Corrosion Of Steel Rebar Research Articles

Influence of graphene nanoplatelets on the passivation and corrosion resistance of carbon steel bars in ordinary portland cement mortar

This study investigates the influence of adding graphene nanoplatelets (GNPs) to mortar mixtures on the corrosion behavior of embedded carbon steel rebars. Mortar mixtures were prepared with a water-to-cement ratio of 0.42 and GNP replacement levels of 0, 0.05, and 1 percent by weight of cement. After 28 days of curing in an environmental chamber, the passivity and kinetics of chloride induced corrosion initiation for the rebars were studied using a suite of electrochemical tests. The results suggest that incorporating GNPs at low concentrations may enhance the passivity and resistance to chloride-induced corrosion of carbon steel rebars; however, due to the large variability in the data, the findings are inconclusive. Potentiodynamic measurements revealed that the estimated average polarization resistance of steel rebars in 0 G (no GNP), 0.05 G, and 1 G specimens in the passive state was on average −182.3, −276.5, and −304.2 kΩ, respectively. Upon exposure to chloride solution, 0 G specimens, with an average corrosion potential of −600 mV vs. SCE, exhibited the lowest resistance, whereas 0.05 G specimens, with an average of −491 mV vs. SCE, showed the highest corrosion resistance. Results from electrical impedance spectroscopy were consistent with the potentiodynamic findings. Surface characterization also revealed that the inclusion of GNPs does not alter the surface roughness of the interface between steel rebar and paste. However, the interface between rebar ribs and mortar paste had higher surface roughness and porosity in all specimens regardless of GNPs replacement level. Visual inspections confirmed that the area around the rebar ribs at the interface is more conducive to the formation of crevice and pitting corrosion.

A New Avrami-Based Exponential Model for Predicting Fiber-Reinforced Polymer Bar Service Life: A Comparison with Existing Models Using a Large Database

The fiber-reinforced polymers (FRP) bar is a promising solution to problems caused by steel rebar corrosion in concrete. To assess the service life of the FRP bar based on accelerated test results, it is crucial to have a reliable model. Here, a modified exponential (MEP) model is proposed based on the Avrami equation. The Avrami equation provides a theoretical foundation for the empirical exponential (EP) model and does not a priori fix the power of the exposure time to one. A database containing 903 data points from 74 groups of test specimens is assembled to compare the reliability of the MEP model vis-a-vis the EP, single logarithmic, double logarithmic, and power function models. The combination of Root Mean Square Error (RMSE), the Mean Absolute Error (MAE), and the coefficient of determination (R2) criteria is proposed for assessing model reliability. It is shown that in certain cases the combined criteria, versus R2 alone, significantly increase the number of test groups meeting the acceptable performance limit. Observed test data aberrations are found to have minor influence on the results of the EP model, but they significantly influence the results of the other four models. The EP model generally predicts the lowest activation energy and the smallest strength retention for similar groups of bars, while the predicted values of the other four models exhibit a relatively small difference. The difference between the predicted strength retention values of the EP and MEP models shows an increasing trend with the increase of the absolute value of (1 − n), where n is the power of the exposure time in the MEP model.

Resilience-Based Restoration Model for Optimizing Corrosion Repair Strategies in Tunnel Lining

In tunnel engineering, the corrosion of steel rebar is a critical factor leading to structural degradation and failure, causing a decline in load-bearing capacity, deformation, and cracking. For decision-makers, identifying the optimal timing for tunnel maintenance and selecting effective repair strategies is of paramount importance. This study introduces a resilience-based restoration model to analyze tunnel failure due to corrosion throughout its service life and to optimize the timing and selection of maintenance strategies. The model generates time-variant failure curves by constructing limit equilibrium equations. The entropy weight method is employed to quantify and weight the impact of various failure modes, determining the timing for maintenance when the failure curve exceeds a predefined threshold. Additionally, the model's uncertainty is effectively reduced through regular inspections and Bayesian updating methods, enhancing prediction accuracy. The study further incorporates a resilience index and a benefit index to provide a quantitative assessment of maintenance plans, assisting decision-makers in selecting the optimal strategy. By exemplifying the model with a case study of steel rebar corrosion in a tunnel, this paper demonstrates the model's applicability and offers a new scientific approach for quantitative maintenance decision-making in tunnel engineering.

