Macrocell Corrosion Research Articles

Research on the Macro-Cell Corrosion Behavior of Alloyed Corrosion-Resistant Steel for a Transmission Line Steel Structure under a Chloride Corrosion Environment

“The article investigates the macro-cell corrosion behavior and corrosion resistance when the alloyed steel and the carbon steel are used together because the traditional carbon steel is difficult to meet the corrosion resistance and durability of the steel structure of the transmission line in the marine environment.” In this paper, a new type of Cr-alloyed corrosion-resistant steel (00Cr10MoV) is used to partially replace carbon structural steel in order to meet the actual needs of corrosion resistance and service life improvement of steel structures for offshore transmission lines. It is important to systematically study the macro-cell corrosion behavior of combinations of the same type of steel and dissimilar steel, induced by the chloride concentration difference in simulated concrete solutions, and employ electrochemical testing methods to scientifically evaluate the corrosion resistance of steel after macro-cell corrosion. The aim is to study and evaluate the macro-cell corrosion behavior of alloyed corrosion-resistant steel and to lay a foundation for its combined use with carbon steel in a chloride corrosion environment to improve the overall corrosion resistance and service life. Under the same concentration difference, the macro-cell corrosion of the alloyed steel combination is milder compared with the carbon steel combination. The corrosion current of the alloyed steel combination at 29 times the concentration difference is only 1/10 of the carbon steel combination. Moreover, at 29 times the concentration difference, the macro-cell corrosion potential of dissimilar steel is only 1/6 of the combined potential of carbon steel combination under the same concentration difference, and the corrosion current is only 1/10 of that of the carbon steel combination.

Microcell and macrocell corrosion kinetics of steel bars in reinforced concrete slabs subjected to alternate wet and dry environments

Electrochemical kinetics of steel bar corrosion in concrete is of complex nature, especially when it is subjected to alternate wet and dry environments with changes in conditions of steel-concrete interface and rust properties. In this paper, a quantitative electrochemical mechanism was proposed based on thermodynamics and anodic polarisation kinetics to account for variations of microcell and macrocell current densities in reinforced concrete (RC) slabs subjected to periodic wetting and drying cycles. Effects of environmental conditions on corrosion process were incorporated into anodic Tafel slope through three quantifiable parameters, namely, corrosion potential, linear polarisation resistance and ferrous ion concentration at the steel bar surface. A numerical model was established based on the proposed mechanism to quantify microcell and macrocell current densities. An experimental programme of two RC slabs with multiple steel bars arranged at different layers was conducted to verify the numerical model. It shows that the model could reasonably predict variations of both microcell and macrocell corrosion under different wet and dry environments. When concrete was moistened, current density was substantially increased compared to that in dry concrete. Macrocell contribution from uncorroded steel bars at different layers was more significant than microcell corrosion on the corroded bar itself, especially in wet environments.

Improving Corrosion Resistance and Prolonging the Service Life of High-performance Concrete Structures Using Fly Ash and Ground Granulated Blast-furnace Slag

This study investigates the impact of ground granulate blast-furnace slag (GGBFS) and fly ash (FA) on both the corrosion resistance of steel reinforcement, assessed through the accelerated macrocell corrosion test (AMCT), and the durability characteristics of high-performance concrete (HPC). Additionally, the study encompasses an analysis of various concrete properties, including the pH of fresh concrete mixtures as well as water absorption, chloride permeability, and surface resistivity (SR) in hardened concrete specimens. Microstructure analysis on HPC specimens as well as the service life prediction of RCS were also performed in this study. Test results show that the HPC incorporating 35% GGBFS or 35% GGBFS + 20% FA as cement replacement resulted in a lowered pH of fresh mixtures while water absorption and chloride permeability of these specimens increased significantly. In addition, the incorporation of 35% GGBFS or 35% GGBFS + 20% FA concurrently enhanced the SR of HPC specimens. Moreover, these HPC specimens exhibited better corrosion resistance ability as their respective AMCT values were about 1.54 and 1.45 times higher than that of the control specimen. Further, the research highlighted a substantial extension in the corrosion initiation time of concrete structures employing 35% GGBFS or 35% GGBFS + 20% FA, about 3 and 6 times longer than the HPC without GGBFA and FA, respectively. The experimental results, confirmed by the substantial microstructural enhancement in the HPC containing GGBFS and FA, also demonstrated a close interplay between durability and other concrete properties such as water absorption, chloride permeability, and SR.

