Concrete Bars Research Articles

RETRACTED: The influence of fiber RC beams under flexure on the chloride-induced corrosion

Corrosion of rebars is the main cause of the deterioration of reinforced concrete structures. In an aggressive marine environment, rebar corrosion occurs due to chloride ion penetration of the reinforced concrete (RC). This paper presents the findings of an experimental study conducted to determine the influence of fiber reinforcement on the chloride-induced corrosion and flexural behaviour of reinforced concrete beams. Uncracked and cracked reinforced concrete beams were exposed to a 16.5% chloride solution in a cyclic immersion for three years, causing them to corrode naturally. The half-cell potential test was carried out to monitor the corrosion potentials, and flexural tests were carried out in a three-point bending configuration to assess the structural performance. Gravimetric tests revealed that bars in conventional concrete had higher degrees of corrosion than those in fiber-reinforced concrete with a variation of 11 %. With increasing crack widths (max 0.2–0.3 mm), there was a tendency toward early corrosion initiation, in contrast, fiber addition delayed the process of corrosion initiation by 6 %. Regarding flexural performance, fiber-reinforced beams are significantly better than conventional concrete beams, especially steel fiber incorporated concrete beam's residual flexural strength 16 % more than the conventional concrete beams.

Spiral Deployment of Optical Fiber Sensors for Distributed Strain Measurement in Seven-Wire Twisted Steel Cables, Post-Tensioned against Precast Concrete Bars.

On-time monitoring and condition assessments of steel cables provide mission-critical data for informed decision making, ensuring the structural safety of post-tensioned concrete structures. This study aimed to develop a spiral deployment scheme of distributed fiber optic sensors (DFOS) and to monitor/assess the post-tensioned force in seven-wire twisted steel cables, based on the pulse-pre-pump Brillouin optical time domain analysis. Each DFOS was placed in a spiral shape between two surface wires of a steel cable and glued to the steel cable by epoxy. Image observations were conducted to investigate the entireness and bonding condition between the optical fiber and the steel wires. Eight concrete bar specimens were cast, each with a pre-embedded plastic or metal duct at its center and each was post-tensioned by a steel strand through the duct once they were instrumented with two strain and two temperature sensors. The strand was loaded/unloaded and monitored by measuring the Brillouin frequency shifts and correlating them with the applied strains and the resulting cable force after temperature compensation. The maximum, minimum, and average cable forces integrated from the measured stain data were compared and validated with those from a load cell. The maximum (or average) cable force was linearly related to the ground truth data with a less than 10% error between them, after any initial slack had been removed from the test setup. The post-tensioned force loss was bounded by approximately 30%, using the test setup designed in this study.

Corrosion resistance of 6061-T6 aluminium alloy and its feasibility of near-surface reinforcements in concrete structure

Abstract The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

Bond performance of ribbed bars in concrete: effects of loading rate and lateral tension

This paper presents an experimental study on the effects of lateral tension and loading rate on the local bond performance of ribbed bars in concrete. The results show that, up to a loading rate of 10 mm/s, the mode of bond failure is independent of the loading rate but is closely related to the cover depth, concrete grade and level of lateral tension. It is also shown that the bond strength of ribbed bars increases with the increase of loading rate but decreases with an increase in lateral tension. The increase or decrease ratio becomes larger when splitting failure occurs. Specifically, for pull-out and splitting failure, the bond strength decreases by 8% and 22% when the lateral tension increases from 0.0 to 0.6 times the tensile strength of concrete but increases by 22% and 28% when the loading rate increases from 0.01 to 10 mm/s, respectively. The slip at peak bond stress is rate-insensitive. It can be taken as 0.18 times the rib spacing for pull-out failure but decreases linearly with the increase of lateral tension for splitting failure. Finally, a bond stress–slip model with three parameters is suggested for different levels of lateral tension and loading rates.

Macro-cell corrosion between crossed steel bars in cracked concrete

• Macro-cell corrosion current I g included crack-induced macro-cell current I g s and current between two crossed steels I g d . • Both I g s and I g d increased in varying degrees with wider crack and the I g s / I g d ratio was always around 2. • Crack location was proved to influence the value and the direction of I g s and. I g d . To investigate the corrosion behavior of coupled crossed steel bars in cracked concrete, a study on the influence of crack width W and crack location L on the microcell and macro-cell corrosion of coupled crossed steels in cracked concrete is presented. The corrosion process of crossed steel bars in concrete specimens with crack widths of 0, 0.1, 0.2, 0.5 and 1.0 mm, respectively, were continuously monitored in an artificially created chloride environment for 26 weeks. The results showed that the corrosion of steel bars in cracked areas was much severer than that of steel bars in uncracked areas. Both microcell corrosion current ( I c o r r ) and macro-cell corrosion current ( I g ) of coupled active steel bars in a cracked area increased with the increase of the transverse crack width, and I c o r r was found to be more sensitive to the change of crack width. The I g / I c o r r ratio decreased with time, which meant that while macro-cell corrosion made a fair contribution, microcell corrosion played a dominant role in the whole corrosion period. In addition, the distance between the concrete crack and the intersection of the crossed steel bars, defined as the crack location L in the study, was proved to have a significant impact on the value and the direction of total macro-cell corrosion current I g .

