Rebar Corrosion Research Articles

Studies on Strength and Flexural Behaviour of Reinforced Concrete Beams with the Corroded Steel Reinforcements as a result of Sodium Chloride (NaCl)

Corrosion on embedded reinforcement is a serious structural failure which its deterioration are rarely concerned. Reinforcing steel are frequently found left unattended on corrosive environment where potential corroding substances might expose surface of rebar resulting in corrosion initiation. This paper reports result of a study conducted to investigate the impact of a rebar corrosion on flexural strength of reinforced concrete beam induced by 10.5% NaCl. Tensile test was conducted in this study to determine the degradation of tensile strength on rebar and was later utilized to analyse the reduction of maximum load bearing capacity on reinforced concrete beam. Both flexural rebar and tensile rebar were corroded using manual basting method which is carried out every day from 08.00 A.M-10 P.M (every 2 hours step). The corrosion area on flexural steel samples is at the maximum flexural strength area (400 mm in the middle of the span) and is later used on flexural testing purposes after casting with concrete, the tensile steel samples which is 600 mm span of rebar is later utilized for tensile testing purposes and is corroded in the middle of the span (185 mm in the middle of the span). Based on test results, it was observed that steel bar suffered significant loss of weights due to corrosion induced by 10.5% NaCl with respect to its corroding duration three and four months are 1.85% and 3.34% reduction of weight from its normal form and its tensile strength degraded, respectively, 6.78 % and 9.86%. Meanwhile, the reinforced concrete beam with corroded steel bars happened to experience degradation of maximum load capacity which are, respectively, 10% and 15% reduction for three and 4 months of corroding duration.

Observation of Rebar Corrosion in a 48-Year-Old RC Building under Airborne Salt Environment

Observation of Rebar Corrosion in a 48-Year-Old RC Building under Airborne Salt Environment

Bipolar electrochemistry for high throughput screening of localised corrosion in stainless steel rebars

The corrosion performance of stainless steel rebars is assessed by using bipolar electrochemistry. This method produces a quasi-linear potential gradient across the sample, with the technique providing rapid access to test for the nucleation and growth of pits across a wide range of applied potentials. The localised corrosion behaviour and resulting growth kinetics of Types 304L and 316L austenitic stainless steels (ASSs) are compared to Type 2101 and 2205 duplex stainless steels (DSSs). The difference in selective phase dissolution between pitting and trans-passive corrosion in DSSs is compared, with critical pitting potential, pit nucleation numbers, growth kinetics, volume loss, and aspect ratio of these four stainless steels discussed.

Durability degradation simulation of RC structure based on gamma process considering two-dimensional chloride diffusion and life probabilistic prediction

In this paper, based on the gamma process, a new method for predicting the life of reinforced concrete (RC) structures eroded by chloride is presented considering two-dimensional (2D) chloride diffusion. First, according to the chloride diffusion theory, an analytical model and a finite difference numerical model considering 2D chloride diffusion under the action of multiple factors were established. Based on this, the Monte Carlo method and method proposed in this study were employed to predict the initial rust time of RC structures eroded by chloride. Histograms of the initial rust time and probability density function obtained using the two methods mentioned above were compared and analyzed to verify the validity of the proposed method. Finally, the life prediction model of the RC structure considering the initial rust time T1, rust expansion cracking time T2, and time when the concrete surface crack width reaches the limit crack width T3 was established, and its applicability was verified through an analysis of an engineering example. The research indicates that the gamma process-based probability models can approximately predict the time required for rebar corrosion of an RC structure eroded by chloride considering 2D diffusion.

