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The corrosion of nuclear containment liners is a serious issue. This study aims to develop a comprehensive understanding of the influence of mill scale on the passivation, depassivation, and corrosion of the specialized steel in simulated concrete pore solutions with varying pH. The formation processes and compositions of passive films and corrosion products were studied utilizing electrochemical measurements and microstructural characterization techniques. The results indicated that the barrier and multichannel effects of the mill scale with local defects negatively affected the passivation and depassivation properties of steel liners, resulting in a passive film of poor quality and premature corrosion initiation. While an increase in pH did not significantly enhance the passivation quality of the as-received steel, it did enhance the critical chloride ion content. In addition, the inhibition mechanism of the mill scale during the continuous corrosion stage of the steel liner was elucidated based on the coupling effects between the mill scale and the rust layer on the steel substrate surface. The results of this study provide a technical reference for the anticorrosion effects of nuclear power plants. [Display omitted] • The intrinsic corrosion-resisting property of the specialty steel for containment liner was explored. • A unified analysis of effects of mill scale on the corrosion of steel liner throughout the whole life period was proposed. • Coupling effects between the mill scale and pH of the solutions were further discussed. • The formation process and compositions of passive films and corrosion products were microscopically explored. [ABSTRACT FROM AUTHOR]

Corrosion of iron materials in the asphalt concrete pavement occurs commonly when the bitumen film peels off, and the generation of corrosion products would affect the healing performance of bitumen. To identify the affection, this research focuses on the influence of iron corrosion products on the healing process of bitumen by molecular dynamics simulation. Firstly, bitumen model and iron corrosion products model were built. Then the healing systems of sandwich structure were constructed, and the simulated temperature were applied to reach equilibrium in the healing process with NVT ensemble (constant number of atoms, volume, and temperature). Dynamic movements of bitumen were characterized by appearance qualitatively. Healing rate of crack and healing rate of bitumen aggregation were held to evaluate the healing effect. Diffusion behaviors, internal force of motivation and interaction effect were also analyzed. The results indicate the duplicity of iron corrosion products in the healing process including the ease for bitumen climbing and the obstruction of bitumen movement. The comprehensive healing index demonstrated that iron corrosion products would reduce the healing degree, which was mainly caused by the obstruction effect and large internal stress generated by severe aggregation of bitumen in the limited space. From the perspective of crack closure and bitumen aggregation degree in the corrosion area, FeO healing systems were healed best, followed by Fe 3 O 4 , Fe 2 O 3 and FeOOH. Furthermore, diffusion period of bitumen molecules on the surface of iron corrosion products during the healing process should be regarded as the important period affecting healing. • The healing model of bitumen with the obstruction of iron corrosion products was constructed. • A comprehensive healing rate combined with crack closure and bitumen aggregation was held. • The dual effect of iron corrosion products to the bitumen healing was investigated. • Interaction effect inside bitumen and between bitumen and iron corrosion products was quantified. [ABSTRACT FROM AUTHOR]

• Different types of corrosion products are non-destructively identified by X-ray µCT. • The evolution of corrosion products can be determined as a function of time and space. • Corrosion mechanism is further discussed according to corrosion evolution characteristic. The main purpose of this study is to non-destructively monitor the formation and development of corrosion products in reinforced mortar with the help of X-ray micro computed tomography (X-ray µCT). A new method based on the relationship between the linear attenuation coefficient and CT number as well as greyscale value is built to identify different type of corrosion products. Based on this method, two categories of corrosion products including iron oxides and iron hydroxides are identified in this research. Additionally, the corrosion mechanism and the interaction between different types of corrosion products are discussed according to the characteristics of corrosion evolution. Furthermore, the volumetric expansion ratio of corrosion products is quantified (from 2.71 to 3.97). This method provides a new angle to investigate the formation and development of reaction products, which contributes to further understand the corrosion process in reinforced concrete. [ABSTRACT FROM AUTHOR]

This study investigated the corrosion performance of reinforcing steels in concrete exposed to flowing 3.5 wt% NaCl solution for 4 years. Two kinds of steels were selected: low-carbon (LC) steel and low-alloy (LA) steel with alloying element Cr. Both steels were prepared with two surface conditions: as-received one (with mill scale) and pickled one (removal of the mill scale). The microstructure of the steel-concrete interface was observed to investigate the effect of steel type and surface condition on the corrosion pattern. The results reveal that the corrosion resistance and the corrosion pattern of steels were largely influenced by the feature of the mill scale. [ABSTRACT FROM AUTHOR]

