Rebar Corrosion Research Articles

Evaluation of Early Concrete Damage Caused by Chloride-Induced Steel Corrosion Using a Deep Learning Approach Based on RNN for Ultrasonic Pulse Waves.

The objective of this study is to explore the feasibility of using ultrasonic pulse wave measurements as an early detection method for corrosion-induced concrete damages. A series of experiments are conducted using concrete cube specimens, at a size of 200 mm, with a reinforcing steel bar (rebar) embedded in the center. The main variables include the water-to-cement ratio of the concrete (0.4, 0.5, and 0.6), the diameter of the rebar (10 mm, 13 mm, 19 mm, and 22 mm), and the corrosion level (ranging from 0% to 20% depending on rebar diameter). The impressed current technique is used to accelerate corrosion of rebars in concrete immersed in a 3% NaCl solution. Ultrasonic pulse waves are collected from the concrete specimens using a pair of 50 kHz P-wave transducers in the through-transmission configuration before and after the accelerated corrosion test. Deep learning techniques, specifically three recurrent neural network (RNN) models (long short-term memory, gated recurrent unit, and bidirectional long short-term memory), are utilized to develop a classification model for early detection of concrete damage due to rebar corrosion. The performance of the RNN models is compared to conventional ultrasonic testing parameters, namely ultrasonic pulse velocity and signal consistency. The results demonstrate that the RNN method outperforms the other two methods. Among the RNN methods, the bidirectional long short-term memory RNN model had the best performance, achieving an accuracy of 74% and a Cohen's kappa coefficient of 0.48. This study establishes the potentiality of utilizing deep learning of ultrasonic pulse waves with RNN models for early detection of concrete damage associated with steel corrosion.

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.

Understanding Chloride Diffusion Coefficient in Cementitious Materials.

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients.

Numerical validation and optimization of hybrid composite beam hull using multiple failure criteria

The number of structurally deficient bridges continues to increase due to corrosion of steel sections and concrete rebar, therefore the replacement of decaying structures and the development of innovative systems have become of high priority to extend the life span of newly built bridges. Hybrid Composite Beam (HCB) produced by Hillman is one of those systems that use a combination of materials i.e., concrete, steel, and Glass Fiber-Reinforced Polymer (GFRP) to integrate each main advantage in a single bridge beam structure. Despite its several apparent advantages; it is not widely spread as expected within the last decade. The HCB is manufactured of self-consolidating concrete (SCC), which is poured in the shape of a traditional arch and tied at its ends by high-strength tendons. A durable FRP composite hull encapsulates the SCC arch and the high-strength tying tendons in order to create a structural beam element for bridge applications. The HCB's design aims to provide pure compressive stresses to the concrete and pure tensile stresses to the steel. The current study performs a deep numerical investigation of the FRP hull instead of other components comprehensively studied. Numerical validation is performed for the deflection results on the experimentally tested Knickerbocker HCB Bridge, the deformations are validated at four stages of HCB manufacturing and testing. Further, the FRP hull strength ratios are quantified for the worst value of four failure criteria. The results showed an excess use of FRP material, where more than 90% of FRP areas have strength ratios of 5 to 50. The FRP hull thickness is minimized using Genetic Algorithm optimization under the worst case of loading. The results achieved more than 60% decrease in FRP weight, that led to only 20% cost difference between traditional precast concrete and HCB girders. It is finally concluded that the overdesign of FRP hull contributed to the high cost of HCB usage consequently inefficient market spread.

Effect of sealing treatment on corrosion resistance of zinc-calcium phosphate coating prepared on HRB335 rebar in simulated concrete pore solution

