Concrete Rebar Research Articles

Effect of Combined Chloride-Sulfate Solutions and Associated Cation Types with Sulfate Ions on Corrosion Performance of Steel Rebar in Concrete

Abstract The rapid deterioration of reinforced concrete structures located in marine environment because of chloride-generated corrosion remains a matter of serious concern. The marine environment mainly comprises chloride (Cl−) ions, sodium (Na+) ions, sulfate (SO42−) ions, and magnesium (Mg2+) ions. The existence of SO42− ions with Cl− ions influences the chloride-generated corrosion behavior because of the binding of these ions with hydrated C3A in concrete. In this research, an experimental study has been conducted to assess the performance of embedded rebar (carbon steel) against corrosion in normal concrete subjected to chloride (NaCl) and combined chloride-sulfate (NaCl with MgSO4 and NaCl with Na2SO4) solutions for 27 months of exposure periods. The results showed that the corrosion performance of the embedded rebar was influenced by SO42− ions and its associated cation (Na+ and Mg2+) type. The SO42− ions associated with Na+ cation resulted in higher corrosion current density (Icorr) as compared to Mg2+ cation in the concomitant presence of Cl− ions. The presence of Cl− ions significantly increased the corrosion rate of steel rebar, whereas the presence of SO42− ions (irrespective of associated cation, i.e., Na+ and Mg2+) in the exposure solution hindered the effect of Cl− ions on increasing the corrosion rate of steel. The established empirical relationship obtained between half-cell potential (E0), and Icorr predicted well the Icorr values obtained from ordinary portland cement with 20 % fly ash concrete used in the present research work and with the results obtained by different researchers in the literature.

Investigation into corrosion-induced bond degradation between concrete and steel rebar with acoustic emission and 3D laser scan techniques

Corrosion-induced bond degradation of deformed steel rebar in concrete is experimentally investigated with acoustic emission (AE) and 3D laser scan technique. Concrete specimens were fabricated and subjected to direct pullout test after being corroded to different levels. The number and width of cracks present during the corrosion tests and the pull-out tests were recorded. The energy released during the pullout tests were captured with AE probes, and the frequency characteristics was analyzed. After pullout tests, the surface morphology of corroded steel rebars was determined with a 3D laser scanner. A modified bond deterioration model was proposed and the parameters associated with the model were analyzed. Results indicated that two types of AE signals were acquired during pullout tests: concrete cracking in high frequency range of 35 ~ 41 kHz and steel-concrete friction in low frequency range of 3 ~ 15 kHz. The bond strength and the bond-slip characteristics depend upon the level of corrosion as well as the number and width of cracks. The reduction factor of the bond-slip model exponentially decreases as a function of the average cross-sectional area loss and linearly decreases with an increase of the rib area loss.

A Preliminary Numerical Study to Compare the Physical Method and Machine Learning Methods Applied to GPR Data for Underground Utility Network Characterization

In the field of geophysics and civil engineering applications, ground penetrating radar (GPR) technology has become one of the emerging non-destructive testing (NDT) methods thanks to its ability to perform tests without damaging structures. However, NDT applications, such as concrete rebar assessments, utility network surveys or the precise localization of embedded cylindrical pipes still remain challenging. The inversion of geometric parameters, such as depth and radius of embedded cylindrical pipes, as well as the dielectric parameters of its surrounding material, is of great importance for preventive measures and quality control. Furthermore, the precise localization is mandatory for critical underground utility networks, such as gas, power and water lines. In this context, innovative signal processing techniques associated with GPR are capable of performing physical and geometric characterization tasks. This paper evaluates the performance of a supervised machine learning and ray-based methods on GPR data. Support vector machines (SVM) classification, support vector machine regression (SVR) and ray-based methods are all used to correlate information about the radius and depth of embedded pipes with the velocity of stratified media in various numerical configurations. The approach is based on the hyperbola trace emerging in a set of B-scans, given that the shape of the hyperbola varies greatly with pipe depth and radius as well as with velocity of the medium. According to the ray-based method, an inversion of the wave velocity and pipe radius is performed by applying an appropriate nonlinear least mean squares inversion technique. Feature selection within machine learning models is also implemented on the information chosen from observed hyperbola travel times. Simulated data are obtained by means of the finite-difference time-domain (FDTD) method with the 2D numerical tool GprMax. The study is carried out on mono-static, ground-coupled GPR datasets. The preliminary study showed that the proposed machine learning methods outperforms the ray-based method for estimating radius, depth and velocity. SVR, for instance, calculates depth and radius values with mean absolute relative errors of 0.39% and 6.3%, respectively, with regard to the ground truth. A parametric comparison of the aforementioned methodologies is also included in the performance analysis in terms of relative error.