• Microstructural and micromechanical analyses of corrosion products were conducted. • Magnetite in natural corrosion products were characterized by EBSD. • Young's modulus and nanohardness of each phase were determined. • The porosity, crystallinity and grain size could affect mechanical properties. • The microstructural features of corrosion products could be revealed by hardness. The mechanical properties of steel corrosion products reported in the literature present a great dispersion. The present study aims to explore the mechanical behavior of naturally generated corrosion products at the microscale level in relation with typical microstructural features. Microstructural characterization was performed on corrosion products by nano-indentation, Raman micro-spectrometry, scanning electron microscopy and electron backscatter diffraction. The Young's modulus and nanohardness range between 66.5 and 158.1 GPa and 2.97–11.71 GPa, respectively. The various morphologies and corresponding mechanical properties of goethite, maghemite and magnetite have finally been discussed, clarifying the influences of porosity, crystallinity and grain size on the mechanical properties. [ABSTRACT FROM AUTHOR]

The effect of degree of pore saturation ( PS ) in concrete on corrosion current is investigated in this paper. Results showed that the maximum of corrosion current appeared in the saturated concrete and it decreased in dried concrete. After the corrosion products were enough, FeOOH in corrosion layer could act as a depolarizer instead of oxygen. As a result, the corrosion rate remained high even when the concrete was completely water saturated. Therefore, oxygen is not the factor controlling corrosion process of steel rebar in concrete, although it is one of the key factors. When the concrete drying process stars from water saturation, there is little difference between the control degree of cathodic reaction and the control degree of anodic reaction on corrosion process; the control type of corrosion reaction is mixed control. Part I of this article presents experimental results obtained from the thermostatic drying tests and the effect of corrosion products on process control of reinforcement corrosion in concrete. The time-dependent dominating factors of rebar corrosion process under different environmental conditions will be discussed in Part 2. [ABSTRACT FROM AUTHOR]

In this paper we quantified the corrosion rates of active steel in atmospheric environment, cyclic wetting and drying, and active steel and passive steel in saturated concrete. The microstructure of the interfacial transition zone between the corroded bar and the concrete was observed with an Electron Microscope. The time-dependent dominating factors in the rebar corrosion processes under different environmental conditions were explained by the polarization curves. Results indicate that the corrosion current ( I corr ) of passive steel in concrete immersed in NaCl solution is low due to low oxygen availability. I corr of the active steel in saturated concrete reaches the maximum because the corrosion product (FeOOH) on the steel surface acts as new strong cathodic depolarization agent. However, the corrosion process stops after FeOOH in corrosion layer is completely consumed. Furthermore, I corr of active steel subjected to cyclic wetting and drying remains at a high level because of high concentrations of FeOOH and oxygen. The maximum I corr corresponds to the area under cyclic wetting and drying. [ABSTRACT FROM AUTHOR]

• Reinforced ternary concretes containing untreated sugarcane bagasse ash were manufactured. • The reinforced concretes were exposed to a Chloride (Cl−) solution for 3000 days. • Corrosion of the steel reinforcement was monitored and the mass loss estimated. • Tensile strength tests of the reinforcing bars were carried out. • Ductilities of rebars in UtSCBA-ternary concretes were larger than those from the control. Mechanical properties of rebars embedded in ternary concretes with fly ash (FA) plus untreated sugarcane bagasse ash (UtSCBA) and immersed in a Cl−-solution for 3000 days were investigated. Reinforced concrete specimens containing Portland cement (PC) only, PC + FA, and PC + FA + UtSCBA were manufactured. The corrosion conditions of the rebars were evaluated by electrochemical testing; then the rebars were extracted and their mass loss estimated. Next, elemental mapping of the concrete/reinforcing steel interfaces using scanning electron microscopy was conducted. Rust was analyzed by X-Ray diffraction and infrared spectroscopy. Finally, the rebars were tested in tension to evaluate their yield and ultimate strengths, fracture loads, and ductilities. Results indicate that rebars from UtSCBA-ternary concretes experienced the lowest mass loss. Moreover, the yield strengths of all rebars were not affected by corrosion, while the ultimate strengths, fracture loads, and ductilities of rebars from UtSCBA-ternary concretes were larger than those from the control. [ABSTRACT FROM AUTHOR]