Physical and mechanical properties and time-varying model of concrete structures under the simulated tidal environment of the South China Sea island and reef

In view of the poorer durability of concrete structures under the tidal environment of the South China Sea island and reef, the effectiveness of durability improvement measures is studied. The deterioration test of concrete, corrosion and tensile test of rebar in concrete and bending tests of reinforced concrete beams after the simulated experiment are tested. The results show that under the simulated tidal environment of the South China Sea island and reef, with the increase of concrete strength grade and the mixing of corrosion inhibitor, the relative dynamic elastic modulus of concrete increases by 21.4% to 39.6%, the mass-loss rate of rebar decreases by 42.1% to 100%, the cracking moment of beams increases by 17.8% to 53.3%, the ultimate moments of beams increases by 1.6% to 15.5%, and the ultimate deflections of beams decreases by 7.1% to 28.6%. The mechanical properties of concrete first increase and then decrease with age, and the physical and mechanical properties of rebar decrease with age. Therefore, the mechanical properties of reinforced concrete beams will be improved briefly. In addition, the univariate quadratic polynomial time-varying model on the deterioration of corroded concrete and the power function time-varying model on the physical and mechanical properties of corroded rebar are proposed and verified. Furthermore, time-varying models of the mechanical properties of reinforced concrete beams considering concrete deterioration and rebar corrosion are also proposed and verified. This study will provide a theoretical basis and method for durability studies of South China Sea island and reef engineering.

Tracking spatiotemporal evolution of cementitious carbonation via Raman imaging

AbstractCarbonation of cementitious systems is an important phenomenon from both durability (rebar corrosion) and greenhouse emissions (CO2 sequestration) perspectives. Several analytical techniques are well‐established for measuring the kinetics of this dynamic phenomenon, ranging from measuring the pH change to quantifying the calcite content over time. However, the majority of these methods (with the exception of electron imaging) rely on bulk measurements which may miss the fine, microstructural changes that occur during carbonation. In this study, we investigate and evaluate the potential of Raman imaging to follow the spatiotemporal evolution of carbonation in cementitious pastes. By analysing mm‐scale maps (1 mm × 1 mm) at the micron‐scale resolution, we find that nearly ~40% of the sample surface was covered with calcite at the end of a 2‐week carbonation exposure. Simultaneously, the portlandite content declined from ~15% to 5% in the same period, suggesting portlandite consumption for the sake of calcite growth. Finally, the difference between the calcite growth rate and portlandite consumption rate strongly suggests simultaneous carbonation of CSH and ettringite—a finding that is in agreement with recent experimental investigations of carbonation kinetics. Overall, these new results on the spatiotemporal evolution of cementitious microstructure pave the way for utilizing Raman imaging for understanding dynamic phenomena in complex systems.

Corrosion prevention of steel rebar embedded in the cement mortar under accelerated conditions: Combined effects of phosphate and chloride ions

The present work focuses on the role of different amounts i.e. 0.295 and 2.95 kg/m3 ammonium phosphate monobasic (NH4H2PO4: APM) inhibitor and 1.2 kg/m3 NaCl as admixtures in cement mortar under wetting–drying accelerated condition to mitigate the corrosion of steel rebar. The results show that phosphate ions (from APM) react with NaCl and ordinary Portland cement (OPC) constituents to form Ca3(PO4)2 and Ca5(PO4)3Cl as hydration products, which led to make the cement mortar matrix dense and compact, and thus, improved the compressive strength after 28 days of water curing. Consequently, the phosphate ions in the cement mortar initiate the oxidation of embedded steel rebars immersed in 3.5 wt. % NaCl solution due to the formation of Fe(H2PO4)2, and FeHPO4 as intermediate. These could be transformed into stable and protective tertiary iron phosphate (FePO4) if optimum amount of phosphate ions is present but in the case of 0.295 kg/m3 APM, mostly phosphate ions consumed in the formation of Ca3(PO4)2 and Ca5(PO4)3Cl. Therefore, this sample became vulnerable to corrosion. On the other hand, 2.95 kg/m3 APM, the phosphate ions are significant and, thus, it helps to properly form the Ca3(PO4)2, Ca5(PO4)3Cl, FePO4 and maghemite (γ-Fe2O3).