Protection of steel hooks embedded in glass-fiber-reinforced concrete against macrocell corrosion

This study evaluated the corrosion behavior of steel hooks embedded in GFRC, which were protected by a zinc-rich (96% Zn) galvanizing coating. The coating provided the hooks with active cathodic protection and a passive physical shield. Macrocell corrosion may form when the anode is smaller than the total steel surface. Thus, the steel hooks at the embedment juncture were additionally sealed against water ingress and air exchange using a construction sealant. The study was conducted in three phases in a salt-spray chamber. First, the electrogalvanized steel hooks embedded in GFRC were allowed to freely corrode for 7 days. In the second phase, the electrogalvanized steel hooks were painted with the zinc-rich coating and observed over 7 days. In the third phase, the steel hooks were protected by the zinc-rich coating together with a primer and construction sealant, and observed over 7 days. To evaluate the electrogalvanized hooks and the corrosion products formed, the thickness of the material was measured. Corrosion on the metal surface was inferred by studying the surface morphology of the hooks at various points of contact and after different periods of time.

Service life modelling of carbonated reinforced concrete with supplementary cementitious materials considering early corrosion propagation

The importance of considering corrosion propagation in service life design of carbonated concrete with supplementary cementitious materials (SCMs) has been highlighted by the decline in carbonation resistance caused by partial replacement of ordinary Portland cement (OPC) with SCMs. This study proposes a novel Carbonation-induced Early Corrosion Propagation based Service-life Assessment Model (CECP-SAM) for carbonated SCM concrete, which is characterized by the considerations of semi-carbonation zone and macrocell corrosion in corrosion propagation with an incipient crack as end of service life. Experimental and field data were used to verify CECP-SAM. The effects of exposure conditions, SCM replacements, water/binder ratio, cover thickness, rebar diameter, semi-carbonation zone and macrocell corrosion on service life are presented. Results indicate that the partial replacement of OPC with pulverized fuel ash (PFA) and ground granulated blast furnace slag (GGBS) can significantly decrease service life from 66 years to 8 years and 17 years, respectively. Corrosion propagation can result in a 91% reduction in service life but service life can be extended from less than 20 years to more than 90 years by considering early corrosion propagation. Practical equations are proposed to facilitate performance-based service life design. Prescriptive limits are also provided for service lives of 50 and 100 years.

Approach to consider self‐corrosion in corrosion monitoring of reinforced concrete structures exposed to chlorides

AbstractCorrosion processes of steel in concrete contaminated with chlorides take place as macrocell corrosion as well as self‐corrosion (i.e., microcell corrosion). While macrocell corrosion can be detected by element current measurement, self‐corrosion cannot be precisely determined electrochemically. This results in deviations in corrosion investigations between the mass losses calculated coulometrically from macrocell current measurements and the actual, corrosion‐related gravimetric mass losses. This is relevant in practice as part of corrosion monitoring. In the following, a simple approach is presented by considering this self‐corrosion current mathematically in the macrocell current measurement. The empirical regression functions determined for this purpose can be applied to a large number of different influencing parameters and allow the determination of the cumulative steel degradation at time‐varying macrocell current densities under consideration of different safety levels. This allows a much more accurate estimation of the actual corrosion‐induced mass losses during corrosion monitoring than previously possible.

Electrochemical Study on the Macro-Cell Corrosion of Pipeline Steel Partially Covered by Different Kinds of Mineral Deposits.

