Realkalization Technique For Carbonated Conerete Structures

The electrochemical realkalization technology for carbonated concrete structure aiming at concrete structure aging is one research hotspots recently. This technology is in the principle of electro-osmosis, electro-migration, diffusion and capillarity to renew the alkaline condition around reinforced bar and realize the realkalization of concrete. This technique is to solve the problem according to the electrochemical corrosion mechanism of steel, and it has many advantages, for example operation is simple and convenient and has no pollution. And wide application was suggested.The electrode reactions process of reinforcement, material transfer and the changes of carbonation concrete in composition and structure during the process of electrochemical realkalization were investigated in detail combining experimental research and theoretical analysis in this paper. And obtained some research results on the realkalization process, and provide theory backup to further improvement of realkalization technology.The first part of the study was that three kinds of electrolyte solution were used on the natural carbonation and artificial carbonation of concrete for simulated acceleration realkalization experiments. Their structures and compositions were tested by using SEM, XRD and JK-W B.E.T NSA. The result shows that three electrolytes all can make concrete pore size small, and the composition change. The smaller concrete pore size can increase density and durability of concrete structures. CaSiO₃ was converted into Ca₂SiO₄ in artificial carbonated sample, and orthosilicate in natural carbonated sample still continued hydration, calcium carbonate was converted into secondary silica gel (C-S-H) when the samples were alkalized. Realkalization time and carbonation decided the structure of gelatinous material.The second part of the study shows that Li⁺,Na⁺,Ca²⁺ can get through concrete cover and reach the reinforcing steel surface,while part of these ions will remain in the concrete.The ion transfer process was completed by the common role of ion concentration difference and electric field. In the early stage of ion transfer, diffusion caused by concentration difference is the main form. In the late stage of ion transfer, electric field is the main form. Acceleratied realkalization experiments used different electrolyte solutions show that these electrolytes could cause concrete aperture smaller, strengthen structure compactness and durability. During the process of realkalization, reduction of rust on the reinforcing steel surface is concurrence, the obtained elemental iron was loose sediment layer, and it's difficult to enter the passive state; But the sediment state could ameliorate when used a combined electric field, also the stability of reinforce steel could be improved. The condition of hydrogen embrittlement sensitivity of reinforcement was in existence during realkalization.In the fourth part, the alkalinity of the concrete around reinforcement increased after realkalization, but the reinforcement was in a highly active state, and the possibility of repassivation of the rebar became lower. On decreasing the corrosion of the rebar through introducing the cationic inhibitors entering the concrete by the applied electric field received the researchers in this field attention. On the basis of these studies, it could suppose that the method adding the cationic inhibitors which could reach the surface of the rebar by the electroosmosis and electromigration during the realkalization to the electrolyte could not only realize realkalization but also protect the rebar. The result shows that inhibition effect is in existence for the rebar embedded in the natural carbonated concrete in a short time after realkalization. Reinforcement has been monitored to prevent the occurrence of hydrogen embrittlement.