Steel Bars In Concrete Research Articles

Optimising the corrosion performance of hot-rolled steel bar in concrete

ABSTRACT To optimising the corrosion resistance mechanism of hot-rolled steel bar, the effects of different tempering temperatures and high-oxygen-rich oxidation times were studied by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, electrochemical and atmospheric corrosion tests. The thickness of the oxide layer of the rebar could reach 10 μm and rarely corroded after high-oxygen-rich oxidation at 850°C for 1 s, which exhibits superior corrosion resistance. The electrochemical test results showed that the I corr value after 1 s of high-oxygen-rich oxidation at 850°C was about 0.02 mA cm−2, which was 56.4% lower than that of the heated specimen at 685°C (0.045 mA cm−2). The results of Raman spectroscopy showed that the rust layer of the heated specimen at 685°C mainly consisted of α-Fe2O3, γ-FeOOH and α-FeOOH, and the oxidised layer after 1 s of high-oxygen-rich oxidation at 850°C mainly consisted of α-Fe2O3 and Fe3O4, which maintained the original oxidised layer morphology.

Effects of natural minor corrosion levels on mechanical property and bond anchorage behavior of CRB600H steel bars

Mechanical property tests and bond anchorage tests of the natural minor corrosion CRB600H steel bars were carried out, and corrosion levels of the steel bars were 0.0%, 1.8%, and 2.1%, respectively. The mechanical property test results showed that the yield strength of the CRB600H steel bars with corrosion levels of 1.8% and 2.1% was approximately 10% and 15% lower than that of intact steel bars, respectively. Still, the strains at the maximum force of the two corrosion levels showed no noticeable change with intact steel bars. The yield strength formula of the natural minor corrosion CRB600H steel bars was regressed. The load-slip curves, failure modes, bond toughness, and bond strength influential factors of natural minor corrosion bond specimens were analysed in the bond anchorage tests. Compared with the control bond anchorage specimens, the bond strength of the specimens with steel bar corrosion levels of 1.8% and 2.1% decreased by 5.4% and 6.3%, respectively. The ultimate bond strength of the natural minor corrosion CRB600H steel bars embedded in concrete was regressed. The development length of the natural minor corrosion CRB600H steel bars satisfying the reliability requirements was calculated using the first-order second-moment method. Based on the calculation results, the calculation formula of the development length for the natural minor corrosion CRB600H steel bars in concrete was regressed.

Experimental study and analytical model of the bond behavior of corroded reinforcing steel bars in concrete

The corrosion of longitudinal rebar and stirrups will cause serious degradation of 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 with electroosmosis/constant current/dry-wet cycling and pull-out tests. 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 also investigated. 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. The modified bond-slip constitutive model was applied to the cohesive element to establish a finite element model of the corroded pull-out specimens, and additional parameters were analyzed.

Corrosion Experimental Research on Local Damage of Epoxy-Coated Steel Bars in Concrete Under Marine Environment

Epoxy coating has been proven to protect steel bars from corrosion. However, the damage of epoxy coating is inevitable, and this may lead to more serious corrosion of steel bar. In order to study the corrosion resistance of steel bars with damaged epoxy coating, two groups of coating-damaged bar and one group of coating-intact rebar were designed, and six specimens were made. The influence of electrolyte concentration on the corrosion rate of steel bars was studied by setting different concentrations. After 30 days of accelerated corrosion, electrochemical data were recorded by the electrochemical workstation. The experimental result shows that the steel bars with coating damage have obvious polarization curve characteristics of corrosion, and corrosion resistance decreases obviously. According to the corrosion current and potential, the larger the damaged area of the coating, the faster will be the corrosion rate. According to the polarization curve data, the polarization resistance is modified, and the result is closer to the real polarization resistance value. The calculated corrosion rate shows that the corrosion rate of reinforcement is affected by both electrolyte concentration and coating damage area, and electrolyte concentration has a greater influence on the corrosion rate.

