Study On Influence Of Cement Inforganic Phases On The Corrosion And Deterioration Of Steel Rebar Reinforced Concrete

This thesis is aimed at the corrosion and deterioration process of steel rebar reinforced concrete,especially emphasizing on the influence of the cement inorganic phase.A number of liquid solutions were made to simulate pore solutions of concrete,and various inorganic powders were synthesized to simulate cement phases in concrete.The corrosion behavior of steel rebar in solid-liquid coexisting systems composed of simulated pore solution and simulated inorganic powders,the ion concentrations of the liquid solutions and their changes,as well as the chemical and structural components of the inorganic powders and their changes,were carefully researched,using electrochemical,analytical chemical and crystallographic measurements.The corrosion tendency and speed of steel rebar electrodes in simulated pore solutions,with the existence of different inorganic powders,different stirring conditions,and the co-influence of traditional corrosion inhibitors as well as gypsum powder,were measured through potentio-dynamic polarization tests.And the results indicated that:the powders C3-A1,C3-S2 and C4-A1-F1 did inhibit the corrosion of steel rebar to a certain extend;Na₂SiO₃ possessed the best inhibiting performance not only because it could transform to C-S-H gel,but also due to its membrane forming ability on the surface of steel rebar electrodes;during the formation of C-S-H gel,the best C / S ratio was 1:1; physical stirring of the solutions accelerated the solid-liquid inter-phase mass transmission process,so as to further inhibit the corrosion of steel rebar electrodes.Chloride ion concentrations in the liquid solutions and their changes during the long-time immersion experiments were monitored,using analytical argentometry and chloride ion selective testing electrodes. Testing results showed that,in solid-liquid coexisting systems,chloride ion concentrations all decreased to different extends with immersing time. The chemical and structural components of percolation residue after the immersion experiments were characterized by means of X-Ray Diffraction(XRD) crystallography analysis.Testing results indicated that: calcium aluminates(C₃A),which was simulated by C3-A1 and C4-A1-F1 powders,can bind chloride ions strongly through ion exchange;and C-S-H gel,which was simulated by C3-S2 powder,can only bind chloride ions weakly through physical adsorption.These two kinds of chloride binding capabilities can effectively reduce the free chloride ion concentrations in pore solutions of concrete,so as to protect concrete coated steel rebar from corrosion.Several sorts of natural clay were selected to react with limestone (CaCO₃) at high temperatures in solid phases,producing various cement-simulating inorganic powders.And long-time immersion experiments were also conducted on the powders.Monitoring of the solutions showed that chloride ion concentrations all decreased with immersing time.XRD crystallography analysis indicated that chemical ion exchange process and physical adsorption process both contributed to the reduction of free chloride ion concentrations.It was also found out that finer powder led to more effective binding of chloride ions,as the contacting area of the solid phase and the liquid phase was larger.