Inhibiting Steel Corrosion in Simulated Concrete with Low Phosphate to Chloride Ratios

Abstract

Phosphate ions are studied as corrosion inhibitors in pore simulating solutions highly contaminated with chloride ions. The investigation aims at understanding the role of phosphates in the corrosion inhibition mechanism, employing potentiodynamic polarization tests, micro-Raman spectroscopy, impedance spectroscopy, X-ray photo electronic spectroscopy (XPS) and weight loss tests. Two inhibitor/chloride ratios were assessed, [PO 4 3 The use of corrosion inhibitors has proven to be an efficient way to prevent rebars corrosion in concrete. [1][2][3] It is well-known that aggressive conditions, such as those associated to concrete carbonation or chloride ions contamination compromise the stability of the protective passive layer naturally formed on steel reinforcements.Two approaches are generally used to study steel corrosion in concrete: using simulated pore solution or using actual concrete or mortar. The use of electrolytes that mimic pore solutions facilitates the control of the many parameters that influence rebar corrosion. This is the approach chosen in the present investigation.For concrete, the most widely used corrosion inhibitor is calcium nitrite.4-7 However, for ecological reasons, it needs to be replaced with less contaminant substances. In this sense, phosphate ions can be used as inhibiting agents as they are inexpensive and present low toxicity.The performance of phosphate ions as inhibitors in simulated pore solutions has not been extensively studied. [8][9][10][11][12][13] The inhibition mechanism in alkaline solutions is still under discussion and a deeper understanding is needed to later evaluate its effectiveness in mortars or in concrete.In a previous work, the effectiveness of a high dosage of sodium phosphate (0.3 mol L −1 ) as corrosion inhibitor was tested in a pore simulating solution contaminated with chloride ions (0.13 Also, a protection mechanism was proposed. 13 In this work, two dosages of sodium phosphate (0.1 and 0.3 mol L −1 ) are compared in a synthetic medium (pH 13) that simulates the interstitial solution of concrete heavily contaminated with chloride ions (0.The conditions chosen for this work include a lower phosphateto-chloride ratio and a higher chloride contamination, as compared to the previous investigation. The lower dosage of inhibitor tested in this work (0.1 mol L −1 ) has been selected in order to reduce costs and minimize changes in the mechanical properties associated to additives. The composition of the passive films is investigated to evaluate changes in the previously proposed protection mechanism that may result from this new phosphate dosage and chloride contamination levels. Materials and MethodsElectrodes preparation.-The electrodes were constructed from construction steel. The main alloying elements are: Mn 0.635%, C 0.299%, Si 0.258% and Cu 0.227%.The rebars were cut into discs * Electrochemical Society Member.z E-mail: mvazquez@fi.mdp.edu.ar and included in acrylic resin, including an appropriated contact. The geometrical area exposed was 0.503 cm 2...

Effect of Phosphate-Based Inhibitor on Corrosion Kinetics and Mechanism for Formation of Passive Film onto the Steel Rebar in Chloride-Containing Pore Solution

“…The EIS results indicated that all samples exhibited two time constants, from high to middle and middle to lower studied frequencies. Therefore, all EIS plots could be fitted into one EEC [31,32,46,48].…”

“…The efficiency (%) of inhibitor can be calculated by [31] E f f iciency (%) = 1 − R 0 (bare) R 0 (with inhibitor) × 100 (4) where R 0 (bare) and R 0 (with inhibitor) are passive/oxide film resistance or charge transfer resistance formed onto the steel rebar surface of bare (without) and with inhibitor-added solution, respectively. The efficiency (%) of steel rebar exposed in 1, 2, and 3% inhibitor-added SCP + 3.5 wt.% NaCl solution was found to be 81.13, 90.01, and 83.40% after 1 h of exposure (Table 2), respectively.…”

“…Lee et al [30] have used sodium hexameta phosphate with sodium benzoate and benzotriazole as corrosion inhibitor in SCP solution contaminated with 3.5% NaCl and they have found that as the amount of inhibitor increased, the efficiency was gradually increased up to 96% in the presence of 5% inhibitor, owing to the adsorption of inhibitor onto the steel surface. However, phosphate ions delay the onset of localized corrosion in simulated pore solution [31,32]. Aluminum triphosphate effectively hindered the pitting corrosion of the steel rebar in carbonated concrete pore solution attributed to the formation of protective passive film [33].…”

Investigation of composition and structure of tripoliphosphate coating on low carbon steel

“…This is achieved by the formation of a protection passivation film with a thickness of several micrometers and [1,7] and of different composition [19,20].…”

Effect of Chloride Ion on Free Nitrite Ion in Cement

“…In summary, the characteristics and influencing factors on the concentration of NO 2 -in cement paste need to be further explored. In particular, the influence and action principle of Cl -on the free-form NO 2 -concentration and its distribution are not yet clear [17][18][19].…”