Lateral Stresses on Bond Strength of Deformed Steel Bars in Concrete: Analytical Model

Lateral Stresses on Bond Strength of Deformed Steel Bars in Concrete: Analytical Model

Interfacial shear stress analysis in single-lap adhesive joints with similar and dissimilar adherends under dynamic loading

Single-lap joints (SLJs) with similar and dissimilar adherends are extensively used in industrial applications. This paper aims to investigate the interfacial mechanical behavior of SLJs subjected to dynamic loading. The shear-lag model is employed to predict the mechanical behavior of SLJs. The analytical expressions of the interfacial slip, normal stress in the adherends and interfacial shear stress are derived for the SLJs with similar adherends by using the method of separation of variables. The Laplace transform method is applied to numerically simulate the dynamic response of SLJs with dissimilar adherends. Results obtained from the finite element simulation are consistent well with the predictive model. It is found that the more unbalanced the SLJ is, the more non-uniform distribution of interfacial stress is, thus reducing the load-bearing capacity of the SLJ. This inspires us to rationally design a balanced joint to improve the load-bearing capacity. While the emphasis of the present study is on the mechanical behavior of SLJs, the analytical model is equally applicable to the interface analysis of other structures (e.g. concrete-steel bar, fiber-matrix in the composites, etc.). Furthermore, this theoretical method can be also simplified to explain the stress transfer subjected to the (quasi-)static loading with approximately zero density or zero loading speed in the governing equation.

Effect of Low-Level Cyclic Loading on Bond Behavior of a Steel Bar in Concrete with Pre-Existing Damage.

Understanding the bond behavior of steel rebar in concrete is important in order to determine the performance of a reinforced concrete structure. Although numerous studies have been carried out by many researchers to develop a robust model for numerical analysis, no consensus has been reached as the bond behavior depends on hysteresis. In this study, the bond behavior of a steel bar in concrete with pre-existing damage is investigated under low-level cyclic loading. Based on the experimental bond stress and slip curve, a numerical model for finite element analysis to simulate the effect of low-level cyclic loading is proposed. The results from the numerical analysis show good agreement with the experimental data, including accumulated damage on stiffness and strength throughout entire load cycles.

Reinforcement Concrete Steel Bar Trim Loss Optimization Using Metaheuristics Particle Swarm Optimization and Symbiosis Organisms Search

Steel rebars for reinforced concrete usually stated in a form of bar bending schedule. In a project, an inefficient activity of cutting steel rebar can result a waste in the form of trim loss. This can lead to profit loss and cause an impact to environment. The optimization needs to be done in order to minimize the trim loss from the steel rebar cutting. Previously, there has been many studies on steel bar trim loss optimization using metaheuristic methods as well as studies on cutting pattern generator. However, if the steel rebar variation is too many, the cutting pattern generator will produce a large number of cutting patterns. Therefore, this study aims to solve the optimization problem by producing more efficient cutting pattern while still obtaining minimum trim loss at any conditions. The data used in this research is obtained from a real-life office project. In the process, the study will be comparing the performance of both PSO and SOS from each cutting patterns generator and conditions. The performance of the two methods is assessed from its minimum, maximum, average, standard deviation and the convergence graph of each iteration. The result shows that SOS performed better in finding the minimum trim loss on undersupply condition.

Durability study of stainless steel rebars in sea water mixing concrete

In order to study the durability of the stainless steel bars (SSRs) in the marine environment, 52.5 Ordinary Portland cement (OPC) and CA50 concrete specimens (CAC), ordinary carbon reinforcing steel bars, and S32304 duplex SSRs were used to make two concrete blocks. Electrochemical monitoring of steel bars in concrete was carried out in two marine environments, i.e. splash zone and full immersion zone, were simulated via alternating dryingwetting cycles and immersion in the simulated sea water solution. Test results show that the durability of concrete structure can be improved by using S32304 duplex SSRs and CA50 concrete specimens.

