Study On Internal Corrosion Behavior Of Concrete Prepared By Recycled Aggregates Carrying Sulfate Ions

The concrete structure has been eroded by sulfate in the external environment for a long time during the service period,and the recycled aggregate prepared by crushing the concrete inevitably carries the sulfate corrosion medium.Concrete is prepared by these recycled aggregates,therefore,also carries sulfate corrosive medium.A series of physical and chemical reactions occur between sulfate corrosion medium and cement hydration products in concrete to form internal corrosion,which in turn affects the long-term performance of the concrete.Existing studies mainly focus on the properties of recycled aggregates,while the effects of adhesive mortars carrying corrosive media on the properties of recycled concrete have received little attention.Based on this,this paper takes the recycled aggregates carrying sulfate ions as the object to study the effect of macroscopic properties of recycled concrete prepared by recycled aggregate carrying sulfate ions,and the effects of the microscopic properties and structures of the recycled aggregates carrying sulfate ions.Quantitatively characterize the diffusion of sulfate ions in concrete;through grey relational theory and analytic hierarchy process,design a quantitative expression representing the corrosion parameters of the interface,in order to explore the micro-macro performance correlation of recycled concrete.The research work of this project could provide theoretical guidance for the durability research and high-performance design of recycled aggregate concrete,and also provide necessary data and theoretical support for the revision of related technical standards.The main research work is as follows:(1)The mechanical properties and shrinkage properties of recycled concrete were experimentally studied from the recycled aggregates carried sulfate corrosion media,the corrosion concentration of recycled aggregates,the replacement rate of recycled aggregates,the water-cement ratio,and the composition of cementitious materials.The time-varying law of macroscopic properties of recycled concrete prepared by recycled aggregate carrying sulfate ions was explored.(2)Based on the nano-indentation test technology,the elastic modulus and the hardness of the interface between the recycled aggregate and the old mortar,the interface between the recycled aggregate and the new mortar,the interface between the new and the old mortar,the recycled aggregate and the mortar were quantitatively tested.Combined with the image binarization technology,the time-dependent change law of the geometric parameters of the interface between recycled aggregate and old mortar,recycled aggregate and new mortar,and old and new mortar was further explored.(3)Based on the two-dimensional morphology of the interface between recycled aggregate and old mortar,between recycled aggregate and new mortar,and the evolution of corrosion products in the mortar was analyzed by the method of the SEM-EDS,the structural change law of the multiple interfaces of recycled concrete and the distribution of corrosion products under the action of internal corrosion was studied.On this basis,the three-dimensional structural characteristics of the multiple interfaces of recycled concrete under the action of internal corrosion were identified by AFM test technology.In addition,MIP was used to test the pore structure distribution of recycled concrete.Combined with the multi-interface microstructure of recycled concrete and the distribution of corrosion products in the mortar,the internal corrosion mechanism of recycled aggregate carrying sulfate ions on concrete was revealed.(4)The self-made mortar rod was soaked in sodium sulfate solution to simulate the regeneration of aggregates carrying sulfate ions.Combined with an external electric field to promote the diffusion of sulfate ions,the diffusion behavior of sulfate ions in the concrete was studied by the method of UV spectrophotometer.The diffusion coefficients of sulfate ions in the interface and in the mortar were calculated based on the Nernst-Einstein equation.The results showed that the ionic diffusion coefficient of interface was much larger than that in the mortar.On this basis,based on the theory of three-dimensional cellular automata,combined with Fick’s second law,the dynamic transport behavior of sulfate ions in concrete was simulated by Python programming.(5)Based on the elastic modulus,hardness,area and other microscopic performance indicators of recycled aggregate,mortar and multiple interfaces,an internal corrosion factor that can comprehensively reflect the microscopic performance characteristics of recycled concrete under internal corrosion was proposed.Based on grey relational theory and analytic hierarchy process,the quantitative expressions of internal corrosion parameters were further determined.Correlation analysis was carried out between internal corrosion parameters and macroscopic mechanical properties of recycled concrete,and a prediction model for macroscopic properties of recycled concrete was established.(6)Based on the damage plasticity model of recycled concrete,combined with the expansion characteristics of corrosion products in the mortar,the damage constitutive relation of recycled concrete under internal corrosion was constructed.Based on the secondary development program of Abaqus-Python,a two-dimensional microstructure model of recycled concrete was established,and the simulation of the mechanical damage process of recycled concrete under the action of internal corrosion was realized.