Nonlinear Finite Element Analysis of Corroded Reinforced Concrete Beams

Corrosion in reinforcing bars is a major cause of concern for sustainability of Reinforced Concrete (RC) structures exposed to extreme environmental conditions. Various RC structures, such as bridges and buildings are adversely affected due to the rebar corrosion, reducing its global load carrying capacity and ductility. In order to ensure an earthquake resistant design of any structure, the ductility of structural members is of chief concern. However, corrosion of reinforcing steel in RC members reduces its seismic performance. Thus, for safety and economic viability of any RC structure, an effective maintenance and repair work strategy is necessary. Based on the strong column - weak beam design concept of RC frames, the beams are the first structural members to absorb damage due to earthquake. Thus, to carry out maintenance and repair work, structural health assessment of RC beams considering the effect of reinforcement corrosion is of utmost importance. The present study aims at establishing a relation between the amount of corrosion induced and its effect on the ductility of an RC beam. A 3D Finite Element (FE) model of an RC beam including the effects of corrosion for nonlinear performance assessment has been modelled in ABAQUS. The FE model is validated with past experimental study including the effects of corrosion. Modelling of uniform corrosion in reinforcement bars involves defining the loss of bond between rebars and concrete, inducing spalling stresses on concrete and reduction in the cross-section area of the rebars. Bond-slip model between surface of concrete and reinforcement has been incorporated through cohesive surface. Spalling stress for uniform corrosion is applied in form of outward uniform pressure on the reinforcement and concrete interface. The cracking of cover concrete due to corrosion along with the flexural cracking in concrete due to incremental loading are implemented together in the present study. A comprehensive FE model is developed in order to obtain correct assessment of corroded beams. As observed from the FE model, the failure mechanism of the considered corroded RC beam is observed to be mostly shear failure as the corrosion level increases. Concrete crushing at the center of the RC beam is identified at the failure point of the beam due to corrosion induced damage. Evolution of displacement ductility index with respect to corrosion is determined for an RC beam based on the numerical study. It has been observed that the displacement ductility index of the beam is reduced significantly after considering a corrosion level of about 12%. Hence, the present study is an effort to establish a relation between structural performance of RC beams and level of reinforcement corrosion, which will be useful in proactive maintenance and repair work for corroded RC beams.

An Experimental Approach to Evaluate the Effect of Reinforcement Corrosion on Flexural Performance of RC Beams

The corrosion of reinforcing steel in concrete has been reported as one of the main durability problems of reinforced concrete (RC) structures exposed to chloride, carbonation or both. To investigate the structural performances of RC structures subjected to corrosive exposure, the corrosion of rebars embedded in concrete is accelerated to induce a targeted degree of reinforcement corrosion in a short time duration. Several earlier researchers have attempted to develop a setup to induce the accelerated corrosion of steel bars in concrete structures. However, the induced corrosion has not been simulative of the naturally occurring corrosion of steel in concrete, causing a lack of accuracy in the test results. In this study, an attempt was made to develop a novel approach that could be utilized to induce required degrees of reinforcement corrosion following a natural pattern. To demonstrate the efficacy of the proposed setup and procedure of introducing uniform reinforcement corrosion, RC beam specimens were designed, cast, and corroded to three different corrosion levels. After inducing reinforcement corrosion, the beams were tested under flexural stress, and then the corroded bars were extracted to measure the mass loss due to corrosion. The visual inspection and gravimetric and flexural test results showed the capability of the proposed corrosion setup and procedure to induce the targeted uniform corrosion of steel bars, simulating a real-life scenario and facilitating the evaluation of the effect of reinforcement corrosion on the flexural performances of RC beams with very high accuracy.

Sustainability assessment of reinforced concrete beams under corrosion in life-span utilizing design optimization