Modified Time-Dependent Model for Flexural Capacity Assessment of Corroded RC Elements

The corrosion of embedded steel bars in concrete is one of the severe deterioration processes that can escalate the risk and reduce the durability and lifetime of concrete structures. Based on the literature, simultaneous corrosion of longitudinal and transverse bar is considered to estimate section capacity. In this research, a flexible multi-stage approach is proposed to differentiate between corrosion levels on longitudinal and transverse reinforcement based on their corrosion initiating time. The result indicated that the multi-stage approach provides higher capacity and curvature for the sections. A significant reduction in reinforced concrete (RC) sections’ ductility after corrosion of confining bars and before starting corrosion of longitudinal rebars was observed, which illustrates the importance of stirrups corrosion effects on the sections’ ductility. In the higher values of corrosion intensity, confined concrete’s ultimate strain tends to reach the unconfined state. Using the energy-based method of calculating ultimate concrete compressive strain instead of approximate methods, a higher value of curvature ductility of corroded RC cross-sections is obtained.

Influence of stone powder content in machine-made sand on mortar concrete

The paper mainly studies that Influence of stone powder content in machine-made sand on mortar concrete. By changing the amount of stone powder in the machine-made sand, the ratio of cement to water and sand to grout, the change in the tensile value of the steel bar in concrete can be found. After a lot of test data to prove that the content of stone powder is 6%, the mortar ratio is 1: 2.5, the water-cement ratio is 0.40, the content of water-absorbent resin is 0.20, and the performance of the C40 concrete is good.

Numerical study on the effect of transverse crack self-healing on the corrosion rate of steel bar in concrete

Reinforced concrete is subject to degradation by cracking of the concrete and corrosion of the steel reinforcing bars. This study explores the influence of transverse crack self-healing on the corrosion rate of steel bars by developing a deformed mesh model. The dynamics of transverse cracking and steel bar surface potential distributions are also explored, and parameter sensitivity analysis of the corrosion current density is conducted. The results show that steel bars have a lower surface potential at transverse cracks than in non-cracked areas, which decreases with exposure time. Crack self-healing not only reduces the corrosion rate and surface potential of steel bars but also reduces the rate of chloride-ion diffusion into concrete. Increasing the thickness of the concrete's protective layer is an effective way to slow the corrosion of steel bars.

電気化学手法を用いたコンクリート中鉄筋の腐食状況を把握する方法の提案

電気化学手法を用いたコンクリート中鉄筋の腐食状況を把握する方法の提案

Quantitative determination of corrosion status of rebar by electrochemical parameters

In this paper, the relationship between electrochemical parameters and corrosion status of rebar was analyzed by measuring macro-current and potential difference of self-made anode ladder monitoring system under different environmental conditions.Laboratory tests show that the anode ladder monitoring system can better judge the corrosion status of steel bars and provide a basis for structural durability evaluation and remaining life prediction. Reinforced concrete is the most widely used building material in engineering. The durability of reinforced concrete structure gradually declines under the long-term action of unfavorable factors in using environment. At present, there are many "models" for predicting the durability life of concrete published in the world, and more researches are being carried out. The most studied "model" is the "model" related to corrosion, especially the relationship between reinforcement corrosion and concrete durability, is the most common and in-depth research. The problem of durability of reinforced concrete structures caused by corrosion of reinforcing bar has been paid more and more attention in engineering field. Early detection and diagnosis of reinforcement corrosion is an important prerequisite for durability evaluation, remaining service life prediction and maintenance scheme selection of reinforced concrete structures.The development of accurate and reliable on-site monitoring technology of reinforcement corrosion has become the focus of scholars at home and abroad. In order to monitor the corrosion of reinforcement in concrete, some electrochemical parameters need to be measured by sensors. These electrochemical parameters include: potential distribution, macrocurrent, concrete resistance, and so on. Among them, the measurement of macrocurrent is a relatively simple and easy method, which has been widely used in the measurement of reinforcement corrosion. Using this method, in recent years, many countries have developed anodic sensor systems for monitoring reinforcement corrosion, a typical non-destructive monitoring system for the embedded durability of TRAPEZOIDAL anode ladder concrete structure is developed by the Institute of Civil Engineering, Aachen University of Technology, Germany, the corrosion degree and depth of steel bar in concrete can be measured for a long time by embedding steel bar sensors with different depths in concrete, which has been put into engineering application in many countries. In this paper, a self-made multi-group anode ladder monitoring system is designed in the laboratory. The corrosion status of each anode steel bar and the change of electrochemical parameters are obtained by using the method of half-cell potential test in the environmental solution of different concentrations, the criterion of electrochemical parameters to determine the corrosion status of rebar was obtained.

