Study On Corrosion Protection Mechanism Of Steel Bars Based On Thermoelectric Effect Of Cement Materials

Use the method of cathode protection to protect steel bars can improve the durability of reinforced concrete structures and prolong its service life in marine environment.But it’s difficult to construct the cathodic protection system and unable to provide the required power of cathodic protection for remote areas because the actual engineering environment is very complex.We constructed cement-based thermoelectric modules that have the advantage of thermal and electric properties and use its thermoelectric voltage or current generated by temperature difference to protect steel bars.In addition,we clarifyed the mechanism of the corrosion self-immunity of reinforcement under the cathodic protection system.The content of as follows:Nano MnO₂ powders were incorporated into cement composites to improve thermoelectric properties of cement-based materials and meet the requirements of high rates of electromotive force for cathodic protection.It were synthesized by hydrothermal method with MnSO₄.H₂O and（NH₄）₂S₂O₈ as starting materials.Crystal structures and morphologies of MnO₂ powders can be controled by change the reactant molar ratio and reaction time.Nano MnO₂ powders were chosen as thermoelectric component and incorporated into cement composites.The thermoelectric property of this cement composites under different dosage of MnO₂dioxide powders were studied.The results show that the Seebeck coefficient of the cement composites increased steadily with the added MnO₂ powders content.The maximum Seebeck coefficient was measured to be higher than 3300μV/℃when the content was 5.0%,which was far higher than that of fiber reinforced cement composites.Although the thermoelectric properties of cement composites have been greatly improved,but their electrical performance is still poor.PANI/MnO₂ composites were chosen as the thermoelectric component to increase the thermal and electric properties of cement composites.The PANI/MnO₂powders were synthesized by polymerization of ANI on the surface of MnO₂.PANI/MnO₂ with high electric potential and low resistvity can preparated by change the content of MnO₂.The thermoelectric property of the PANI/MnO₂ cement-based composites was explored with different dosage of PANI/MnO₂ powders.The results show that the Seebeck coefficient and conductivity of the cement composites increased with the added PANI/MnO₂ powders content.The maximum Seebeck coefficient was higher than 2200μV/℃and the conductivity was higher than 0.01S/cm when the PANI/MnO₂ content was 5.0%.The thermoelectric efficiency of the material is significantly higher than that of the MnO₂ cement-based composites.Finally we homemade thermoelectric power generation system to conduct cathodic protection for steel bars in the concrete simulation that mixed with 3.5%sodium chloride.Thermoelectric power generation system was based on the cement-based thermoelectric modules which were series connected by PANI/MnO₂cement-based composites.In addition,we use electrochemical method to evaluate the effectiveness of cathodic protection.For example,the half-cell potential method,polarization curve,AC impedance method and so on.The results show that the thermoelectric voltage or current generated by the thermoelectric modules under the temperature difference can reduce the corrosion rate of the steel bars and play a very good protective effect on the steel bars.