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To investigate the corrosion degradation law and service life of reinforced concrete in various salt solution environments, reinforced concrete specimens were semi-immersed in 3% Na2CO3(N3-0-0), 3% Na2CO3+3% NaCl (N3-Cl3-0) and 3% Na2CO3+3% NaCl+3% Na2SO4(N3-Cl3-S3)salt solutions. The electrochemical workstation was used for regular non-destructive testing, and the polarization curve and related electrochemical parameters were used as the macroscopic durability evaluation indicators, while microscopic analysis of steel bar corrosion products was performed in combination with SEM and EDS. In addition, the corrosion current density degradation model of GM (1,1) was established and compared with the modified GM (1,1)-Markov degradation model. The results showed that the prediction error of the GM (1,1)-Markov model was smaller and more accurate than that of GM (1,1). The reinforced concrete specimens in the N3-0-0, N3-Cl3-0 and N3-Cl3-S3 solutions reached the failure state in 3.08, 1.67, and 2.30 years, respectively, as predicted by the GM (1,1)-Markov model. According to ESM and EDS microscopic analysis of reinforcement, carbonate had no significant effect on reinforcement corrosion, chloride ions played a dominant role in reinforcement corrosion, and sulfate ion improved concrete's resistance to chloride ion corrosion. Based on GM (1,1)-Markov model, the failure and damage of reinforced concrete in saline soil areas can be quantitatively evaluated in the whole life cycle, which provides a theoretical basis for the early maintenance or reinforcing of reinforced concrete. [ABSTRACT FROM AUTHOR]

The effects of rare earth La on the microstructure, hardness, and corrosion resistance of A356 aluminum alloy were investigated by optical microscopys, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The experimental results showed that with the addition of rare earth La, the microstructure was refined, and both Si phases and β-Al5FeSi phases were transformed from long needle-like to short rod-like. The optimal microstructure and mechanical properties of the alloy were obtained when 0.6 wt% La was added. Compared with A356 aluminum alloy (88.36 HV), the hardness of A356 aluminum alloy modified with 0.6 wt% La (106.83 HV) was increased by 20.1%. The results of the immersion corrosion test and electrochemical experiments showed that the corrosion current density of A356 aluminum alloy modified with 0.6 wt% La (132.51 μA cm−2) was 24.8% lower than that of the matrix (176.24 μA cm−2), and the polarization resistance (668.56 Ω cm2) was 235.2% higher than that of the matrix (199.47 Ω cm2). This may be because the addition of rare earth La significantly reduced the cathode phases grain size in the corrosion micro-battery as well as the formation of intermetallic compounds containing rare earth La, leading to a decrease in the reaction rate of the cathode during corrosion. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High entropy alloys (HEAs) are alloys based on a minimum of five principal elements, which can also have some minor elements for improving the properties according to the applications. The present study deals with the minor elements (Al and Mn) containing CoCrFeNiTi-based HEAs and discusses the effect of Ti on the corrosion behaviour of the HEAs. The HEAs were synthesized in an inert atmosphere using a vacuum arc melting furnace. The as-synthesized HEA samples were characterized for microstructure, phases, hardness, and density. The hardness and density were influenced by changing the amount of Ti in HEAs. The electrochemical corrosion behaviour was analysed using a potentiostat in 3.5% NaCl and 0.1M H2SO4 solutions. The corrosion results suggest that the high Ti-containing HEAs show better corrosion resistance in the NaCl and H2SO4 solutions due to the formation of TiO2 on the sample surface. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The nanocomposites of 2024 Al reinforced with CeO2@GNPs (graphene) nanoparticles were fabricated using the hot-press sintering method. With the addition of 0.5 wt% CeO2@GNPs, the YS and UTS of the fabricated nanocomposites increased by 21.1% and 24.7%, respectively. The load transfer effect and optimization of the interfacial bonding were the main factors to improve the mechanical properties of the composites. The effect of the surface modification of GNPs on the corrosion resistance of the composites was investigated, demonstrating that the addition of GNPs weakened the corrosion resistance of the fabricated nanocomposites. Meanwhile, the corrosion current density (2.776 × 10−3 A·cm−2) and polarization resistance (13,971.37 Ω cm2) of the prepared composites with CeO2 nanoparticle-layered GNPs exhibited a significant decreasing trend compared with the composites without a CeO2 nanoparticle layer (3.540 × 10−3 A·cm−2, 10,199.72 Ω cm2). Optimizing the dispersion of GNPs and their interfacial bonding with the aluminum matrix promoted the reduction in the corrosion area and the possibility of micro-couple formation, leading to an effective enhancement of the corrosion resistance of the nanocomposites. [ABSTRACT FROM AUTHOR]

In the field of healthcare and dentistry, 316L stainless steel is widely used for its corrosion resistance. However, the presence of lactic acid in salivary solutions can affect its surface reactivity. This study employed electrochemical methods to investigate the influence of lactic acid on 316L stainless steel's corrosion resistance in Fusayama Meyer saliva and saliva doped with varying lactic acid concentrations. The results revealed a significant decrease in polarization resistance as the lactic acid concentration increased, despite a shift toward more positive corrosion potentials. Consequently, the study suggests that the lactic acid presence in salivary solutions should be considered when evaluating the corrosion susceptibility of 316L stainless steel devices. [ABSTRACT FROM AUTHOR]

A MA8 magnesium alloy substrate was pre-impregnated in aqueous solutions of cerium(III) nitrate and glycerol before microarc oxidation, which was used to form oxide ceramic coatings from a silicate–alkaline electrolyte containing fluoride ions. The corrosion-protection properties of these coatings on the pre-impregnated alloy surface were assessed using potentiodynamic polarization curves. Electrochemical parameters calculated from the potentiodynamic polarization curves showed that the presence of the oxide ceramic coating on the surface of MA8 magnesium alloy significantly reduces the corrosion current density and increases the polarization resistance. It was determined that the pre-impregnation of the MA8 magnesium alloy substrate in aqueous solutions of cerium(III) nitrate and glycerol affects the mechanism of the corrosion damage. [ABSTRACT FROM AUTHOR]

