Study On Inhibition Performance And Mechanism Of Microcapsule-based Chemical Self-healing Systems

Steel corrosion in concrete can lead to concrete cracking,shortening the service life of the structure.To protect the steel from corrosion,the capsule-based technology provides a novel method to improve the durability of reinforced concrete,which is of great value for protecting the service performance of the structure in the coastal environment.Based on the theory related to corrosion and the capsule-based technology,this study designed and prepared two kinds of chemical self-healing systems.The basic properties of different microcapsules were analyzed and discussed.The X-ray computer microtomography?X-ray?CT?technique was used to trace the corrosion process of the reinforcing bars in chemical self-healing system nondestructively.Under the coastal environment,the ingress of chloride ion into concrete induces initial corrosion of steel and prompts the concrete cracking.To mitigate the negative effect caused by chloride,two kinds of microcapsules with forming a protective layer function,sodium monofluorophosphate/ethyl cellulose microcapsule?MFP/EC?and sodium nitrite/ethyl cellulose microcapsules?NaNO₂/EC?,were proposed and prepared.The mechanism of these two kinds of microcapsules for protecting steel is clear.After sodium monofluorophosphate releasing from the capsule core,the healing agency?MFP?reacts with calcium hydroxide to form a firm layer on the surface of steel.Likewise,sodium nitrite can release from the core and reach to the surface of steel,and react with steel for forming a protective layer.The walls of both kinds of microcapsules are ethylcellulose.Basic performance analysis should be carried out after prepared microcapsules.The microcapsule morphology,particle size distribution range and mechanical properties are the most basic performance indicators.The results of these indicators show that the microcapsules have a relatively rough surface,a moderate particle size,and good mechanical properties after mixing with concrete.Through the test of basic performance,it is clear that the cores are encapsulated well by the shell.After preparing the chemical self-healing systems,the wet-dry cycles as the acceleration test were carried out in the NaCl solution.The corrosion processes of the chemical self-healing system and the control system?without microcapsule?were visually traced via X-ray?CT.The X-ray?CT test results were reconstructed,and the quantitative analysis was carried out through the results of the loss volume,and the corrosion rate of the steel bar were obtained by fitting linear.The research indicates that:1.NaNO₂/EC chemical self-healing system and MFP/EC chemical self-healing systems achieve the aim of hindering the corrosion process.Protection behavior showed an obvious delay of the corrosion process.2.The volume loss ratios of NaNO₂/EC chemical self-healing system and MFP/EC chemical self-healing system were all lower than that of the control system during the acceleartion tests.By the linear fitting of the volume loss,the corrosion process of the chemical systems were slower than that of the control system.3.The comparison between the two-dimensional picture obtained by the X-ray ?CT test and the actual cross-section obtained by scanning electron microscope shows that the statistical results of both are almost the same,indicating that the X-ray?CT test results is reliable.4.After the experiment was completed,the capsule wall remained intact and the capsule core had been lossing,which can be found from the electron microscopy.The energy spectrum analysis verified that the capsule core had been released into the concrete.The results show that the microcapsules in the chemical self-healing systems are effective,and the protection effect of the chemical self-healing system is outstanding.In order to expound the corrosion inhibition behavior of chemical self-healing system,this paper uses the non-destructive and repeatable method,X-ray?CT testing technique,to characterize and quantify the system,which provides the possibility for the engineering application of chemical self-healing system.The X-ray?CT technology also provides a new perspective and analysis method to characterize the process of corrosion inhibition of steel.