Study On Preparation Of Corrosion Inhibitor Intercalated Hydrotalcite And Its Anti-corrosion Performance And Mechanism

Reinforced concrete is the most widely applied building material in the world today.Chlorine salt erosion is the main reason of steel corrosion in concrete.Layered double hydroxides（LDH）is a natural carrier of layered double hydroxides with good structure memory effect and ion exchange properties.Corrosion inhibitor intercalation LDH（INT-LDH）can be produced by loading corrosion inhibitor into hydrotalc intercalation LDH（Int-LDH）,which can release corrosion inhibitor and adsorb free chloride in concrete and realize the synergistic protection of chloride ion curing and steel bar erosion resistance.In this regard,it is of great application value to study INT-LDH construction method and its mechanism of erosion prevention of reinforced concrete systematically and deeply.With the support of the Key Project of National Natural Science Foundation of China（U22A20229）,the effects of calcination temperature on the loading rate,microstructure and phase components of NO₂-LDH and VB3-LDH were systematically studied during the preparation of NO₂-LDH and VB3-LDH by calcine-recovering method.Through systematically analyzing the effects of NO₂-LDH and VB3-LDH on cement hydration process,the compatibility of NO₂-LDH and VB3-LDH with cement-based materials was clarified.The corrosion inhibition effect and mechanism of NO₂-LDH and VB3-LDH were investigated by simulating concrete environment with concrete simulated pore solution,so as to further reveal the slow-release and replacement mechanism of NO₂-LDH and VB3-LDH;mortar specimen doped with chlorine salt were prepared to study the corrosion inhibition effect and mechanism of NO₂-LDH and VB3-LDH in the real mortar environment with high chlorine salt.Specific conclusions are as follows:（1）The effect of roasting temperature on the synthesis of NO₂-LDH and VB3-LDH was studied.From the perspective of effect of calcination temperature on loading rate of corrosion inhibitor for NO₂-LDH and VB3-LDH,for NO₂-LDH,the best calcination temperature is 500°C,and the C/N ratio of NO₂-LDH obtained by calcine-recovering method can reach 1.17 at this temperature.For VB3-LDH,the most calcination temperature is 450°C,and the VB3 loading rate of VB3-LDH obtained by calcine-recovering method at this temperature is 21.3%.This is because the anion radius of the two anti-erosion agents and the affinity of hydrotalcite materials are different.When the temperature is too low,the surface energy of hydrotalcite can not be fully excited,which makes the combination of nitrite and hydrotalcite surface more difficult.When the roasting temperature is too high,it may cause irreversible damage to LDH to a certain extent,which makes it more difficult for VB3 to enter the hydrotalcite layer.（2）The anti-erosion properties of NO₂-LDH and VB3-LDH on carbon steel in concrete simulated hole solution were studied,and the adsorption mechanism of chloride ion and the release mechanism of anti-erosion agent in concrete simulated hole solution were revealed.The electrochemical test showed that NO₂-LDH and VB3-LDH had significant anti-corrosion effect on the steel bar in the simulated hole solution,and the anti-erosion efficiency was up to 99.87%and 98.61%,respectively.The adsorption capacities of VB3-LDH and NO₂-LDH were 59.8 mg/g and 58.6 mg/g,respectively,in a single chloride ion environment.According to the fitting results of kinetic equation and internal particle diffusion,the main limiting step of VB3-LDH and NO₂-LDH for chloride ion adsorption process is chemical reaction.According to the adsorption isotherm curves of VB3-LDH and NO₂-LDH for chloride ions in the simulated pore solution environment,VB3-LDH and NO₂-LDH have the characteristics of uniform and single-molecular layer adsorption for chloride ions.In the simulated pore solution of concrete,the release of erosion inhibitor was first fast and then slow.The maximum release of erosion inhibitor was 70.92%and 73.33%,respectively.The release process of erosion inhibitor anion was more in line with the quasi-second model and Bhaskar model.（3）The effects of NO₂-LDH and VB3-LDH on hydration,pore structure and mechanical properties of cement were studied.The research finds that:NO₂-LDH and VB3-LDH can promote cement hydration,and no new hydration products are produced in the process of cement hydration.However,with the increase of INT-LDHs content,the content of calcium hydroxide in hydration products increases.After hardening,the total porosity of cement decreases significantly,the compactness increases,and the compressive strength of cement is improved.When the content of NO₂-LDH and VB3-LDH is 2%of the cement mass,the compressive strength of cement has the most obvious improvement.This is mainly because NO₂-LDH and VB3-LDH exert the crystallization nucleation effect,micro-aggregate filling effect and internal curing effect to promote the hydration of cement,so that more hydration products fill the material pores.（4）The corrosion resistance of NO₂-LDH and VB3-LDH to reinforcement in mortar environment was studied.By electrochemical test,it is found that NO₂-LDH and VB3-LDH have significant anti-corrosion effect on the reinforcement in the mortar environment,and increasing the amount of INT-LDH can significantly improve the anti-erosion effect.In the mortar environment mixed with sodium chloride,after 60 days of corrosion,the corrosion rate of steel bars in the 2%NO₂-LDH group is 0.28%,and the corresponding corrosion rate of steel bars in the 2%VB3-LDH group is 0.31%.This is because after NO₂-LDH and VB3-LDH enter the mortar environment,on the one hand,they can promote the hydration process of cement-based materials,reduce the pore structure in the cement paste,and thus increase the difficulty of chloride ion transmission in the mortar.On the other hand,after entering the mortar environment,NO₂-LDH and VB3-LDH will carry out ion exchange in the mortar environment,release the erosion resistance anions between layers,and adsorb the chloride ions inside the mortar,reduce the chloride ion content in the slurry,and play a role in corrosion inhibition of reinforcement.