Transport Of Chloride In Concrete Subjected To Coupling Flexural Load And Wetting-Drying Cycles

Transport of chloride in concrete subjected to coupling flexural load and wetting-drying cycles is an important issue for concrete structure in marine environment. Natural immersion method was used in this word and test methods of chloride transport in concrete under coupling sustaining flexural load and environmental factors in marine environment were established. Chloride transport processes in concrete in submerged condition and cyclic condition was simulated. Models of chloride apparent diffusion coefficient influenced by water to binder ratio, dosage of GGBS and curing time in submerged condition and cyclic condition were established after studying the transport of chloride in concrete under a single, double and multiple factors. Time dependency of apparent diffusion coefficient and surface chloride concentration were studied in submerged condition and cyclic condition. Considering the influence of continuous flexural load, wetting-drying cycles, water to binder ratio, dosage of GGBS, curing time temperature, relative humidity and chloride binding, the chloride transport model under the action of multiple factors in concrete was established. The main study conclusions and innovation results were list as following.The choice of sustained loading method and the establishment of test method coupling sustaining flexural load and environment factors in marine environment.Continuous flexural loading device suitable for wetting-drying cycles test was chosen considering the advantages and disadvantages of various sustained loading device and loading methods. Test method and experiment system of chloride transport in concrete coupling the continuous flexural load and environmental factors in marine environment were established.Study of chloride transport in concrete in submerged condition and wetting-drying cycles condition.Chloride transport in concrete in submerged condition and cyclic condition was studied through the simulation of actual conditions in underwater area, splash zone and tidal zone. It was indicated that, chloride apparent diffusion coefficients in submerged condition and wetting-drying cycles condition increased with water to binder ratio. The influence of water to binder ratio to apparent diffusion coefficients was increased by the role of wetting-drying cycles. The relationship between chloride apparent diffusion coefficients and dosage of GGBS corresponds quadratic polynomial. Chloride apparent diffusion coefficients adding GGBS as admixture was less than the one without GGBS as admixture. Chloride apparent diffusion coefficients in submerged condition and wetting-drying cycles condition decreased with curing time. The relationship between chloride apparent diffusion coefficient and curing time corresponds power function. Models of chloride apparent diffusion coefficients influenced by water to binder ratio, dosage of GGBS and curing time in submerged condition and wetting-drying cycles condition was established. Chloride apparent diffusion coefficient decreased with exposure time in submerged condition and cyclic condition. Compared with submerged condition, wetting-drying cycles increased apparent diffusion coefficient. The ratio of apparent diffusion coefficient between submerged condition and wetting-drying cycles increased with exposure time. And model of the apparent diffusion coefficient ratio between submerged condition and wetting-drying cycles condition over exposure time was established. On this basis, general factors model of chloride apparent diffusion coefficient in concrete was established according to the influence of water to binder ratio, dosage of GGBS and curing time on apparent diffusion coefficient. And the value of model parameters was determined based on experimental data.Time dependency of apparent diffusion coefficient and surface chloride concentration.Time dependency of apparent diffusion coefficient and surface chloride concentration in submerged condition and wetting-drying cycles condition was studied systematically. The results show that time dependency of apparent diffusion coefficient in submerged condition and wetting-drying cycles condition decreased with exposure time approximating to power function. The constant of time dependency of apparent diffusion coefficient increases with water to binder ratio and dosage of GGBS. The relationship between the constant of time dependency and water to binder ratio or dosage of GGBS can be described as the form of line function. The influence of curing time did not considered in the model of time dependency of apparent diffusion coefficient; it’s hard to establish the relationship between the constant of time dependency and curing time. A new method was used to research the influence of curing time to diffusion coefficients, considering the apparent diffusion coefficients as the average integration value over exposure time, and transforming the apparent diffusion coefficient to instantaneous diffusion coefficient. Then the relationship between constant of time dependency on instantaneous diffusion coefficients and curing time was established. The relationship between constant of time dependency on instantaneous diffusion coefficient and curing time exhibited square root function. A comprehensive model of time dependency was proposed based on the influence of water to binder ratio, dosage of GGBS, curing age and wetting-drying cycles. The relationship between apparent diffusion coefficient and instantaneous diffusion coefficient was analyzed. How to introduce the time dependency model into chloride diffusion models has been discussed.Surface chloride concentration increased with exposure time. Its growth rate become slowing, and stabilized after a certain period. Time dependency model of surface chloride concentration corresponded the form of square root function in submerged condition and the form of square root function with a initial value in wetting-drying cycles condition.Sustaining flexural load coupling submerged condition and wetting-drying cycles condition on chloride transport in concrete.Chloride transport in concrete coupling the continuous flexural load and submerged condition or wetting-drying cycles condition has been studied systematically. It was found that sustaining flexural load does not change the influence of water to binder ratio, dosage of GGBS and curing time to apparent diffusion coefficient. Chloride apparent diffusion coefficients increased with stress ratio in submerged condition and cyclic condition. The relationship between apparent diffusion coefficient and stress or stress ratio can be represented as a quadratic polynomial. The ratio of apparent diffusion coefficients between submerged condition and wetting-drying cycles condition coupling sustaining flexural load increased with exposure time. And model of the apparent diffusion coefficient ratio between submerged condition and wetting-drying cycles condition over exposure time correspond with the form of exponential function.Chloride transport model considering sustaining flexural load and wetting-drying cycles.The influence of deterioration factors, chloride binding capacity, temperature, relative humidity and time-dependency of chloride diffusion coefficient and surface chloride concentration on transport model was analyzed. Based on Fick’s second law, considering the influence of sustaining flexural load, wetting-drying cycles, water to binder ratio, dosage of GGBS, curing time, temperature, relative humidity and chloride binding, the chloride transport model under the action of multiple factors in concrete was established. The parameters in model in submerged condition and wetting-drying cycles condition with or without sustaining flexural load was discussed in this section. The influence of water to binder ratio, curing time, sustaining flexural load and wetting-drying cycles on the transport model was studied. And the transport model was verified with field exposure data.