Experimental-Numerical Analysis of the Effect of Bar Diameter on Bond in Pull-Out Test

Bar diameter is one of the basic factors affecting bond behavior, which is still of interest due to opposing opinions regarding its effect on bond behavior in the pull-out test. This paper presents an experimental and numerical bond analysis of ribbed reinforcing bar in concrete. The aim was to experimentally evaluate the effect of bar diameter on the bond behavior in the pull-out test and to perform numerical simulations of the conducted experiments in ABAQUS to verify their convergence to the obtained experimental results. The experiments used concrete of C35/45 grade and B500SP reinforcing steel bars of three diameters: 10, 12, and 16 mm. FEA simulations employed the Concrete Damaged Plasticity (CDP) material model and the Contact Cohesive Behavior (CCB) method to model the concrete–bar interface. The study shows that bar diameter significantly affects the bond, both on the bond stress–slip relationship and the type of bond failure, as well as on the bond strength. FEA simulations correctly reflected the bond behavior observed in the specimens. The analytical models presented estimates that were too conservative regarding the maximum bond stress relative to the experimental results.

Machine Learning Models for Predicting Bond Strength of Deformed Bars in Concrete

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Side-Face Blowout Failure of Headed Bars in High-Strength Concrete

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Effects of Mineral Admixtures on Macrocell Corrosion Behaviors of Steel Bars in Chloride-Contaminated Concrete

Based on the macrocell corrosion theory and by alternating the microcell corrosion state and macrocell corrosion state, the influence of mineral admixtures, such as fly ash, slag, and limestone powder, on the macrocell corrosion behaviors of steel bars embedded in chloride-contaminated concrete were investigated and clarified. The results indicated that the inhibition effect induced by slag on macrocell corrosion and microcell corrosion was obviously better than that induced by fly ash or limestone powder. The presence of slag in chloride-contaminated concrete could remarkably decrease the corrosion area ratios of anodic steel, even if the replacement levels of slag to cement reached 70%. With the addition of mineral admixtures into concrete, the ratio of macrocell current density to microcell current density was decreased to some extent, depending on the types, replacement levels, and replacement ways of mineral admixtures. The use of slag and fly ash in chloride-contaminated concrete can effectively weaken the macrocell corrosion and make the corrosion be dominated by microcell corrosion. The types and replacement levels of mineral admixtures also had a remarkable influence on the control mode of macrocell corrosion. The use of slag was more effective than that of fly ash or limestone to weaken the cathode control mode of macrocell corrosion and made the control mode of macrocell corrosion be dominated by jointed control.

A predictive model for determining shear strength and shear fracture energy of FRP bars in alkali-activated slag seawater coral aggregate concrete

Bond parameters between alkali-activated slag seawater coral aggregate concrete (ASSCAC) and fiber reinforced polymer (FRP) bars are necessary to be determined rationally for future service of the new concrete structures in marine environment. The intention of this paper is to develop a predictive model for determining the realistic local shear strength and shear fracture energy incorporating the heterogeneity and discontinuity in the interface region. First, central pull-out tests were performed to study the bond properties between FRP bars and ASSCAC. Ordinary Portland cement CAC (OPCAC) was prepared for comparison. It is found that the ribs on the bar surfaces were seriously abrased and the extent of damage was more serious in the ASSCAC. Subsequently, a microstructure characteristic parameter was introduced indicating the heterogeneity of the interface region and determined as the rib spacing on the bar surface according to the analysis of failure process. The shear crack propagation was discretized by a discrete number. The local shear strength and shear fracture energy were then linked to the maximum pull-out load via the microstructure characteristic parameter and discrete number. Once the maximum load was given from the test, the two bond parameters were conveniently predicted from each specimen. The results indicated that the predicted local shear strength was apparently higher than the maximum average bond stress which was usually used to represent the local shear strength in traditional methods. As the bond length-to-microstructure characteristic parameter ratio increased, the predicted local shear strength showed a certain reduction but the predicted local shear fracture energy was significantly enhanced because of the reduced boundary effect. Moreover, the predicted bond parameters of the FRP bars in the ASSCAC were generally larger than those in the OPCAC.

