Penetration Of Chloride And Life Prediction Of Concrete Structures

Chloride is the most important cause which induces damage to the durability of concrete structures.Chloride diffusion properties are currently the focus of the investigation at home and abroad.This paper carries on the exploratory and innovative research work in the following areas:1) The of durability of existing reinforced concrete structures in Qingdao City were investigated,the exposure condition and the durable performance of concrete structures were analyzed.Results show that factors inducing durability degradation for reinforced concrete structures exist in design,construction and maintenance.At the process of using construction,the fact that durability of the structure will be are reduced by scarce of reasonable maintenance should not be ignored.2) The insufficient of durability for concrete structure under chloride environment induced by material and environmental factors were analyzed and discussed.Results show thatthe forms of chloride profiles are different in actual exposure conditions,the surface chloride concentration of concrete in theory obtained by extrapolation from chloride profile are relatively stable,local environment has significant impact on chloride ingress,the chloride diffusion coefficient is in the order of 10^-13m²/s magnitude to normal portland cement concrete after more than two decades exposure,significant differences of the diffusion property exist in inner and outer region of concrete.3) Under marine environment,the carbonation is very limited and the carbonation is dominated by incomplete carbonation zone.Depth of carbonation in the surface layer of concrete is not exceeding 12mm to concrete construction in splash and tide zone. Although chemical analysis shows that leaching of calcium exist,salt crystallization and carbonation block the pores in surface area of concrete induce the decreasing of porosity and reduce the chloride ingress.4) The diffusion properties of actual concrete structure and laboratory concrete were evaluated by methods of chloride profiles fitting,natural immersion,RCM and diffusion sell.Diffusion coefficient obtained by RCM is the highest,and that of natural immersion and natural diffusion sell are moderate and similar;the value of diffusion coefficient obtained by fitting is the lowest,which is ten times less than the result of RCM method and lower than which obtained by laboratory test and exposure test at seashore.The attenuation index of chloride diffusion coefficient is 0.525 to ordinary portland cement concrete after long-term exposure in splash zone5) Significant differences exist in life prediction with chloride diffusion coefficient obtained from different methods.Obvious differences exist in attenuation index of diffusion coefficient to concrete in laboratory and exposed conditions.Not only the hydration but also environmental factors should be considered when evaluate changes of the chloride diffusion coefficient.Differences of diffusion coefficient in space should be considered and concrete should be divided into diffusion zone and convection zone. Characteristics of probability distribution of influencing factors to durable life of concrete structures under chloride environment were explored.The law of development of durable reliability was analyzed.The life prediction model under chloride ion environment was set up in considering differences in space and time-dependent of the chloride ion diffusion coefficient.Effectiveness and practicality of this method was expounded through specific example and comparing with other models.The diffuse performance of chloride ions in concrete structures were evaluated though laboratory test,exposing test and cores drilling from concrete after long time exposing. The quantitative relationship between durability indexes in laboratory and performance indexes of actual exposure construction was established.Life prediction model based on reliability was set up in considering time and spatial dependence of the chloride ion diffusion coefficient.Theoretical basis and specific methods for the durability design and construction of concrete structure under chloride environment were provided.