Evaluation of the corrosion behavior of galvannealed steel in chloride aqueous solution and in tropical marine environment

An investigation was made into the corrosion behavior of commercial galvannealed steel in 10⁻² mol dm⁻³ NaCl aqueous solutions and in a tropical marine environment, using scanning electron microscopy (SEM), galvanostatic electrochemical stripping (GES), potentiodynamic linear polarization (PLP), and electrochemical impedance spectroscopy (EIS) techniques and open circuit measurements (E _oc). For purposes of comparison, a commercial galvanized steel was also subjected to similar corrosion tests. GES and SEM techniques allowed for the identification of ζ, δ and Γ intermetallic phases and revealed cracks in the galvannealed steel. The PLP, EIS and E _oc results indicated that the galvannealed coating was more corrosion resistant than galvanized coating in an aqueous medium, but that their corrosion behaviors were similar in the marine environment. The corrosion behavior of the galvannealed steel was affected by the evolution of the cracking process in the Zn–Fe layer due to the dissolution of zinc-rich phases, while the galvanized steel displayed generalized corrosion in the aqueous medium and localized corrosion in the marine environment.     

Study of the degradation and recyclability of polyethylene and polypropylene present in the marine environment

Polypropylene (PP) and polyethylene (PE) are two of the most widely used polymers in the world, and consequently the main polymer waste that contributes to the pollution of the oceans. Because they are considered inert to degradation, such waste becomes a threat to marine life. In this study, it was possible to collect data on the recyclability of PP and PE waste collected from the Great Pacific Garbage Patch. First, the degradation conditions suffered by these materials were evaluated. The Fourier transform infrared spectroscopy assays presented different levels of carbonyl in different layers below the surface of each material and scanning electron microscopy tests showed cracks and microorganisms. The mechanical and rheological properties were evaluated in order to evaluate the recyclability of samples exposed to the marine environment. From the study, it can be concluded that, despite the levels of degradation of the samples, it is possible to obtain satisfactory properties for mechanically recycled products. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48215.     

Microstructural investigation of long-term degradation mechanisms in GFRP dowel bars for jointed concrete pavement

Steel dowel bar is used to transfer loads in concrete pavement slab. However, once the steel dowel bar corrodes, it may cause faults, such as joint freezing in concrete pavement, level differences resulting from spalling or decreased efficiency of load transfer, etc., which are the same problems experienced by typical reinforcing steel. This study evaluated the applicability of glass fiber-reinforced polymer (GFRP) dowel bar as a substitute for steel dowel bar. A microstructural analysis was conducted to examine the decrease in durability of GFRP dowel bar exposed to deterioration environments. To analyze the deterioration mechanism of GFRP dowel bar, scanning electron microscopy was employed and the porosity was measured by the gas absorption method. It was concluded that the longer the GFRP dowel bar was exposed to deterioration environments, the more the interlaminar shear stress decreased. This result was validated by the microstructural analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

海洋操作平台钢结构用防护涂料的制备与性能

以聚己内酯、新戊二醇与顺丁烯二酸酐合成了聚酯树脂,然后与六亚甲基二异氰酸酯(HDI)反应以提高支化度,引入有机硅后再同丙烯酸单体反应制得丙烯酸改性聚酯树脂。以此丙烯酸改性聚酯树脂和适量的颜填料为甲组分、拜耳3390固化剂为乙组分,开发了适用于海洋气候的钢结构表面防护涂层。研究了顺丁烯二酸酐含量、丙烯酸改性聚酯树脂羟基含量、n(─NCO)∶n(─OH)值和聚合条件对面漆性能的影响。当顺丁烯二酸酐的用量为聚酯树脂的5%,自制的丙烯酸改性聚酯树脂羟基含量为4.5%±0.3%,n(─NCO)∶n(─OH)=1.1~1.4时,所制备的丙烯酸改性聚酯树脂面漆配以环氧富锌底漆及环氧云母氧化铁中涂漆得到的涂层体系能够满足海上平台钢结构的防护要求。     

Corrosion mechanisms of steel concrete moulds in the presence of a demoulding agent

The behaviour of E24 mild steel, the constituent steel of most moulds for concrete, was studied by voltamperometry and electrochemical impedance spectroscopy in two electrolytes: (i) a filtered cement solution and (ii) a homogeneous mortar without large air cavities. Experiments were carried out with and without Aquadem^®, a demoulding agent in aqueous phase. In the filtered cement solution, the E24 steel is passivated and the passivation mechanism is totally controlled by the anodic process, not by oxygen reduction. Whatever the experimental conditions (O₂ concentration, rotation speed, immersion time), the corrosion current, i _cor, is equal to the anodic plateau current and is of the order of 0.8 A cm^–2. Therefore i _cor can be directly assessed from the steady state current–potential curves. The E24 steel in contact with a homogeneous mortar without large air cavities is passivated as well as in the filtered cement solution. For both electrolytes, the results are independent of the presence or absence of Aquadem^®. Therefore the pitting corrosion observed in service conditions does not arise from the presence of a solid phase in the electrolyte but may result from the heterogeneity of concrete created by air cavities.     