Experimental study on bond performance of advanced material based on composite Portland cements developed for anchoring systems with post-installed reinforcement bars in concrete

Abstract This paper presents an assessment study on the bond performance of new advanced mortars based on composite Portland cements. These developed mortars are used as anchoring material for post-installed reinforcement steel bars in concrete. The anchoring mortars were developed by laboratory studies in the recent years and they met several performance criteria regarding the properties in plastic state as consistency, cohesiveness, stability and in hardened state as strength, rigidity, deformation volume and bond to support. Anchoring systems with post-installed reinforcement steel bars are obtained through installation of reinforcement bars into drill holes in hardened concrete and filled with flowable mortars which may be polymer or cement-based mortars. Generally, post-installed reinforcement bars are used to connect layers of new concrete to old concrete and also new members to old concrete members. So far, the most employed anchoring material is the polymer-based chemical resin which have some undisputed advantages, but the durability and long-term performance along the expected service life is questionable. Recently, inorganic-injection-type anchors have been developed in Japan. These anchors are composed of cement, aggregate and additive agents. In this study, the employed anchoring-mortars are exclusively based on hydraulic binder, namely composite Portland cements which are included in the European class of cement CEM II. These composite cements contain supplementary cementing materials (SCM) as fly-ash or limestone which are combined with Portland clinker at the manufacture. The bond strength of the reinforcement steel bars was assessed based on the prescriptions provided in the European assessment document EAD 330087 and EN 1881. These two technical norms are limited only to deformed reinforcement bars with characteristics in conformity with EN 10080 and designed based on EN 1992-1-1. Within this study, the shear load on the reinforcement bars post-installed into hardened concrete is not considered.

Strength and ductility performance of corroded steel bars in concrete exposed to 2D chloride ingress

AbstractThis paper presents the residual tensile strength test results of corroded high yield steel bars. Single steel bars were embedded at a cover depth of 20 mm in 150 × 150 × 625 mm long cracked concrete beam specimens made with 70/30 PC/FA and 50/50 PC/SL binders with a constant w/b ratio of 0.40. The steel bars were placed in the cross-section centre and near the orthogonal edge of the beams, and selected beam faces epoxy-coated in order to simulate, respectively, 1D and 2D chloride ingress. The beams were subjected to 2-week wetting (with 5% NaCl) and 2-week air-drying cycles in the laboratory for 110 weeks after which the corroded steel bars were extracted, assessed for corrosion morphology, and tested in tension for ultimate strength, fracture strength and ductility performance. The steel bars in concretes exposed to 1D chloride ingress had isolated corrosion pits while both general and isolated corrosion pits were observed in specimens exposed to 2D chloride ingress. The residual ultimate and fracture tensile strengths, and ductility of corroded steel reinforcing bars in concretes exposed to 2D chloride ingress are lower than those for steel bars in concretes exposed to 1D chloride ingress.

Effects of Corrosion to the Performance of Steel Reinforcement Embedded in Concrete under Different Aggressive Environments

