Steel Rebar Research Articles

Retraction Note: Investigation of bond-slip in reinforced steel rebar using concrete damage-plastic model

Retraction Note: Investigation of bond-slip in reinforced steel rebar using concrete damage-plastic model

The role of overstrength in welded joints for rebar substitution in damaged RC columns

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University’s laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated.

Construction of Ce3+ modified conversion film on oxide scale of plain steel rebars to greatly enhance the corrosion resistance

Steel rebars with oxide scale, which is usually rich of defects, are widely used in industry. On the surface of the oxide scale, it is difficult to prepare a conversion film with desirable corrosion resistance because of the acidity of conventional conversion solutions. In this work, a sol–gel solution (pH = 11) was employed to retard the diffusion of cerium ions avoiding the formation of cerium salt precipitates at room temperature. After treatments, the diffusion of cerium ions would be accelerated and a protective conversion film would form to repair natural defects on oxide scale of steel rebars at a higher temperature. This strategy can not only avoid the peeling of the oxide scale by the acid solution, but also prevent a large amount of non-uniform precipitation of the film-forming Ce3+ ions. The conversion film@oxide scale was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve (PPC) etc. It is found that the corrosion resistance of the prepared film@oxide scale was enhanced greatly when the concentration of added cerium ion (III) was 0.5 M, with pH adjusted to 11. After 30 days of immersion, Rct of surface treated rebar is more 180 times that of blank sample. The excellent corrosion resistance is closely related to the double-layer structure of the prepared sol-gel film, especially an about 2 nm inner layer of cerium oxide.

Effect of carbonation on the corrosion behavior of steel rebar embedded in magnesium phosphate cement

Magnesium Potassium Phosphate Cement (MKPC) as a protective binder for steel rebars has been well-established. However, corrosion performance of steel rebars in MKPC subjected to carbonation is still unknown. This investigation aimed at revealing the impact and mechanism of carbonation on corrosion performance of steel rebars in MKPC using electrochemical techniques and surface analyses. The findings indicate that, unlike Portland cement (PC) system, carbonation positively influences corrosion performance of steel rebars when embedded in MKPC, as demonstrated by comparable (M/P = 7) or even higher (M/P = 12) corrosion resistance values. Under carbonation, the ingressive CO2 reacts with Mg-bearing phases in MKPC to form nesquehonite with a higher pH, while the MgO still keep supersaturated. The resultant increase in pH facilitates formation of ferrous oxide and iron phosphate/borate within oxide film developed on steel surface, which enhances protective capability of oxide film and consequently improves the corrosion resistance of the steel rebars.

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.

Case Study on Replacing Steel Rebars with CFRP in Concrete Structures

Case Study on Replacing Steel Rebars with CFRP in Concrete Structures

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.

Axial bearing capacity and ductility of seawater sea sand coral aggregate concrete (SSCC) columns reinforced with hybrid GFRP and corrosion resistant rebars

The shortage of fresh water and river sand resources and steel corrosion are becoming increasingly prominent in engineering construction. Seawater sea sand coral aggregate concrete (SSCC) and corrosion resistant reinforcement are promising materials in replacement of conventional concrete and steel in building structures in island and reef construction. This study investigated the axial compression performance of GFRP (glass fiber reinforced polymer) and corrosion resistant rebars hybrid reinforced seawater sea sand coral aggregate concrete columns. A total of eighteen short columns were tested for axial compression performance, including three reinforcement ratios (1.01%, 1.56%, 2.26%) and 5 reinforcement types (pure GFRP reinforcement or G, pure stainless steel reinforcement or S, pure epoxy coated steel rebar (ECSB) reinforcement or E, GFRP-stainless steel reinforcement or GS and GFRP-ECSB or GE). The failure modes of the column are recorded and analyzed, and the axial bearing capacity and ductility are calculated and analyzed. Results show that the bearing capacity of columns is positively correlated with the reinforcement ratio. Generally, the bearing capacity of S-SSCC column and E-SSCC column are not significant different, but both are larger than that of G-SSCC column. The bearing capacity of hybrid reinforcement GS-SSCC and GE-SSCC column is between S-SSCC column and G-SSCC column. Meanwhile, it indicates that the theoretical calculation results of bearing capacity agree well with the experimental results. The ductility analytical results exhibit that the studied column specimens have the highest ductility when the reinforcement ratio is 1.56%. Among different reinforcement types, the ductility of G-SSCC is the smallest and the GE-SSCC and GS-SSCC column show improved ductility compared with G-SSCC columns.

Performance Prediction of Hybrid Bamboo-Reinforced Concrete Beams Using Gene Expression Programming for Sustainable Construction.