Magnesium oxychloride cement recycled concrete (MOCRC) has the advantages of low carbon emissions and energy savings. To better understand the rebar corrosion problem in MOCRC under a salt lake environment, this paper presents the investigation of rebar corrosion behavior in MOCRC, as well as the difference of protective influence between single and double protective methods. During the investigation, the concrete surface strengthening materials and rebar type selection were selected as protective methods, and an electrochemical test based on linear polarization method and Tafel method was introduced. According to the time-varying characteristics of corrosion current density and mass loss of rebar in different specimens, a time-varying model of corrosion current density of rebar was established. The results show that the B values of corroded hot-rolled plain steel (HS), corroded HS with self-developed coating (CS), uncorroded CS, and uncorroded stainless steel (SS) were 28, 34, 41, and 45 mV, respectively. Also, the rebar type selection has far better protective influence than the concrete surface strengthening materials, and the double protective method was better than the single protective method. Besides, it was noticed that the time-varying characteristic of rebar corrosion in MOCRC conformed to the logarithmic-type time-varying model, which has an upward trend in the earlier stage and exponential-type time-varying model with a downward trend in the later stage. Finally, this study presents a profound investigation for the reinforcement corrosion in low-carbon and energy-saving building MOCRC structures. [ABSTRACT FROM AUTHOR]

To clarify the corrosion mechanism of 304L stainless steel in the first circuit of nuclear power plant，304L stainless steel was immersed in a solution simulating the water environment in the first circuit of nuclear power plant which contained different concentrations of zinc and aluminum ions for 168 hours at 290 ℃to form an oxide film on its surface.Then，the resulting oxide film was tested by means of potentiodynamic scanning，AC impedance spectrum test，Mott-Schottky curve test and photo-electrochemical test，and the polarization curves，electrochemical parameters，semiconductor type，flat band potential，carrier concentration，band gap potential and phase composition of the oxide film were obtained.Results showed that the simultaneous addition of zinc and aluminum ions could significantly reduce the corrosion rate of 304L stainless steel.When the concentration of Zn ion was 40 μg/L and the concentration of Al ion was 90 μg/L，the corrosion current density of the oxide film formed on the surface of 304L stainless steel was the smallest，and the corrosion resistance of the oxide film was the best.Compared to the oxide film formed with the injection of zinc ion alone into the first circuit of a nuclear power plant，the film on the surface of 304L stainless steel showed a double-layer structure，its semiconductor type was n-type，the flat band potential shifted negatively，and the carrier concentration decreased.Compared to the oxide film formed without the addition of zinc and aluminum ions，two more phases of ZnAl2O4 and α-FeOOH emerged in the phase composition of the oxide film.Therefore，adding zinc and aluminum ions to the simulated solution under high-temperature and high-pressure conditions could effectively increase the corrosion resistance of 304L stainless steel.

Imposing anode current is widely used in the artificial accelerated corrosion of steel rebars.However，the uneven current distribution in series or parallel accelerated corrosion circuits often lead to uneven corrosion degree of steel bars.In order to optimize the accelerated corrosion method of steel rebars by imposing anode current，a multidirectional hybrid connection circuit was proposed and the accelerated corrosion test of steel rebars was carried out.The current，change of corrosion potential and corrosion current density，corrosion rate and corrosion products of each group of steel rebar specimens under three accelerated corrosion modes of hybrid connection，series connection and parallel connection were compared and analyzed.Results showed that the current distributions of steel rebars in series and parallel circuits were different，which led to different corrosion degree of steel rebar.In the hybrid connection，the current distribution was uniform and the corrosion degree of steel rebar surfaces were similar，and the corrosion rate of each steel rebar was close to the theoretical value.The uniform accelerated corrosion of steel rebars or reinforced concrete specimens could be realized through the multidirectional hybrid connection circuit，which effectively optimized the effect of accelerated corrosion of steel rebars and provided reference for accelerated corrosion of steel rebars or reinforced concrete members.

In cold spraying, formation and adhesion of the coating is mainly due to the kinetic impact of the powders as they impinge on the substrate, at velocities above the critical value, causing substantial plastic deformation of both the particles and substrate. Most of the research around cold spraying focuses on preheating the gas before spraying; however, this article is aimed at preheating the substrate only and evaluating its effect on the microstructure of the coating. Before deposition the substrate was preheated at different temperatures to understand its effect on the corrosion behavior. The analysis shows that the powder particle could efficiently deposit, by increasing the substrate temperature up to at least 250 °C. The corrosion current density extracted from the Tafel plot shows a decreasing trend than bare 1020 steel in 3.5 wt.% NaCl solution. However, at higher temperatures the corrosion behavior detriments due to an increase in the oxygen content of the coating during deposition. An estimation of the gas velocity shows that substrate heating is beneficial in obtaining high deposition efficiencies even with low gas velocities, much below the theoretical critical velocity for nickel. [ABSTRACT FROM AUTHOR]

This study aims to explore the effects of different Ca(OH)2 contents on the mechanical performance and corrosion behaviors of steel in Calcium sulfoaluminate (CSA) cement, where compressive strength, corrosion potentials of reinforcements, corrosion current density, pH of pore solution as well as mortar resistivity of CSA/Ca(OH)2 mortar were researched, and the corrosion behaviors were further interpreted by the clarification of hydration phases through microstructural analyses. The initial results highlighted the positive effects of using adequate Ca(OH)2 (~ 6%) in CSA mortar in terms of strength, yet its excessive addition could delay the subsequent hydration reaction of CSA. Meanwhile, with an increased quantity of Ca(OH)2, the amount of some hydration phases, such as Al(OH)3 reduced, resulting from their reaction with Ca(OH)2. Finally, the corrosion current density increased with the reduced mortar resistivity when the reinforcement in CSA/Ca(OH)2 system was corroded, and their relationship was also provided in this study. [ABSTRACT FROM AUTHOR]