Repairment of carbon steel oxide scale using Ce³⁺ and Ni²⁺ doped sol-gel technique

Corrosion of carbon steel rebars in concrete structures significantly compromises their safety, reliability, and environmental performance. This work focuses on enhancing rebar corrosion resistance by repairing the defects of oxide scale. Here, sol-gel was employed as a carrier, by which Ce3+ and Ni2+ were transferred to the oxide scale defects based on the isoelectric point theory, and deposited at these defects with the pH variation as temperature. The repaired oxide scale showed enhanced uniform elemental distribution and improved electrochemical properties, maintaining integrity even under prolonged exposure to Cl−-rich environments. Notably, the impedance modulus at 0.01 Hz (|Z | 0.01Hz) of treated samples was six times higher than untreated ones, indicating superior performance against high electric fields. This strategy shows great potential for enhancing the durability of concrete structures.

Effect of Fluoride in Alkali-Free Liquid Accelerator on Corrosion of Reinforced Shotcrete by Chloride Ion.

Shotcrete is a crucial component of tunnel engineering. To investigate the impact of fluoride-containing alkali-free liquid accelerators on the structural safety of shotcrete, this study prepared shotcrete using three different fluoride-based alkali-free liquid accelerators: magnesium fluosilicate, fluosilicic acid, and hydrofluoric acid. The corrosion of steel rebar within the shotcrete was examined and compared with that of shotcrete prepared using a fluoride-free alkali-free liquid accelerator. Analysis of the hydration products and pore structure of the shotcrete revealed that fluoride-containing accelerators inhibited the hydration of C3S, increased the content of harmful pores, reduced the pH value, and decreased the chloride ion binding capacity of the shotcrete. As a result, steel reinforcement within the fluoride-containing shotcrete was not effectively protected during the early stages. Detection of corrosion products indicated that shotcrete containing fluosilicic acid and hydrofluoric acid accelerators led to the rapid formation of loose corrosion products, primarily Fe2O3, thereby accelerating the corrosion rate of the steel reinforcement. Among the accelerators studied, hydrofluoric acid posed the most severe threat to the reinforcement, with the open circuit potential reaching -520.2 mV after 24 days of accelerated corrosion testing. Additionally, the mechanisms by which fluorides influence the corrosion of steel reinforcement in shotcrete were explored through the analysis of concrete hydration products and corrosion products on the steel rebar.

Flexural behavior of corroded RC beams repaired with high performance cementitious mortar under cyclic loading

AbstractThe understanding of the cyclic performance of reinforced concrete (RC) elements is of vital importance in relation to the extent of the service life of buildings and infrastructures. Steel rebar corrosion plays a major role in this regard because it significantly affects the overall structural integrity, especially under cyclic loads, leading to reduced stiffness and load‐bearing capacity of structural elements. Cyclic condition has the potential to accelerate the corrosion‐induced cracking and spalling, the effectiveness of the bond strength between rebar and concrete, and also the ductility and energy dissipation characteristics of the structure. The primary objective of this study is to investigate the effectiveness of a high‐performance thixotropic repairing cementitious mortar in improving the fatigue behavior of RC elements through a multiscale experimental approach. First, at the material scale of concrete specimens, two different concrete classes together with the repairing one‐component, pre‐blended, thixotropic cementitious mortar, were tested under incremental cyclic condition. Based on the results obtained from material scale, four reinforced concrete beams were exposed to different levels of accelerated corrosion by means of the impressed current technique and, subsequently, repaired by bonding a layer of the thixotropic high‐performance mortar onto the tension side. Finally, beams were tested under incremental cyclic four‐point bending test to investigate the fatigue behavior in terms of crack onset, propagation and energy dissipation. The resulting cyclic properties and cracking behavior of the structural elements were related to the level of corrosion achieved through the accelerated test and the effectiveness of the structural repair mortar was proven. In terms of code compliance, the repairing mortar was able to fulfill the requirements of frequent and quasi‐permanent combination of loads, remaining below all the threshold values provided by the Italian NTC2018 and Eurocode.