Bond behaviour of stainless-clad bimetallic rebar in concrete

Stainless-clad (SC) bimetallic rebar combines benefits in terms of both high corrosion resistance and low cost, and therefore has great potential for usage in infrastructure engineering. In order to study the bond behaviour of the SC bimetallic rebar in concrete, a series of tests are carried out and presented herein, with various parameters such as anchorage length, diameter of stirrup and cover thickness being incorporated. Based on the test results, the failure modes, bond-slip curves, bonding strength, residual strength of bond and corresponding slippage are obtained, on which effects of the various parameters are clarified. Comparisons of the bond slip relations of the SC bimetallic rebar with that of ordinary hot-rolled conventional mild steel and stainless steel ones as well as that given in national standards are carried out. Finally, a constitutive relationship model and design suggestions for the bond between the SC bimetallic rebar and concrete are developed, which may provide valuable reference for their use in practice.

Detection of early-stage rebar corrosion using a polarimetric ground penetrating radar system

As a non-destructive testing method, ground penetrating radar (GPR) has been applied to monitor the corrosion of reinforced bar (rebar) in concrete. However, a traditional GPR system employs a pair of antennas, and can only measure single-polarization radar signals. In this paper, a hybrid-polarization GPR system is proposed for detection and evaluation of rebar corrosion. It can record rebar reflections in two orthogonal polarimetric channels, from which a full-polarimetric scattering matrix can be estimated through polarimetric decomposition and calibration. An accelerated corrosion experiment was conducted and the results prove that radar signal in the polarization channel perpendicular to the rebar orientation is more sensitive to the corrosion, compared with the commonly-used parallel polarization channel. Analysis of the scattering mechanism through H-Alpha decomposition shows that the corroded rebar shifts from the low-entropy dipole scattering to the low-entropy surface scattering. By filling the migrated GPR image with the color of the H-Alpha scattering classification, it is able to visually evaluate the early-stage corrosion of rebar in concrete.

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.

Production and compatibility assessment of denitrifying biogranules tailored for self-healing concrete applications

Microbial granules have been mostly used for wastewater treatment. Recently, biogranules consisting nitrate-reducing microorganisms have appeared as a unique healing agent providing simultaneous self-healing of cracks and corrosion inhibition of rebar in concrete. Yet, information about the production process and microbial activity of these biogranules as well as their compatibility with cementitious materials remains unknown. This study presents the biogranule production procedure in detail and evaluates the compatibility of the produced biogranules with the cementitious composites. In the form of biogranules, bacteria doses varying between 0.25% and 3.00% w/w cement were incorporated into mortar and the variations in fresh and hardened properties of mortars were evaluated with respect to abiotic mortars. Biogranules were also tested for their compatibility with concrete at minimum and the defined maximum tolerable doses. Biogranules with a NOx-N reduction activity of 0.10 g NOx-N.g−1 bacteria.d−1 and organic carbon oxidation activity of 1.50 g HCOO⁻.g−1 bacteria.d−1 were produced successfully by using minimal medium. It was found out that biogranules enable bacteria incorporation into mortar up to a dose of 2.50% w/w cement without compromising fresh and hardened properties of cementitious composites. It was revealed that the compatibility of the biogranules was due to the mineral layer surrounding the biogranules which prevented interaction between the cement matrix and the microbial content. The thickness of the protective mineral layer around the granules was varying between 50 and 300 μm depending on the granule size. Net yield for concrete compatible biogranule production was determined as 0.05 g biogranule.g−1 HCOO⁻.