Abstract The use of reinforced concrete is common in marine structures. Failure of reinforcement due to corrosion has detrimental impacts on nearly all of these structures. Hence, proposing an accurate and reliable model was imperative. The goal of this paper is to develop a new hybrid model by combining Particle Swarm Optimization (PSO) with Dragonfly Algorithm (DA) for Adaptive Neuro-Fuzzy Inference System (ANFIS) to predict the corrosion current density (C 11) of marine reinforced concrete. The neuro-fuzzy-based methods have emerged as suitable techniques for encountering uncertainties associated with the corrosion phenomenon in marine structures. To the best of our knowledge, this is the first research that predicts the C 11 through a model integrating fuzzy learning, neural learning rules, and meta-heuristics. 2460 data are collected from 37 regions in Persian Gulf. The input parameters are age, concrete repairing history, height above the sea level, distance from sea, concrete compressive strength, rebar diameter, concrete cover depth, concrete electrical resistivity, chloride ion concentration and pH. The proposed rules for the estimation of C 11 based on collected dataset are assessed based on the several metrics such as R 2, efficiency, mean absolute percentage error (MAPE), and median of absolute error (MEDAE). According to the results, ANFIS-PSO–DA enables to predict C 11 by R 2 (0.92), MAPE (1.67), MEDAE (0.14), and EF (0.97). The results of sensitivity analysis revealed that concrete compressive strength and pH are the most effective parameters on the corrosion current density of reinforced concrete.

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract The service life prediction of reinforced concrete (RC) structures in marine environment is essential in structural repair and health monitoring. In this paper, a numerical model for predicting the service life of reinforced concrete is first developed which considering the time-varying boundary of chloride concentration, critical chloride concentration and density of corrosion current. Based on the model, the effects of water–cement ratio, reinforcement diameter, concrete cover thickness and critical chloride ion concentration on the service life and deterioration duration of RC structures are investigated. The key factors affecting the service life of reinforced concrete structures are determined. More importantly, based on regression analysis, a new simplified empirical model for predicting the service life of RC structures is also developed. It provides a fast assessment tool for practical engineers. Both the numerical model and empirical model validated are suitable for practical engineering applications. The results show that with the increase of water–cement ratio, the service life of reinforced concrete structure decreases exponentially. And with the increase of the thickness of the concrete cover, the service life, deterioration duration, and safety reserve increase linearly. However, the influence of the diameter of the reinforcing bar on the service life can be ignored.

[Display omitted] • The XGBoost and GBDT models demonstrated the highest accuracy in predicting i corr and E corr. • The models exhibit good generalization performance with a small deviation from experimental results. • This paper applies ML to predict the short-term electrochemical corrosion behavior of HEAs. In this study, machine learning (ML) models were successfully employed to predict the short-term electrochemical corrosion behavior of high-entropy alloys (HEAs) based on their chemical compositions. Considering the vast compositional space of HEAs, which restricts the development of corrosion-resistant HEAs, and the lack of non-destructive methods to qualitatively assess their corrosion resistance, this work represents a significant advancement in the field. The "three-step" method was applied to select the optimal feature set from 38 features, and six ML regression models were trained and compared. The eXtreme Gradient Boosting (XGBoost) and Gradient Boosting Decision Tree (GBDT) algorithms demonstrated the highest predictive accuracy (R2 = 81.02 % and 84.64 %, respectively) among the six algorithms. The model's robust generalization capabilities were confirmed through validation on an additional dataset. Moreover, the interpretability of the model was enhanced by employing two analysis methods, which revealed that pH as an environmental factor, electronegativity difference and average electronegativity as empirical parameters, and the concentrations of Cr and Cu as compositional parameters have the most significant impact on the corrosion resistance of HEAs. The proposed methodology and framework have the potential to optimize alloy composition, facilitating the design and development of new corrosion-resistant HEAs. [ABSTRACT FROM AUTHOR]

The nanocomposites of 2024 Al reinforced with CeO2@GNPs (graphene) nanoparticles were fabricated using the hot-press sintering method. With the addition of 0.5 wt% CeO2@GNPs, the YS and UTS of the fabricated nanocomposites increased by 21.1% and 24.7%, respectively. The load transfer effect and optimization of the interfacial bonding were the main factors to improve the mechanical properties of the composites. The effect of the surface modification of GNPs on the corrosion resistance of the composites was investigated, demonstrating that the addition of GNPs weakened the corrosion resistance of the fabricated nanocomposites. Meanwhile, the corrosion current density (2.776 × 10−3 A·cm−2) and polarization resistance (13,971.37 Ω cm2) of the prepared composites with CeO2 nanoparticle-layered GNPs exhibited a significant decreasing trend compared with the composites without a CeO2 nanoparticle layer (3.540 × 10−3 A·cm−2, 10,199.72 Ω cm2). Optimizing the dispersion of GNPs and their interfacial bonding with the aluminum matrix promoted the reduction in the corrosion area and the possibility of micro-couple formation, leading to an effective enhancement of the corrosion resistance of the nanocomposites.