Research Progress in Corrosion Behavior and Anti-Corrosion Methods of Steel Rebar in Concrete

The corrosion of steel rebars is a prevalent factor leading to the diminished durability of reinforced concrete structures, posing a significant challenge to the safety of structural engineering. To tackle this issue, extensive research has been conducted, yielding a variety of theoretical insights and remedial measures. This review paper offers an exhaustive analysis of the passivation processes and corrosion mechanisms affecting steel rebars in reinforced concrete. It identifies key factors such as chloride ion penetration and concrete carbonization that primarily influence rebar corrosion. Furthermore, this paper discusses a suite of strategies designed to enhance the longevity of reinforced concrete structures. These include improving the concrete protective layer’s quality and bolstering the rebars’ corrosion resistance. As corrosion testing is essential for evaluating steel rebars’ resistance, this paper also details natural and accelerated corrosion testing methods applicable to rebars in concrete environments. Additionally, this paper deeply presents an exploration of the use of X-ray computed tomography (X-CT) technology for analyzing the corrosion byproducts and the interface characteristics of steel bars. Recognizing the close relationship between steel bar corrosion research and microstructural properties, this paper highlights the pivotal role of X-CT in advancing this field of study. In conclusion, this paper synthesizes the current state of knowledge and provides a prospective outlook on future research directions on the corrosion of steel rebars within reinforced concrete structures.

Gaussian process regression driven rapid life-cycle based seismic fragility and risk assessment of laminated rubber bearings supported highway bridges subjected to multiple uncertainty sources

Structural attributes, corrosion of steel rebars in reinforced concrete (RC) columns, thermal oxidative aging of inherent rubber in laminated rubber bearings (LRBs), replacement of LRBs, and the time-dependent seismic hazard level at the bridge site are well recognized as the main factors that affect the accurate assessment of the seismic performance of RC bridges implemented with LRBs. However, the probabilistic seismic demand model (PSDM) and probabilistic structural capacity model (PSCM) of deteriorated bridge components may not exhibit homoscedastic log-linearity. And the expansion of seismic fragility surfaces and seismic risk curves in the temporal dimension requires a considerable computational cost on the nonlinear analysis, which regretfully has not been well addressed in current studies. To fill in this gap, this study proposes a life-cycle based seismic fragility and risk assessment framework for LRBs supported RC bridges considering deterioration mechanisms of bridge components during their life cycles demonstrated by a three-span LRBs supported highway bridge considering multiple uncertainties such as the replacement interval for LRBs. In this framework, Gaussian process regression (GPR) is employed to effectively construct the PSDM and PSCM of deteriorated bridge components, and then the time-dependent seismic fragility surfaces of bridge components and bridge system are established. Life-cycle based seismic risk analysis is conducted to quantify the coupled time-dependent effects of deterioration and site seismic hazard on a newly built bridge during its design service life and a deteriorated bridge within its remaining service life, respectively. Results indicate that GPR can successfully capture the nonlinearity and heteroscedasticity characteristics of PSDM and PSCM, leading to a significant reduced number of nonlinear analysis cases to generate the time-dependent seismic fragility surfaces and seismic risk curves. Consequently, the proposed framework using GPR can significantly improve the accuracy and efficiency of life-cycle based seismic performance assessment when uncertainties of structural attributes, deterioration progress and seismic hazard are taken into consideration.

