Compressive Strength And Chloride Ion Resistance Of Fly Ash Geopolymer

The cement industry has always been one of the largest sources of carbon dioxide emissions.A large amount of carbon dioxide is produced during its manufacturing process,causing a series of environmental problems such as the greenhouse effect.At the same time,the corrosion of steel bars in ordinary cement concrete is a problem to be solved.The series of problems caused by corrosion not only bring potential safety hazards to the structure itself,but also bring certain losses to the national economy.Therefore,it is urgent to find a material to replace cement,reduce environmental pollution and improve the durability of concrete.Geopolymer,as a new green cementitious material,has become one of the best substitute materials for cement due to its excellent properties such as rich raw material,low production energy consumption and strong durability.This thesis uses numerical methods to study the mechanical properties and chloride ion resistance of fly ash geopolymer.According to the compressive strength of fly ash geopolymer,the microstructure evolution model of geopolymer slurry was established.Based on the reaction mechanism of geopolymer,the generated geopolymer gradually fills in the pores,resulting in the microstructure of the slurry gradually compacting and the porosity decreasing.At the same time,the empirical formulas of compressive strength and porosity of fly ash geopolymer were used to predict the compressive strength of geopolymers.The microstructural evolution of fly ash geopolymer paste was realized by MATLAB programming,and its predicted value is in good agreement with the test value in the literature.Numerical analysis method was used to study the chloride ion migration performance of fly ash geopolymer concrete.Based on the mass conservation equation and Poisson’s equation,the model of chloride ion migration in fly ash geopolymer concrete under the action of an external electric field was established,and the model considers the interaction in the process of ion migration.The reliability of the model was verified by experimental data in the literature,and the influence of the initial concentration of ions in the pores of fly ash geopolymer concrete on the migration of chloride ions was analyzed.Based on Fick’s second law,a model of chloride ion migration in fly ash geopolymer concrete under natural diffusion was established,and the simulation results under the action of an external electric field and natural diffusion were compared and analyzed.The influence of aggregate parameters on chloride ion migration was studied,and it was found that the more aggregate content,the smaller the chloride ion erosion depth.Aiming at the corrosion resistance of fly ash geopolymer reinforced concrete,the electrochemical corrosion model considering the influence of chloride ions on corrosion was established.The changes of chloride ion content,current density,corrosion depth and corrosion rate on the surface of steel bars in fly ash geopolymer concrete components were analyzed,and used to predict the time of corrosion onset and changes in the corrosion morphology of steel bars.The corrosion laws of single and multiple steel bars in fly ash geopolymer concrete members were studied,and it is found that the closer to the chloride ion erosion boundary,the earlier the steel bars will corrode,the corner steel bars will corrode before the middle steel bars,and the steel bars are non-uniformly corroded and have an elliptical corrosion appearance.The effect of steel corrosion on the mechanical properties of geopolymer reinforced concrete was discussed.