Time-varying Similarity And Micro Mechanism Of Chloride Ion Penetration In Cement-based Materials In Simulation Tidal Environment

In the natural tidal environment,the problem of durability failure of concrete structures which are led by chloride ion erosion has become increasingly prominent.However,the durability failure of concrete structures under actual tidal environment is a long and slow process,and there are many influence factors in chloride erosion of concrete.Therefore,it is important to study the time variation law of chloride ion erosion in concrete.On the basis of existing research,a series of long time ingress test for chloride ion erosion in cement-based materials was designed and implemented under artificial simulation environment for ocean tidal range,the pore characteristic parameters and distribution change of pore diameters of concrete after different erosion time were obtained by mercury intrusion porosimetry.In this paper,the main contents and results are as follows:1.According to simulation test of artificial tidal environment,the free chloride concentrations in concrete at various time points were measured by extending the erosion time to 400 days,effect of erosion time and water cement ratio on the performance of chloride ion erosion was studied,the long term attenuation law and time-dependent model of chloride diffusion coefficients are explored and established.The results show that compared with the original time-dependent model,the calculated diffusion coefficients obtained by the updated model are consistent with the measured values,and errors are smaller.2.Exposure test of cement-based materials with different admixtures under artificial simulated environment for ocean tidal range,the free chlorine ion concentrations were measured after different erosion time,the effect of different admixtures on the anti-chloride erosion performance of cement-based materials was studied,the attenuation law and time-dependent model of chloride ion diffusion coefficients of cement-based materials after adding admixture was analyzed and established.The results show that the other admixtures can effectively reduce the diffusion performance of chloride ion in cement-based materials,except for addition of the igneous rock fiber The effect of different admixtures on the time attenuation coefficients of diffusion coefficient of cement-based materials is different.3.Based on the similarity theory,the test results of chloride ion erosion in cement-based materials under different dry-wet cycling environment were compared and studied,the time variant similarity and random characteristic similarity of the main chloride erosion characteristic parameters in concrete between the simulated test and field tidal environment were analyzed,a uniform time-dependent model of chloride ion diffusion coefficient in concrete and mortar under different test environment was obtained respectively.4.According to the results of mercury intrusion porosimetry,the changes of pore characteristics and pore diameters distribution in concrete after different erosion time in artificial simulated environment for ocean tidal range were analyzed,the relationship between the pore characteristic parameters and the chloride diffusion coefficients in concrete was analyzed.The results show that there is a good correlation between the total porosity and capillary porosity of concrete and its chloride ion diffusion coefficient;There was a good negative correlation between the pore surface fractal dimension of big capillary pore and the chloride diffusion coefficient in concrete.