This study presents the impact of mineral deposits (SiO2, Al2O3, and CaCO3) on the corrosion behavior of X65 pipeline steel in CO2-containing brine solution with low pH. The study investigates the initiation and propagation of under deposit corrosion (UDC) using a wire beam electrode (WBE) partially covered by different mineral deposit layers, in conjunction with electrochemical measurements and surface characterization. The results indicate that the corrosion behavior varies, depending on the characteristics of the deposit. During the test period, the Al2O3-covered steel acted as the main anode with more negative potential, while the bare steel acted as the cathode. The SiO2-covered steel acted as the cathode with more positive potential and a localized FeCO3 layer formed beneath the silica mineral. The CaCO3-covered steel initially acted as an anode with a more negative potential but transformed into the cathode at the end of the test. Additionally, shallow and small pits were observed beneath the deposits with the depth in the sequence Al2O3 > SiO2 > CaCO3.

Modelling of 3D periodic cathodic protection problems in reinforced concrete structures with accelerated boundary element method

The steel used for concrete reinforcement exhibits either active or passive electrochemical behavior. As long as the concrete environment remains highly alkaline, the steel remains passive. However, carbonation and/or chloride contamination of concrete will cause steel to become active and corrode. In the latter case, a common strategy is the use of cathodic protection (CP) systems to lower the potential of the steel at a protective level. The numerical modelling of cathodically protected concrete buildings and infrastructures usually requires large-scale models due to their size and complex geometry. An efficient modelling approach is to consider any possible periodicity in these problems by applying periodic boundary conditions to a representative volume element of the structure. The boundary element method (BEM) is extensively used for solving CP problems. A BEM formulation is proposed for solving 3D periodic CP problems in this work. The computation cost is reduced by applying acceleration techniques based on adaptive cross approximation (ACA). As an engineering application, a sacrificial anode CP system of a reinforced concrete column is designed, illustrating the importance of detailed modelling in the design of such systems. To this end, the macrocell corrosion problem is initially solved, and a parametric study with respect to concrete conductivity is carried out.

Research Progress of Macrocell Corrosion of Steel Rebar in Concrete

Macrocell corrosion of steel rebar in concrete induced by corrosive environments has attracted widespread attention in the engineering community due to its rapid corrosion rate, diverse forms, and multiple incentives. Potential differences between dissimilar coupled rebar or different parts of the same rebar mainly cause macrocell corrosion of steel rebar. The more significant the potential difference, the faster the corrosion rate of the macrocell. Based on the existing research reports on macrocell corrosion of reinforced concrete, this review paper comprehensively discusses the macro- and micro-corrosion behavior of various types of steel rebar, and a variety of induction factors, such as dissimilar metals and concentration differences of the service environment, development rules. and electrochemical mechanisms for corrosion of rebar macrocells are summarized. ZRA (zero-resistance ammeter), micro-area electrochemical testing technology and evaluation techniques commonly used in the laboratory, and electrochemical testing techniques used in engineering testing are listed. Common experimental models for corrosion of rebar macrocells are briefly introduced. Based on the internal characteristics of macrocell corrosion of reinforced concrete, this paper further proposes the control strategy of macrocell corrosion, starting from the improvement of the corrosion resistance of the rebar and regulating the service environment of the reinforced concrete structure (RCS). Meanwhile, the future direction of macrocell corrosion of steel rebar is also preliminarily prospected.

Probing top-of-the-line corrosion using coupled multi-electrode array in conjunction with local electrochemical measurement

An experimental method has been developed for probing top-of-the-line corrosion (TLC) of pipeline steel based on the use of the wire beam electrode (WBE) in conjunction with local electrochemical measurements. Results show that the location of the droplet, the droplet retention time, the water condensation rate and the local TLC rate could be well determined through the macro-cell current mapping and local electrochemical measurements. The precipitation and the scaling tendency of the FeCO3 beneath the droplet were quantitatively estimated. The micro-cell corrosion was significantly influenced by the thickness of the condensed water film and the protectiveness of the FeCO3 layer. The discrepancy of the film formation inside and outside the droplets was the driving force of macro-cell corrosion. The in-situ measurement and visualization of the corrosion processes and kinetics using the modified WBE could be conveniently used to facilitate the understanding of the initiation and propagation of localized TLC.

