The Evolution Of Chloride Ion Permeability And Microstructure Parameters In Cement-Based Materials Under Tidal Environment

Under the tidal environment,the durability damage of cement-based materials and concrete structures will occur,due to the ingress of chloride ion and other environmental factors.However,the durability failure of cement-based materials is a long and complicated process.In this process,the macroscopic permeability and microstructure parameters of cement-based materials both vary with time,which will then effect the durability of materials.Therefore,it is important to study the timedependent characteristic of the permeability and microstructure parameters of cement-based materials under the tidal environment.On the basis of existing researches,a long time accelerated simulation experiment of cement-based materials under an artificial climate environment was designed.The microstructure parameters in different exposure times were tested by mercury intrusion porosimetry and nuclear magnetic resonance,respectively.Then,the evolution process of the microstructure parameters were analyzed.In this paper,the main contents and results are showing as follows:1.An exposure test of concrete with different admixtures and mortarwas completed under artificial simulated environment for 400 d exposure times.The free chlorine ion concentrations were measured after different exposure times.The influences of admixture types on the chloride ion permeability of concrete and the effects of water-binder ratio and admixture types on the chloride ion permeability of mortar under the long-term dry-wet cycle environment were studied.And then the time-dependent models of chloride diffusion coefficients of concrete and mortar were established respectively.The results show that,under the long-term dry-wet cycle environment,the time-dependent models of chloride diffusion coefficients can reflect the decay process of concrete and mortar effectively.The admixtures can obviously reduce the diffusion property of concrete and mortar,however,the decrease level depended on the admixture types.Moreover,the water-binder ratio will influence the diffusion property of mortar significantly.2.Based on the similarity theory,the similarity of time dependent characteristics of chloride ions exposure parameters in concrete and mortar between the accelerated simulation environment and the field tidal environment were investigated,and the unified time-dependent models of chloride diffusion coefficients in the environments mentioned above were provided.The results show that,there is an obvious similarity of exposure parameters existed between the accelerated simulation environment and field tidal environment.Moreover,the accelerated simulation environmentcan accelerate the exposure of concrete and mortar.3.The pore characteristics of concrete with different admixtures were tested by mercury intrusion porosimetry(MIP)and nuclear magnetic resonance(NMR)after different exposure times.The relationship between diffusion properties and pore characteristic parameters of concrete with different admixtures was analyzed.The results show that there is an obvious time dependent characteristic of pore characteristics in the concrete with admixtures,regardless of the test methods.In addition,the time dependent characteristic is related to the chloride ion diffusion of concrete.4.The pore characteristics tested by MIP and NMR were compared from the aspects of test principle,test range and sample processing method.The reasons which caused the test results differences were analyzed.The results show that the numerical value of pore characteristics obtained by MIP and NMR is different,but their variation trend is similar.