Evaluation of corrosion in steel reinforced concrete with brick waste

The massive demolition of old buildings in recent years has generated tons of waste, especially brick waste. Thus, a concern of recent research is the use of this waste for the production of environmentally friendly concrete. At the same time, corrosion of the reinforcement steel rebar in classical concrete is a current problem. In this context, in the present paper a study was carried out on the corrosion of metal reinforcement in cement mortars with added brick waste. The corrosion process was analyzed on four compositions of mortars without and with 15%, 25% and 35% brick waste replacing the sand. The brick waste has majority content in SiO2, Al2O3, FeO3 and CaO. The grain size distribution of brick waste was close to that of the sand (dmax = 2 mm). The preparation method of the samples was similar to ordinary mortars. The corrosion action on the rebar in concrete, at different brick waste concentrations, was investigated by electrochemical measurements (polarization curves and electrochemical impedance spectroscopy (EIS)) at 1 month and 26 months. The results obtained at 26 months revealed that the addition of the brick waste in mortar improved the anticorrosion properties in the case of all samples compared with the etalon mortar. The best results were obtained in the case of the sample with 15% brick waste (the efficiency was ≈ 90%). The corrosion intermediary layer formed on the rebar surface was evidenced by SEM-EDX.

Study of corrosion property and mechanical strength of eco-friendly fabricated superhydrophobic concrete

The complex corrosive environment in the ocean and the hydrophilicity of concrete often leads to corrosion of the rebars in concrete. Endowing concrete with superhydrophobicity is an effective measure to prevent the internal rebars from being corroded. Here, an eco-friendly green method was proposed for fabricating superhydrophobic concrete by adding non-toxic lauric acid into concrete to reduce surface energy and covering stainless steel mesh to obtain rough hierarchical structures. The superhydrophobic concrete exhibited WCA of 153° and WSA of less than 10°. The corrosion property of fabricated concrete immersed into simulated seawater for different time was studied. The results show that the superhydrophobic concrete possesses better corrosion resistance to internal rebars than ordinary concrete. The compressive and flexural strengths of samples with different curing ages were studied. This eco-friendly green method for fabricating superhydrophobic concrete with corrosion resistance may have good application prospects in coastal engineering.

Application of Superabsorbent Polymer as Self-Healing Agent in Self-Consolidating Concrete for Mitigating Precracking Phenomenon at the Rebar–Concrete Interface

Improved autogenous healing capacity of concrete using superabsorbent polymers (SAPs) was used as an efficient approach for mitigating damage between steel rebar and self-consolidating concrete (SCC). The results for normal concrete (NC) and those for SCC mixtures were compared. Two SAPs with different particle sizes and chemical compositions were used in the experimental program. Results showed that despite the greater reduction effect of SAP with a smaller particle size on compressive strength, SCC containing this type of SAP had the highest bond strength in uncracked specimens, compared with SAP with larger particle sizes, for SAP-modified NC and SCC mixtures. Moreover, results showed that SCC and NC containing SAP had considerably greater healing improvement factors for large crack widths (w≥0.30 mm) compared with mixtures without polymers; almost 46%, 30%, and 24% healing improvement factors were obtained for average bond stress, bond strength, and residual bond stress of SAP-containing concrete mixtures, respectively. Furthermore, complete strength recovery (100% healing improvement factor) was obtained for SCC mixture with w=0.10 mm after a 28-day healing period.

Experimental investigation on the flexural behaviour of basalt fibre reinforced polymer rebar concrete