Minimizing the economic and environmental burden is considered the most critical goal in sustainability assessments, the best approach of which is to implement optimization. In this research, the life-span design of corroded reinforced concrete (RC) beams was addressed through cost and carbon dioxide (CO2) footprint optimizations. Accordingly, the cost-optimized and CO2 footprint-optimized sections were obtained in the presence of corrosion. Displacements were then calculated using a neural network trained on the basis of finite element (FE) modeling results. In addition, the number of required modeling efforts was ensured in key model detection using the Taguchi design containing six control factors of rebar corrosion percentage, beam section height and width, concrete compressive strength, steel yield stress, and reinforcement diameter. Two coding languages were used, in parallel, in order to avoid possible errors and increase accuracy, the results of which were observed to be practically identical. Also, the regression plots displayed an overall R-value of 0.999, indicating the high accuracy of the applied neural network. In addition, the FE modeling results were verified with several experimental RC beams in the literature in terms of load-displacement curves. The results of the numerical approach were in good agreement with the experiments. Furthermore, the FE outputs were compared to those of the neural network demonstrating a relatively good accord. The results of the proposed methodology were found to be more favorable than the previous studies, with a significant cost savings of more than 22%. In this respect, the optimization process was so well balanced that the CO2 footprint resulting from the cost-optimized section was less than 3% different than that from the CO2 footprint-optimized section. Similarly, the cost obtained from the CO2 footprint-optimized section was less than 4.5% different compared to that obtained from the cost-optimized section. It was also revealed that the most economical sections not only do not lead to more pollution, but they are almost the cleanest ones. According to the cost optimization results, short span beams (up to 8 m) were recommended to be designed without regarding corrosion at first. On the other hand, considering the anticipated corrosion from the beginning of the design process is more economical for beams with longer spans (longer than 9 m).

Studies on corrosion monitoring of reinforced concrete in a chloride environment using an embedded solid-state reference electrode

In the present study, the corrosion status of steel rebars embedded in concrete with various cover thicknesses and exposed to conditions simulating a marine environment (3.5 % NaCl) was monitored by an embedded solid-state reference electrode (ESSRE). Electrochemical impedance spectroscopy (EIS) results confirm that corrosion initiation of the steel rebars occurred at 702, 1144, 1469 and 2454 h for C10, C15, C20 and C30 concrete specimens, respectively. Further, the relationship between the free and bound chlorides for C15, C20 and C30 specimens were defined by Temkin isotherm. In addition, the time to crack initiation was predicted by the El Maaddawy model. This study has successfully demonstrated that the solid-state MnO2 electrode is reliable for monitoring the onset of steel rebar corrosion in concrete by a non-destructive method.

Integration of laser level survey, photogrammetry and GPR to examine the deterioration of Roman mosaics: A case study of Venus house, Volubilis, Morocco

AbstractVolubilis was founded in the second century B.C. and was one of the largest cities on the fringe of the Roman Empire. In 1997, it was listed as a world cultural heritage site by United Nations Educational, Scientific and Cultural Organization (UNESCO) and is one of the most important archaeological sites of Morocco. Volubilis is renowned for its large number of mosaic floors. Among the major mosaics of Volubilis, and undoubtedly the most remarkable ones given their aesthetic and the variety of themes they hold, are found in the house of Venus. These mosaics have been restored between the 1940s and 1950s, but unfortunately, most of these restorations are past due or nearing their ends. Today, the mosaic floors are becoming unleveled, fractured and separated from their surrounding walls. These deteriorations can be triggered by many factors including inadequate foundation, a clayey soil beneath it sensitive to moisture and the heaving of the thin concrete layer due to the expansion of the soil. The corrosion of the reinforcing bars within these concrete slabs is enabling these deformations as well. The objective of this study is to examine the causes of the mosaics' deterioration by integrating three techniques including a laser level survey, photogrammetry using a small unmanned aircraft vehicles (UAV) and ground‐penetrating radar. The methodology adopted herein can generate documentation that can be used during the preparation and decision making prior to any restoration. The restoration should not only be focused on the visible tesserae on the surface but must also consider the entire layer of the mosaics. These techniques were applied to several mosaics in Volubilis, yet only two mosaics within the house of Venus were selected for this study, and the following findings were accomplished: (1) Void spaces were found beneath the mosaic floors, (2) presence of sinking and heaving of concrete slabs and (3) potential corrosion of rebars. The three methods used in this study were in perfect concurrence in showing how the settling of the concrete slab was directly related to the deteriorations visible on the mosaic surface.