Schiff's bases such as (E)-3-(3-hydroxybenzylideneamino)-2-(3-hydroxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (SB-1) and (E)-3-(5‑bromo-2-hydroxybenzylideneamino)-2-(5‑bromo-2-hydroxyphenyl)-2,3-dihydraquinazolin-4(1H)-one (SB-2) were synthesized and investigated to the surface interactions & corrosion protection performance on mild steel (MS) in 2 M HCl medium by means of weight loss, electrochemical polarization and electrochemical impedance spectroscopic (EIS) techniques. Tafel polarization measurements showed that, the synthesized compounds were exhibited as mixed type (cathodic / anodic) inhibitors and the maximum protection efficiencies of 86.44% and 87.36% for SB-1 and SB-2 respectively were observed at optimized concentration. The corrosion control of MS in presence of inhibitors could evaluate through adsorption phenomenon and fitted to Langmuir's adsorption isotherm. Activation energy (Ea) values in absence of the inhibitor is minimum 51.45 kJ mol−1 and higher values of 89.98 kJ mol−1 and 70.09 kJ mol−1 in the presence of SB-1 and SB-2 respectively. Thermodynamic adsorption parameters such as ∆Hads, ∆Gads & ∆Sads were correlated to the corrosion inhibition process. Quantum chemical analysis revealed the nature of chemical interaction established between the inhibitor molecules and metal atoms. The change in surface morphology of mild steel and chemical interactions of inhibitor molecules on specimen surface were evaluated through FT-IR, Scanning electron microscopic linked with EDX, Atomic force spectroscopy and Contact angle techniques. Atomic force microscopic results revealed that, an average roughness of the mild steel surface has been reduced from 443 nm to 11.0 nm and 26.9 nm in presence SB-1 and SB-2 respectively.

The structural phase composition and some properties of a modified medium-carbon steel 45 surface after being subjected to cathodic plasma electrolytic nitriding in ammonium chloride and ammonia solution were studied. It was shown that the steel surface cathodic nitriding is accompanied with a high-temperature oxidation along with formation of FeO, Fe2O3, and Fe3O4 oxides, as well as nitrogen diffusion and quenching with formation of FeN, Fe3N, and Fe4N phases, martensite, and residual austenite. A competitive effect was revealed of the surface erosion resulting from the discharges and high-temperature oxidation on the morphology and surface roughness. It was found that the maximum microhardness of the modified layer reaches 1040 HV, and the current density of the nitrided surface corrosion decreases by 1.5–2.4 times. [ABSTRACT FROM AUTHOR]

The use of reinforced concrete is common in marine structures. Failure of reinforcement due to corrosion has detrimental impacts on nearly all of these structures. Hence, proposing an accurate and reliable model was imperative. The goal of this paper is to develop a new hybrid model by combining Particle Swarm Optimization (PSO) with Dragonfly Algorithm (DA) for Adaptive Neuro-Fuzzy Inference System (ANFIS) to predict the corrosion current density (C11) of marine reinforced concrete. The neuro-fuzzy-based methods have emerged as suitable techniques for encountering uncertainties associated with the corrosion phenomenon in marine structures. To the best of our knowledge, this is the first research that predicts the C11 through a model integrating fuzzy learning, neural learning rules, and meta-heuristics. 2460 data are collected from 37 regions in Persian Gulf. The input parameters are age, concrete repairing history, height above the sea level, distance from sea, concrete compressive strength, rebar diameter, concrete cover depth, concrete electrical resistivity, chloride ion concentration and pH. The proposed rules for the estimation of C11 based on collected dataset are assessed based on the several metrics such as R2, efficiency, mean absolute percentage error (MAPE), and median of absolute error (MEDAE). According to the results, ANFIS-PSO–DA enables to predict C11 by R2 (0.92), MAPE (1.67), MEDAE (0.14), and EF (0.97). The results of sensitivity analysis revealed that concrete compressive strength and pH are the most effective parameters on the corrosion current density of reinforced concrete. [ABSTRACT FROM AUTHOR]

Zinc protection of galvanized steel is initially dissolved in alkaline solutions. However, a passive layer is formed over time which protects the steel from corrosion. The behavior of galvanized steel exposed to strong alkaline solutions (pH values of 12.7) with a fixed concentration of sulfate ions of 0.04 M is studied here. Electrochemical measurement techniques such as corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy are used. Synergistic effects of sulfate ions are also studied together with other anions such as chloride Cl− or bicarbonate ion HCO3− and with other cations such as calcium Ca2+, ammonium NH4+ and magnesium Mg2+. The presence of sulfate ions can also depassivate the steel, leading to a corrosion current density of 0.3 µA/cm2 at the end of the test. The presence of other ions in the solution increases this effect. The increase in corrosion current density caused by cations and anions corresponds to the following orders (greater to lesser influence): NH4+ > Ca2+ > Mg2+ and HCO3− > Cl− > SO42−. [ABSTRACT FROM AUTHOR]

This study investigated Cu-doped a-C films prepared under a substrate bias gradually reducing from 120 to 60 V and different Cu target currents of 0, 0.15, 0.2, 0.3, 0.5 A, respectively, using closed field unbalanced magnetron sputtering physical vapour deposition technique. While the Cu-doped a-C film at the lowest Cu target current of 0.15 A (A0.15) remained an amorphous microstructure, Cu nanoprecipitates occurred at Cu target currents of 0.2–0.5 A. All the Cu-doped a-C films prepared exhibited good combination of corrosion resistance to a corrosive chemical mixture of 0.5 M H 2 SO 4 + 5 ppm HF (as suggested by the corrosion current densities) and interfacial electric conductivity (as demonstrated by the interfacial contact resistance, ICR). Among all coatings, A0.15 showed the best corrosion resistance and interfacial electric conductivity, which is attributable to the precipitate-free Cu-doped amorphous microstructure. The measured current density of A0.15 was 1.95 × 10−7 A/cm2 at 0.6 V (vs. SCE) during potentiodynamic polarization, which was lower than that of the Cu-free a-C film at 7.34 × 10−7 A/cm2. The ICR value of A0.15 was 4.40 mΩcm2 at an assembly pressure of 1.4 MPa, which is about one third of the Cu-free a-C film. This study demonstrates a new deposition strategy combining Cu-doping and the control of substrate bias to improve the corrosion resistance and interfacial electric conductivity of a-C films for PEMFC. [Display omitted] • A transition of microstructure from amorphous Cu solid solution to Cu-nanoprecipitation is observed. • The compactness and uniformity of a-C films can be enhanced due to Cu doping. • The film at the lowest Cu target current shows the best combination of corrosion resistance and interfacial conductivity. • A new deposition strategy combining Cu-doping and decreasing substrate bias is demonstrated. [ABSTRACT FROM AUTHOR]

