A Study On The Hardening Process Of The Alkali Activated Material By Using Electrochemical Impedance Spectroscopy

Since the traditional cement industry is an energy-intensive and highly polluting industry,the mass production of Portland cement is contrary to the requirements of energy conservation and environmental protection,which is not conducive to the sustainable development of mankind.On the other hand,the industrial solid waste represented by blast furnace slag,coal gangue and metakaolin is produced in large quantities every year,and the landfill disposal will cause pollution of the water resources,the soil and the atmospheric environment.Therefore,in order to maximumly utilize the industrial by-products and to reduce pollution in the cement industry,the research and application of alkali-activated materials has attracted more and more attention in the academic research.Alkali-activated materials is a complex three-phase porous media material.At present,it is still a difficult problem to describe the hardening structure of alkali-activated materials in micro and macro scale.Although a large number of studies have been carried out using traditional testing methods,such as SEM,XRD,MIP,to analyze the hardening reaction process of alkali-activated materials,and the composition and structure of reaction products.However,these testing techniques have certain limitations.The original samples need to be pretreated before the test.These destructive pretreatment methods may cause some damage to the original microstructure and properties of alkali-activated materials.In this study,the non-destructive electrochemical impedance spectroscopy?EIS?was innovatively used to study the impedance characteristics of hardening reaction of alkali-activated materials with different water-slag ratio,alkali content,metakaolin content,coal gangue content and curing age.According to the test results,it is found that these factors have a great influence on the electrochemical impedance properties of alkali-activated materials.The main reason is that the hardening reaction of alkali-activated materials is a dynamic process.In this process,the pH of the pore solution,the changes of the ion concentration of the pore solution,the porosity,the compactness of the paste,etc.,will affect the conductivity of the material,which leads to the change of bulk resistance of the paste.By using the equivalent circuit model to simulate the impedance results and analyzing it with the traditional test method,it is found that although the electrolyte resistance R_s and the resistance of the the hydration electron transport process R_ct1 shows an increasing trend over the whole testing period,the R_s can indicates the evolution of the porosity to a certain degree.While the R_ct1 has a similar growth trend and strong correlations with the compressive strength,which means that the electrochemical impedance spectroscopy technique can be used to non-destructively predict the 28-day strength development of alkali-activated material paste,providing a new perspective for the further research on macro-properties and micro-structure of alkali-activated materials.