This study experimentally explores the effects of applying various types of fibres to concrete mixes on the flexural behaviour of longitudinal structural members with basalt fibre reinforced polymer (BFRP) bars. The main objective is to research the viability of using new advanced fibres of basalt to enhance the concrete response. Basalt fibre and basalt fibre reinforced polymer rebar and compared with the conventional concrete and with a 40 MPa compressive strength target, eighteen beams were fabricated and tested; twelve with basalt fibre reinforced polymer rebar concrete and six with conventional concrete Basalt fibre lengths 30 mm with 15 µm and BFRP bar length of 800 mm with 8 mm diameter were taken into account. Flexural tests were done using a four-point test setup on both of the BFRP- conventional concrete (CC) beams. The test matrix would include BFRP bar reinforcing beams and conventional steel rebar for comparative purposes. Results showed that the application of basalt fibres to concrete enhanced the ductility of these beams' curvature. Due to the delay in the concrete failure in the compression zone, a significant improvement in bending ability was also reported, which supported the BFRP bars achieved a higher ultimate strength. The opening and deep formation of a crack have been effectively limited by the aggregate interlock of basalt fibres, which maintained the crack widths lower than in the 0.7 mm permissible maximum in service. Basalt fibres of 4%, 6%, and 8% were done. Compared to conventional concrete 6% basalt fibre at 28 days of the curing period, the maximum compressive strength was attained 52.38 N/mm2, tensile strength was attained 5.55 N/mm2, Flexural strength increases to 7.45 N/mm2. However, basalt fibre reinforced polymer rebar concrete was larger than conventional concrete beams.

Numerical simulation of a magnetic corrosion detector for corrosion detection of steel rebar in concrete

Numerical simulation of a magnetic corrosion detector for corrosion detection of steel rebar in concrete

Study of Behavior of Jute Fiber Concrete including Glass Fiber Reinforced Polymer Rebar’s

Glass Fiber strengthened chemical compound Rebar’s (GFRP) has associate rising various solution of steel reinforcement for concrete structures thanks to its upgraded properties like high durability, light-weight, and corrosions resistance. The general purpose of this study is to interchange longitudinal steel with GFRP rebar in Fiber reinforced concrete (FRC) for pier to boost its performance. During this study the proportion of cement sand aggregate and water is 1:2:3:0.60, with the addition of fifty five jute fibers by mass of cement, having forty five millimeter length is used. The mechanical properties (splitting tensile and compressive strengths), are investigated during this study. We have found that compressive strength and split tensile of JFRC specimen is decreased but flexural strength is increased as compared to normal concrete but the axial strength of prototype pier including glass fiber reinforcement is decreased.

Evaluation of post-fire pull-out behavior of steel rebars in high-strength concrete containing waste PET and steel fibers: Experimental and theoretical study

The present research addressed the post-fire bond performance between high-strength concrete incorporating waste polyethylene terephthalate (WPET) and steel reinforcement; a subject that had not been previously addressed. Further, the impact of incorporating steel fiber, as a commonly used material, into the mixture on the bond improvement was assessed. To this end, the content of WPET substituting for the fine aggregate by volume (0, 5, and 10%), volume fraction of steel fibers (0, 0.5, and 1%), applied temperature (25, 200, 400, and 600 °C) were considered as variables in a total of 108 samples that were produced. Afterward, the samples were subjected to the pullout test to examine different parameters. These parameters included the bond behavior, failure mode, bond stress-slip response, and bond strength-compressive strength behavior. Based on the results, with the incorporation of 5 and 10% volume content of WPET replacing fine particles, the bond strength declined by 4 and 26%, respectively, and as the temperature was raised, this reducing effect increased. Furthermore, the presence of steel fiber had a positive impact in the samples with the splitting failure mode, while it had a negligible or sometimes even negative impact in the samples with the pull-out failing mode. Lastly, multivariate prediction models were proposed for the bond behavior and bond-slip response as a function of the concrete compressive strength, WPET content, content of steel fiber, and the target temperature. Afterward, a comparison was made between the empirical results and the predictions of models developed by other researchers and the fib Model Code 2010 and ACI 408-12 codes.

Carbonation and Electrochemical Corrosion Resistance of Mild Steel Rebar in Concrete Modified by Sodium Polyacrylate as Super Absorbent Polymer exposed to 3.5 wt% NaCl Solution

Carbonation and Electrochemical Corrosion Resistance of Mild Steel Rebar in Concrete Modified by Sodium Polyacrylate as Super Absorbent Polymer exposed to 3.5 wt% NaCl Solution

Crevice corrosion of steel rebar in chloride-contaminated concrete

In this paper, crevice corrosion was proposed as one of the important mechanisms responsible for the damage of steel rebar in concrete, which was experimentally verified in simulated concrete pore solution (SCPS) and concrete blocks. The effects of chloride concentration and temperature on the crevice corrosion were comparatively investigated by means of potentiodynamic polarization, immersion, electrochemical impedance spectroscopy (EIS) and galvanic current measurements. The crevice corrosion products in chloride-contaminated SCPS were examined by X-ray photoelectron spectroscopy (XPS). The results indicated that chloride contamination and temperature elevation could significantly accelerate the crevice corrosion.