This study investigated the effectiveness of sodium nitrite (NaNO2) as a corrosion inhibitor against chloride-induced steel rebar corrosion in fly ash–ground granulated blast furnace slag (GGBS)–based geopolymer concrete (GPC). The GPC was prepared with two different blends of fly ash and GGBS and two different molarities of sodium hydroxide solution. Sodium chloride (NaCl) and sodium nitrite (NaNO2) were admixed in the GPC mix during preparation. The effectiveness of NaNO2 against chloride-induced corrosion in GPC mixes was evaluated through corrosion measurements. The microstructure of GPC in the presence of NaCl and NaNO2 was studied through X-ray diffraction (XRD) analysis and energy-dispersive X-ray spectroscopy (EDS) analysis. The obtained results showed that NaCl decreased the workability, whereas NaNO2 improved the workability of the GPC mix with a significant effect at higher dosages. The NaNO2 reduced the compressive strength of GPC with more effects at higher dosages. However, the retarding effect of NaNO2 on strength development decreased with age. The addition of NaNO2 in chloride admixed GPC lowered the probability of occurrence of corrosion and the corrosion current density of steel rebar. The inhibiting efficiency of NaNO2 against chloride-induced rebar corrosion in GPC was enhanced with an increase in its dosage. Furthermore, the inhibiting efficiency of NaNO2 decreased with age. However, the reduction with age was significantly less at a higher dosage. The variation in compressive strength of GPC in the presence of NaCl and NaNO2 is in line with the variation in the formation of N-(C)-A-S-H and N-A-S-H type gels as observed from the XRD analysis. [ABSTRACT FROM AUTHOR]

The effects of temperature on the chloride-induced corrosion behavior of reinforcing steel in simulated sea-sand concrete pore solution are studied by means of linear polarization resistance. The results show that the Ecorr (corrosion potential) and icorr (corrosion current density) of the reinforcing steels are temperature and/or chloride concentration (CCl)-related parameters. A linear correlation between Ecorr and temperature and a natural logarithmic correlation between icorr and CCl are observed. It is proved that the relationship between the corrosion rate and temperature follows the Arrhenius equation, whereas the activation energy of corrosion reaction increases with the increase of CCl. [ABSTRACT FROM AUTHOR]

The service life prediction of reinforced concrete (RC) structures in marine environment is essential in structural repair and health monitoring. In this paper, a numerical model for predicting the service life of reinforced concrete is first developed which considering the time-varying boundary of chloride concentration, critical chloride concentration and density of corrosion current. Based on the model, the effects of water–cement ratio, reinforcement diameter, concrete cover thickness and critical chloride ion concentration on the service life and deterioration duration of RC structures are investigated. The key factors affecting the service life of reinforced concrete structures are determined. More importantly, based on regression analysis, a new simplified empirical model for predicting the service life of RC structures is also developed. It provides a fast assessment tool for practical engineers. Both the numerical model and empirical model validated are suitable for practical engineering applications. The results show that with the increase of water–cement ratio, the service life of reinforced concrete structure decreases exponentially. And with the increase of the thickness of the concrete cover, the service life, deterioration duration, and safety reserve increase linearly. However, the influence of the diameter of the reinforcing bar on the service life can be ignored. [ABSTRACT FROM AUTHOR]

The objective of this research was to determine the influence of using recycled concrete aggregates (RCA) on the time for corrosion-induced cracking. Three levels of replacement by recycled aggregates were adopted, i.e., 0%, 50% and 100% by volume. Corrosion of reinforcement was accelerated using DC current. The compressive and tensile strengths were also investigated. The results showed that the reinforcement mass losses of the RCA were 2.5% and 2.4% higher than those of the NAC for 50% and 100% replacement, respectively. The corrosion-induced cracking times of the RAC were 5.6% and 8.6% longer than those of the NAC for 50% and 100% replacement, respectively. Additionally, the Maaddawy’s and Modified Maaddawy’s models were found to be acceptable for predicting concrete cover cracking time.

The effectiveness of extended curing on the corrosion resistance with regard to predefined corrosion degree for reinforced concrete specimens with different fly ash replacement ratios was tested. The specimens were subjected to saline solution to initiate and propagate the corrosion of reinforcement. Corrosion process for fly ash concrete with regard to electrochemical and other corrosion parameters was discussed. It was observed that extended curing for fly ash concrete effectively postponed the corrosion initiation and propagation period as equated to ordinary Portland concrete nevertheless had intensified the likelihood of pitting corrosion. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of coral sand powder (CSP) and corrosion inhibitors (SBT®‐ZX(V), SBT®‐RMA(II)) on reinforcement corrosion in coral aggregate seawater concrete (CASC) in a marine environment. A reasonable time‐variation model for reinforcement corrosion in CASC is proposed and verified. Based on the time‐variation model and chloride diffusion model, the cracking time and service life of CASC are predicted. The results show that the replacement of cementitious materials by 5% CSP can improve the corrosion resistance of steel bar in CASC. Both SBT®‐ZX(V) and SBT®‐RMA(II) can reduce the corrosion rate of steel bar in CASC, and this effect of SBT®‐RMA(II) is more effective than that of SBT®‐ZX(V). Among all CASC, CASC containing 5% CSP and SBT®‐RMA(II) possesses the best corrosion resistance. The results also reveal that the corrosion current density of steel bar in CASC increases firstly and then decreases over time. The ascending segment of the fitting curves for reinforcement corrosion in CASC conforms to the logarithmic‐type time‐variation model, and the descending segment of the fitting curves for reinforcement corrosion in CASC conforms to the exponential‐type time‐variation model. The cracking time and service life of CASC containing 5% CSP and SBT®‐RMA(II) will reach more than 10 years when the thickness of protective layer is 30 mm. [ABSTRACT FROM AUTHOR]

