Research On The Service Behavior And Mechanism Of Cement-based Materials In Chloride Environment

The main reason of concrete deterioration are reinforcement corrosion, freeze-thawing damage and the physical and chemistry reaction in corrosive environment, among the factors reinforcement corrosion is primacy; and that chloride ion is the main factors to cause reinforcement corrosion in concrete; and we carry on research in depth on the service behavior and mechanism of cement-based material in chloride environment; grasp the penetrability, diffusibility and chloride binding law of cement-based , which will be significant in guiding to optimize cement-based material compositions, also in improving cement-based durability.This thesis uses electrochemical methods, SEM-EDS analyses and mercury intrusion method systematically to study high performance cement-based material, mainly the chloride ion penetrability, reinforcement corrosion and mechanism in multifactor synergistic combination of the chloride + stress, chloride + freeze- thawing and chloride + stress + freeze-thawing.The grey system theory, chemical analysis, microscopic test, etc were applied to research systematically and intensively into the performance and mechanism that cement-based materials bind chloride ion from environment. It is key to study that the relationship between cement mineral composition, the categories and dosage of mineral additives, service environment and cement-based materials binding chloride. This article also applies ANN(artificial neural network) technology to establish model forecasting chlorine permeability and chloride binding of cement-based materials.This article demonstrates through intensive research on chlorine ion permeability performance and pore structure, these mineral additives such as coal gangue, fly ash can enhance impermeability of cement-based materials, reduce diffusion velocity of chlorine ion permeability, and even can have more splendid effect in advancing impermeability with the hydration age to prolong, especially the effect of coal gangue is superior to that of fly ash in improving pore structure and reducing permeability of cement-based materials. In the effect of multifactor synergistic combination to cement-based materials, the infiltration rate of chlorine ion advances; the depth of permeability increases. The acting on improving chlorine ion penetrability with multifactor synergistic combination as follows: chloride+ freeze-thawing +stress > chloride + freeze-thawing > chloride + stress > chloride. EDS tests to shows that,cement-based materials, which is mixed up with coal gangue, contains little chlorine element in the boundary area between aggregate and slurry, and has no chloride element enrichment; which is mixed up with fly ash contains more in the boundary area; whereas pure Portland cement-based materials is the most, and has chlorine element enrichment.The grey system theory were used to analyze correlation coefficient between cement mineral and its, therefore the research proclaims their association degreebetween the binding chlorine ion ability and every kind of mineral composition is: C3A>C3S>C4AF>C2S. This article establishes a set of evaluation methods and parameter to measure effect of mineral additives binding chlorine ion, which can quantitatively reflect their respective contribution extent of cement and mineral additives, and conduct to optimize material component. The coal gangue can improve the ability in cement-based material binding chlorine ion, if it is mixed up with high cementitious cement (C3S content is greater than 70%), its binding ability is larger than that of which is mixed up with Portland cement produced by industrialization currently, but there exists optimal mixture quantity.Through X-rays and DSC-TG, the analytic result indicates that cement slurry still will produce Friedel's salt after a long time of hydration when it is eroded by chlorine ion, furthermore, with the increasing coal gangue in cement, the Friedel's salt enhances, but if the mixture quantity reach 30% and on , the amount of Friedel's salt will reduce. Fly ash and slag also advance chemical binding chloride ability of cement-based material, the contribution for chemical binding ability is: slag > coal gangue > I -fly ash > II -fly ash; cement-based material with high cementation has larger ability to binding chlorine ion.For cement-based material, the environmental factors has great effect on binding chlorine ion. With the temperature increasing between zero centigrade and forty centigrade, the ability of cement-based material to bind chloride ion grows, especially for the materials mixed with mineral additive, which is better. Chloride cationic style has heavy impact on binding chlorine ion for cement-based materials, and the ability in different kinds of chloride is CaCl2 > KCl > NaCl. The existence of sulfate ion do harm for cement-based material to bind chlorine ion. If pH increases in corrosion liquid , the ability to binding chlorine ion will decrease; and if water-cement ratio of material increases, whereas it will increase such ability.It states by research that ANN is applied to predict chlorine ion permeability and binding performance of cement-based material, especially Matlab neural network technology, which can directly employ neural network design and training program in toolbox as required that can make prediction performance of cement-based materials more convenient.Current step method (CSM) is applied to test ohm resistance of concrete protection layer, and to show concrete compactness. The test shows that mixing with coal gangue can increase concrete resistance, advance concrete compactness. In terms of equal content, slag can do best in performance to advance concrete compactness, and coal gangue do better than fly ash do. All kinds of factors to accelerate concrete reinforcement corrosion with the act of multifactor synergistic combination are: chloride + freeze- thawing + bending stress > chloride + freeze-thawing > chloride+ bending stress > chloride corrosion.