Suitability of electrochemical test methods for evaluating corrosion of steel in alkali-activated slag concrete

The electrochemical tests commonly used for evaluating reinforcement corrosion in Portland cement-based concrete may not be appropriate for testing alkali-activated slag (AAS) concrete due to its different pore structure and pore solution composition. In this article, corrosion behaviour of the steel bars in 12 AAS concrete mixes with different alkali concentration and modulus of sodium silicate solution was monitored by using gravimetric mass loss measurement. The results obtained from other electrochemical tests were compared to the gravimetric mass loss to determine their suitability for assessing the corrosion of steel in AAS concrete. It was found that only 7.8–28% of the mass loss was accounted for by the macrocell current for AAS concretes, indicating that this type of test underestimates the corrosion of the steel in AAS concrete. The steel bars in the AAS concretes gave a much higher negative half-cell potential value, presumably due to the influence of sulfides. In summary, it has been established that the criteria for assessing the onset and progress of corrosion of steel in Portland cement concrete are not suitable for the same purpose in the range of AAS concretes studied.

Anti-Corrosion Performance of Migratory Corrosion Inhibitors on Reinforced Concrete Exposed to Varying Degrees of Chloride Erosion.

This study investigated the anti-corrosion performance of commercial amino alcohol migratory corrosion inhibitors (MCIs) on concrete that underwent varying degrees of chloride erosion. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PD), scanning electron microscopy, and energy dispersive spectroscopy (SEM-EDS) analyses were performed to study the anti-corrosion performance and mechanism of the MCIs on the steel bars. The results indicated that the corrosion resistance of the steel bars in concrete was significantly improved by coating with the MCIs, and the earlier the specimens were coated with the MCIs, the higher the anti-corrosion efficiency. The anti-corrosion efficiency was 55.35% when the MCIs coating was applied before chloride erosion; however, the anti-corrosion efficiency decreased to 3.40% when the MCIs coating was applied after the ninth drying–wetting cycle. The improvement in corrosion resistance of the steel bar in concrete coated with MCIs was due to the protective MCIs-molecule film that formed on the steel bar surfaces, and the oxidative dissolution of iron at the anode was effectively inhibited by the MCIs coating.

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.

Experimental study on lap behavior of CFRP indented bars in UHPC

The lap behavior of Carbon Fiber Reinforced Polymer (CFRP) indented bars in Ultra-High Performance Concrete (UHPC) were investigated based on pullout test under direct tension on 27 specimens in total. The test variables include splice length, UHPC strength and stirrup ratio. The lap failure mechanism of CFRP bar embedded in UHPC and the influence of test parameters on lap performance were analyzed. Test results showed that the failure modes, pull-out and rupture of CFRP bar, in those lap-spliced specimens were governed only by the splice length of the CFRP bar embedded in UHPC. The pullout failure was caused by the shearing off of indented ribs on the surface of the bars and the fracture failure was governed by the tensile strength of the bars. The bond strength of lap-spliced indented CFRP bars in UHPC is mostly dependent on the shear strength of indented ribs on CFRP bars, little on the UHPC strength and stirrup ratio. For CFRP bars with a 2480 MPa tensile strength and a 9.8 mm diameter (d), a splice length of 30d in UHPC can fully develop the tensile strength of the bar. A simplified equation for predicting the critical splice length of CFRP bars in UHPC was proposed. Compared with the results on anchorage of CFRP bars in UHPC, the critical splice length of CFRP bar in UHPC was 1.45 times the corresponding anchorage length.

Spatial characteristics of stray current corrosion of reinforcing bars in pseudo concrete

AbstractThis paper focuses on the spatial characteristics of reinforcing‐bars corrosion under stray current. In the study, a corrosion experiment using a specimen with three steel bars embedded in pseudo concrete was carried out, the distribution of corrosion was obtained by three‐dimensional scanning. Further, a numerical model with the same dimension of the specimen was simulated to explain experimental results. The distribution of electric field driven by stray current was discussed in detail. Results show that by observation through the transparent matrix and by three‐dimensional scanning, the distribution of corrosion could be estimated qualitatively and quantitatively. Additionally, the spatial characteristics of corrosion state under stray current could be realized by the numerical simulation which combines polarization reaction with an extra stray current field. The stray current field around reinforcing bars was uneven in the cross‐sectional plane, leading to the difference of corrosion rate, which reflects the strong positive correlation between the field and corrosion rate.