The building and construction industry's demand for steel reinforcement bars has increased with the rapid growth and development in the world. However, steel production contributes to harmful waste and emissions that cause environmental pollution and climate change-related problems. In light of sustainable construction practices, bamboo, a readily accessible and eco-friendly building material, is suggested as a viable replacement for steel rebars. Its cost-effectiveness, environmental sustainability, and considerable tensile strength make it a promising option. In this research, hybrid beams underwent analysis through the use of thoroughly validated finite element models (FEMs), wherein the replacement of steel rebars with bamboo was explored as an alternative reinforcement material. The standard-size beams were subjected to three-point loading using FEMs to study parameters such as the load-deflection response, energy absorption, maximum capacity, and failure patterns. Then, gene expression programming was integrated to aid in developing a more straightforward equation for predicting the flexural strength of bamboo-reinforced concrete beams. The results of this study support the conclusion that the replacement of a portion of flexural steel with bamboo in reinforced concrete beams does not have a detrimental impact on the overall load-bearing capacity and energy absorption of the structure. Furthermore, it may offer a cost-effective and feasible alternative.

Bond properties between lapped steel rebars and UHPC under direct tension

Ultra-High Performance Concrete (UHPC) is a highly advanced cement-based composite that offers higher mechanical properties and exceptional durability over Normal-Strength Concrete (NSC). Bond properties between steel rebars and UHPC are the key to designing reinforced UHPC structures. The goal of this study was to characterize the bond properties between lapped steel rebars (uncoated) and UHPC. A total of 20 modified pullout tests having two-row lap splices were performed to examine the variation of diameters of 10, 14, 20, 25 and 32 mm. It was shown that the splitting of UHPC covers was a dominant failure mode, and samples with smaller bar diameters exhibited good ductility. Higher bond strengths were found in samples with smaller bar diameters. Specifically, bond strengths in samples having diameters of 20 mm, 25 mm, and 32 mm showed reductions of 14.8 %, 27.6 %, and 35.2 % in comparison to those featuring a diameter of 10 mm. The distributed curves of bond stress with two peaks were identified when maintaining a lapped length of four times the bar diameter. Furthermore, the mechanical model for lapped steel rebars in UHPC and the theoretical equation for calculating the bond-splitting strength and minimum lapped length were presented and validated by the available studies.

Experimental study with DIC technique on the bond failure of structural concrete under repeated reversed loading with different amplitude

The bond between deformed steel rebar and concrete plays a critical role against seismic action, thus it is important to capture the dynamic bond loss and establish the bond-slip model with cyclic loading. To explain the macroscale performance such as bond-slip relationship and establish the bond strength model, it is meaningful to capture the mesoscale and local behaviors between ribs and concrete. In this paper, pull-out specimens with rebar embedded in concrete and small windows excavated in the cover concrete are adopted with DIC technique to monitor the strain variation and crack development along the interfaces under static and reversed loading of different amplitude. From the test, it is found that DIC is an effective approach to obtain the localized characteristics including the normal and shear deformations. Through parametric study, the effects of concrete cover depth and the existence of stirrups on bond deterioration in terms of both global and local behaviors are studied. Interestingly, the global slip and local crack-width show synchronically increase under the pulling-out action, which demonstrates that the macroscale behaviors could be clarified from mesoscale measurement with the aid of DIC technique.

Interphase corrosion inhibition mechanism of sodium borate on carbon steel rebars in simulated concrete pore solution

Sodium borate (Na2B4O7) corrosion inhibition mechanism was studied on carbon steel rebars in 0.6 mol/L Cl– simulated concrete pore solution (SCPS) at different temperatures and concentrations. Electrochemical testing including cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky plots were utilized to understand the influence of inhibitor concentration and temperature on the thermodynamics of the adsorption and activation processes. It was found Na2B4O7 imparts corrosion protection due to the formation of a 3D Fe–B–O stable interphase passive film, achieving an inhibition efficiency up to 86%. This can be attributed to the film having a lower donor current density and less vacancies, according to the Mott–Schottky tests. The formed interphase passive film was more stable and compact with less point defects compared to the blank due to Na2B4O7 adsorption, this phenomenon was substantiated using the atomic packing factor, film thickness, and Mott–Schottky plots. It was revealed, using adsorption isotherms, that Na2B4O7 interacted with the surface via physiochemical adsorption, creating a thinner/compact passive film composed of a rhombohedral calcite-type structure. SEM, XRD, and XPS were used to illustrate that Na2B4O7 aides in the formation of a stable double-layered net structure Fe2O3/FeBO3 passive oxide film. Finally, an interphase corrosion inhibition mechanism of Na2B4O7 was proposed.

