Study On Similarity Of Chloride Erosion Of Concrete Under Marine Dry-wet Cycles And Sustained Compressive Loading

In an actual marine environment,concrete structures in service are usually not only affected by several environmental factors such as drying-wetting cycles,but also suffered from different degrees of external loads.The mechanism of chloride ingress into concrete subjected to the combined action of drying-wetting cycles and external loads is relatively complex.External loading action could cause the interior damage or microcracks inside concrete,which significantly affects the chloride transport behavior in concrete.Therefore,it is of great practical importance to conduct an investigation on the chloride transport behavior in concrete under the coupled actions of drying-wetting cycles and sustained compressive loading as well as the similarity relationship between the real marine exposure and simulated marine tidal environment in the laboratory.Based on this,the chloride ingress tests of the loaded concrete under the real marine exposure and indoor simulated tidal environment were conducted,and the influence of different axial compressive loading levels,exposure time and concrete type on the chloride transport properties were studied.Combined with the similarity theory and probability statistical methods,the prediction analysis of similarity probability for the two exposure environments was further explored.Based on the convection-diffusion model of chloride transport in unsaturated concrete,the numerical simulation of chloride transport in concrete damaged by sustained compressive loading under the drying-wetting cycles was conducted.The main research work and the obtained conclusions are shown as follows:(1)Based on the self-designed artificial simulated marine tidal automatic testing device,the laboratory test of chloride ingress behavior in concrete subjected to the sustained compressive loading was carried out,and the real marine exposure test was further conducted.The spatial distributions of free chloride content in ordinary concrete(C30,C50),strain hardening cement-based composites(SHCC)and alkali-activator concrete(AAC)under different stress levels(0fc,0.1fc,0.3fc and 0.5fc)and different exposure times(30d,60 d,90d and 180d)were analyzed.The variation laws of the key parameters of chloride transport performance,such as surface chloride concentration(Cs)and apparent chloride diffusion coefficient(Dapp),were investigated.The results showed that the compressive stress levels had significant effects on the free chloride content,Cs and Dapp.Compared with ordinary concrete of the same strength grade,both the SHCC and AAC specimens showed the better resistance to chloride ingress.The calculation results indicated that the instantaneous chloride diffusion coefficients(Dins)in the two exposure environments were all smaller than the apparent chloride diffusion coefficient(Dapp).The values of Dins in the real exposure environment were smaller than those in the indoor simulated environment,which was consistent with the results of Dapp.The convection depths of chloride ingress into concrete in the two exposure environments were obviously increased with the extension of exposure time,and this changing trend obeys normal distribution.(2)A probabilistic time-varying model of chloride ingress behavior in concrete considering the effects of water-cement ratio,cementitious materials and load action was established.According to the Bayesian Theory and Markov chain Monte Carlo method(MCMC),the collected test data of chloride transport performance in real exposure and indoor simulated tidal environment was used to determine the key parameter values,and then the similarity relationship of chlorine ingress behavior was further analyzed to develop the probability prediction model of similarity.The results showed that the similarity factor K of Cs and Dapp under the two exposure environments was less than 1.It indicated that the indoor simulation environment can accelerate the effect of chloride ingress,and there was a similar relationship in the two exposure environments.The comparison and analysis with the collected data proved that the established probability model of similarity can better predict Cs and Dapp under real exposure environment.The distribution of probability model in 95% confidence interval range could be obtained by using probability statistics method to validate its effectiveness and accuracy.(3)Based on the Mazars damage theory,the damage deterioration degree of concrete subjected to compressive loading was characterized.Combined with the unsaturated theory of chloride transport,a convection-diffusion model of chloride transport in damaged concrete under the drying-wetting cycles was established.The Monte Carlo method was used to establish two-dimensional random numerical models of different concrete types considering the principle of aggregate random distribution.Numerical simulation analysis of chloride transport in concrete damaged by sustained compressive loading under the drying-wetting cycles action was conducted to validate the accuracy of the developed model.The results show that when the compressive stress level was lower than 0.3fc,there was no obvious damage inside concrete.With the increase of the stress level(more than 0.3fc),the damage inside concrete could be obviously observed,and the damage degree of SHCC was obviously lower than that of ordinary concrete.The chloride content calculated by numerical simulation method was in good agreement with the test results,illustrating that the numerical simulation of chloride transport in damaged concrete exhibited the better feasibility.Finally,the probability analysis of similarity and numerical simulation were combined to predict the distribution of chloride content of C50 and AAC under real exposure environment for 5 years.