Steel Bars In Concrete Structures Research Articles

Pullout behavior of the steel-FRP composite bar with the anchor head made of the grout-filled steel tube

Steel-fiber reinforced polymer composite bars (SFCBs) offer a viable solution to replace steel bars in concrete structures and mitigate their corrosion issues. However, the inflexibility of SFCBs weakens their bond with concrete. This study addressed this gap by employing a steel tube connected to the end of SFCB using grout as its anchor head. Subsequent pullout tests were conducted on SFCBs with and without anchor heads, exploring variables such as SFCB diameter, anchorage length, anchor-head diameter, concrete-cover thickness, and spiral ratio. Various failure modes were observed, including SFCB rupture, and concrete cracking with and without stirrups. Anchor heads significantly enhanced the bearing capacity and bond stiffness of SFCB specimens, notably reducing splitting forces. Augmenting anchorage length and anchor-head diameter improved the bond stiffness of SFCBs in concrete. The anchor-head diameter should not be less than 2.4 times the SFCB diameter. Furthermore, an increase in concrete-cover thickness or spiral ratio notably heightened the concrete’s resistance to cracking. The contribution ratio of bond force increases with the anchorage length and decreases with the slip, SFCB diameter, and anchor-head diameter. A predictive method for determining concrete-cover thickness and spiral ratio was developed to ensure SFCB pullout specimens steer clear of concrete splitting.

Quantitative Characterization of Passivation Process of Steel Reinforcement in Concrete towards Durability against Anticorrosion Based on Electrochemical Methods

The passivation behavior of steel reinforcements in concrete is significantly influenced by the environment, concrete pore solution, and the passive film formed on the steel surface. The present study used electrochemical methods to successfully characterize the passivation process of steel reinforcements in concrete. The passivation behavior of commonly used HRB400 steel reinforcement material in concrete was studied using various electrochemical parameters quantitatively. As the soaking test time increased, the OCP gradually increased and stabilized after 5 days, indicating that the steel electrode transitioned from an active state to a passive state in the simulated liquid environment of concrete. The steel reinforcement developed a protective passive film that reduced its tendency to corrode. According to EIS, after soaking for one day, the steel electrode showed significant early passivation, indicated by an increase in its arc diameter. The WE arc gradually increased in the first 5 days of immersion, suggesting dynamic passive film formation and development. Beyond 5 days, the passive film stabilized with minimal further changes in its impedance spectrum, indicating carbon steel electrode passivation. The working electrode’s impedance increased significantly on the fifth day, and gradually increased slightly after 10 days, indicating comprehensive coverage by the oxide film. Attributed to the growth and development of the oxide film, the electrode resistance reached a relatively stable state after the fifth day. The shift in corrosion potential offers an indication of the level of passivation of the steel reinforcements. The decrease in the anode Tafel slope and increase in the corrosion potential indicate the formation and stabilization of an oxide film on the steel surface, which is beneficial for its long-term durability in concrete structures. By analyzing the OCP, EIS, and dynamic potential polarization curve method data, it is possible to gain insights into the passivation behavior of steel reinforcements in concrete structures. This study aims to provide a basis for optimizing the corrosion protection of steel reinforcements in concrete structures. The significance of this study lies in a deep understanding of the passivation behavior of steel bars in concrete, providing a theoretical basis for improving the durability and lifespan of steel bars in concrete structures.

Effects of eccentric loading on performance of concrete columns reinforced with glass fiber-reinforced polymer bars.

Glass fiber-reinforced polymer (GFRP) reinforcements are superior to traditional steel bars in concrete structures, particularly in vertical elements like columns, and offer significant advantages over conventional steel bars when subjected to axial and eccentric loadings. However, there is limited experimental and numerical research on the behavior of GFRP-reinforced concrete (RC) columns under eccentric loading having different spacing of stirrups. In this study, six specimens were cast under three different values of eccentricities (25mm, 50mm, and 75mm) with two groups of stirrups spacing (50mm and 100mm). The experimental results showed that by increasing the eccentricity value, there was a reduction in the load-carrying capacityof the specimens. The finite element ABAQUS software was used forthe numerical investigation of this study.The results from the finite element analysis (FEA) were close to the experimental results and within the acceptable range. The maximum difference between theexperimental and FEA resultswas 3.61% for the axial load and 12.06% for the deformation.