Corrosion inhibition of steel rebar in chloride-contaminated concrete pore solution: Ecofriendly glutamic acid inhibitor and its synergy with galvanized coating

In this study, we explore the effectiveness of glutamic acid as corrosion inhibitor for protecting steel rebars within a concrete pore solution contaminated with chloride (CCCPS) along with its synergy with galvanized coating are investigated. The study is defined in two phases: (a) examining the inhibition efficiency (%IE) of glutamic acid at various concentrations of 0.25, 0.50, 0.75, and 1 g/L using a combination of experimental and theoretical methods, and (b) evaluating its synergistic effect with Zn present in the galvanized coating. In the first phase, various electrochemical tests and theoretical investigations are employed. The electrochemical examinations consistently demonstrated that at a concentration of 1 g/L, the maximum %IE reaches ∼ 80 %. Langmuir adsorption isotherm fitting effectively describes the relationship between inhibitor concentration and its coverage percentage. Thermodynamic data indicate the adsorption of these inhibitors on the steel surface involves both physical and chemical adsorptions with a ΔG°ads (standard free energy of adsorption) of around –23.5 kJ/mol. Moreover, the activation energy for corrosion of steel rebar increases from 55.8 kJ/mol for the blank CCCPS to 78.3 kJ/mol for the inhibited CCCPS. Molecular dynamics simulations validate the binding of glutamic acid molecules to the surface of the steel, primarily through nitrogen atoms orientation towards d-orbitals of steel substrate. In the second phase, the carbon steel rebar underwent hot-dip galvanization, resulting in a galvanized coating with a thickness of approximately 36 µm. The synergistic effect of glutamic acid at its optimum concentration (0.75 g/L) was investigated with comparison of the corrosion behavior of three samples: bare steel, galvanized steel, and scratched galvanized steel in simulated CCCPS with and without the inhibitor. Results indicate that the presence of the inhibitor significantly enhances the %IE, up to 99 %, for scratched galvanized steel. FESEM/EDS analysis further reveals a substantially lower volume of corrosion products in the scratched area of the latter sample compared to its counterpart in the inhibitor-free solution. Furthermore, as indicated by the findings from X-ray photoelectron spectroscopy (XPS), the interactions between the N and Fe atoms, acting as donors and acceptors, respectively, hold significant importance in the chemisorption process.

Experimental and numerical assessment of GFRP and synthetic fiber reinforced waste aggregate concrete members

Improper disposal of plastic waste (P-waste) poses significant pollution and health risks to the environment. Additionally, steel rebar corrosion in concrete structures reduces their strength and serviceability. To address these issues, this study explores using glass fiber-reinforced polymer (GFRP) rebars and replacing natural coarse aggregates with P-waste aggregates for sustainable and eco-friendly construction. This work investigates the axial performance of polypropylene structural fiber-reinforced P-waste aggregate concrete (SFPC) compressive components having GFRP-reinforcement (GSFPC) under various loading conditions. For comparison, steel-reinforced SFPC compressive components (SSFPC) were also fabricated. Eighteen circular components with 1200 mm height and 300 mm diameter were tested and compared under different loading conditions. SSFPC components exhibited up to 21.9 % higher axial strength but up to 27.4 % lower ductility compared to GSFPC components. Eccentric loading similarly reduced axial strength in both GSFPC and SSFPC components. A 3-D finite element analysis (FEA) of GSFPC components was proposed using a modified damaged plastic model for SFPC which showed deviations of 2.3 % in axial strength and 7.7 % in equivalent axial shortening, demonstrating a good accuracy of the FEA model.

