Study On Similarity Between Indoor Simulation And Marine Exposure On Chloride Penetration Into Concrete In Splash Zone

The corrosion of steel bars caused by chloride ingress into reinforced concrete is one of the most important factors that result in the durability deterioration of concrete structures.The transport behavior of chloride in concrete structure is quite different between the natural environment and indoor simulated environment.Therefore,in order to accurately analyze the durability deterioration of concrete structures and further establish an effective prediction model of service life,the key problem is to determine the chloride transport law in concrete and explore the similar mechanism of the key parameters for the chloride ingress process between the long-term exposure in the real-marine and short-term accelerated indoor simulation.Based on this,the tests of chloride ingress into ordinary concrete（C30 and C50）,strain-hardened cement-based composites（SHCC）and alkali-activator concrete（AAC）exposed to the splash zone environment at real-marine exposure and indoor simulation were carried out,and the time-varying evolution law of key parameters affecting durability evaluation was analyzed.Based on the collected statistical data of real marine exposure and indoor simulation,the Markov chain Monte Carlo method（MCMC）and Bayesian method were combined to establish a probabilistic model of environment-time similarity between indoor simulation and real marine exposure.The main work and conclusions of this paper are as follows:（1）Based on the test of chloride ingress into concrete in the real-marine exposure environment of the splash zone,the influences of concrete type（C30,C50,SHCC and AAC）and exposure time（90 d,180 d,360 d,720 d）on the content distribution of free chloride were studied.The results show that chloride content decreases with the increase of concrete strength and increases with the increase of exposure time.Fiber concrete has better resistance to chloride ingress when exposed for a long time,and alkali-activator concrete has the best resistance to chloride ingress.Combined with the real-marine exposure data,the factors affecting and the time-varying evolution law of surface chloride concentration and apparent chloride diffusion coefficient were further analyzed.The time-varying model of the key parameter considering the influence of cementitious materials and the water-cement ratio was established.The solution method of instantaneous chloride diffusion coefficient was studied,and the difference between apparent and instantaneous chloride diffusion coefficient was compared and analyzed.Also,the established model of chloride ingress into concrete that takes into account the time-varying properties of surface chloride concentration and chloride diffusion coefficient,and the free chloride content was verified.The results show that the surface chloride concentration increases with the increase of exposure time,while the apparent chloride diffusion coefficient decreases,and both tend to be stable gradually,and the time-varying law conforms to the reciprocal model.The apparent chloride diffusion coefficient is obviously larger than the instantaneous chloride diffusion coefficient under the same exposure conditions.（2）The self-designed integrated automatic testing machine of artificial simulated marine tidal and splash zone was used to investigate the process of chloride ingress into concrete in the artificial simulated marine splash zone.The effects of the concrete type,exposure time and drying-wetting cycles mechanism（the drying-wetting ratio is 3:1,11:1and 85.4:1）of the chloride content were also analyzed.A model of chloride transport in unsaturated concrete under the drying-wetting cycles was established,and the Crank-Nicolson finite difference method was used to numerically solve the process of chloride transport.The mesoscale numerical simulation of chloride transport in unsaturated concrete under the drying-wettig condition was carried out,and the sensitivity of the key parameters in the model was analyzed.The results showed that the free chloride content,surface chloride concentration and chloride diffusion coefficient all firstly increased and then decreased with the increase of drying-wetting cycles time ratio,and the peak of chloride on the concrete surface can be divided into convection zone and diffusion zone.With the increase of drying-wetting cycles time ratio,the content of chloride convection zone and the total amount of chloride ingress firstly increased and then decreased.The depth of chloride diffusion increases with the increase of initial saturation of internal pore in concrete.（3）150 groups of real-marine exposure data and 300 groups of indoor simulation test data were collected and analyzed by statistical probabilistic method.The influence of subjective uncertainty and objective uncertainty was comprehensively considered.The combined method of MCMC and Bayesian principle was used to determine the key parameters in the probability model of the chloride ingress.The probability prediction model of surface chloride concentration and apparent chloride diffusion coefficient considering the water-cement ratio and cementitious materials were established and verified to reasonably describe the probability distribution characteristics of the chloride ingress.The confidence interval of different confidence coefficient according to probability statistics method can be determined.Based on the established probability prediction model,the correlation coefficients of key parameters were introduced to analyze the similar relationship of chloride ingress between indoor simulation and real-marine exposure.It was found that the similarity coefficient of the key parameters for four kinds of concrete was less than 1,indicating that the apparent chloride diffusion coefficient(D_appm)and surface chloride concentration(C_sm)at the real-marine exposure environment was less than those of the indoor simulated environment(D_appi and C_si).The surface chloride concentration of concrete in the indoor simulated environment with exposure time of 30 d can be used to better predict the chloride ingress in real-marine for360 d or even 720 d.The apparent chlorine diffusion coefficient of the indoor simulated environment with an exposure time of less than 90 d can be used to better predict the real-marine’s chlorine ingress within 180 d.Based on the linear relationship between C_sm and C_si,D_appm and D_appi,the similarity relation probability model of the key parameters of the chloride ingress was established,which can better predict D_appm and C_sm,and it has good applicability for describing the probability distribution characteristics of the similar relationship between C_sm and C_si,D_appm and D_appi.