Bond strength of post-installed high strength deformed rebar in concrete

One of the major aspects of retrofitting or strengthening of existing concrete structures is to install rebars using chemical adhesives. In a view to lighten the disturbance of existing structures by reducing the number of holes, high strength rebars (80 grade; nominal yield strength of 550 MPa) are more preferable for repairing and strengthening structural components. Here, a total of 108 specimens were prepared to evaluate the performance of post-installed high strength deformed rebar (PIHSDR) in concrete using pull-out tests. Test parameters included concrete compressive strength (fc' ), rebar diameter, embedment length of rebar into concrete and concrete cover to rebar diameter ratio (c/db) to investigate the bond behaviors of PIHSDR at the epoxy-concrete interface. Bond stress-slip relationships for PIHSDR were obtained, investigated, and hence compared with previous research and available codes. It was observed that most of the specimens showed concrete rapture, splitting, or rebar rapture failure and none of them showed pull-out failure which indicates that the epoxy resins are very much effective as bonding chemicals for retrofitting concrete structures in the steel-concrete interface. Besides, regression analyses were performed using the experimental data to obtain a closed-form equation for predicting the bond strength for PIHSDR. The predicted bond strengths were observed close to the actual test data with a high coefficient of determination (R2 = 0.99) and very low root mean square error (0.078).

Study on Sectional Nonuniform Corrosion and Bond Strength of Plain Rebar Embedded in Concrete

The assessment of nonuniform corrosion of rebar is a key issue concerning the reliability of reinforced concrete structures. In this paper, the sectional nonuniform corrosion of plain rebar and the effect of corrosion on bond strength with concrete are studied. The plain rebar in concrete of 52 specimens were fast corroded by using electrochemistry method in a 5% sodium chloride solution. The bond strength of corroded plain rebar in concrete was measured by the central pull-out test. The sectional contour, diameter loss and sectional area loss of corroded plain rebar were detected within the bond length corresponding to the mass loss from 0.1 % to 11.9%. Based on the oretical analysis and test data, the predictive models of the corroded sectional contour line and the bond strength of corroded plain rebar to concrete are built up. The results indicate that the nonuniform corroded sectional contour of plain rebar is approximate elliptical shape, the bond strength can be predicted by using the diameter loss of corroded rebar. Finally, the adaptability of the predictive models is ascertained with the experimental results.

Evaluation of Chloride Ion Concentration and pH on Depassivation of Steel Rebar in Concrete Investigated by Electrochemical Impedance Measurement of Probe Electrodes

Evaluation of Chloride Ion Concentration and pH on Depassivation of Steel Rebar in Concrete Investigated by Electrochemical Impedance Measurement of Probe Electrodes

Experimental study on longitudinal seismic damage progress and failure mode of a three-tower extradosed bridge

To understand the longitudinal seismic damage progress and failure mode of extradosed bridges, an experimental investigation was conducted on a 1/20 scaled shake table test model. Detailed design of the test model is firstly introduced. During the experimental investigation, the test model was longitudinally subjected to the site-specific artificial ground motion with the peak ground acceleration (PGA) ranging from 0.1 g to 1.5 g. Test results show that the seismic damage progress of the extradosed bridge could be categorized into four stages: (1) No damage (PGA = 0.1 g − 0.3 g); (2) Mild damage (PGA = 0.4 g − 0.6 g); (3) Moderate damage (PGA = 0.7 g − 1.2 g); (4) Severe damage (PGA = 1.3 g − 1.5 g). The bottom and top regions of four-column piers are earthquake-vulnerable regions, while short towers are not. The failure mode of the test model could be characterized by buckling of the rebar and crushing of the core concrete at the bottom region of four-column piers. Moreover, unlike conventional cable-stayed bridges, the longitudinal deformation of the short tower is quite small in each loading case, and the residual longitudinal displacement of the test model is negligible after the whole tests.