To investigate the slight corrosion to steel bars due to the bittern in magnesium cement, a durability test was carried out on magnesium cement concrete components. Combined with different environments, concrete protective layer thickness and increasing steel coating, the electrochemical test of steel in the specimen was carried out, and the specimen was determined by SEM topography and XRD diffraction. The results show that under natural dry environment, the corrosion processes of magnesium cement components with 25 mm and 50 mm concrete protective layer thicknesses are about the same, and the steel bars with 50 mm concrete protective layer thickness are more susceptible to corrosion. Under the condition with 25 mm concrete protective layer thickness, the corrosion of steel bars in magnesium cement concrete components in chloride and natural dry environments shows that the presence of coating can effectively reduce the corrosion current density of steel bars, and the protective effect of steel bars is more prominent under the condition with chloride salts. [ABSTRACT FROM AUTHOR]

Mix proportion design has a significant influence on the durability of reinforced concrete (RC). Conventional simple equations encounter challenges in effectively guiding the enhancement of durability in the design process. To address this issue, a backpropagation neural network (BPNN) model with a topological structure of 6–16–2 is devised to build a prediction model for RC durability, offering both forward design and reverse guidance for determining optimal mix proportion. Moreover, the model is optimized by the Bat Algorithm (BA), Ant Colony Optimization Algorithm (ACO), and Particle Swarm Optimization (PSO) Algorithm. The input layer parameters of the model consist the water-binder ratio and the quantity of cement, coarse aggregate, river sand (RS), fly ash (FA), slag, while the output layer parameters include the failure time for corrosion current density of reinforcement (T 1) and the failure time for concrete damage degree (T 2). The dataset for the model comprises 100*2 sets, which are divided into 70*2 sets for training data, 15*2 sets for validation data, and 15*2 sets for testing data. The relationship between the experimental raw materials and the durability of RC was determined through correlation analysis, and comparative analysis was conducted on the durability evaluation indices for RC. The results indicate a positive correlation between cement content and the durability of RC, whereas the content of RS, coarse aggregate, FA and slag, and water-binder ratio exhibit negative correlation with concrete durability. Among the RC groups, the A 3 group demonstrated the highest performance, and the D group stood out as the optimal mineral admixture group. Utilizing the PSO-BPNN model, the following performance indices were predicted for T 1 : R2=0.850, MAE=38.14, MAPE=0.094, RMSE=47.218, and for T 2 : R2=0.872, MAE=34.541, MAPE=0.071, RMSE=42.355. Consequently, the PSO-BPNN model demonstrates the highest accuracy in predicting the correlation between concrete mix proportions and the durability of RC, thereby offering valuable guidance for the mix proportion design of RC. • Hybrid-BPNN are recommended to predict the durability of RC. • The cement content is in a positive correlation with RC durability. • PCA evaluated the RC's performance of different mix proportion. • The PSO-BPNN is found to be the most suitable algorithm in RC durability. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is the primary pollutant in industrial atmospheres, leading to significant damage to industrial buildings. The corrosion caused by SO 2 in concrete, including neutralization and solid phase volume expansion, poses particular concerns. However, there is a lack of research on the electrochemical behaviour and corrosion mechanisms of reinforcing bars embedded in concrete. This study conducted indoor simulations of reinforced concrete specimens exposed to industrial SO 2 corrosion utilizing an SO 2 testing chamber. The corrosion behavior of the reinforcing bars was monitored through half-cell potential, weak polarization, and electrochemical impedance spectroscopy (EIS). Additionally, the corrosion mechanisms of the reinforcing bars under SO 2 exposure were investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and Raman spectra. The results demonstrated a consistent correlation between variations in corrosion potential (E corr) and corrosion current density (i corr) of steel rebars in different types of concrete. The corrosion rates of the reinforcing steel in C1 (w/b=0.57), C2 (w/b=0.47), and C3 (w/b=0.37) concrete exceeds 0.1 μA/cm2 after 42, 72, and 90 days of SO 2 corrosion, respectively. At this time, the ratio of the depth of neutralization to the thickness of the protective layer is 0.51–0.65. The rust exhibits a layered structure with a presence of S elements adsorbed and deposited on the surface of the rust layer. Moreover, the research has identified the accumulation of S elements within corrosion pits, which can be attributed to localized acidification reactions. The rust products identified include iron hydroxide (FeOOH), and iron oxide (Fe 2 O 3), rozenite (FeSO 4 ·4 H 2 O). The formation of FeSO 4 ·4 H 2 O in corrosion pits suggests that significant localized corrosion on the surface of reinforcing bars in concrete under the impact of SO 2. ● Simulate typical industrial SO 2 corrosion environments. ● Surface analysis reveals the corrosion mechanism of steel rebars in concrete. ● Corrosion products contain ferrous sulphate hydrates. [ABSTRACT FROM AUTHOR]