Assessing the effect of sodium nitrite as corrosion inhibitor against the corrosion of steel rebar in alkali-activated concrete

The aim of this study is to investigate the effectiveness of corrosion inhibitor against chloride-induced corrosion of steel rebar in fly-ash (FA) and GGBS (ground granulated blast furnace slag) and Nanofine-based alkali-activated concrete. The Alkali-Activated Concrete (AAC) was prepared from FA, ground granulated blast furnace slag (GGBS), and Nanofine with Sodium hydroxide (NaOH) and Sodium Silicate (Na2SiO3) solutions. The concentration of NaOH varies to 10 M, 12 M, and 14 M, and all the specimens were subjected to accelerated corrosion, to perform the non-destructive test after the corrosion of the steel rebars. Fourier Transform Infrared (FTIR), scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDS), and Electron Backscatter Diffraction (EBSD) were used to examine the microstructure of AAC in the presence of Nano-Fine GGBS (NF), Sodium Chloride (NaCl), and NaNO2 and to compare the strength and corrosion properties with AAC and OPC. The ratio of sodium silicate to sodium hydroxide was taken as 2.5 and the solution-to-binder ratio was taken as 0.5. The compressive strength and ultrasonic pulse velocity (UPV) test of the Nano-fine based alkali-activated concrete increases as compared to the control concrete. The increase in the dosages of corrosion inhibitor and nano-fine increases the compressive strength of the control concrete and alkali-activated concrete. The half-cell potential of the control concrete and nano fine admixed with alkali-activated concrete mixes with different molarities is uncertain. The increases in the dosages of corrosion inhibitors reduce the occurrence of corrosion in the steel reinforcement rebars.

Effects of electroless nickel -coating on tribological and corrosion behaviour of TMT steel rebar with multi-walled carbon-nanotube and titanium dioxide nanoparticles

This study incorporated Multi-walled carbon nanotube particles (MWCNTs) and Titanium Dioxide Nanoparticles (TiO2) into a metal matrix composite in Ni–P coated substrate using an Electroless technique. This study significantly improves the tribological properties, enhances corrosion resistance, increases durability and extends the service life of coated rebar. Coated rebar helps make infrastructure more sustainable by extending the life of buildings and lowering their material consumption, trash output, and ecological footprint. The tribological behaviour of steel rebar has been studied by using a variety of characterization techniques, like X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (EDX) including the corrosion test and the hardness test. The topographical roughness of the bare specimen, Ni–P coated specimen, CNT coated specimen and TiO2 coated specimen are 67.4 nm, 112 nm, 201 nm, and 162 nm respectively. The microhardness of the bare substrate, Ni–P coated, CNT doped coated, and TiO2 dopped coated specimens was done using Vicker's Hardness tester and the mean values were 455 HV, 580 HV, 810 HV, and 680 HV respectively. Resistance to corrosion of TMT steel rebar of Fe500 was examined using the polarisation method and Electrochemical-Impedance-Spectroscope (EIS) method. These techniques were examined in 3.5 wt% aqueous medium of NaCl and analysed the Ecorr (corrosion potential) and Icorr (Corrosion current density) of the bare substrate, Ni–P coated, Ni–P/CNT and Ni–P/TiO2 substrate. The corrosion inhabitation efficiency of the Ni–P-CNT doped was 22.5% more than the Bare substrate, and the TiO2 doped coated specimen was 10.63% more than the bare substrate. Resistance to corrosion of the CNT-coated substrate is better than Ni–P/TiO2 and Ni–P-coated specimens.

Effect of loading level on the corrosion resistance of a novel self-healing cementitious composite

A novel self-healing cementitious composite SMA-ECC is utilized to enhance corrosion resistance and maintain mechanical properties in chloride environment. The purpose of this study is to investigate the impact of the loading level on embedded steel rebar corrosion and the self-healing performance of SMA-ECC. The study examined the damage conditions, mechanical properties, and rebar corrosion resistance following a loading test. Chloride ingress depth and electrochemical tests were adopted to evaluate the corrosion resistance of the specimens. The findings reveal that SMA-ECC exhibits remarkable self-healing abilities in terms of damage recovery and restoration of mechanical properties. Cracks smaller than 50 μm can achieve a 100 % closure rate in SMA-ECC. It was observed that specimens with less damage (50 %, 70 % damage conditions) displayed improved chloride resistance (SMA-ECC in 50 % damage condition has equivalent corrosion resistance in terms of corrosion current density compared to intact NC control specimens), leading to higher corrosion resistance for SMA-ECC according to the electrochemical test results.