Macrocell Corrosion Currents in Simulated Concrete Pore Solution and Reinforced Concrete

Chloride-induced rebar corrosion is one of the main causes of damage in reinforced concrete structures (RCS). Chloride attacks lead to depassivation creating pits, which can imply major losses of sections. The current generated at these spots (microcell) is contributed by the current produced between corroded and uncorroded areas (macrocell). The influence of both currents has been deeply investigated based on solution studies, which do not actually represent the behaviour of concrete-embedded elements. The studies about macrocell currents in solution are interesting to analyse this phenomenon quickly and simply. However, they must not be interpreted as the reality of RCS because this requires studies using rebars embedded in concrete. The performed experimental plan verified this fact. In addition, another objective of this study was to analyse the influence of concrete’s electrical resistance and the limiting effect of the cathode/anode surface (Cs/As) ratio on macrocell currents in solution and in concrete. For this study, specimens manufactured using concretes with different properties were used: standard concrete (SC), high-performance concrete (HPC), very high-performance concrete (VHPC) and ultra-high performance-fibre reinforced concrete (UHPFRC). The conclusions show how the Cs/As ratio plays a key role in regulating macrocell current intensity, but what really governs this phenomenon is concrete resistivity because it regulates the participation of a bigger or smaller cathode surface. The influence of this parameter as a limiting factor of macrocell currents is fundamental, especially in high resistivity concretes like VHPC and UHPFRC.

Microcell and macrocell corrosion of steel bars in reinforced concrete slabs under different corrosive environments and cathode/anode configurations

This paper presents an experimental study and electrochemical mechanisms of microcell and macrocell corrosion kinetics of steel bars in reinforced concrete slabs subjected to three different corrosive environments and three configurations of uncorroded/corroded steel bars. Effects of combined chloride contamination and carbonation were investigated and compared to individual causes either from chloride contamination or carbonation. Under each corrosive environment, two cathode/anode area ratios, as well as steel bars-contact and -noncontact conditions, were tested. As a result, the combined chloride contamination and carbonation induced larger microcell and macrocell corrosion rates than those attacked by solely chloride or solely carbonation. Although a larger cathode/anode ratio increased macrocell current density, it actually decreased microcell rate compared to a smaller ratio. In addition, when corroded steel bars were in contact, microcell and macrocell current densities became larger than those in noncontact samples for all three corrosive environments. Based on the test results, electrochemical mechanisms of both microcell and macrocell corrosion were proposed using thermodynamic theory, anodic and cathodic polarisation kinetics to draw precious insights into the corrosion behaviour under different corrosive environments and cathode/anode ratios.

Space Averaging of Electric Field accompanying Corrosion of Reinforcement and its Verification by Pseudo-Concrete

This paper aims to verify a space-averaged electric filed simulation, where the whole surfaces of reinforcing bars are blended into the 3D finite volume for identifying the electric potential to drive the macro-cell corrosion of structural concrete. Experimental verification is conducted with transparent pseudo-concrete, which has chemical pore-solutions similar to those of concrete, and with which the location of anodic poles accompanying brownish rusts and the cathodic ones surrounded by hydrogen bubbles may be visually identified. The proposed electro-chemical analysis platform to be integrated with ion transport and equilibrium is adopted for full consistency with dispersed reinforcing bars. Global macro-cell corrosions of tunnel mockup and reinforcement layers induced by electric current leakage are verified quantitatively with dispersed multi-ion concentration as well as corrosion profile.