In order to reduce the corrosion of HRB335 rebar in a concrete environment and ensure the service life of reinforced concrete structures, a zinc-calcium phosphate coating was prepared on the surface of HRB335 rebar. The dehydration antirust oil, chromate solution, and silicate solution were used for the sealing treatment of the phosphate coating. The experimental results show that the zinc-calcium phosphate coating possesses many compact and spherical particles, which evenly and completely cover the surface of rebar substrate. The surface morphology, thickness, composition and corrosion resistance of the phosphate coating do not change significantly after sealing treatment in dehydrating antirust oil. However, sealing treatment in chromate solution and silicate solution can block the intergranular pores, improve the compactness and change the composition of phosphate coating to enhance the corrosion resistance of phosphate coating in simulated concrete pore solution. The main composition of the phosphate coating after sealing treatment in silicate solution are Zn, Ca, P, O, C and Si elements, and the compactness is slightly better than that of the phosphate coating after sealing treatment in chromate solution. Compared with rebar substrate, the corrosion current density of the phosphate coating after sealing treatment in silicate solution is reduced by nearly two orders of magnitude, and the protection efficiency toward rebar substrate reaches 98.2 %, which can enhance the corrosion resistance of rebar substrate in simulated concrete pore solution for a long time. Silicate solution is less harmful to the environment and has a good sealing effect, so it has potential application in the sealing treatment of phosphate coating.

Combined GPR and Self-Potential Techniques for Monitoring Steel Rebar Corrosion in Reinforced Concrete Structures: A Laboratory Study

Steel rebar corrosion is one of the main causes of the deterioration of engineering reinforced structures. Steel rebar in concrete is normally in a non-corroding, passive condition, but these conditions are not always achieved in practice, due to which corrosion of rebars takes place. This degradation has physical consequences, such as decreased ultimate strength and serviceability of engineering concrete structures. This work describes a laboratory test where GPR and SP geophysical techniques were used to detect and monitor the corrosion phenomena. The laboratory tests have been performed with several reinforced concrete samples. The concrete samples were partially submerged in water with a 5% sodium chloride (NaCl) solution. Therefore, an accelerated corrosion phenomenon has been produced by a direct current (DC) power supply along the rebar. The geophysical measurements were performed with a 2.0 GHz centre frequency GPR antenna along several parallel lines on the samples, always being the radar line perpendicular to the rebar axis. The GPR A-scan amplitude signals were elaborated with the Hilbert Transform approach, observing the envelope variations due to the progress of the steel rebar corrosion in each concrete sample. Moreover, Self-Potential acquisitions were carried out on the surface of the concrete sample at the beginning and end of the experiments. Each technique provided specific information, but a data integration method used in the operating system will further improve the overall quality of diagnosis. The collected data were used for an integrated detection approach useful to observe the corrosion evolution along the reinforcement bar. These first laboratory results highlight how the GPR should give a quantitative contribution to the deterioration of reinforced concrete structure.

鋼繊維が鋼繊維補強コンクリートのひび割れ部における鉄筋腐食に及ぼす影響に関する基礎的研究

Experimental studies were conducted to clarify mechanisms of corrosion inhibition of rebar by steel fibers in steel fiber reinforced concrete, SFRC. Test specimens with an artificial crack were made from concrete and SFRC, and steel fibers were arranged in the crack for some of concrete specimens. Specimens were exposure under wet-dry cycle and salt water were poured through the artificial crack when wet condition. After prescribed cycles, rebar corrosion was evaluated and impacts of steel fibers on that were discussed. As the results, it was confirmed that steel fibers inhibited the rebar corrosion, and its effect was appeared when fibers existed in the artificial crack mostly. The corrosion inhibition was shown for large crack specimens as well as small crack ones. An electrochemical factor due to corrosion of steel fibers themselves was supposed as main mechanisms of corrosion inhibition from the experimental results.

Degradation of Steel Rebar Tensile Properties Affected by Longitudinal Non-Uniform Corrosion.

Rebar corrosion is the primary cause of the durability degradation of reinforced concrete (RC) structures, where non-uniform corrosion is the typical pattern in engineering. This study experimentally and numerically investigated the tensile degradation properties of non-uniform corroded rebars. Corrosion morphology was accurately determined by three-dimensional (3D) laser scanning techniques, studying the characteristics of longitudinal non-uniform corrosion. The results showed that the non-uniformity of corrosion increased with an increase in corrosion levels. From tensile tests, the differences in nominal stress-strain curves among rebars with similar average corrosion levels indicated that corrosion non-uniformity has appreciable effects on the tensile behavior of rebars. The residual load-bearing capacity of corroded rebars was dominated by the reduced critical cross-section, while residual ductility was associated with the cross-section loss throughout the entire length of rebars. The degradation relations of nominal yield and ultimate strength, ultimate strain, and elongation after fracture were better correlated to the maximum cross-section loss than to the average volume loss. Additionally, numerical calculation based on the cross-sectional areas of corroded rebars was conducted to evaluate the tensile behavior of non-uniform corroded rebars. Equivalent distribution models simulating the longitudinal non-uniform corrosion were proposed, on the basis of probability characteristics of cross-sectional areas, for practical application of the numerical method.