Performance of doubly reinforced concrete beams with GFRP bars

Abstract The study focused on examining the behavior of six concrete beams that were reinforced with glass fiber-reinforced polymer (GFRP) bars to evaluate their performance in terms of their load-carrying capacity, deflection, and other mechanical properties. The experimental investigation would provide insights into the feasibility and effectiveness of GFRP bars as an alternative to traditional reinforcement materials like steel bars in concrete structures. The GFRP bars were used in both the longitudinal and transverse directions. Each beam in the study shared the following specifications: an overall length of 2,400 mm, a clear span of 2,100 mm, and a rectangular cross-section measuring 300 mm in width and 250 mm in depth. To apply loads for testing, two-point static loads were placed at the middle third of the beam’s span, creating a shear span of 700 mm in length. The beams were categorized into three groups depending on the GFRP longitudinal reinforcement ratio in the tension and compression zones of the section. GFRP bars with a diameter of 15 mm were employed as longitudinal reinforcement, while closed GFRP stirrups with a diameter of 8 mm at 100 mm were utilized as transverse reinforcement throughout the structural element. Test results have indicated that the ultimate load capacity of doubly GFRP-reinforced concrete beams varies compared to singly GFRP-reinforced beams. The range of variation observed is between an increase of 8% and a decrease of 4%. Accordingly, the contribution of the GFRP bars in the compression zone is insignificant and could be ignored in design calculations. It was observed that the loading level at which crack spacing stabilized ranged between 31.3 and 87% of the experimental failure load. It seems that the crack spacing decreased with the increase in the reinforcement ratio.

Investigation of Circular Hollow Concrete Columns Reinforced with GFRP Bars and Spirals

Glass fiber-reinforced polymer (GFRP) reinforcements are useful alternatives to traditional steel bars in concrete structures, particularly in vertical structural elements such as columns, as they are less prone to corrosion, and impart increasing strength and endurance of buildings. There is limited research on the finite element analysis (FEA) of the structural behavior of hollow glass fiber-reinforced polymer reinforced concrete (GFRPRC) columns. The hollow portion can be used for the service duct and for reducing the self-weight of the members. Numerical analysis of the compressive response of circular hollow concrete columns reinforced with GFRP bars and spirals is performed in this study. This article aims to investigate the axial behavior of hollow GFRP concrete columns and compare it with that of solid steel reinforced concrete (RC) columns as well as hollow steel RC columns. The Abaqus software is used to construct finite element models. After calibration of modeling using an experimental test result as a control model, a parametric study is conducted. The columns with the same geometry, loading, and boundary conditions are analyzed in the parametric study. It is resulted that the hollow GFRP concrete columns provide a greater confinement effect than the solid steel RC columns. The average variation in the ultimate axial load-carrying capacities of the experimental results, from that of the FEA values, is noted to be only 3.87%, while the average difference in the corresponding deformations is 7.08%. Moreover, the hollow GFRP concrete columns possess greater axial load and deformation capacities compared with the solid steel RC columns.

Corrosion potential of coated steel bar embedded in sea-water mixed mortar

Corrosion of embedded steel bars in concrete structures is the most impactful deterioration case in the world therefore many researchers and engineers are looking for the unknown mechanism related to the occurrence process, the effect of the damaged structures to its capacity and serviceability, and the intervention methods to control the rate of corrosion nowadays. One of the most prevalent liquid materials used in concrete is freshwater. However, the lack of freshwater for basic requirements in certain regions necessitates the adoption of an alternate material. Seawater, abundant in Indonesia, has the ability to substitute freshwater in concrete mixtures. However, its high concentration of chloride ions might raise the risk of corrosion in reinforced concrete structures. The laboratory experiment was proposed to find the empirical test result of the performance of corrosion prevention to the seawater mix RC structures. Three type of cements (PPC, PCC, and PPC-PCC mixture) were used as binder and two type of protection (steel coating and no coating) were applied in this research. One day after specimen casting, it were demolded and cured under water condition until 28 days. After that, the cylindrical and beams specimens were tested and the cubical specimens were exposed to three conditions (air-dry, wet, and dry-wet cycle) until a half-year and the half-cell potential test was conducted periodically every week. Based on the results, it demonstrated that the steel coating is the most suitable corrosion prevention method and PCC is recommended to maintain the corrosion potential stable to be passive.

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.

