Study On Properties Of Cement-based Composites Based On Ion Conduction

The traditional conductive concrete is mostly based on the principle of electronic conduction.Steel fiber,carbon fiber,graphite,carbon black and other materials are used as the conductive phase materials,and the conductivity is formed by the movement and migration of free electrons inside the concrete.However,some inherent defects of traditional conductive phase materials greatly affect their practical applications.Different from the traditional conductive concrete,the ion conductive mortar is based on the principle of ion conduction,and realizes the conduction by utilizing the directional movement of various ions in the electrolyte solution under the effect of an applied electric field.The raw materials of the ion conductive mortar are cheap and easy to obtain,the preparation process is simple,and it has good electrical conductivity and good application prospects.Based on the previous research of our group,this paper focused on the ion conductive mortar specimens,started from its conductive principle,the effects of air entraining agent and water-cement ratio on mechanical properties,porosity,electrical resistivity,microstructure and macroscopic pore structure of ion conductive mortar were systematically investigated;based on the principle of permeation,the infiltration method of ion conductive mortar was compared and optimized,and the open circuit potential test was carried out on the mortar specimen by electrochemical workstation,and the permeability performance was qualitatively analyzed;at the same time,the influence of the porosity of the specimen,the concentration of the electrolyte solution and the type of electrolyte solution on the AC impedance characteristics of the mortar specimen were systematically investigated by electrochemical AC impedance technology.Based on the above-mentioned numerous experiments,the temperature rise performance and sealing material of the mortar specimen were studied.It laid the foundation for the practical application of ion conductive mortar.Specific research work includes:?1?Based on the conductive principle of ion conductive mortar,the porosity has a crucial influence on the penetration process of the mortar specimen and the final conductive performance.In this paper,the effects of air entraining agent and water-cement ratio on mechanical properties,porosity,macroscopic pore structure,microstructure and late resistivity?conductivity?of mortar specimens were investigated systematically.The test results showed that the electrical conductivity of mortar specimens were affected by changing water cement ratio and adding air entraining agent.Among them,when the aluminum powder and SJ-2were respectively 0.075%and 0.02%of the cement mass,and the water-cement ratio was 0.7,the resistivity of the specimen at the 150-day age was only 5.385?·m,and the electrical conductivity is the best among all the specimens.?2?The effectiveness of the infiltration process determines the conductivity of the ion conductive mortar.On the premise of systematically optimized the porosity and pore structure of the specimens in the previous chapter,the infiltration method of the specimens is optimized from the infiltration process of the specimens in order to improve the permeability and permeability efficiency of the specimens.In this paper,the two methods of natural immersion and vacuum infiltration were compared,The results showed that the electrolyte solution infiltrated more into the specimen under the action of pressure gradient when the specimen was in the vacuum state,and the penetration efficiency is higher than that under the natural state.Moreover,under vacuum infiltration conditions,the retention rate of the specimen resistivity was better than that of natural immersion.On the other hand,the electrochemical workstation was used to test the change of open circuit potential during the infiltration process of the specimen to detect the penetration law of the specimen.The research showed that the larger the porosity,the more favorable the penetration of the specimen;within a certain range,the greater the concentration of the electrolyte solution,the more favorable the penetration of the specimen and the higher the conductivity of the specimen.However,if the concentration exceeded a certain concentration value,the excessive concentration may adversely affected the electrical conductivity of the specimen.Therefore,the concentration of the electrolyte solution should not be too large in order to meet the corresponding conductivity requirements of the ion conductive mortar.?3?This paper innovatively used the electrochemical workstation to study the AC impedance spectrum characteristics of ion conductive mortar specimens to establish a circuit model of ion conductive mortar.The test results showed that the solution resistance R_S and the charge transfer resistance R_ctt decreased with the increase of the porosity of the mortar specimen and the electrolyte solution concentration of the mortar specimen,the interfacial capacitance CPE increased.In different kinds of electrolyte solutions,the relationship between the solution resistance R_S and the charge transfer resistance R_ctt is:CuSO₄>CaCl₂>NaCl,and the interface capacitance CPE was in the opposite direction,NaCl was the largest,and CuSO4 was the smallest.?4?In this paper,the temperature rise performance of ion conductive mortar specimens under different voltage types and different voltage levels was studied.The test results showed that at a higher voltage of 30V,the temperature of the specimen rised higher,and consequently evaporated and lost a large number of electrolyte solution inside the specimen,which is unfavorable to the later conductivity of the mortar specimen;while at a lower voltage of 10V,the temperature rise of the specimen is reasonable,the retention of electrolyte solution was relatively ideal,and the conductivity of the specimen was also better in the later stage.Unlike alternating current,the mortar specimen had a polarization effect under direct current conditions,which caused the resistance of the specimen to increase and the electrical conductivity to decrease.Therefore,a lower AC voltage should be used when tested the temperature of the mortar specimen.For the sealing materials of the specimen,the sealing effect of the specimen which was not coated with the sealing material and the epoxy resin AB glue and the melted solid paraffin were respectively compared.The results showed that the sealing material was crucial for the retention of the resistivity of the specimen.The resistivity of the specimen which was not applied with any sealing materials increased extremely rapidly,and in the comparison of the epoxy resin AB glue and the melted solid paraffin wax,the melted solid paraffin wax was more effective.