The influence of vanadium transition metal alloying on the structure, corrosion resistance and tribological properties of a binary Al-Li alloy containing 6 wt % Li was investigated in this research. Varying vanadium contents of 0.05 wt %, 0.1 wt %, 0.5 wt %, and 1.0 wt % were examined. The results demonstrate that the addition of 1.0 wt % vanadium optimally enhanced the corrosion resistance and wear resistance of the alloy. With 1.0 wt % V, the wear rate decreased from 3.6 ± 0.50 × 10−2 m3/m to 1.5 ± 0.07 × 10−2 m3/m, the hardness increased from 51.7 ± 7.3 HV to 77.6 ± 4.1 HV, and the corrosion current density decreased from 43.6 µA/cm2 to 3.9 µA/cm2. Microstructural analyses revealed significant grain refinement induced by the addition of vanadium. The grain size decreased by 36.7 %, and the dendrite arm spacing (DAS) decreased from 35 µm to 8 µm. Adding vanadium reduced the overall porosity of the alloy resulting from a peritectic reaction leading to the formation of vacancy-solute complexes at the grain boundaries. Phase and chemical composition analyses confirmed the formation and presence of δ (AlLi) strengthening phase within the interdendritic regions, particularly with the addition of 1.0 wt % V. The presence of this phase strongly contributed to the observed improvements in corrosion resistance and tribological properties of the vanadium-modified alloy. [Display omitted] • Increased Lithium content to 6 % for improved strength stability and exceptional weight reduction in Al-Li alloy. • Successful alloying with 1.0 wt % vanadium optimally enhanced corrosion resistance and wear resistance. • Microstructural analyses revealed significant grain refinement induced by vanadium addition. • Vacancy-solute complexes formation from peritectic reactions reduced porosity of graphite mold cast specimen. • The presence of δ (AlLi) phase contributed to observed improvements in corrosion resistance and tribological properties. [ABSTRACT FROM AUTHOR]

Zinc protection of galvanized steel is initially dissolved in alkaline solutions. However, a passive layer is formed over time which protects the steel from corrosion. The behavior of galvanized steel exposed to strong alkaline solutions (pH values of 12.7) with a fixed concentration of sulfate ions of 0.04 M is studied here. Electrochemical measurement techniques such as corrosion potential, linear polarization resistance and electrochemical impedance spectroscopy are used. Synergistic effects of sulfate ions are also studied together with other anions such as chloride Cl− or bicarbonate ion HCO3− and with other cations such as calcium Ca2+, ammonium NH4+ and magnesium Mg2+. The presence of sulfate ions can also depassivate the steel, leading to a corrosion current density of 0.3 µA/cm2 at the end of the test. The presence of other ions in the solution increases this effect. The increase in corrosion current density caused by cations and anions corresponds to the following orders (greater to lesser influence): NH4+ > Ca2+ > Mg2+ and HCO3− > Cl− > SO42−.

The effects of temperature on the chloride-induced corrosion behavior of reinforcing steel in simulated sea-sand concrete pore solution are studied by means of linear polarization resistance. The results show that the Ecorr (corrosion potential) and icorr (corrosion current density) of the reinforcing steels are temperature and/or chloride concentration (CCl)-related parameters. A linear correlation between Ecorr and temperature and a natural logarithmic correlation between icorr and CCl are observed. It is proved that the relationship between the corrosion rate and temperature follows the Arrhenius equation, whereas the activation energy of corrosion reaction increases with the increase of CCl.

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We perform the comparative analysis of the corrosion resistance of St3ps steel in demineralized water and in saturated solutions of the Nurelle-D insecticide and UN-32 complex liquid fertilizer. It is shown that, in demineralized water, the general corrosion of the steel surface is predominant. In a solution of insecticide, parallel with general corrosion, we observe a partial realization of pitting corrosion. In a medium of mineral liquid fertilizer, we observe the passivation of the metal surface caused by phosphorus-containing corrosion inhibitors, which leads to the inhibition of the general corrosion. However, local violations of the passive state of the metal surface lead to the intense formation of corrosion pits, which is dangerous due to the possibility of their development accompanied by the initiation of cracklike defects in the structures. [ABSTRACT FROM AUTHOR]

Electrodeposition of ZnZr and ZnVoxide composites was performed under galvanostatic conditions at 313K on unagitated pH 2 sulfate solutions containing Zn2+ and Zr4+ or VO2+ ions and an additive such as polyethylene glycol (PEG). The effects of PEG addition on the codeposition of Zr and V oxides and their polarization behavior, and on the microstructure of the deposits, were investigated. Although the Zr content in the deposits obtained from the ZnZr solution in the absence of PEG was approximately zero, it increased significantly at a current density of above 1000 A·m-2 following the addition of PEG. In the ZnV solution, the V content in the deposits obtained from 100 to 2000 A·m-2 was higher with PEG than without it. In the presence of PEG, the cathode potential polarized, the rate of hydrogen evolution increased, and the hydrolysis reaction of Zr4+ and VO2+ ions proceeded smoothly, resulting in an increase in the Zr and V content in the deposits. Additionally, the crystal platelets of Zn in the ZnZr and the ZnVoxide films became fine, and the surface coverage of the spongiform Zr and film-like Voxides increased. Furthermore, the corrosion current densities of the ZnZr and ZnVoxide films obtained from the solution with PEG were lower than those from the solution without it. The reduction rate of dissolved oxygen decreased in the films in the presence of PEG, thereby leading to a decrease in the corrosion current density. [ABSTRACT FROM AUTHOR]

The steel corrosion in magnesium oxychloride cement (MOC) restrains the application and popularization of MOC products. However, MOC is a green cementitious material. Therefore, it is necessary to solve the steel corrosion in MOC. Aiming at this issue, firstly, the Stern–Geary constant (B) applied to the steel corrosion in MOC was calculated and verified. Secondly, the influence of different steel and mineral admixtures on the steel corrosion in MOC was studied by electrochemical method. Thirdly, the time‐varying models of steel corrosion were given. Fourthly, the life of the steel‐MOC system was calculated based on the time‐varying model. Finally, the time‐varying characteristics of steel corrosion in MOC was proposed. The results show that B of 25 mV is suitable for the corroded steel, whereas B of 40 mV is appropriate for uncorroded steel, in MOC. In addition, the type of steel has a significant effect on steel corrosion in MOC. The anticorrosive effect of metakaolin is less than that of fly ash. The anticorrosive effect of MOC with single admixture is better than that with compound admixture. Besides, the development process of steel corrosion in MOC can be divided into three stages: the descending phase conforming to the exponential time‐varying model in the early stage, the ascending phase conforming to the logarithmic time‐varying model in the middle stage, and the descending phase conforming to the exponential time‐varying model in later stage. [ABSTRACT FROM AUTHOR]