Experimental and theoretical study on bonding performance of FRP bars-Recycled aggregate concrete

Fiber Reinforced Polymer (FRP) bars-Recycled Aggregate Concrete (RAC) can alleviate the environmental damage caused by the massive exploitation of natural aggregates and solve the problem of corrosion of steel bars in concrete structures. However, the bonding performance of FRP bars-RAC determines whether it can replace the original reinforced concrete structure in buildings. In the current study, FRP bars-RAC bond performance factors and bond strength theory have been comprehensively investigated through pull-out tests performed for a large number of FRP bars-RAC. In this context, the effects of Recycled Aggregate (RA) replacement rate (0 %, 25 %, 50 % and 100 %), FRP bar diameter (8 mm, 10 mm and 12 mm) and RAC cover thickness (20 mm, 30 mm, 40 mm and 70 mm) on the bond strength, fracture mode, and bond-slip curve of FRP bars-RAC were investigated. Overall, the findings showed that the inclusion of RA reduces the ductility of concrete. Increasing the recycled aggregate replacement rate resulted in gradual losses in bond strength and ultimate slip of FRP bars. In addition, the increase in the diameter and anchor length of the FRP bars led to a gradual decrease in the bond strength between the FRP bars and the RAC. Nevertheless, through increasing the strength of RAC and the thickness of the concrete protective layer, the bond strength between FRP bars-RAC can be enhanced. Through the analysis of test data, the bond strength model of FRP bars-RAC was established based on the thick-walled cylinder theory. In the model, the diameters of FRP bars, rib inclination angle, rib spacing, RAC strength, and protective layer thickness were taken as variables. While the high degree of agreement between the values calculated from the model and the measured values revealed the success of the established modeling, the ratio of the calculated value of the model to the experimental value was measured as 0.66–1.

Corrosion evaluation of carbon steel bars by magnetic non-destructive method

ABSTRACT Reinforced concrete structures undergo various degradation processes, mainly rebars corrosion. Recently, magnetic non-destructive tests have been used to study the steel components used in concrete structures. This paper proposes a non-destructive method, based on the electromagnetic induction technique, capable of identifying corrosion in steel bars. Therefore, through signals obtained from sinusoidal and triangular waveform excitations, magnetic hysteresis loops were determined in steel bars of 5.0, 6.3, 8.0, 10.0, 12.5 and 16.0 mm diameters at 0, 10 and 20 mm depths. Magnetic tests were performed in uncorroded steel bars and in bars that have been exposed to corrosion by the salt spray test. The magnetic responses, remanence, coercivity and the maximum values of hysteresis curves obtained were organised into classes for uncorroded and corroded bars of each steel diameter, totalling 12 classes. A statistical analysis of the experimental results has been performed, and a detailed analysis of the data has also been performed by using the pattern classification techniques, namely, principal component analysis, Karhunen–Loéve transformation, Gaussian classifier and artificial neural network. The results show that the investigated method has great potential of becoming an electromagnetic non-destructive technique for the identification of corroded steel bars in concrete structures.

Experimental Research on Material Behaviour of Glass Fiber Reinforced Polymer Bars in Tension

Glass Fiber Reinforced Polymer (GFRP) rebars have been widely used to solve the corrosion problem of steel bars in concrete structures. It has been produced as a lightweight and corrosion-resistant than steel reinforcement in many structural applications. They are regarded as a promising substitute for steel bars in concrete infrastructures. It is necessary to test GFRP bars to fully understand their material properties to ensure the safe and efficient use of the material. In this study, five specimens of each type of GFRP bars with a diameter of 6, 8, 10, 12, and 14 mm were tested under tension. Therefore, a total of 25 samples were examined from the same manufacturer. According to ASTM’s recommendations (D7205/D7205M-06) for tensile tests of GFRP bars, the diameter and thickness of the steel pipes for both ends were considered in the preparation of the test specimens to keep the GFRP bars consistent and aligned throughout the experiment. The experimental test results included the stress-strain curves, tensile strength, ultimate strain, and modulus of elasticity. The study showed an accurate result that indicated the tensile strength of the GFRP bars can be expressed by a linear distribution. For a bar diameter of 10mm, the length to diameter ratio L e /d b =8 showed a maximum tensile to compressive strength ratio. In the failure results of the test, there were two-mode failures of GFRP bars: fracture failure and pull-out failure of GFRP bars. Most of the specimens had GFRP bar fracture failures, only two specimens (GBT1-10-2 and GBT1-10-3) were damaged due to the pull-off of the GFRP bars which was not a typical failure mode. Keywords: GFRP Bars, Tensile Test, Stress-Strain Curve, Fracture Failure DOI: 10.7176/CER/13-5-05 Publication date: August 31 st 2021

Design Study of Steel Fibre Reinforced Concrete Shaft Lining for Swelling Ground in Toronto, Canada