环氧粉末涂料在跨海大桥钢管桩防腐的应用

通过研究对比采用目前较先进的防护涂层,即单层、双层及三层重防腐环氧粉末涂料防腐结构相结合,最大限度的保护杭州湾跨海大桥钢管桩,阻缓钢管桩腐蚀。着重阐述多层防腐环氧粉末涂料制造,多层结构的特点并设计说明工艺,结果表明功能性多层环氧防腐粉末涂料能够满足杭州湾跨海大桥钢管桩的防腐要求。     

Corrosion behavior of reinforcing steel in simulated concrete pore solutions: A scanning micro-reference electrode study

The scanning micro-reference electrode (SMRE) technique was used to study the corrosion behavior of reinforcing steel in simulated concrete pore (SCP) solutions with different pH values. The early stage as well as the propagation of the localized corrosion of reinforcing steel in different solutions was explored. The results indicated that the potential distribution on the reinforcing steel surface changed in homeostasis and the steel remained passive in the pure simulated concrete pore solution. The solution pH had a significant effect on the localized corrosion of reinforcing steel, and the critical pH value for localized corrosion of reinforcing steel in SCP solutions was between 11.46 and 11.31.     

Corrosion performance of coated reinforcing bars embedded in concrete and exposed to natural marine environment

Corrosion behavior of mild steel plain bar embedded in concrete with 28 days compressive strength of 40 N/mm² exposed to natural marine environment at a location in the Gulf of Mannar was studied. This paper reports the results of 1-year study conducted on the reinforced concrete specimens exposed to three different levels. The performance of three different types of corrosion protection by specialty coatings to rebars, namely cement polymer composite, interpenetrating polymer network coating and epoxy coating was also evaluated periodically by measuring open circuit potential measurements and the results are discussed. Biofouling was predominant on completion of 3 months immersion.     

Electrochemical behavior of coupled carbon fiber-reinforced polymer (CFRP) rods in concrete

This paper presents results on the electrochemical behavior of carbon fiber-reinforced polymer (CFRP) composite rods in contact with steel or epoxy coated steel bars in chloride-contaminated concrete. Twelve concrete prisms reinforced by CFRP rods electrically connected to plain or epoxy coated rebars were exposed to 80% humidity for 345 days. Four identical specimens that were not electrically connected served as controls. Measured galvanic currents densities were found to be as much as 100 A cm^–2, raising concerns about the degradation of both CFRP and steel. Electrochemical impedance spectroscopy (EIS) tests were performed to detect possible changes in the electrochemical parameters of CFRP due to galvanic interaction with active steel. Equivalent circuit simulations of the pre- and post-galvanic interaction of CFRP rods with active steel were also evaluated. EIS data indicated that the composite surface was altered so as to have porous electrode characteristics. Optical microscopy provided visible evidence of interface changes on the composite surface, supporting EIS data. The preliminary findings suggest that it would be unwise to permit CFRP to be directly in contact with steel in reinforcing or prestressing applications.     

Effects of cathodic prevention on the chloride threshold for steel corrosion in concrete

This paper presents the results of long-term experimental tests aimed at studying the effects of cathodic prevention on the critical chloride threshold for the onset of pitting corrosion on steel bars in concrete. Cathodic prevention is applied when the structure is new and rebars are still passive being in contact with alkaline and chloride-free concrete. The results obtained showed that even very low values of current densities can increase the critical chloride threshold and, therefore, contribute to increase the service life of reinforced concrete structures in chloride-bearing environments.     

潮差区混凝土结构表面防腐涂装质量控制

根据潮差区混凝土结构腐蚀环境和涂装环境特点,从涂料产品、施工工艺和涂层质量检验3个方面对混凝土结构表面涂层防腐技术的质量控制进行了全面论述。指出只要合理选材,施工过程控制到位,就能取得理想的防护效果。     

Corrosion measurements of steel reinforcement in concrete exposed to a tropical marine atmosphere

As part of a broad research program, reinforced concrete cylinders of different qualities were exposed to the marine atmosphere of North Peninsula of Yucatán. The cylinders were electrochemically monitored over a period of 56 months. The time for the onset of active corrosion was shorter for rebars in concretes with a high water-to-cement (w/c) ratio compared to that for rebars in low w/c ratio concrete. Results also indicate, as expected, that for equal periods of exposure, nominal corrosion current density (i_corr) values were generally higher for rebar in concrete with higher w/c ratio than those for rebar in low w/c ratio concrete. Analysis of the observed impedance spectra in terms of a modified Randles circuit (in which the ideal capacitor is replaced by a constant phase element (CPE)) appeared to be a reasonable approximation.     

