The Influence Of Mineral Admixtures On The Corrosion Resistance Of Reinforced Concrete And Its Mechanism Analysis

Chloride attack in marine environments is considered as the main cause of the steel corrosion as well as decrease of durability and service life on concrete structures.Appropriate mixing of mineral admixtures such as slag and fly ash can effectively improve the microstructure of concrete and highly slow down the penetration process of chloride ions from the seawater to the steel surface,which is good for enhancing the durability of concrete.Based on it,the corrosion test of specimens with different contents of slag and fly ash has been carried out,the effects of replacing cement with slag and fly ash on the durability of reinforced concrete structures in chloride environment has been studies,and the mechanism behind it has been researched to provide a basis for durability assessment and life prediction of reinforced concrete structures in marine environment.The main contents and results of this paper are as follows:The time-varying laws of electrochemical parameters such as open circuit potential,corrosion current density and charge transfer resistance of different mineral content specimens are analyzed by Tafel polarization and EIS.The results show that: It takes about 150,360,420,450,510,600 and 690 days for C-A-3,20S-A-1,40S-A-3,10F-A-2,20F-A-1,10FS-A-2 and 20FS-A-4-which respectively specimens replaced cement with 0%,20% slag,40% slag,10% fly ash,20% fly ash,10% slag + 10% fly ash and 20% slag + 20% fly ash-to reach stable corrosion state.Thus,replacing cement with slag or fly ash can greatly improve the durability of concrete in chloride environments.Besides,the degree of improvement from large to small is 20% slag+20% fly ash,10% slag+10% fly ash,20% fly ash,10% fly ash,40% slag and 20% slag.The porosity,Ca/Si of C-S-H gel and phase composition of each specimen are analyzed by means of saturated-dry weighing,SEM/EDS and XRD.The results show that: after replacing cement with different proportions of slag and fly ash,there occurs a decrease on the Ca/Si of C-S-H gel while there is an increase of the initial total-porosity as well as the content of C-S-H gel and Friedel’s salt.Besides,the larger the replacing contents of cement,the higher the changing degree of the above parameters.Thus,after replacing the cement with slag and fly ash,the increase of C-S-H gel and Friedel’s salt content in the slurry is the main reason for the improvement of durability of concrete in chloride environment.The free chloride ion content of each kind of specimens are measured by the traditional chloride titration and Korean DY-2501 B tester.The results show that: after replacing cement with different proportions of slag and fly ash,the chloride threshold value of specimens occurs a different degree of decrease,the larger the replacing contents of cement,the higher the decreasing degree of chloride threshold value.Thus,after replacing cement with slag and fly ash,the improvement of durability of concrete in chloride environment is not directly related to the change of chloride threshold value on the surface of steel.