Abstract: Predicting concrete cover cracking due to steel bar corrosion in concrete is an important problem for durability of reinforced concrete structures. A basic question in the prediction is distribution of corroded part of steel bar section. The corrosion products have characteristic of volume expansions; that leads to expansive pressure in the concrete. At present, an assumption of uniform corroded pattern along the perimeter of the steel bar has been adopted for analyzing the effect of corrosion products expansion and building the model. In this paper, the steel bars in concrete were corroded under artificial climate environment for accelerated aging. The propagation of the corrosion products layer between steel bar and concrete and its microstructure are discussed; and then, the corrosion products distribution called corrosion products layer on the steel bar in concrete is revealed. The distribution before corrosion cracking; the corrosion products distribute on the half circumference of the steel bar facing the concrete cover only, and the distribution has the shape of a half ellipse. Because of expansive characteristic of corrosion products, the distribution pattern of the corroded part of the steel bar section is proportional to the distribution of the corrosion products layer. Therefore, the configuration model of corroded steel bar section is built. [Copyright &y& Elsevier]

• Three main accelerated corrosion methods for steel-reinforced concrete were reviewed. • Comparative evaluation of each method had been done in terms of main input parameters. • Corrosion products and mass loss for the methods were comprehensively discussed. Rebar corrosion has been recognized as a major durability issue of the reinforced concrete (RC) structures over recent decades, prompting the necessity to study the corrosion behavior of steel in concrete during the service life. To estimate service life of RC structure, the corrosion of reinforcing steel is generally accelerated by means of the impressed current technique in limited available time. In the literature, several accelerated laboratory corrosion methods have been proposed, however the results varied greatly as chloride concentrations and testing conditions were different. Researchers are unsure which testing methods can be used to give reliable results to simulate the real-life corroded RC structure. This review paper aims to systematically compare and evaluate different methods of accelerating chloride-induced corrosion of steel reinforcement in concrete. First, the accelerated methods categorized into three groups namely, the impressed current (IC), the chloride ion diffusion (CID) and the artificial climate environment (ACE) are briefly discussed. Then, the key influencing factors (i.e. current density, salt concentration, service load) affecting the corrosion results in different methods are compared and evaluated. Finally, the corrosion products and acceleration method are comprehensively discussed. By this comparative review, it is believed that researchers can have a better understanding of different accelerated corrosion methods along with the influencing factors. So they could select or even develop the most suitable techniques to yield reliable corrosion test results. [ABSTRACT FROM AUTHOR]

• The growth of corrosion products around the steel-concrete interface is investigated. • Statistically significant number of samples are measured by using BSE imaging. • Corrosion induced by impressed current is non-uniformly distributed around the steel-concrete interface. • Most corrosion products reside at the bottom side of steel bar with respect to casting direction. • The amount of corrosion products increases with the increase of w/c ratio. • Smaller concrete cover results in smaller corrosion layer initially but larger in longer term. • The proposed equivalent uniform thickness of corrosion layer is in line Faraday's law. The expansive nature of corrosion products at the steel-concrete interface directly leads to the cracking and spalling of steel reinforced concrete, and its premature failure. In this paper, fundamental causes that affect the distribution and growth of corrosion products at the steel-concrete interface are quantitatively examined. The thickness of the layer of corrosion products and its growth with time are measured accurately using the technique of backscattered electron imaging and with a statistically significant number of samples, which are then verified with Faraday's law. A model for the distribution and growth of the non-uniform corrosion layer is developed. It is found in the paper that the corrosion products are non-uniform around the steel-concrete interface, with the maximum at the bottom side of steel bar with respect to casting direction. It is also found that the amount of corrosion products increases with the increase of water to cement ratio of concrete. The significance of this research is that it has quantitatively examined the effect of microstructure of the steel-concrete interface, a fundamental factor, on the distribution and growth of corrosion products. Findings presented in the paper can contribute to the accurate prediction of corrosion-induced cracking of steel reinforced concrete and hence prevent its premature failure. [ABSTRACT FROM AUTHOR]

• Mill scale properties have a marked impact on the distribution of corrosion products at the steel-concrete interface. • The interaction of corrosion products and mill scale is affected by steel type. • Different corrosion inducing methods result in diverse steel corrosion patterns. In this study, corrosion products of a Cr-bearing low-alloy (LA) steel and the conventional low-carbon (LC) steel with intact mill scale at the steel-concrete interface were investigated by means of backscattered electron (BSE) images. Furthermore, the effect of mill scale properties and corrosion inducing methods (long-term natural exposure to chloride solution and accelerated corrosion by chloride electromigration) on the distribution and penetration of corrosion products was compared. Complex interactions were highlighted between the corrosion products and the mill scale of LC and LA steels at the steel-concrete interface. In addition, different corrosion patterns of both steels were evident when subjected to different corrosion inducing methods. [ABSTRACT FROM AUTHOR]