Effect of Pore Physical and Chemical Microstructure Properties on Durability and Rebar Corrosion of Self-Compacting Concretes Containing Silica Fume and Metakaolin

Effect of Pore Physical and Chemical Microstructure Properties on Durability and Rebar Corrosion of Self-Compacting Concretes Containing Silica Fume and Metakaolin

Classification of Corrosion Severity in Concrete Structures Using Ultrasonic Imaging and Linear Discriminant Analysis

The deterioration of concrete structures due to rebar corrosion is a key issue affecting the safety and service life of civil infrastructure. Reinforced concrete (RC) structures in coastal areas are subjected to harsh environmental conditions that cause rebar corrosion. From the perspective of safety, repair, and structural rehabilitation, it is essential to ascertain the level of corrosion severity and associated damage in RC structures through non-destructive evaluation (NDE) techniques. In this study, the potential of pattern recognition techniques for ascertaining the severity damage at various stages of rebar corrosion in concrete samples was explored. A contact ultrasonic compressional wave transducer pair with 250 kHz centre frequency was used as source and reflected signals from the rebar were acquired using a tied-together scanning approach. To expedite the corrosion process in the laboratory, accelerated corrosion of the embedded rebar was employed. The synthetic aperture focusing technique (SAFT) was applied to reconstruct the image of the concrete subsurface from the acquired B-scans. Two approaches, i.e., the Mahalanobis distance (MD) and linear discriminant analysis (LDA), were adopted; both methods correctly classified the level of corrosion severity and damage to the concrete. The developed pattern recognition techniques can, therefore, be potential tools for generating important information towards economical and timely repair of damaged concrete structures affected by rebar corrosion.

Experimental investigation of corrosion effect on bending deflection of shield tunnel segment containing transverse cracks

AbstractCorrosion of the steel rebar will be generated in the cracked concrete of the shield tunnel during the operation period, which will reduce the bending performance of the tunnel segment. In this study, the effect of the rebar corrosion on the bending deflection of the shield tunnel segment that contains transverse cracks is investigated by experimental tests. The initial transverse cracks of the segment are simulated by a bending load device, and the galvanostatic method is used to simulate the corrosion of the segment rebar. The degradation of the segment bending deflection after the rebar corrosion process is measured and compared with the non‐corroded segment. The results reveal that when the depth of the transverse crack does not exceed the thickness of the protective layer, the corrosion of the rebar has little effect on the bending degradation. However, when the width and depth of the transverse crack reach approximately 1.2 and 210 mm, respectively, the degradation rate of bending deflection begins to increase rapidly.

Bond-Slip Model of Corroded Reinforced Concrete and Its Application in Members

ABSTRACT The corrosion of longitudinal rebar and stirrups will cause serious degradation to the bond performance between steel bars and concrete. To investigate the impact of both longitudinal rebar and stirrup corrosion on the bond behavior, 35 reinforced concrete (RC) pull-out specimens were subjected to accelerated corrosion tests of electroosmosis-constant current-dry wet cycles and pull-out tests, and then the influence laws of the degree of corrosion of the longitudinal reinforcement, degree of corrosion of the stirrups, cover thickness, stirrup spacing and longitudinal reinforcement diameter on the bond performance were studied. The bond behavior between corroded steel bars and concrete was analyzed from the aspects of corrosion form, failure mode and bond strength. Subsequently, based on the experimental data, a modified bond-slip constitutive model that considers the design parameters, stirrup corrosion and longitudinal rebar corrosion was built and verified. Finally, based on the established modified bond-slip constitutive model, the corroded RC column was simulated, and the accuracy of the established modified bond-slip constitutive model was verified at the component level.

Parametric Study to Evaluate the Geometry and Coupling Effect on the Efficiency of a Novel FMM Tool Embedded in Cover Concrete for Corrosion Monitoring

Rebar corrosion represents a major threat to the durability of reinforced concrete structures, primarily in marine environments. Various Non-Destructive Evaluations (NDE) have been developed to detect rebar corrosion; although most of these have delivered successful results, a lack of reliable techniques for proper corrosion prognosis still remains. Under the French Research Agency (ANR) project’s “LabCom OHMIGOD” framework, we introduce here a novel embedded tool to evaluate the level of cover concrete contamination from aggressive agents responsible for causing corrosion. This tool is divided into two parts: a reactive part exposed to corrosion, and a permanent part protected against corrosion. Using magnetic materials in both parts entails “Functional Magnetic Materials” (FMM) and generates a Magnetic Observable (MO). Through the evolution of corrosion on the reactive part, its magnetic properties become affected, which in turn modifies the MO. By means of regular monitoring of MO variations, it is possible to evaluate the aggressive agent ingress. Consequently, by using a variety of FMM tools placed at different concrete depths, it is possible to indirectly evaluate the rebar corrosion risk. This paper presents a numerical model of the tool employing Ansys software. The underlying objective is to investigate tool accuracy through its key parameters, namely, geometry, relative distance to the receiver, coupling effect, and border effect from the rebar. Simulation results demonstrate that by choosing an efficient geometry for the reactive part (25 mm × 25 mm × 1 mm) and position for the tool (between 1 and 3 mm), both a sufficient MO variation range and a negligible coupling effect can be obtained when the FMM is more than 5 cm from any ferromagnetic material.

