Research On Flexural RC Components Exposed To Marine Environments: Durability And Life Prediction

The study of durability evaluation and life prediction method of RC components in marine environments has important social significance and application value. The research object is durability and service life prediction of RC components exposed to marine environments in the thesis. Based on on-the-spot investigation and durability experimental study, durability failure process and its regularity of concretes in marine splash zone, submerged zone, tidal zone and salt-spray zone are discussed. Degradation process and degradation mechanism of marine concretes exposed to seawater are analysis, including chloride ion diffusion law, relative dynamic modulus loss, mass loss. Main contents of each chapter are mentioned as follows:In Chaper 1, durability of concrete exposed to marine environments and service life predicting methods were summarinzed and the research progress are reviewed. Problems remaining to be investigated were also proposed, and on the basis of this study research scheme and content are determined.According to the widely existence of chloride ion in marine environments and its harm to marine concrete, analysis on the durability and service life of RC structures exposed to southern and northern coastal areas in china has been carried out in Chaper 2. Then the basic conditions, mechanism and influencing factors of rebar corrosion in marine concretes are explored. Finally the basic transmission mechanism and degradation mechanism of marine concrete are mainly discussed. Thus it can lay a foundation for establishing life prediction model of concretes exposed to different marine regional environment.In Chaper 3, first preliminarily selected several mineral admixtures mixing proportion of concrete, ordinary concrete, high-performance concrete, and the mineral admixtures concrete methods of preparation and basic properties are briefly introduced. In order to study the durability of the concrete materials and RC components in marine environment, field exposure test and laboratory tests of marine concrete durability and designed, including: (1) field exposure test and indoor temperature soak corrosion test of concrete materials; (2) field exposure test environment and indoor simulation accelerated tests of RC components.In Chaper 4, comparative experiments of concrete materials and RC components are conducted in laboratory by simulating marine environments, and combining with non-destructive detection and analysis, the relative dynamic modulus and mass loss rate are determined, and the spalling appearance of specimens are observed. Damage rules and characteristics of marine concrete are investigated. Lastly, the damage relationship of concrete materials and RC components are studied. In Chaper 5, based on field exposure tests and indoor simulation tests, the total and free chloride ion concentrations at different depth of concrete specimens were measured. Chloride ion diffusion law of concretes exposed to marine environments and the relationship are studied. Then according to different marine environments and different concrete types, the concrete chloride diffusion characteristics are probed into.In Chaper 6, adopting corroded RC components as research object, the test results of bending bearing capacity and the destruction mode of RC components are analyzed and discussed according to the natural exposure method in field marine environment and the accelerated corrosion in laboratory. Meanwhile, based on marine regional environment, an analytical model of rebar corrosion rate is established, and the influencing of mineral admixture on rebar corrosion rate is discussed, also the relationship between rate corrosion rate and steel surface chlorine ion concentration is given. Finally, considering the influence of rebar corrosion rate on performance of rebar and stick performance of rebar and concrete, the flexural capacity evaluation model of corroded RC components is put forward based on current structure design codes, and the model has clear concept, wide serviceability and more reasonable. Furthermore, the results show that there is a good agreement between measured value and calculated value, which indicates that the evaluation model has high value; it can be applied to reality RC engineerings.In Chaper 7, based on the residual life of rust RC structure, analyzes the research status of the damage process of RC are analyed, and the definition of service life are given, then put forward the service life prediction model of two stages. (1)The first stage: On the basis of Khatri's model, an improved model for calculating service life of marine concrete is proposed. Influencing factors of chloride diffusivity, chloride binding capacity, critical chloride concentration, structural defects are taken into consideration. The result from the improved model is in good agreement with those of Clear's experimental model. (2)The second stage: definite the bearing capacity drops to certain scope as the end mark of the durability life of corroded RC components. After derived, when rebar corrosion rate from 0 to 5%, t corcan be calculated.A summarization of this main work and conclusions was presented in chapter 8. Suggestions for further researches were put forward.