyand innovatively (namely CPS-NEL and CPS-ASTM C1202). It realizes themonitoring of chloride ion permeability on line under the condition of stress. Thismethod has the features of quick operation, accurate evaluation and practical. It is akind of new pattern method of permeability in the concrete used in the evaluation ofchloride ion.The permeability characteristics of concrete to chloride ion under the conditionof stress were analyzed systematically. The methods of CPS-NEL and CPS-ASTMC1202were applied to the investigation of the permeability of the concrete of C30and C60to chloride ion. The influence of stress intensity (the stress ratio is0.1,0.3,0.5,0.7) and stress variety (tensile stress and pressure stress) on the permeability ofconcrete were studied. The transmission rule of chloride ion in the surface layer ofconcrete under the condition of stress and the stress threshold value of chloride ionpermeability were obtained.The change law of permeability of concrete to chloride ion under the coupling ofstress and wetting-drying cycles of concrete was studied, and the chloride ironpermeability model considering stress and drying-wetting cycles was established andproved innovatively. The influence of stress and wetting-drying cycles on thepermeability of concrete was analyzed by determining the chloride ion concentrationin the concrete. In the meanwhile, the result of chloride iron content under the coupling of wetting-drying cycles and stress was measured by the method of silvernitrate coloration. The chloride ion permeability model (SDWM Model) was set upunder the coupling of stress and wetting-drying cycles based on Fick’s second law.The calculated value from chloride ion penetration model (SDWM Model) andmeasured chloride ion concentration were very close to each other, indicating that themodel has good reliability.The influence of internal damage on permeability of concrete to chloride ion wasanalyzed by using modern test equipments including ultrasonic, SEM and MIP. Theinternal damage defect of concrete caused by stress was analyzed by the method ofultrasonic with the acoustic parameters changing curve. The internal micro structureof concrete under the coupling of the stress and wetting-drying cycles was observedby SEM. The porosity and pore structure distributions of concrete under the couplingof the stress and wetting-drying cycles were determined by MIP. The test results ofultrasonic, SEM and MIP explained the permeability changing law of concrete underthe coupling of stress and wetting-drying cycles.Based on the SDWM Model of concrete under the coupling environment ofstress and wetting-drying cycles, the life of entity structure was predicted. The“PERMIT” device was adopted to conduct the test for the concrete structure entity.The chloride ion concentrations of the contact interface between concrete andreinforced bar were calculated at different ages based on the SDWM Model. The lifeof the entity structure was predicted according to the critical concentration of chlorideion corrosion of steel. |
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