Experimental evaluation of the corrosion influence on the structural response of Gerber half-joints

The assessment of the Gerber half-joints (or saddles), widespread in the infrastructure heritage of different countries, is nowadays a topical problem since they are often affected by chloride corrosion phenomena due to their positioning under the deck joint. In this paper, the influence of steel rebar corrosion on the experimental response of Gerber half-joints is experimentally analysed and discussed. In particular, four elements were cast in Laboratory of University of Rome “Tor Vergata” two of which subjected to accelerated corrosion, and then tested up to failure. The specimens were designed with typical strut and tie models, with the aim of achieving different failure modes governed by the concrete crush or by the tensile rebar breaking. Particular care was devoted to the corrosion process, in order to simulate decay scenarios typical of these structures. The experimental outcomes, expressed in terms of load–displacement curves, crack patterns and failure mechanisms show that also medium-slight degree of pitting corrosion can cause great reductions in capacity and ductility of the saddles, modifying, in addition, their failure mechanism. Finally, from the experimental outcomes, the sensitivity of these peculiar structures, not only to the corrosion amount, but also to its spatial distribution among the different steel rebars, and its morphology (pitting or uniform corrosion) is clearly underlined. As a consequence, the necessity to accurately and properly account for the corrosion phenomenon in the structural assessment is remarked.

The impact of non-uniformity and resistivity on the homogenised corrosion parameters of rebars in concrete – a circuit model analysis

ABSTRACT When rebar corrosion parameters are characterised from an electrochemical polarisation curve, the non-uniform rebar surface conditions need to be considered. In this research, a circuit model was developed to simulate the polarisation behaviour of rebar in concrete. It is found that the resistivity of concrete leads to non-uniform potential on the rebar, which causes the polarisation curve of the entire rebar to deviate from the Butler–Volmer kinetics. This, in turn, leads to an overestimation of the Tafel constants and the corrosion current density. Such deviations are more pronounced with higher concrete resistivity, especially when the active and passive rebar surfaces have a similar area ratio. The study recommends using potentiodynamic scans of representative reinforced concrete samples of the field conditions or the calculated parameters using an averaging technique, such as the proposed circuit model, to obtain accurate E-I curves or parameters for electrochemical modelling and corrosion rate prediction.

Gaussian Mixture Model-Based Classification of Corrosion Severity in Concrete Structures Using Ultrasonic Imaging

Corrosion in reinforced concrete (RC) structures is associated with a reduction of the rebar diameter, loss of interfacial bond, cracking, and eventual spalling and probable collapse of the structure. The negative effects of corrosion on structural safety, durability, and longevity imposes significant costs on the national economy. Therefore, planned non-destructive testing (NDT) of concrete structures is essential to enhance the safety and economic sustainability of infrastructure. Previous work by the research group has established the capability of the ultrasonic Synthetic Aperture Focusing Technique (SAFT) as a tool for detection of rebar corrosion. This work extends the previous research towards application of statistical learning for ascertaining the corrosion severity through analysis of SAFT images of the rebar. Using features extracted from images, a Gaussian mixture model (GMM) is implemented to classify the severity of corrosion damage to the rebar. The results from the research positively demonstrate the potential of the proposed technique as an enabler for decisions pertaining to maintenance and timely repair of concrete infrastructural assets.

Degradation Mechanisms and Residual Mechanical Properties of Reinforcing Steel Bars Exposed to Natural and Artificial Corrosion – Review & Analysis

Reinforcement corrosion is the most problematic phenomenon and one of the main sources for the degradation of structures and infrastructures all across the world, that leads to their premature deterioration before design life has been attained. Therefore, the structural effects of rebar corrosion are crucial in determining the structural performance and residual strength of impaired structures. In the present work, the corrosion initiation mechanisms, corrosion products, corrosion types, corrosion consequences on structural performance and detrimental factors related to corrosion were presented in brief. Moreover, the propagation period and the main consequences on mechanical properties of steel and concrete are analyzed. Analyses of the available statistical data collected from literature were performed for 443 specimens. The findings are further interpreted from structural point of view, and deterioration equations for the mechanical properties of the corroded reinforcements are developed. The relations are well analyzed, leading to the definition of decay equation for yielding and ultimate stresses, and ultimate strain. It was found that the mass loss of 1% due to the rebar corrosion can cause the strength loss of 1.34%, 1.30%, and 3.54% respectively for yield strength, ultimate strength, and elongation. The suggested formulas can be applied in analytical and numerical structural applications.

Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars

In this research, methods of increasing the corrosion resistance of reinforced concrete were experimentally investigated. The study used silica fume and fly ash at optimized percentages of 10 and 25% by cement weight, polypropylene fibers at a ratio of 2.5% by volume of concrete, and a commercial corrosion inhibitor, 2-dimethylaminoethanol (Ferrogard 901), at 3% by cement weight. The corrosion resistance of three types of reinforcements, mild steel (STt37), AISI 304 stainless steel, and AISI 316 stainless steel, was investigated. The effects of various coatings, including hot-dip galvanizing, alkyd-based primer, zinc-rich epoxy primer, alkyd top coating, polyamide epoxy top coating, polyamide epoxy primer, polyurethane coatings, a double layer of alkyd primer and alkyd top coating, and a double layer of epoxy primer and alkyd top coating, were evaluated on the reinforcement surface. The corrosion rate of the reinforced concrete was determined through results of accelerated corrosion and pullout tests of steel-concrete bond joints and stereographic microscope images. The samples containing pozzolanic materials, the corrosion inhibitor, and a combination of the two showed significant improvement in corrosion resistance by 7.0, 11.4, and 11.9 times, respectively, compared to the control samples. The corrosion rate of mild steel, AISI 304, and AISI 316 decreased by 1.4, 2.4, and 2.9 times, respectively, compared to the control sample; however, the presence of polypropylene fibers reduced the corrosion resistance by 2.4 times compared to the control.

Performance of bacterial mediated mineralization in concrete under carbonation and chloride induced corrosion

Prevention of concrete structures from early deterioration under aggressive environments is a major challenge. The present study investigated the performance of bacterial-treated concrete structures under harsh conditions such as carbonation and chloride exposure. Improvement in the mechanical strength and reduction in penetration properties was recorded in bacterial-treated specimens. The maximum carbonation depth of 18.27 mm and reduction of pH (8.6) were recorded in control specimens during carbonation exposure (5% CO2) for 120 days, whereas significant resistance against CO2 diffusion and much-reduced carbonation depth was observed in BAC specimen (9.28 mm) and BSC (11.13 mm) specimens. Due to accelerated carbonation conditions, further increment in mechanical strength and reduced penetration was observed in control and bacterial treated specimens due to microstructure densification caused by carbonation reaction products. During chloride exposure (5% NaCl) for 120 days, the control specimen showed the initiation of rebar corrosion with Ecorr and Icorr values of −522.2 mV/SCE and 0.34 μA/cm2, respectively. However, bacterial-treated reinforced specimens (BARC and BSRC) significantly resisted the penetration of chloride ions. At the end of chloride exposure, BARC and BSRC specimens showed lower Ecorr values of −203.4 mV/SCE and −301.4 mV/SCE and Icorr values of 0.03 μA/cm2 and 0.02 μA/cm2, respectively. These results suggested that the biogenic treated concrete specimens resisted from the deterioration effects of chloride and carbonation exposure and improved their durability properties.

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.

A review on eminent application and performance of nano based silica and silica fume in the cement concrete

In last few years, the revolution of nanotechnology has escalated great in varied science streams. In the, study of effective utilization of Nano particles in construction industry has become a conspicuous one. While implementing the sustainability in construction, the adoption of nanotechnology has done a greater impact and there is still need more to explore. The Nano particles are usually possess incredible physical and chemical properties that enable it to use as a better constructionmaterials which help to enhance the properties like strength, durability and rheology of concrete and it also helps to counteract the environmental pollution. Additionally, the cement based materials which is prepared along with Nanomaterial helps to assess and examine the resistance towards deterioration in concrete and the extent of rebar corrosion. This paper reviews the literature on the nanotechnology application particularly in the construction industry. At first, the preliminary details of nanotechnology have been discussed and then, it exclusively focuses the effective nanoparticles like Silica fume and Nano silica which are proved as a ready thing to improve the property of concrete.