Analysis of the Effectiveness of the Application of Corrosion Inhibitors to Steel Re-Bars Embedded in Concrete

Reinforced concrete is the most widely used material in the construction of building structures, being noted for its versatility and low cost. However, the durability of reinforced concrete structures can be compromised by the corrosion of steel re-bars, especially in the presence of chlorides. To address this challenge and promote sustainability, the use of corrosion inhibitors has been researched as a way to extend the lifespan of structures. This study assessed the effectiveness of using a commercial corrosion inhibitor on steel re-bars embedded in types of concrete with different chloride percentages, using electrochemical methods to measure the corrosion rate and potential. The results indicate that, in the absence of corrosion inhibitors, corrosion rates become unacceptable with chloride percentages equal to or higher than 0.8% by weight of cement. The application of inhibitors significantly reduced the corrosion rate, particularly at chloride percentages of 0.8% and 1.2%, maintaining the re-bars in a passive state or at moderate levels of corrosion. However, for chloride percentages higher than 1.6%, high levels of corrosion were observed, even in the presence of inhibitors. The findings suggest that the use of inhibitors can be an effective strategy in preventing corrosion in reinforced concrete structures, contributing to their structural integrity and long-term sustainability.

Corrosion of Steel Rebars in Construction Materials with Reinforced Pervious Concrete

Pervious concrete has great potential for use in many practical applications as a part of urban facilities that can add value through water harvesting and mitigating severe damage from floods. The construction and agricultural industries can take direct advantage of pervious concrete’s characteristics when water is a key factor included in projects as part of the useful life of a facility. Pervious concrete also has applications in vertical constructions, fountains, and pedestrian crossings. This work evidences that pervious concrete’s corrosion current increases with increasing aggregate size. Also, corrosion is a factor to consider only when steel pieces are immersed, aggravated by the presence of chlorine, but it drains water and does not retain moisture. Steel-reinforced pervious concrete was studied, and the grain size of the inert material and the corrosion process parameters were investigated. The electrochemical frequency modulation technique is proposed as a suitable test for a fast, reproducible assessment which, without damaging reinforced cement structures, particularly pervious concrete, indicates a trend of increasing corrosion current density as the size of the aggregate increases or density diminishes.

Investigating non-uniform corrosion induced concrete cover cracking with a fracture-contact coupled computational method

Corrosion of steel rebar causes cracks in concrete, significantly impacting the durability of reinforced buildings. While various computational methods aim to simulate this process, only a few successfully handle both internal corrosion pressure and surface crack width evolution. To address this limitation, the study introduces an innovative mesoscale fracture-contact coupled computational method that seamlessly integrates with ABAQUS. Unlike current methods, it creatively utilizes interface elements to model stress transfer and crack propagation under tension in concrete. Additionally, it includes an additional contact model to represent the material's response to compression and shear forces. These innovations allow for accurate simulation of plain concrete mechanical properties under both tension and compression, effectively illustrating the development and failure patterns of cracks in the reinforced concrete cover. After calibrating and validating the method, the study thoroughly analyzed the process of concrete cover cracking, considering factors such as water to cement ratio, spatial location, geometry and size of coarse aggregate, rebar diameter and cover thickness. The modeling results reveal the following findings: (i) Changes in the shape and size of coarse aggregates have minimal effects on internal pressure and crack width. (ii) Higher concrete strength correlates with increased pressure on the outer surface of the rebar in an almost linear fashion, but it has little impact on surface crack width. (iii) Increasing the bar diameter decreases rust pressure but results in more cracks and wider surface cracks. (iv) Augmenting the cover thickness intensifies rust-induced pressure while simultaneously widening surface cracks.

