Research On The Preparation Of Maize Protein Corrosion Inhibitor And Its Inhibiting Mechanism For Reinforced Concrete

In view of the chloride corrosion problem in reinforced concrete structure,and based on the idea of competing with chloride ion adsorped on the steel surface in concrete to prevent corrosion,taking into account that nitrogen,oxygen and sulfur elements in natural plant protein have the ability to donor electron.Moreover,the amino and carboxyl groups produced by protein hydrolysis in the alkaline concrete pore solution are excellent roups with lone pair electrons.Therefore,choosing the byproduct of maize gluten meal as the raw materials,the alkali soluble maize protein is extracted as a novel environmental corrosion inhibitor for reinforced concrete.The inhibitor of maize gluten meal extract(MGME)contains amide I and amide II bond,which is composed of glutamic acid,proline,and leucine.The corrosion inhibition effeciency and mechanism of inhibitor in the simulated concrete pore solution containing 3 wt.% Na Cl were systematically studied by the electrochemical impedance spectroscopy,polarization curve,ATR-FTIR and SEM-EDS,etc.The electrochemical results indicate that the inhibition efficiency increased with the increase of MGME concentration;And it is a mixed type inhibitor resulting from inhibiting both anode and cathode corrosion.The main reason of inhibition is the physical adsorption of MGME on the steel surface,which is consistent with Langmuir adsorption characteristic.In addition,the main contribution of MGME' anticorrosion is from glutamic acid,proline and leucine,which exhibit the negative synergistic effect on the steel anticorrosion.Furthermore,the quantum chemical calculation and Monte Carlo simulation studies show that the inhibitor adsorped on steel is mainly by the contribution of lone pair electrons(HOMO)of amino and pyrrole rings to the "d" space orbit of iron atom,which is also verified by the occurring peaks of C-NH-C in pyrrole ring and the C-N-steel bond in XPS spectra.The inhibition effecicency and mechanism of MGME are revealed from the corrosion results of steel in mortar contaiminated by 1 wt.% chloride.It is found by ATR-FTIR that when the steel are placed in the fresh mortar,the inhibitor has been adsorbed on the steel bars to form the timely anticorrosion layer.When the steel is corroded in polluted mortar with 3% MGME for 450 days in 3 wt% Na Cl solution,the SEM-EDS results show that the chloride concentration in the hydration products is much higher than that on the steel surface,and the polishing scratches on the steel surface are still clear,no corrosion products are produced.Moreover,the anodic polarization curves show that the passivation film on the surface of the reinforcement was complete,and its Raman spectra show that the main composition of the passivation film on steel was Fe OOH.Therefore,the adsorption layer of MGME formed on the surface of the reinforcement in mortar can play an effective role in the chloride corrosion process.Its recommended content is 3 wt.% of cement,and its inhibition efficiency is equivalent to that of calcium nitrite,up to 97.86%.Based on the analysis of cement hydration heat,XRD,DSC-TGA,FTIR and microstructure of pastes,the mechanical property and durability of mortars,it can be seen that MGME inhibitor composed of a variety of amino acids with peptide chain structure have a significant impact on the hydration,setting and hardening process of cement as well as the micro-structure and macro-performace of its hydrates.Firstly,MGME inhibitor plays a role in retarding the formation of ettringite and calcium hydroxide in the early stage of cement hydration,inhibiting the hydration of C2 S and C3 S,prolonging the induction period of hydration,reducing the hydration rate in the acceleration period,and greatly increasing the setting time of cement.With the increase of MGME content,both the content of calcium hydroxide and the hydration degree decreases.Secondly,it is worth mentioning that the overall porosity of paste changes little,but the content of aire pores and caplliary pores larger than 50 nm increases gradually with MGME added,which subsequently leads to the decrease of compressive strength,flexural strength,and resistivity of mortar with MGME added.Accordingly,its electric flux,water absorption and chloride diffusion coefficient increase step by step.Finaly,in order to improve the deterioration of mortars caused by the introduction of MGME,the novle green additive can be used in combination with mineral admixture(silica fume)and accelerator(triethanolamine)to optimize the structure and performance to meet the concrete technical requirements of field practice.