Key Points for Construction Quality Control of Steel Bar Concrete Structure

In view of the good effect of steel bars in improving the elastic-plastic and flexural properties of concrete structures, combined with the good compressive strength of concrete, steel bars in the traditional reinforced concrete column and shear wall structures can greatly improve the performance of the main stress-bearing structures of super high-rise buildings. In order to clarify the key points of construction quality control of steel bar concrete structure, the control points are analyzed by theoretical analysis method combined with an engineering example. The results show that it is feasible to replace the traditional solid web section steel with the scattered steel bars to solve the difficult problem of the layout of the stirrups and longitudinal bars of the solid web section steel reinforced concrete column, and the ear plate connection of the steel bars is feasible; BIM Technology can realize the accurate positioning of steel bars and greatly improve the construction quality of steel bar concrete structures; During the construction process, it is very important to strictly control the verticality of steel bars, the spacing between steel bars, the spacing between steel bars, the distance from the outside of steel bars to the reinforcement at the column edge, and strictly control the quality of formwork installation and concrete pouring to ensure the quality of steel bar concrete structure.

Evaluation of cyclic bond-slip behavior of smooth bars in low strength concrete: An experimental and stochastic study

The vulnerability of non-engineered/substandard reinforced concrete (RC) members could arise from the bond-slip failure due to low interaction between the smooth bar and poor-quality (low-strength) concrete. Therefore, the cyclic bond-slip response of plain round bars in poor-quality concrete is characterized by experimental and stochastic approaches. To this end, beam-type bond-slip specimens are first exposed to quasi-static cyclic loading. Then, mathematical models are derived from the experimental hysteric responses. Inherent uncertainties in nominally identical tests reveal the high scatter in the response parameters. Therefore, finite element (FE) models generated by implementing the proposed mathematical expressions for bond-slip response are combined with a suitable stochastic sampling technique, which is Latin Hypercube Sampling (LHS). The apparent outcome is the set of load–displacement curves, which formed an envelope around the deterministic model. The peak capacity is captured satisfactorily by the stochastic-numerical models whereas the overall cyclic response is reproduced less accurately. The evaluated bond stress values and corresponding slips in the confined concrete are higher than the ones in the unconfined concrete. Moreover, the cyclic excitation impacts on the bond strength are more recognizable than monotonic loading. The sensitivity analysis, which grades the contribution of the material parameters on the global response, points out the tensile strength of concrete fct as the most significant parameter while the remaining ones have a weak or no influence.

Neural network model for bond strength of FRP bars in concrete

Interest in FRP composite bars as reinforcement to concrete has increased over the years as it showed solutions to the drawbacks of steel such as its corrosion issues and vulnerability when employed in adverse environmental conditions. However, it is still not widely incorporated as a replacement to conventional steel primarily due to the complexity of its bond strength mechanism. This, therefore, imposes the need to establish a comprehensive relationship for the bond property of the FRP reinforced concrete. This paper developed a novel Artificial Neural Network (ANN) bond strength prediction model for FRP reinforced concrete using 184 hinged beam database from various existing experiments. From series of simulations performed, the model N 7-10-1 with ten nodes in the hidden layer appeared to be the best fit with the experimental results yielded the most favorable performance among other existing models. From the parametric analysis conducted, the compressive strength of the FRP reinforced concrete has proved to be the most dominant parameter in evaluating its bond behavior as determined by relative importance of 17.82%. Overall, the proposed ANN model has demonstrated the best prediction for FRP bond strength in comparison to previous studies and code equations.

Deterioration of basalt/carbon-based hybrid-FRP bars in a simulated pore solution of seawater sea-sand concrete

Hybrid-fibre-reinforced polymer (HFRP) bars comprising basalt and carbon fibres are expected to be more durable than BFRP bars in seawater sea-sand concrete (SWSC) environments. This study was aimed at investigating the effects of carbon-fibre content on the durability of newly developed HFRP bars conditioned in a simulated SWSC pore solution. Tensile strength was adopted as a measure of the degree of deterioration and correlated with water uptake. The deterioration mechanism was analysed by digital microscopy (DM), Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, matrix digestion analysis, and inductively coupled plasma mass spectrometry (ICP-MS). The results indicated that increasing the carbon-fibre content clearly reduced the water uptake and tensile strength attenuation rate of the HFRP bars. An unambiguous correlation was established between tensile strength and water uptake. The resin swelled, hydrolysed, and plasticised after absorbing water, which initiated the deterioration of the HFRP bars. The annular basalt–carbon-fibre interfacial areas in the HFRP bars alleviated their overall deterioration but induced local degradation. The findings of this study provide insight into the development of FRP materials with improved durability.

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.