Accelerated Electromigration Approach to Evaluate Chloride-Induced Corrosion of Steel Rebar Embedded in Concrete

Two distinct binary blended concrete mixes were prepared for the study. The first mix involved a cement replacement of 50% slag, denoted as SL. The second mix incorporated a cement replacement of 20% fly ash, referred to as FA. No chlorides were added during the preparation of these concrete specimens. To accelerate chloride transport, electromigration was employed by placing specimens with varying reservoir lengths (ranging from 2.5 cm to 17.5 cm) on their top surfaces. These reservoirs were subsequently filled with a 10% NaCl solution. In this paper, corrosion propagation was monitored over a period of approximately 650 days using electrochemical measurements such as open circuit potential, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The evolution of rebar potential, polarization resistance, solution resistance, and corrosion current were analyzed to understand the corrosion behavior. This paper focuses on how the length of the solution reservoirs influences the corrosion-related parameters such as polarization resistance, solution resistance, rebar potential, and corrosion current. During the monitored propagation period, the corrosion current values (last 7 sets of readings) exhibited higher magnitudes for the embedded rebars in specimens made with SL mix in comparison to those made with FA mix. Corrosion current measurements likewise showed an increasing trend as the reservoir lengths increased. None of the specimens had any visible cracks or corroded products that could reach the concrete surface throughout the monitored period. The experimental results provide insights into the corrosion mechanisms and the effectiveness of accelerated corrosion techniques in simulating real-life conditions.

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

Statistic investigation on chloride ions distribution based on numerical reconstruction of in situ meso-structure of concrete

To study the non-uniform corrosion of steel rebar induced by chloride ions invasion under marine environment, the three-dimensional characteristic distribution of aggregates and pores in concrete was numerically extracted and reconstructed through X-ray CT technique. Based on the 3D in-situ meso-structure model of concrete, the random characteristics of chloride ions transport in concrete was investigated by numerical simulation. Through a fitting and hypothesis test on the concentration distribution histogram of chloride ions, a reliable probability density distribution function of chloride ions concentration was proposed. And the influence of ITZ and aggregate shape on the random diffusion of chloride ions was studied. The research indicates that that the spatial distribution of coarse aggregates and pores is the main reason leading to the non-uniform distribution of chloride ions. The chloride ions concentration under a certain time follows the Lognormal distribution. The discreteness of chloride ions distribution in concrete decreases when the interfacial transition zone is not considered in the model. And an increase of the irregularity of aggregate shape will cause an increase in the tortuosity of chloride ions transport path, and the discreteness of chloride ions distribution will enhance accordingly.

The influence of longitudinal rebar type and stirrup ratio on the bond performance of reinforced concrete with corrosion

This study investigated the bond-slip mechanism of eccentrically pulled out rebar under different corrosion level. The variation patterns of the bonding performance between two types of steel rebars (i.e., plain round rebar and ribbed rebar) and concrete with different stirrup ratios were obtained with respect to the amount of steel rebar corrosion. The differences in bonding performance between plain round rebars and ribbed rebars with concrete were compared, and the bond-slip mechanisms of plain round rebars and ribbed rebars with concrete were elucidated. The influence of longitudinal bar type and stirrup ratio on the ultimate bond strength and bond-slip constitutive curve was analyzed. It has been determined that in the case of uncorroded specimens featuring ribbed bars, the ultimate bond strength exhibits an approximately linear increase in relation to the stirrup ratio. Conversely, the stirrup ratio does not have a significant impact on the ultimate bond strength of uncorroded specimens with plain round bars. Transverse reinforcement plays a crucial role in mitigating the effects of cracked concrete by delaying the reduction in bond stress caused by the corrosion rate of longitudinal reinforcement. This phenomenon becomes increasingly prominent when higher stirrup ratios are utilized in the case of plain round reinforcement. Transverse reinforcement serves to suppress the occurrence of the brittle failure stage that follows the peak bond stress in specimens exhibiting a low corrosion rate. The magnitude of this effect becomes more pronounced as higher transverse reinforcement ratios are employed.