Reinforced concrete (RC) is a widely used construction material around the world. RC has many advantages in terms of structural stability. However, the reinforcement of RC requires extensive labour costs. Steel fibre reinforced concrete (SFRC) has been widely studied to replace steel bars in concrete structures over the decades. However, most underground structures, such as tunnel lining, are usually designed using conventional RC for long-term stability due to unexpected geotechnical characteristics, such as directional and depth-dependent varied lateral pressure, earthquakes, groundwater, and time-dependent swelling behaviour. In this paper, an alternative design of shaft structure using SFRC, based on the original RC designed data in the Toronto region, was studied to evaluate the feasibility of SFRC replacing conventional RC. A key geological feature of the site is that the bedrock is comprised of Georgian Bay shale, which exhibits long-term time-dependent deformation (TDD). The capacities of RC and SFRC for the shaft lining were calculated based on the Canadian concrete design codes CSA A23.3 and RILEM TC 162-TDF, to assess the benefit of adding steel fibre, and several analytical solutions were used to calculate the applied load on the lining. A specialised TDD constitutive model in Fast Lagrangian Analysis of Continua (FLAC) 2D was developed to estimate whether the optimum installation time of the shaft lining, based on the geological reports, is appropriate under swelling behaviour, and evaluate the resultant long-term stability. The calculated hoop thrust and bending moment for several loading cases were within the capacity of the SFRC shaft lining. The numerical analysis demonstrated that the proposed lining installation time could be reduced, despite consideration of the long-term TDD behaviour.

Effects of environmental Water-Level changes and bidirectional electromigration rehabilitation on durability of concrete

Steel bars in concrete structures can become severely corroded in chloride salt-containing environments, which can shorten the service life of the structure. Bidirectional electromigration rehabilitation (BIEM), a novel type of durability repair technology used on reinforced-concrete (RC) structures experiencing chloride corrosion, involves applying an electric field to discharge chloride ions from concrete and simultaneously applying a rust inhibitor to the steel surface. In this study, indoor experiments were performed to analyse the migration of chloride ions and the corrosion inhibitor in RC structures in the atmosphere and water-level-fluctuating areas. An electroosmotic device enhanced the efficiency of BIEM. The BIEM was particularly effective in wet–dry areas and inside the electroosmotic device. More than 90% of the chloride ions on the steel surface were removed within 15 mm of the electroosmotic device, and the chloride ion migration rate on the steel surface was 40%–60%. Scanning electron microscopy revealed that the surface of the steel bars was smooth after BIEM treatment, with no obvious pitting or corrosion products. The service life of concrete was calculated according to the prediction method of concrete. It can be expected that the concrete enters the early warning zone after 15 years and the rust zone after 30 years.

Evaluating Stress-Strain Properties of Reinforcing Steel for Reinforced Concrete

Abstract The stress-strain properties of reinforcing steel for reinforced concrete are related to the design of reinforced concrete structures. In China Codes, steel bars for the prestressing of concrete (PCB) and hot-rolled ribbed bars in grade 600 (HRB600) were introduced to design concrete structures. However, the stress-strain properties of high-strength steel bars are not defined by the standard. In this paper, reinforcing steel for reinforced concrete in a China Code included hot-rolled plain bars (HPB), HRB, cold-rolled ribbed steel bars (CRB), PCB, hot-rolled wire rod for prestressed steel (PSW), and screw-thread steel bars for the prestressing of concrete (PSB), which were tested under axial tension. Results showed that the reinforcing steel was divided into two types: HPB, HRB, and CRB600H with yield plateau and PCB, PSW, PSB, and CRB550 without. Based on the experimental results, the tensile mechanical indicators of reinforcing steel were determined and the stress-strain curves prediction models of reinforcing steel were developed. The stress-strain curves prediction models of steel bars can predict the tensile properties of steel bars accurately, which can be used in finite element software to simulate the tensile properties of steel bars and explore the stress development of steel bars in concrete structures.

Numerical simulation of steel corrosion in chloride contaminated concrete

Corrosion is one of the main reasons for the degradation of reinforced concrete structures, especially of those exposed to a chloride-contaminated environment. To study the effect of chloride ions on the corrosion of steel embedded in concrete, two electrochemical parameters, namely, the anodic Tafel slope and potential, were theoretically analyzed and semi-empirically modified by the concentration of chloride ions in concrete. Subsequently, a numerical model that couples the mass transport and electrochemical corrosion process was established to simulate the transport of chloride ions and the evolution of steel corrosion that occurred simultaneously in the concrete. Based on the proposed numerical model that incorporated the appropriate electrochemical parameters, the corrosion current density and corrosion potential were obtained numerically and they coincided well with the experimental data. Finally, the proposed model was applied to study the chloride ion distribution as well as the corrosion current density around the cross-section and circumference of the steel bar in concrete members with single or multiple steel bars. The results indicate that the proposed numerical modelling method can be used to predict the corrosion-initiation time, as well as the development of the morphology of the corrosion profile of steel bars in concrete structures.