Decoupling free chloride and water ingress in concrete by a dielectric resonant sensor

The origin of rebars corrosion in concrete infrastructures is frequently associated with the ingress of chloride ions present in water. This is particularly the case of infrastructures located in marine environments or exposed to deicing salts. The present study aims at developing a radio-frequency dielectric sensor dedicated to free chloride ingress monitoring in a well-defined volume of the material. A resonant method operating in a wide frequency range is selected to separate the effects associated with the variation of the real part of the dielectric permittivity and tangent loss. As it will be shown, the method provides useful information on the presence of free chloride in concrete and can be used for the monitoring of chloride diffusion. For this purpose, considering the variation of the transmission parameter S12 value presents clearly some advantages with respect to the frequency shifts of resonances. This allows to decouple water and chloride content.

マンションの老朽化認定の評価方法に関する検討 その2：判定式および判定基準

For proffer the authorization standard of the act on facilitation reconstruction of deteriorated condominium buildings, studied on evaluation methods and criteria about buildings having the risk of falling cover concrete caused by rebar corrosion. Based on the concept of the binomial test, the number of the deteriorated reinforced concrete elements which highly probable to be the reinforcing bar corrosion higher, is determined by using the data from a survey of the actual buildings. And then, each number of survey points, the criteria for certification was set.

Life-Cycle Cost Assessment Using the Power Spectral Density Function in a Coastal Concrete Bridge

Recently, the repair and maintenance of structures has been necessary to prevent these structures’ sudden collapse and to prevent human and financial damage. A natural factor in marine environments that destroys structures and reduces their life is the presence of chloride ions. So regular health monitoring of concrete coastal buildings for on-time repair is essential. This study investigates the performance of the power spectral density (PSD) method as a non-destructive damage-detection method to monitor the location and amount of damage caused by chloride ions during a structure’s life using different approaches according to life-cycle assessment (LCA) and life-cycle cost assessment (LCCA). In this regard, chloride corrosion damage dependent on zone distance from seawater was first calculated to obtain the service life of each part of a coastal concrete bridge according to the conventional method. Based on rebar corrosion each year, the next stage forecasted the bridge’s concrete deterioration. The PSD method monitored the annual loss of reinforcement cross-sectional area, changes in dynamic characteristics such as stiffness and mass, and the bridge structure’s life using sensitivity equations and the linear-least-squares algorithm. Finally, according to the location and quality of damage in each year of bridge life until the end of life, LCC and maintenance and repair costs of the PSD method were compared with the conventional method. The results showed that this strategy was very effective at lowering and optimizing the costs of maintenance and repair caused by chloride corrosion.

Experimental Investigation of the Effect of Steel Fibers on the Flexural Behavior of Corroded Prestressed Reinforced Concrete Beams

Rebar corrosion and its consequences are one of the most common damages to reinforced concrete (RC) structures. In structures with greater sensitivity, such as prestressed reinforced concrete (PRC) structures, where steel elements, including prestressed tendons, play a more significant role in supporting the structure, the importance of this issue increases. Methods for repairing and reinforcing such structures have been developed, including incorporating fibers into the concrete mixture to improve its mechanical properties, particularly its bending resistance. This paper presents the results of an experiment that studied the influence of steel fibers on the flexural behavior of PRC beams subjected to accelerated corrosion. Twelve beams with a rectangular cross-section of 150 mm × 300 mm and a length of 2000 mm were fabricated. The steel fibers used in the experiment were corrugated and hooked-end types, with volume fractions of 0.5% and 1.0% in the concrete. Nine beams were subjected to accelerated corrosion testing, with three of them being without fibers and the remaining six being reinforced with steel fibers at volume fractions of 0.5% and 1.0%. Each group of three beams was exposed to three different levels of corrosion, namely 5%, 10%, and 15%. The specimens were tested after exposure to corrosion through a four-point bending load. The accelerated corrosion was induced using an electric current on the prestressing tendons. The results indicated that different levels of corrosion reduced the final bearing capacity and other behavioral characteristics of the specimen, including the amount of energy absorption, effective hardness, and midspan displacement. Adding fibers to the concrete mixture positively affects the compensation of these reduced capacities. Moreover, the amount of this compensation was directly correlated with the volume fraction of used fibers.