Corrosion Resistance Enhancement of Reinforced Concrete in Marine Environment by Partial Replacement of Black Rice Husk Ash

In this work, the black rice husk ash (BRHA), a pozzolanic material, was used as a partial replacement in concrete with the weight percentages of 0%, 10%, 20%, 30%, 40% and 50% for enhancing the corrosion resistivity in the marine environment. The compressive strength, corrosion by accelerated corrosion test by impressed voltage (ACTIV), and chloride (Cl−) penetration of concrete specimens were investigated after 28 days of curing. For corrosion and chloride penetration analyses, the 20% of BRHA replacement specimen was the most effective concrete specimen because the deformation was not observed within 19 days of the test. The cement specimens with lower BRHA percentages were cracked due to the development of stress by the rust formation. For higher BRHA percentages, the protective Fe2O3 was dissolved due to the acidic environment caused by higher chloride accumulation in the cement specimens. The steel rebar was then aggressively attacked by the chloride and it was finally broken. Therefore, the optimization of the BRHA percentage is needed to minimize corrosion. However, the longer curing time of 20% BRHA replacement specimen is required for increasing the compressive strength because its compressive strength is slightly lower than the standard.

Cost-effective methods for flexural strengthening of one-way RC precast flat slab bridges in South Carolina

In South Carolina, there are one-way precast RC flat slab bridges that were constructed in the 1950 s for H-10 and H-15 design trucks (lower than the current design standards) and have deteriorated over time. To ensure public safety and continued usage, strengthening the bridges is imperative. Various methods exist for flexural strengthening, including application of UHPC from above and strengthening from below with FRP, steel plates, and external prestressing. However, these methods may compromise the ductile behavior of the slabs and they are also challenging, labor-intensive, and expensive to apply. The innovation of this paper lies in investigating the methods for strengthening from above that have the potential to improve both the flexural strength and ductility of slabs, while offering advantages in terms of ease of implementation and cost-effectiveness compared to existing methods. Five slabs obtained from decommissioned bridges in South Carolina were tested under monotonic loading to failure: one reference slab; one slab strengthened with steel channel sections from above; one slab strengthened with steel plate sections from above, and two slabs connected at the joint by near surface mounted steel rebars for strengthening. Strengthening the slabs with steel channel sections from above effectively improved the flexural strength and ductility of the slabs while being more economical and easier to implement than other methods of strengthening. Following strengthening, some slabs may require overlays to cover the steel sections and ensure that bridge traffic may go on them. Even after accounting for reduction in strength gain due to the deadload of the overlay, a positive net strength gain in measured peak moment was observed in the strengthened slabs. The moment capacities of the slabs, as determined through design calculations following the ACI 318–19 code, exhibit a good agreement with the measured peak moment observed in experimental tests, thus validating their reliability as a dependable alternative to solely relying on experimental tests.

Development of green and sustainable corrosion inhibitor for steel rebar in chloride-polluted simulated concrete pore solution using seed extract of Psoralea corylifolia (Badranj Boya)

Abstract The present research aims to develop green and sustainable corrosion inhibitors based on plant extract. Herein, we have screened the inhibitory performance of Psoralea corylifolia (Badranj Boya) (PCS) seeds in chloride-polluted simulated concrete pore solution (SCPS) for the protection of steel rebar. Electrochemical experiments manifest that PCS can restrain reactions of the cathode and anode of steel rebar. The results reveal that the inhibitory performance magnitude is 95.1 % at 75 mg/L dosing amount after 72 h dipping time. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) examination support the creation of an inhibitive layer of PCS over the steel rebar surface. Furthermore, adsorbed PCS over the steel rebar was justified via X-ray photoelectron spectroscopy (XPS). Finally, PCS is a green and long-term efficient corrosion inhibitor for concrete structures.

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

Investigation on influence of corrosion and protective coating on steel rebars on flexural performance of RC beams

Self-centering capacity of RC columns with smart plastic hinges of martensitic NiTi SMA bars