Effects of chloride ions on carbonation rate of hardened cement paste by X-ray CT techniques

Corrosion of steel bars in concrete structures is initiated as a result of concrete carbonation and/or chloride intrusion, and influenced by their interaction. This paper presents an experimental investigation into the effect of chloride ions on carbonation of cement paste by means of X-ray CT techniques and mercury intrusion porosimetry (MIP), which is benchmarked by the conventional phenolphthalein method. A group of the cement paste cylinders with different amounts of chlorides ions were manufactured and cured before they were subjected to an accelerated carbonation process in a conditional cabinet regime for different ages. The carbonation front of the cement paste was first evaluated using phenolphthalein method. This was followed by an investigation of microstructure evolution of the cement paste using XCT and MIP techniques. The experimental results show that the carbonation of a cement paste increases with its water to cement ratio and with carbonation ages, but decrease with its amount of chloride ions. In particular, it has been found that increases of chloride ion of a cement paste refine its porous structures, decrease its porosity and eventually mitigate its carbonation rate. The relevant results can be referred to for durability design and prediction of reinforced concrete structures.

Modeling of carbonation in tensile zone of plain concrete beams damaged by cyclic loading

Concrete in bridge structures is constantly subjected to CO2 ingression as well as fatigue damage caused by repeated vehicle loads. This paper presents a general modeling process for carbonation in fatigue-damaged concrete beams. The key point of considering effects of fatigue damage on concrete carbonation is determining diffusivity of CO2 in fatigue-damaged concrete. To do so, residual strain was chosen as an indicator to evaluate fatigue damage states and a Fictitious Distributed Crack Mode of fatigue-damaged concrete beams was proposed to incorporate residual strain into diffusivity of CO2. Subsequently, the partial differential carbonation equation for fatigue-damaged concrete beams was established and a Keller Box Scheme was implemented to solve it. The numerical solutions were verified by accelerated carbonation tests for concrete beams damaged by cyclic loading. Finally, through parametric study for usual ranges of various influencing factors, a simplified carbonation model for fatigue-damaged concrete beams was proposed. Model predictions of carbonation depths were in acceptable agreement with test results as well as numerical solutions. The simplified model could be used to design concrete cover and help accurately predict or estimate initiation time of corrosion of steel bars in concrete structures.

Corrosion of zinc‐coated reinforcing bars in tropical humid marine environments

PurposeReinforcing steel bars in concrete structures exposed to tropical marine atmospheres experience very high corrosion rates due to several environmental factors. The aim of this research was mainly to elucidate if zinc‐coated rebars may delay the onset of corrosion and/or extend the service life of infrastructure in the tropics, as the approach is promising in other atmospheres.Design/methodology/approachHot‐dip zinc‐coated and plain steel rebars were embedded in concrete cylinders made with local aggregates and having four different water‐to‐cement ratios. Samples were exposed during 24 months at the marine breeze in a coastal site in the Gulf of Mexico. The corrosion behaviour of zinc‐coated and uncoated rebars was monitored by means of corrosion potential and linear polarization resistance techniques. Also, carbonation penetration and the chloride ingress were measured and correlated with the corrosion behaviour.FindingsOnly under the worst case conditions (concrete with 0.7 w/c ratio) did galvanized steel experience corrosion initiation. It was shown to resist higher chloride levels than uncoated steel and extended the onset of corrosion.Originality/ValueThe effectiveness of the zinc‐coated bar for corrosion control is controversial and its use mainly is supported by accelerated tests or application in cold or subtropical environments. This research showed the corrosion behaviour in an extremely corrosive tropical zone.

Study of aging and embrittlement of microalloyed steel bars

The aging of hooks, anchors, and other bent reinforcing steel bars in concrete structures are considered in modern international standards. Rebend test procedures have been designed in order to predict the aging embrittlement susceptibility by submerging bent reinforcing bar specimens in boiling water. Subsequently the bars are rebent or straightened in order to determine the loss of ductility or embrittlement of the aged material. The present work considers the influence of carbon, sulfur, and niobium on the performance of reinforcing bars in rebend tests of 300 heats of microalloyed steel bars with a variety of compositions. The microstructural evidence and the statistical results clearly indicate the strong influence of carbon and sulfur on rebend failure, while niobium-rich precipitates contribute to the hardening of the ferrite grains during aging.