A predictive phase-field approach for cover cracking in corroded concrete elements

Steel bar corrosion is a crucial problem in reinforced concrete structures. Corrosion, being one of the most prevalent deterioration mechanism in concrete elements, has a significant impact on the structure's serviceability and durability, since the cross section of the steel reinforcement is reduced and the mechanical steel performances deteriorate. Additionally, residual material is created as a result of the steel oxidation process, and the volume occupied by the reinforcement grows, forcing the concrete cover to crack and spall. The carbonation-induced rebar corrosion and the subsequent cover cracking are simulated via the usage of a predictive model which combines the concrete carbonation process with the phase-field technique for brittle fractures. First, the carbon dioxide transport within the concrete is described using the Fick’s second diffusion law. Then, the corrosion process is estimated via the electrochemical kinetics equations providing the associated steel expansion. The steel deformation and strain are calculated with the Faraday Law. Finally, a phase field approach for brittle material is used to reproduce rupture in the concrete cover. The developed model is validated against examples available in literature and representative examples are illustrated, describing the capability of the proposed approach to replicate the cover cracking in concrete.

Corrosion of rebars in recycled glass concrete under tropical marine environment

AbstractThis study demonstrates the potential use of recycled powder glass as cement replacement to prepare durable concrete and avoid infrastructure corrosion in tropical marine environments using limestone as fine and coarse aggregates. Samples for corrosion measurements were prepared with #3 (∼9.5 mm) bars and without reinforcement for carbonation, chloride penetration, and mechanical strength tests. Powder glass was used as partial cement replacement by 0 %, 5 %, 10 %, and 15 % (weight percent). Over two years, the corrosion behavior of rebars was recorded through corrosion potential measurements and linear polarization resistance. In addition, carbonation depth and chloride penetration were analyzed from samples that were not reinforced. Results showed that replacing cement with glass does not change the mechanical strength at 28 days, but after 90 days of curing showed an increment as a function of time and recycled glass powder amount. The chloride penetration and the carbonation front are reduced substantially. Consequently, a moderate corrosion level was observed when the corrosion onset was established. Excellent corrosion protection was identified for a 0.70 water to cement ratio and 5 % cement replacement.

Study on rust layer distribution of cracked segment at tunnel arch waist under stray current and chloride ion corrosion

AbstractDuring subway operation, cracks may appear at the arch waist of tunnel segment surface. Under the acceleration of stray current, chloride ion in groundwater will penetrate into the surface of rebar through cracks, resulting in segment rebar corrosion and structural stiffness degradation. In this article, the rebar corrosion calculation model of tunnel segment contained transverse crack under stray current and chloride ion was established, and the coupling of electric field and chemical field in cracked concrete was realized. The effects of chloride ion content and input voltage on the rust layer distribution of cracked segment were studied. The results shows: Under the action of stray current and chloride ion, the 3D rust layer of cracked segments at the arch waist can be described by Gaussian mixture function. In the longitudinal direction, the rust layer at the crack section is located at the peak of the rust layer curve, and the increase of chloride ion content has a greater influence on the rust layer shape than the increase of stray current. When the chloride ion content and stray current are doubled, respectively, the maximum rust layer thickness of rebar will increases by 34% and 16%, respectively. In the circumferential direction, the nonuniform coefficient of elliptical rust layer will change with the increase of segment crack width and chloride ion content, but it will not be affected by stray current intensity.