The objective of this study was to examine the self-centering capacity of reinforced concrete (RC) columns with martensitic shape memory alloy (SMA) bars in the plastic hinge region. To achieve this, three RC columns were prepared: one was conventional and the other two had SMA bars in the plastic hinge zone. The columns had a diameter of 400 mm, height of 1400 mm, and aspect ratio of 3.5. The 400 mm long SMA bars were connected to the steel rebars using specially devised couplers. A cyclic lateral load was applied at the top of the columns, and the lateral displacements along the height of the columns and the corresponding forces were measured during cyclic lateral loading. The strain in the SMA bars was also measured. The RC column with SMA bars exhibited a plastic hinge around the couplers, thus concrete damage from cracking was concentrated at this site. This was completely different from the failure mode of the conventional RC column. The SMA bars in the column were in an elastic state, whereas the steel rebars yielded inside the couplers. The RC column with SMA bars exhibited excellent self-centering capacity, and its displacement recovery ratio was approximately 95% at a drift of 5%. However, its energy-dissipation capacity was lower than that of the conventional RC column. The equivalent damping ratio of the RC column with SMA bars was approximately 3% after 1.75% drift. It is conjectured that the excellent self-centering of the RC column with SMA bars was caused by the elastic behavior of the martensitic SMA bars.

Corrosion state assessment of the rebar: Experimental investigation by ambient temperature and relative humidity

One of the most crucial elements affecting the durability and stability of concrete construction is steel rebar corrosion. The primary cause of structural degradation in buried rebar is the generation of corrosion byproducts and the resulting volume expansion. The increased volume of the rebar within the concrete can exert tensile forces, leading to crack formation and concrete spalling. Therefore, the evaluation and prevention of rebar corrosion play a crucial role in ensuring the longevity and stability of structures, addressing concerns regarding their service life and structural integrity. The objective of this study is to measure and analyze the voltage potential at the target corrosion rate of the steel rebar. To achieve the precise target corrosion rate of the rebar, image processing was employed to measure the corrosion rate. By eliminating light reflection and noise, image processing enabled precise calculations based on the extracted corroded portions of the rebars. To evaluate the influence of temperature and relative humidity on the surface corrosion rate, voltage potential measurements were conducted. The results revealed that the voltage potential exhibited minimal sensitivity to temperature variations. However, it displayed a significant response to changes in relative humidity. Notably, smaller-diameter steel rebars exhibited increased variations in voltage potential in accordance with changes in the rate of relative humidity. This can be attributed to the small diameter and cross-sectional size of the steel, which facilitate electron mobility and, consequently, exhibit a high sensitivity to environmental changes.

Two-Way Time-Dependent Prestress Losses of Prestressed Concrete Containment with Bonded Prestressing Strands

Prestressing plays a pivotal role in ensuring the tightness and integrity of prestressed concrete containment in nuclear power plants. The prestress loss reduces the compressive stress in concrete resulting from the prestressing strands and increases the risk of containment leakage under severe accident conditions. Therefore, the accurate prediction of prestress loss is essential for the design and in-service management of prestressed concrete containment. Unlike one-way beams or girders in building structures and bridges, two-way prestressing systems are used in prestressed concrete containment. In the current simplified method for evaluating time-dependent prestress loss, the interaction of concrete creep in two directions resulting from the two-way prestressing strands and the influence of the steel liner and mild steel rebars in two directions are neglected. In this study, based on the principle of creep superposition, the age-adjusted effective method for the creep estimation of concrete, and considering concrete shrinkage, concrete creep, and the relaxation of prestressing strands, as well as the influence of the steel liner and mild steel rebars in two directions, a sectional analysis is performed for prestressed concrete containment with bonded prestressing strands, and equations for calculating the two-way time-dependent prestress losses are derived. The results of the two-way time-dependent prestress losses predicted by the derived equations are compared with those of tests in the literature, and great agreement is achieved. Finally, a case study is given to show the application of the proposed method for the prediction of prestress loss in prestressed concrete containment in the nuclear power plant.

FRP RC beams by collected test data: Comparison with design standard, parameter sensitivity, and reliability analyses

In the last few years, there has been a significant increase in the utilization of Fiber Reinforced Polymer (FRP) materials as reinforcing elements in concrete structures due to their excellent properties. Unlike traditional steel rebars, FRP rebars do not rust, which helps to prevent degradation and deterioration of the concrete structure over time. This growth has resulted in a rise in the application of design regulations for FRP-reinforced concrete (RC) members. There are currently no European standards that offer suggestions about FRP RC structures. This paper aims to assess the load- carrying capacity and deflection of FRP RC beams with large number of test data available against design standards. The results are compared with ACI 440.1 R-06 specifications and EC2 concepts available in fib Bulletin No. 40. It was found that both ACI and EC2 underestimate the shear flexural capacity. Both design codes presented 38% and 62% of the collected data that overestimated and underestimated the calculation of the deflection, respectively. A parameter influence analysis is performed considering the database collected, and a reliability analysis based on Annex D EN 1990 (2002) is conducted. The reliability analysis allowed suggestion new partial safety factors values of 1.45 and 1.65 for moment and shear capacities, respectively, which can be used by design engineering communities.