The corrosion of reinforcement steel bars in concrete has been established as the major factor causing widespread degradation of concrete structures. Corrosion of reinforcement in concrete leads to reduction of good bonding between steel and concrete, decrease of steel cross-sectional area, cracking and loss of serviceability. This paper investigates the behavior and Performance of reinforcement bar embedded in concrete structure under a variety of aggressive environments. The study used 16 mm diameter reinforcement bars embedded in concrete with a uniform cover of 50 mm in 200 mm x 200 mm x 750 mm concrete beam, the curing period of concrete is 28 days. After completion of 28 days’ moisture curing period, the beam was loaded in flexure causing cracking of the concrete, thereby exposing the steel reinforcements. The cracked reinforced concrete beams were then immersed in different aggressive solutions of H2So4 (Sulfuric Acid), HCl (hydrochloric acid), HNO3 (hydrogen trioxonitrate), NaOH (sodium hydroxide) and NaCl (Sodium Chloride) for a duration of six months. At the end of this curing period, the embedded steel reinforcement was removed and cleaned off the attached concrete, and then tested for change in strength, diameter, and weight loss. The results obtained shows that corrosion affect steel reinforcement in concrete under HCl, H2SO4 and HNO3 with 15%,13% and 11% very high rate change in strength respectively. Also, the NaCl and HCl, were recorded with 15% and 11% very high rate effects on reduction/addition in diameter of steel reinforcement respectively. And finally, the HCl, and H2SO4 were recorded with 24.1% having the same and very high rate effects on reduction in weight (weight loss).

Characterization of steel reinforcement corrosion in concrete using 3D laser scanning techniques

In this work, to investigate the characteristics of non-uniform corrosion of steel bars more accurately, a new experimental method was proposed, which can rapidly generate non-uniformly distributed rust around steel bars in concrete. The precise average and critical cross-sectional area along the longitudinal direction of corroded steel bars were then obtained using the three-dimensional (3D) laser scanning. Based on critical section loss rate, the effects of non-uniform corrosion on the degradation of mechanical properties of steel bars were studied. The corrosion morphology, mechanical properties, and tensile failure patterns of uniformly and non-uniformly corroded steel bars were compared and elaborated.

Evaluation of Concrete Filled Steel Tube Column Confined with FRP

Abstract The main objective of this study was to assess the concrete-filled steel tube column confined with fiber-reinforced polymers (FRP) experimentally and numerically, where it can be used as a composite concrete column with high resistance and ductility. One of the weaknesses of reinforced concrete structures is the corrosion of steel reinforcement in concrete. This weakness can be resolved using FRP I-shaped composite structural sections instead of reinforcing steel bars in concrete. The composite profile was surrounded by the cylindrical concrete column and glass FRP (GFRP). A GFRP cylinder as a template acts in its place. In addition, it can provide a passive confinement for the composite column. Therefore, three columns have been tested in the experimental program under monotonic axial compressive loading. Furthermore, they have been numerically analyzed by means of a finite element method, employing ANSYS software (Ansys, Inc., Canonsburg, Pennsylvania). The ultimate capacity of each tested composite column has been compared to the theoretical capacity of the proposed numerical model. The results demonstrated that there was good compatibility and agreement between the experimental specimens and numerical analysis.

Using the Response Surface Method to Optimize Weight Loss of Steel Bar in Concrete Exposed to Chloride

The corrosion of reinforced concrete that is exposed to chloride corrosive environment reduces the effective life of concrete structures. The response surface method is based on the central composite design and is used to optimize the relationship among weight loss percentage, additive material percent, concrete cover and water-to-cement ratio. In this research, reinforced concretes made with independent variables, which include additive materials, such as glass, microsilica, and limestone powder, various concrete covers on steel bar and water-to-cement ratios. All samples are exposed to a 3.5 wt% NaCl corrosive environment for 180 days. Experimental methods are used to determine the corrosion of reinforced concrete using the weight loss percentage of steel bar, the chloride penetration rate in reinforced concrete, X-ray diffraction and scanning electron microscope of the steel bar. The result indicates that the least penetration of chloride occurs in reinforced concrete with 10% microsilica powder, 8-cm concrete cover and a water-to-cement ratio 0.45 with superplasticizer. The Minitab software with the response surface method model is used to determine the significance of the independent variables, and their interactions are tested by the variance analysis. The equation among weight loss percentage and independent variables with response surface method model is optimized. The response surface model shows an almost well-optimized performance with R2 (90%) for variables such as weight loss percentage of the steel bar and independent variables.