Competitive role of inhibitive and aggressive ions in the corrosion of steel in concrete

The effect of various inhibitive ions (hydroxide, citrate, stannate) for the corrosion of steel in concrete was studied by weight loss measurements, chronopotential studies, anodic polarization technique and compressive strength tests. The salient features of the investigation were: in 100% OPC as well as in OPC + fly ash (3:1 ratio) extracts the passivity of steel was readily destroyed even by the presence of 10 000 ppm of chloride. However in 100% OPC and also in OPC + fly ash (3:1 ratio) extracts containing inhibitive and complexing agents like hydroxide, citrate and stannate, the passivity of steel was maintained even in the presence of 30 000 ppm of chloride. The addition of inhibitive ions like hydroxide, citrate and stannate not only decreased the corrosion rate of steel in simulated concrete environments but also increased the compressive strength of mortars. Citrates, stannates and CaO are effective inhibitors of the corrosion of steel in concrete.     

Impedance study on calcium nitrite as a penetrating corrosion inhibitor for steel in concrete

Penetrating corrosion inhibitors are thought to be able to penetrate through the capillary structure of concrete to reinforcing steel and to reduce the already initiated corrosion of steel. In this work the ability of calcium nitrite to inhibit the chloride induced corrosion of steel was studied. The test protocol was adjusted to simulate the performance of penetrating corrosion inhibitors in concrete structures. Steel samples were first prepassivated in saturated solution of Ca(OH)₂ and then exposed to the same solution with 1% NaCl addition, simulating pore liquid in chloride contaminated concrete. After the initiation of steel corrosion, the first dose of calcium nitrite was added, and then its concentration was gradually increased and the inhibition effect was related to the molar ratio of chloride to nitrite ions [Cl⁻]/[NO₂⁻]. Different rates of the increase in the inhibitor concentration were applied.Electrochemical impedance spectroscopy was used to follow the behaviour of steel at different stages of the corrosion process. The evolution of acquired spectra reflected the initiation of localized corrosion of steel and then the gradual inhibition with increasing concentration of the inhibitor. It was found, that calcium nitrite is able to inhibit the initiated corrosion (pitting) of steel and the optimum inhibitor efficiency was observed for the [Cl⁻]/[NO₂⁻] ratio below 1. The inhibition efficiency was larger, when this value of the [Cl⁻]/[NO₂⁻] ratio was reached in early stages of the corrosion development. Calcium nitrite can be effective as a penetrating corrosion inhibitor for steel in concrete, if it will be present in the sufficient concentration at the steel surface in early stages of the corrosion development.     

Application of electrochemical techniques for the control of cracks and steel corrosion in concrete

Electrochemical techniques are becoming increasingly popular as a means of rehabilitating deteriorated reinforced concrete. In this paper we explore the possibility of using an electrodeposition technique for repairs of land-based cracked concrete structures and investigate the effect of this technique on various concrete properties. Concrete specimens reinforced with steel rebars were used as test specimens in this study. The specimens were first precracked by exposing rebars to chloride-induced corrosion, and then immersed in a solution of zinc sulfate and subjected to a constant d.c. current. The current was applied between the reinforcing steel in the concrete and an external electrode immersed in the solution for eight weeks. The degree of crack closure, water permeability, condition of reinforcing steel, and chloride concentration were investigated in order to assess the effectiveness of this method as a potential rehabilitation technique. The results indicate that the formation of electrodeposits caused the closure of cracks and led to improvement of the concrete watertightness. In addition, the investigation shows that the application of the electrical current increases the passivity of steel in concrete.     

Corrosion behavior of polypyrrole coating doped by dodecylbenzenesulfonate for mild steel in acidic media

This paper describes the electrochemical synthesis of a dodecylbenzenesulfonate doped polypyrrole (PPy-DBS) coating on a passivated mild steel (MS) and investigation of its corrosion protection behaviors. This coating was prepared by cyclic voltammetry technique and characterized by Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FESEM). The corrosion protection features of the PPy-DBS coated MS were studied in different acid media (0.5?mol L^?1 H₂SO₄ and 0.5?mol L^?1 HCl solutions) using linear potentiodynamic polarization, electrochemical frequency modulation and, electrochemical impedance spectroscopy methods. Electrochemical measurements and FESEM images reveal that the PPy-DBS coating presents effective protection for the MS against corrosive species. This may be ascribed to the barrier effect of the polymer coating and utilization of the dodecylbenzenesulfonate dopant with large size during the electropolymerization process.     

