| Corrosion of concrete reinforcement is one of the main reasons resulting in premature deterioration of reinforced concrete structures, and the corrosion protection and repairing of reinforced concrete were widely investigated during last decades. Among numerous corrosion protection techniques, electrochemical chloride extraction(ECE) and migrating corrosion inhibitor(MCI) are considered as the very effective and practical methods. However, due to their own disadvantages, there are some limitations for them in practical application, e.g. the corrosion potential of reinforcement significantly shifts to the negative direction after ECE treatment, leading to possible ??secondary corrosion‘‘ of the reinforcement under ingressive environment; the migration rate of many MCI is very slow in concrete, resulting in low corrosion protection efficiency. In order to solve the above problems, in this study, the design and development of an electro-migrating corrosion inhibitor(EMCI) was proposed. When the EMCI is utilized during the ECE process, it can quickly penetrate into concrete matrix. Therefore, not only can Cl- ions be effectively extracted from concrete and the alkalinity of concrete be increased, but also the quickly penetrated EMCI can adsorb on reinforcement surface, and effectively prevent the ??secondary corrosion‘‘. In this way, a multiple corrosion protection for the steel reinforcement can be achieved, leading to a significant improvement of the corrosion inhibition efficiency and reduction of the repair time and cost. This paper is focused on the molecular structure design and synthesis of the EMCI, and the related mechanism of its corrosion inhibition effect on the reinforcement. The research works mainly include: according to the migration rate in concrete and corrosion inhibition effect on the reinforcement, the molecular structure of the EMCI was functionally designed, and a cationic type of imidazoline quaternary ammonium salt(IQS) was synthesized; the relationships between the molecular structure of IQS corrosion inhibitor and its corrosion inhibition effect on the reinforcement, the migration kinetics of IQS in concrete were investigated. In addition, the influence of the electro-migrating IQS corrosion inhibitor on the composition, microstructure and material properties of concrete were also investigated. The research works in this thesis are summarized in detail as follows:(1) Based on the technical requirements of rapid migration in concrete under electric field and effective corrosion inhibition performance, the IQS corrosion inhibitors, in which the imidazoline heterocyclic acted as the primarily inhibition group and presented a good dissolution in water to produce a cationic corrosion inhibition functional group, were chosen and subsequently synthesized. Considering all the factors influencing the type and yield of the synthetic product, the appropriate synthesis conditions were proposed, and the yield was up to 90 %.(2) The corrosion inhibition performance of the synthesized IQS on the reinforcement in simulated concrete pore(SCP) solution containing 3. 5% Na Cl were investigated. The IQS presented a good corrosion inhibition effect on the reinforcement in the SCP solution; further, in the presence of 1.0 % IQS, the corrosion inhibition efficiency was significantly higher than 2 % alcohol amine. The maximum electron charge densities were related to the 1N and 4N atoms in the imidazoline heterocycle group of the IQS molecule, indicating that 1N and 4N atoms were the most important adsorption and bonding centers between the IQS corrosion inhibitors and Fe atom on reinforcement surface, and the corrosion inhibition effect of IQS was mainly depended on the amounts of charge carried by the two N atoms. Therefore, higher corrosion inhibition efficiencies of IQS were related to larger number of the imidazoline heterocyclic group and longer length of the carbon chain in their molecule. In addition, due to the colloid properties of IQS corrosion inhibitor, the suspended emulsion tended to form ??flocculations and agglomerates‘‘ when content above the critical concentration, reducing the corrosion inhibition effect on reinforcement.(3) The migration kinetics of IQS corrosion inhibitor in concrete under the electric field was investigated. The migration of IQS corrosion inhibitor was significantly accelerated under the electric field, and concentrated nearby the reinforcement surface. After 28 d electro-migration treatment, the maximum concentration of IQS corrosion inhibitor at the concrete/reinforcement interface was 1.0 mg/g. The migration rate of IQS corrosion inhibitor was mainly depended on the electric driving force and molecular structure of IQS corrosion inhibitor: a larger electric driving force and charge carried by IQS, and a smaller molecular weight of IQS corrosion inhibitors were beneficial for the faster migration in concrete.(4) According to Nernst-Planck equation, a mathematical model of the ions transport was established to analyze the migration and distribution of the IQS, Cl-, Na+ and K+ ions in concrete during the electro-migration treatment. The concentrations of different ions predicted by this model were in a good agreements with the experimental results, thus according to the properties and structure parameters of concrete, the boundary conditions of this model can be modified to quantitatively analyze the distributions of IQS, Na+, K+ and Cl- ions in concrete during the electro-migration treatment process. In this way, the suitable technical parameters for the practical application of IQS corrosion inhibitor can be determined.(5) The influence of the electro-migration treatment of IQS on the composition, structure and material properties of reinforced concrete were investigated. The electro-migrated IQS corrosion inhibitor lead to the decomposition of partial hydration products, e.g. C-S-H, AFt et al, and significantly increased of the amount of Ca(OH)2 in concrete. Further, due to the pore-blocking effect of the IQS corrosion inhibitor, the pore structure of concrete was altered: the total porosity of the outer layer was significantly reduced, but the critical pore size was increased; however, the total porosity of the inner layer was increased, whereas the critical pore size was reduced. After the electro-migration treatment, the impermeability of concrete was greatly improved, which is beneficial for solving the excessive deterioration of concrete impermeability after ECE treatment.(6) The corrosion inhibition mechanisms of the IQS corrosion inhibitor on reinforcement were revealed. The corrosion inhibition effect of the IQS corrosion inhibitor is related to the combined effects as follows:(a) the effective adsorption of IQS molecule on reinforcement surface, forming an adsorption film to block the aggressive ions contacting with reinforcement surface;(b) the extraction of Cl- from concrete under the electric field;(c) the increased alkalinity at the concrete/reinforcement interface. These effects prevents the ―secondary corrosion‖ derived from ECE treatment, therefore, the corrosion resistance of reinforced concrete is enhanced. |
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