Mechanistic study of macrocell effect on corrosion initiation and propagation of reinforcement in submarine immersed tunnel

Submarine immersed tunnel (SIT) is generally in a specific corrosive environment with inner marine atmosphere and outer high-pressure seawater. In this work, a setup was designed to simulate the specific structure and corrosive environment of the SIT, and the mechanism of the macrocell corrosion of reinforcement in SIT was investigated. The chloride threshold value (CTV) and the corrosion rate of macrocell corrosion were obtained and mainly discussed. The results indicated that the anodic corrosion process could be accelerated by increasing SC/A and reducing the thickness of the concrete layer (d) at the cathode. The corrosion initiation was promoted drastically, and the corrosion current density was increased. A remarkable decrease of CTV was discovered in the condition of higher SC/A and reducing d (mainly to improve oxygen acquisition) coexistent. The time to onset of corrosion could be reduced by up to 33%, and the CTV was decreased from 0.749% to 0.562% (by weight). The corrosion will occur earlier, and the damage to the structure will be more severe where the macrocell effect exists in the reinforced concrete structure.

Experimental and numerical investigations on macrocell corrosion of partially carbonated reinforced concrete with supplementary cementitious materials

The use of supplementary cementitious materials (SCMs) has led to a decrease in the corrosion initiation of carbonated reinforced concrete (RC). Hence, studies on the corrosion propagation of carbonated SCM concrete are becoming important but remain limited. In this study, ordinary Portland cement (OPC) was partially replaced with pulverized fly ash (PFA), ground granulated blast-furnace slag and silica fume, using two replacement levels. Experiments were conducted to investigate the microcell and macrocell corrosion behaviors of carbonated SCM concrete under wetting and drying cycles. A novel numerical model is proposed and validated to examine the effect of macrocell corrosion on the duration of corrosion propagation. Results show that macrocell corrosion plays a more important role in carbonated SCM concrete compared with OPC concrete. The corrosion of carbonated PFA concrete can be accelerated by 170% upon galvanic coupling, resulting in a decrease of 47% in the duration of the corrosion propagation.

Macro-cell corrosion between crossed steel bars in cracked concrete

• Macro-cell corrosion current I g included crack-induced macro-cell current I g s and current between two crossed steels I g d . • Both I g s and I g d increased in varying degrees with wider crack and the I g s / I g d ratio was always around 2. • Crack location was proved to influence the value and the direction of I g s and. I g d . To investigate the corrosion behavior of coupled crossed steel bars in cracked concrete, a study on the influence of crack width W and crack location L on the microcell and macro-cell corrosion of coupled crossed steels in cracked concrete is presented. The corrosion process of crossed steel bars in concrete specimens with crack widths of 0, 0.1, 0.2, 0.5 and 1.0 mm, respectively, were continuously monitored in an artificially created chloride environment for 26 weeks. The results showed that the corrosion of steel bars in cracked areas was much severer than that of steel bars in uncracked areas. Both microcell corrosion current ( I c o r r ) and macro-cell corrosion current ( I g ) of coupled active steel bars in a cracked area increased with the increase of the transverse crack width, and I c o r r was found to be more sensitive to the change of crack width. The I g / I c o r r ratio decreased with time, which meant that while macro-cell corrosion made a fair contribution, microcell corrosion played a dominant role in the whole corrosion period. In addition, the distance between the concrete crack and the intersection of the crossed steel bars, defined as the crack location L in the study, was proved to have a significant impact on the value and the direction of total macro-cell corrosion current I g .

Effect of curing temperature and water-to-cement ratio on corrosion of steel in calcium aluminate cement concrete

• CAC specimens were made with different w/c, and cured at different temperatures. • The w/c and temperature played a crucial role in the porosity of CAC. • Increasing the curing temperature can improve the corrosion resistance of CAC. This study evaluated the corrosion resistance of pure calcium aluminate cement (CAC) concrete specimens made with water-to-cement ( w/c ) ratios of 0.4, 0.5, and 0.6 and cured at 4, 21, and 90 °C following the ASTM G109 standard. Thermogravimetric analysis results showed increased CAC conversion with increased curing temperature. Compressive strength and bulk electrical resistivity measurements showed that the CAC specimens had lower strength and higher bulk electrical resistivity than ordinary portland cement (OPC) concrete. Macrocell corrosion currents measured after cyclic exposure to chloride solutions showed that the CAC specimens were highly permeable and less resistant to chloride-induced corrosion than OPC concrete. Among the different CAC specimens tested in this study, the specimens made with a w/c of 0.4 and cured at 90 °C showed the highest corrosion resistance.