An effective approach to make better use of the salt‐brine resistance of magnesium oxychloride cement concrete (MOCC) and reduce "magnesium damage" (the concentrate of magnesium resources) that destroys the ecological balance in salt lake areas is to apply MOCC widely. However, the first problem is the high chloride ion content in MOCC, which corrodes reinforcement easily. Concrete cover depth, the experimental environment, and surface treatment of rebar were considered factors study in reinforcement corrosion in MOCC. Based on the tests conducted, a time‐dependent model for reinforcement corrosion in MOCC was proposed, and its life time (initial corrosion and initial cracking time) was calculated and verified in tests. The results showed that proper coating could inhibit reinforcement corrosion and increase the service life of rebar significantly. Further, the salt lake environment had little influence on reinforcement corrosion in MOCC. For exposed rebar in MOCC, the larger the concrete cover depth, the more serious the reinforcement corrosion, while, for coated rebar, the converse was true. All cases of reinforcement corrosion in MOCC conformed to the logarithmic‐type time‐dependent model before concrete cracking. Accordingly, reinforcement corrosion in MOCC and the excess of magnesium resources are expected to be solved. [ABSTRACT FROM AUTHOR]

The objective of this research was to clarify the mechanism of concrete cover cracking time due to reinforcement corrosion in steel fiber-reinforced concrete. An experimental study and analytical study were conducted. For the experimental study, 3 in. (76.2 mm) diameter and 6 in. (152.4 mm) length cylindrical concrete specimens with reinforcement placed in the middle were prepared. Conventional and steel fiber-reinforced concrete with three levels of compressive strength were used in the study. A strain gauge was installed along the specimen's circumference and the corrosion of reinforcement was accelerated using anodic DC current. Concrete surface strain and impressed anodic current were recorded via a data logger and a multimeter, respectively. Concrete cover cracking time was also investigated. After corrosion acceleration, reinforcement weight loss was evaluated and internal pressure due to the reinforcement corrosion product was calculated. The analytical study was conducted using finite element with four-node bilinear plane strain in a two-dimensional (2-D) model. In the finite element method (FEM) model, the reinforcement was removed and the internal pressure result from the expansion of corrosion products was applied, similar to the problem of cylinder under constant internal pressure. The relationship between concrete surface strain and internal pressure from the analytical study was compared with the experimental study. It was found that corrosion current density of the reinforcement embedded in the fiber-reinforced concrete was higher than that of conventional concrete. Concrete cover cracking time increased with increase of concrete tensile strength. In addition, the relationship between concrete surface strain and the internal pressure could be predicted by the FEM results within an acceptable margin of error. [ABSTRACT FROM AUTHOR]

Abstrac: t—The results of plasma-electrolytic polishing of steel specimens after their anodic diffusion saturation with elements, which form interstitial solutions, are considered. The structure and phase composition of the modified layers are studied using the X-ray diffraction analysis and electronic microscopy. The surface roughness and corrosion resistance of specimens in the 3.5% sodium chloride solution are measured. Various morphology of oxide layer is revealed after nitrocarburizing, nitriding, boronizing and borocarburizing of carbon structural steels 20 and 45. The versions of treatment and electrolyte compositions are determined that reduce the surface roughness from 1.00 μm for the control specimen to 0.23 μm after borocarburizing in the solution of boric acid, glycerol and ammonium chloride followed by polishing in the sulfate electrolyte and to 0.40–0.42 μm after nitriding in the ammonia and ammonium chloride solution followed by polishing in the sulfate or chloride electrolyte. It is shown that the corrosion current density of steel 45 can be reduced by almost 4 times after nitriding and polishing in the sulfate or chloride electrolyte. [ABSTRACT FROM AUTHOR]

The objective of this research was to determine the influence of using recycled concrete aggregates (RCA) on the time for corrosion-induced cracking. Three levels of replacement by recycled aggregates were adopted, i.e., 0%, 50% and 100% by volume. Corrosion of reinforcement was accelerated using DC current. The compressive and tensile strengths were also investigated. The results showed that the reinforcement mass losses of the RCA were 2.5% and 2.4% higher than those of the NAC for 50% and 100% replacement, respectively. The corrosion-induced cracking times of the RAC were 5.6% and 8.6% longer than those of the NAC for 50% and 100% replacement, respectively. Additionally, the Maaddawy's and Modified Maaddawy's models were found to be acceptable for predicting concrete cover cracking time. [ABSTRACT FROM AUTHOR]

33ACI Materials Journal/March 2020ACI MATERIALS JOURNAL TECHNICAL PAPER Because of ordinary reinforced concrete’s poor durability in saline soil areas and Qinghai Salt Lake, magnesium oxychloride-coated steel-cement concrete was adopted in this area. The process of the degradation of coated steel bars’ durability was evaluated according to the actual service situation of magnesium-oxychloride-coated reinforced concrete in saline soil areas and Qinghai Salt Lake. The corrosion parameters of coated steel bars in magnesium oxychloride cement concrete were obtained by the accelerated immersion and natural corrosion tests in a drying environment. Using the Copula function as the connection function, the corrosion current density of the coated steel obtained by accelerated tests and natural rust tests was adopted as the degradation factor of the edge distribution function. The results demonstrated that the Clayton-Copula function reflects the actual process of the degradation in durability of coated steel bars well, and the coated steel bars reached a severe state of corrosion at 18,250 days. [ABSTRACT FROM AUTHOR]