Time-varying Similarity Of Permeability And Micro Mechanism Of Fly Ash Concrete Under Simulation Tidal Environment

With the widely application of RC structures,the durability problems of structures become more and more serious,especially for those structures under dry-wet cycle environment.The addition of fly ash into concrete can greatly improve the durability of concrete structure.As we all know,the durability failure of concrete structures is a long and slow process,and the concrete permeability is one of the important indicators of its durability.Therefore,it is important to study the time-varying similarity of fly ash concrete permeability between the simulated tidal environment and field tidal environment.In this paper,the main contents and results are shown as follows:(1)Based on the existing tests,the exposure test of concrete under natural tidal environment after prolonging the exposure time to 840 days is carried out,and the time-varying process and correlation of water and gas permeability as well as chloride ion diffusion of fly ash concrete are analyzed.The results show that the three permeability coefficients of concrete all decrease to different degrees with the extension of exposure time.The correlation between water and gas permeability coefficients of concrete is high,but the addition of fly ash reduces the correlation between these two coefficients(2)According to the test results by the mercury intrusion porosimetry(MIP)and nuclear magnetic resonance(NMR)methods,the time-varying deformation of pore structure parameters of fly ash concrete with different exposure times under natural tidal environment is studied.The relationship between the permeability and porosity or pore size distribution of concrete is analyzed.The results show that the porosity and pore diameter proportion of concrete exhibits an obvious time variation.The apparent chloride diffusion coefficient of concrete has a high correlation with porosity,but has a poor correlation with pore size distribution above 100 nm.(3)The exposure test of concrete with different fly ash contents under the artificial simulated ocean tidal environment is designed and completed,the three permeability coefficients of concrete after different exposure times are tested,the relationship between time reduction coefficient and fly ash content is studied,and the relationship between the three permeability coefficients and the porosity of concrete is analyzed,respectively.The results show that with the increase of fly ash content,the time reduction coefficient of concrete permeability coefficient also increases.The simulated environment reduces the correlation between the porosity and the apparent chloride diffusion of fly ash concrete,but increases the correlation between porosity and water permeability.(4)Based on the exposure test results of fly ash concrete under the natural tidal environment and simulated tidal environment,the similarity of time reduction coefficient and time-varying similarity of permeability coefficient of concrete between the simulated environment and field tidal environment were analyzed,and the similarity of apparent chloride diffusion coefficient reduction rate and porosity of concrete between the simulated environment and field tidal environment were analyzed.The results show that the simulated environment increases the time reduction coefficient of the three permeability coefficients of concrete and the reduction rate of chloride diffusion coefficient.