Monitoring of steel corrosion in concrete by electrode arrays and electrical resistance probes

In the present work two relatively new methods were implemented, in order to follow exactly the time and spatial evolution of steel corrosion in concrete. Measuring with a coupled electrode array is by some means the advancement of electrochemical noise (EN) with electrically connected micro-electrodes, which are spatially arranged, the assessment of anodic and cathodic currents distribution in time is possible. An electrical resistance (ER) probe can provide general corrosion rate, which is calculated from the thickness reduction; however, its response to localize corrosion is limited. The measurements were performed in concrete specimens, which were exposed to periodic wetting and drying cycles. The results of both used methods were compared and related to the conditions of the micro-electrodes and the ER probes after the test was finished. It was found that micro-electrode arrays can monitor the time and spatial evolution of steel corrosion in concrete. The measured currents reliable indicate the temporal anodic and cathodic activities of individual electrodes, and the assessment of general corrosion rates is also possible. Two characteristic fluctuations of the measured currents from the micro-electrode arrays were defined: slower fluctuations and shorter transients. It is believed that the slower fluctuations were generated by rather general corrosion of the electrodes, whereas the shorter transients were very probably generated by the initiation of pits. In accordance with the results of our previous study, it was confirmed that electrical resistance probes (ER) are able to measure reliably the cumulative corrosion damage, as well as the average general corrosion rate. The general corrosion rates obtained by using ER probes were generally slightly higher than those estimated from the measured currents. It should be mentioned that due to the relatively short duration of the experiments, the reliability of the methods for long-term practical applications still needs to be assessed.     

Modern concept of acoustic emission (AE) coupled with electrochemical measurements for monitoring the elastomer-coated carbon steel damage in phosphoric acid medium

Elastomer coatings (rubber) are industrially used to protect phosphoric acid storage tanks against corrosion. Rubber constitutes a barrier against the penetration of H₃PO₄ to metallic surface. Coatings damage induces both acid infiltration and steel corrosion. In this concept, acoustic emission (AE) monitoring technique could be used for the detection of coatings damage as well as for steel corrosion under the coating. In the present work AE was coupled to electrochemical measurements (EM) for rubber damage evaluation and steel corrosion on three types of steels (XC48, E20 and A60) at room temperature in concentrated phosphoric acid (30% P₂O₅) contaminated by Cl⁻, F⁻, SO₄²⁻. Electrochemical behaviour of steels was studied and characterized by potentiodynamic curves and polarization resistance measurement. A good correlation between acoustic emission and polarization resistance or corrosion potential measurements was found during stages of coatings damage and steels corrosion. The majority of AE activity recorded during experiments is related to hydrogen bubbles release. The release of hydrogen bubbles gives rise to two populations of signals: one impulsive and another one resonant.     

Study on the corrosion behavior of reinforcing steel in simulated concrete pore solutions using in situ Raman spectroscopy assisted by electrochemical techniques

In situ Raman spectroscopy, electrochemical impedance spectroscopy (EIS) and polarization curves were used to study the corrosion behavior of reinforcing steel in simulated concrete pore (SCP) solutions (saturated Ca(OH)₂ solutions). Results indicated that the reinforcing steel remained passive in chloride-free SCP solutions. However, the anodic polarization curve of the steel did not exhibit a stable passive region in the SCP solution with 0.5 M NaCl, the corrosion current density exceeded 0.1 μA cm⁻², the steel surface was unstable with chloride attack and localized corrosion appeared on it with FeCO₃ and Fe₂O₃ as the main corrosion products.     

Performance evaluation of polyaniline pigmented epoxy coating for corrosion protection of steel in concrete environment

Corrosion protection of mild steel reinforcement offered by a newly developed epoxy based coating system containing inherently conducting polyaniline as one of the pigments has been studied. The synthesis of polyaniline and preparation of epoxy based coating system containing this polyaniline are described here. The corrosion resistant property of epoxy polyaniline system, coated on mild steel was evaluated by various techniques such as electrochemical impedance spectroscopy, potential time studies, cathodic disbondment test, anodic polarization study, salt spray test and chemical resistance test. The corrosion resistance of epoxy polyaniline coating system coated on reinforcement bars embedded in concrete was also studied by an accelerated time to cracking study. The formation of polyaniline was characterized using FTIR, UV, GPC, particle size analyzer and fineness studies. Electrochemical impedance studies reveal that the resistance of the coating decreased initially and then increased due to passivating ability of the polyaniline pigment. Based on the results of different techniques, it is found that epoxy coating with polyaniline pigment is effective in corrosion protection of steel in concrete environment.