Study On The Diffussion Performance Of Chloride Ion In Concrete Under Mechanical Load And Life Prediction

Reinforced concrete has found widely application at present. Since chloride fromengineering environment can play a role of accelerating corrosion of steel in concretestructure service life is shortened. The durability problem induced by chloride hasaroused great attention in recent decades years. However, in the past more concretechloride ion diffusion studies in the laboratory to start with little regard for the actualservice conditions such as load-induced concrete cracking and the influence of chlorideion diffusion, even in the limited research, there is a great contradictions. Therefore, itsfindings will inevitably be out of touch with the actual, so that can not or can not bewell applied to engineering practice. But, the influence mechanism of load to concretepermeability is very complex, and there were no accurate unified conclusion, can onlythrough the test to make a conclusion. Because previous studies have not established therelationship of different load levels and types and chloride ion diffusion properties, socannot accurate enough for real in the prediction of concrete life because cannotaccurately considering load effect.Aiming at solving of these problems, this paper studies the transport mechanism ofchloride ion in concrete under no load, and on the basis of the theory, combined withthe problems existing in the present research, carried out the experimental study ofconcrete crack and chloride ion diffusion under the load, the main research contents areas follows:(1) Carry out strain measurement of concrete under axial compressive loads,determine and analysis chlorine ion content in concrete under load after immersion inchloride solution. Study finds the influence of axial compressive load on concretedamage and micro cracks can not only be reflected in the various mechanical properties,but also can use noninvasive estimation method of volumetric strain caused by themicro cracks quantificate the crack development degree. Meanwhile, the method is notsubject to the concrete block size type and strain measurement of part constraints.Chloride diffusion velocity increases with the residual volumetric strain. When theresidual volumetric strain were50με and140με, chloride ion diffusion coefficientchange ratio is achieved respectively1.1and1.25times. There is some relationshipbetween chloride ion diffusion in concrete after axial compressive loading and the axialcompressive load level. In addition, adding fly ash and prolonging curing period can effectively improve the properties of resisting the chloride ion diffusion in concrete.(2) Determine and analysis the chlorine ion content in two mix concrete under thebending load and exposured in different saline environment. Study finds that thebending load on chloride diffusion effect mainly depends on the type and size of loadlevel. When the loads for compression type, the curve isy=11.09x+2.67x~2; whenload type is drawn, the curve isy=10.11x+2.93x~2; chloride ion diffusioncoefficient of the tensile region is significantly larger than the compressive region.Laboratory conditions and the actual marine environment conditions exist somedifferences. Adding mineral admixture and reduce the water cement ratio can makeattenuation coefficient of time larger.(3) Establish the chloride ions diffusion model in concrete under load based on thetest results and previous studies, predict the service life of concrete structure under load.Example shows the practicality of the chloride ions diffusion model in concrete underload in the prediction of service life of concrete structures, and describes the load factorcan not be ignored when the service life of concrete structures is predicted. In addition,thickness of concrete protective layer is also an important aspect in affecting the servicelife of concrete.Study on transfer mechanism of chloride ion in concrete and erosion model under loadhas an important theoretical significance and application value, and it is an importantdevelopment direction for marine engineering structure durability research in thechloride environment under load, and is an important basis for the concrete structuredurability evaluation, design, life prediction.