On the corrosion rate measurement of reinforcing steel in chloride induced macrocell corrosion

This study investigates the corrosion rate measurement of reinforcing steel under chloride-induced macrocell corrosion in reinforced concrete (RC). The corrosion rates of RC columns with different cover thicknesses and chloride concentrations were evaluated using different techniques and cathode over anode ratios. The applicability of the Stern-Geary equation on the macrocell corrosion of RC was studied. The results show that the corrosion rate of highly corroding steel can be underestimated by an order of magnitude by the linear polarisation resistance method due to a failure to compensate for diffusion resistance. The effect of macrocell corrosion on the measurement of polarisation resistance is moderate with a relative error less than 2. The galvanostatic polarisation technique can eliminate the influence of diffusion resistance and therefore reliably measure polarisation resistance. A B value of 52 mV is recommended under macrocell corrosion.

Effect of recycled aggregate and supplementary cementitious material on the chloride threshold for steel bar corrosion in concrete

Under marine environment, the passive film on the surface of steel bar embedded in reinforced concrete structures will be broken once a threshold value of chloride, i.e., chloride threshold (Cth), is reached at the rebar-concrete interface by diffusing through the concrete cover. The value of Cth is essential for determining service life of concrete structures. In this investigation, the effect of recycled aggregate (RA, i.e., recycled coarse aggregate) and supplementary cementitious material (SCM), including ground granulated blast furnace slag, red mud and glass powder, on the value of Cth was investigated. A chloride threshold test method for accurate determination of Cth was proposed by the alternation of accelerated chloride migration test and artificial-natural diffusion test, which can simulate the marine environment and accelerate the diffusion of chloride. The corrosion activity of steel bar was monitored using two electrochemical methods, including linear polarization resistance method and macro-cell corrosion method, to detect the initiation of corrosion. Immediately after the corrosion initiation, corresponding specimen was taken out to measure the chloride content of concrete adjacent to the surface of steel bar. A calculating method of chloride threshold Cth was presented considering the actual distribution of coarse aggregate in concrete adjacent to the surface of steel bar. The results of the chloride threshold tests show that RA and SCM have a significant influence on the protective properties of passive films, and it is worth noting that the positive effect of RA on the quality of passive film has been observed. For concrete with the same substitution level of SCM, the chloride threshold Cth increases linearly with RA content. Subsequently, the suggested values of Cth for natural aggregate concrete (NAC) with different substitution level of SCM are given, and the suggested values of Cth for corresponding recycled aggregate concrete can be given by an amplified factor kRA multiplied by Cth for NAC with ± 10% relative error.

Effects of Mineral Admixtures on Macrocell Corrosion Behaviors of Steel Bars in Chloride-Contaminated Concrete

Based on the macrocell corrosion theory and by alternating the microcell corrosion state and macrocell corrosion state, the influence of mineral admixtures, such as fly ash, slag, and limestone powder, on the macrocell corrosion behaviors of steel bars embedded in chloride-contaminated concrete were investigated and clarified. The results indicated that the inhibition effect induced by slag on macrocell corrosion and microcell corrosion was obviously better than that induced by fly ash or limestone powder. The presence of slag in chloride-contaminated concrete could remarkably decrease the corrosion area ratios of anodic steel, even if the replacement levels of slag to cement reached 70%. With the addition of mineral admixtures into concrete, the ratio of macrocell current density to microcell current density was decreased to some extent, depending on the types, replacement levels, and replacement ways of mineral admixtures. The use of slag and fly ash in chloride-contaminated concrete can effectively weaken the macrocell corrosion and make the corrosion be dominated by microcell corrosion. The types and replacement levels of mineral admixtures also had a remarkable influence on the control mode of macrocell corrosion. The use of slag was more effective than that of fly ash or limestone to weaken the cathode control mode of macrocell corrosion and made the control mode of macrocell corrosion be dominated by jointed control.