Study On Inhibition Effect Of Some Organic Inhibitors On Carbon Steel In Carbonated Simulatied Concrete Pore Solutions

Reinforced concrete structure is the most widely used construction structure,while corrosion of reinforcing steel is the main reason leading to the premature deterioration of reinforced concretes.Corroison of reinforcing steel is related to the carbonation of concrete and the presence of chloride ions.Several techniques have been employed to reduce corrosion of reinforcing steel,among which corrosion inhibitor is the most practical method owing to its advantages of low cost,high efficiency and wide applicability.Howerver,many commercial inhibitors remain unfriendly to the environment.In recent years,researchers have paid considerable attention towards the development of various more effective and green inhibitors to prevent corrosion of rebars,especially for the inhibitors that could prevent both general corrosion and localized corrosion.Due to the acidification of the atmospheric environment and the application of new type concretes,the corrosion of reinforcing steel becomes an urgent problem.In this paper electrochemical measurements are used to study the inhibition effect of some organic inhibitors on carbon steel in simulated carbonation concrete pore solutions,and surface analysis technologies are used to understand the inhibition mechanism.The corrosion behavior of Q235 carbon steel and 304 stainless steel(SS)were studied by potentiodynamic polarization in four types of simulated concrete pore solutions(pH 13.3,11.5,9.7).The results showed that both steels maintained good passivation in the pore solutions,demonstrating similar corrosion resistance.The addition of 0.05 mol/L of Cl-had no influence on the corrosion resistance of 304 SS in the solutions,whereas pitting corrosion susceptibility of Q235 carbon steel increases in the carbonated solutions.304 SS performed much better than Q235 carbon steel in carbonated pore solutions with the critical chloride concentration 100 times higher than that of Q235 carbon steel.The presence of NaHCO3 and Na2CO3 increased the critical[Cl-]for pitting corrosion because of the inhibitive effect of HCO3-/CO32-on pitting corrosion.The inhibition effects and mechanism of five organic carboxylate compounds with different alkylene chain lengths on Q235 steel in a simulated carbonation concrete pore solution(pH 11.5)were studied.Quantum chemical calculation results show that the adsorption capacity of the inhibitors increases with increasing distance between C=C bond and-COO-group.The weight loss test confirmed the quantum chemical calculation results and shows the adsorption of carboxylate compounds on steel surface follows Langmiur isotherm.The carboxylate compounds act as mix-type inhibitor for carbon steel in carbonation concrete environment,and the inhibition effect increases as the inhibitor concentration increases.Under the same concentation,the inhibition effect increases as the alkylene chain length increases,and the adsorption film formed by inhibitor on steel surface by forming Fe-OOC-Cx bonds and the C=C bonds could enhance the adsorption process.Undecylenic acid showed the best inhibition,which could inhibit both uniform corrosion and localized corrosion,and the best inhibition effecicy is 91%.Corrosion inhibition efficiency of La(4-OH cin)3 on Q235 carbon steel in 0.01 mol/L chloride solution with a large pH range(pH 2.5-11.5)was studied with electrochemical measurements and surface analysis.Under all test conditions,La(4-OH cin)3 shows inhibition effect with the inhibition efficiency IE%between 55%and 80%.The inhibitor could increase the pitting potential of steel,preventing both general corrosion and localized corrosion,and shows better inhibition effect in alkaline environment.At pH 2.5,5.5 and 8.5 an inhibition film containing La may form on steel surface,while a complex layer formed by reactions between La3+ and the corrosion products would further deposit on the surface.The inhibition film and the deposited layer would together inhibit further corrosion.Particularly,the inhibitor tends to be enriched in the dissolved areas,which would depress the dissolution of active area and decrease the surface roughness.While at pH 11.5,the steel is passivated and a thin inhibition film may be formed on the surface,with some deposited particles containing Fe and La,corrosion is more effectively inhibited.The inhibition behavior of La(4-OH cin)3 for Q235 carbon steel in acidic 0.01 M NaCl solutions(pH 2.5 and 5.5)for different immersion time was investigated with electrochemical measurements and surface analysis.The results show that the inhibitor could effectively prevent corrosion for carbon steel in the acidic environments.The inhibitor act mainly as anodic type inhibitor and the inhibition efficiency increases as the inhibitor concentration increases.With addition of 600 ppm La(4-OH cin)3 the highest inhibition efficiency reaches 97.4%at pH 2.5 and 99.5%at pH 5.5 respectively.As the immersion time increases,the inhibition efficiency increases in the first 24 h and then slightly decreases.A complex film containing organic anions and the oxides/hydroxides of La and Fe was formed on the surface,which provides good inhibition for the steel.The inhibition effect of calcium lignosulfonate(CLS)on both uniform corrosion and localized corrosion for carbon steel in carbonation concrete system was confirmed by the electrochemical test results.Sodium molybdate could enhance the passivation film in the carbonation concrete environment to portect the carbon steel surface.CLS and Na2MoO4 have synergistic inhibition effect in the test environment,and 400 ppm CLS compound with 600 ppm Na2MoO4 is the optimum ratio.The inhibition effect of compound inhibitior increases as the immersion time increase.The surface analysis results show that molybdate could promotestability of the passive film;the insoluble molybdenum componds and CaO/Ca(OH)2,deposit on steel surface could enchance the adsorption of CLS,and forming a complex film.The compounded film effectively inhibits corrosion of the carbon steel.