Concrete Rebar Research Articles

Comparative Studies on the Anti‐Corrosive Action of Waterproofing Agent and Plant Extract to Steel Rebar

AbstractReinforcement of steel rebar in concrete infrastructure practices for a long time, mostly to improve tensile strength as well their service time. However, shortcomings related to damage of reinforced concrete (RfC) infrastructures becomes the business of corrosion researchers over the past few years, primarily from a safety and economic perspective. In general, the steel‐reinforced concrete (SRC) infrastructures are porous, and thence water as well different atmospheric pollutant gases penetrate it, causing the corrosion damages of the rebar, which shorten the prolonged existence of the RfC structures. The research aims to differentiate the efficacy and prosperity of waterproofing chemicals and methanol extract of Mangifera indica plant leaves for controlling the RfC susceptibility using a half‐cell corrosion potential measurement method following ASTM standard. The methanolic extract of M. indica leaves and waterproofing agents show high anti‐corrosion characteristics and can prescribe for the protection of the RfC infrastructures. The corrosion controlling performance level of 1000 and 2000 ppm M. indica extracts on the steel rebars in concrete has higher than the additions of alike concentration of both the water‐repellents depend on open‐circuit corrosion potential (CoP) shifting values to a noble direction.

Research Progress of Macrocell Corrosion of Steel Rebar in Concrete

Macrocell corrosion of steel rebar in concrete induced by corrosive environments has attracted widespread attention in the engineering community due to its rapid corrosion rate, diverse forms, and multiple incentives. Potential differences between dissimilar coupled rebar or different parts of the same rebar mainly cause macrocell corrosion of steel rebar. The more significant the potential difference, the faster the corrosion rate of the macrocell. Based on the existing research reports on macrocell corrosion of reinforced concrete, this review paper comprehensively discusses the macro- and micro-corrosion behavior of various types of steel rebar, and a variety of induction factors, such as dissimilar metals and concentration differences of the service environment, development rules. and electrochemical mechanisms for corrosion of rebar macrocells are summarized. ZRA (zero-resistance ammeter), micro-area electrochemical testing technology and evaluation techniques commonly used in the laboratory, and electrochemical testing techniques used in engineering testing are listed. Common experimental models for corrosion of rebar macrocells are briefly introduced. Based on the internal characteristics of macrocell corrosion of reinforced concrete, this paper further proposes the control strategy of macrocell corrosion, starting from the improvement of the corrosion resistance of the rebar and regulating the service environment of the reinforced concrete structure (RCS). Meanwhile, the future direction of macrocell corrosion of steel rebar is also preliminarily prospected.

Numerical validation and optimization of hybrid composite beam hull using multiple failure criteria

The number of structurally deficient bridges continues to increase due to corrosion of steel sections and concrete rebar, therefore the replacement of decaying structures and the development of innovative systems have become of high priority to extend the life span of newly built bridges. Hybrid Composite Beam (HCB) produced by Hillman is one of those systems that use a combination of materials i.e., concrete, steel, and Glass Fiber-Reinforced Polymer (GFRP) to integrate each main advantage in a single bridge beam structure. Despite its several apparent advantages; it is not widely spread as expected within the last decade. The HCB is manufactured of self-consolidating concrete (SCC), which is poured in the shape of a traditional arch and tied at its ends by high-strength tendons. A durable FRP composite hull encapsulates the SCC arch and the high-strength tying tendons in order to create a structural beam element for bridge applications. The HCB's design aims to provide pure compressive stresses to the concrete and pure tensile stresses to the steel. The current study performs a deep numerical investigation of the FRP hull instead of other components comprehensively studied. Numerical validation is performed for the deflection results on the experimentally tested Knickerbocker HCB Bridge, the deformations are validated at four stages of HCB manufacturing and testing. Further, the FRP hull strength ratios are quantified for the worst value of four failure criteria. The results showed an excess use of FRP material, where more than 90% of FRP areas have strength ratios of 5 to 50. The FRP hull thickness is minimized using Genetic Algorithm optimization under the worst case of loading. The results achieved more than 60% decrease in FRP weight, that led to only 20% cost difference between traditional precast concrete and HCB girders. It is finally concluded that the overdesign of FRP hull contributed to the high cost of HCB usage consequently inefficient market spread.

Combined GPR and Self-Potential Techniques for Monitoring Steel Rebar Corrosion in Reinforced Concrete Structures: A Laboratory Study

Steel rebar corrosion is one of the main causes of the deterioration of engineering reinforced structures. Steel rebar in concrete is normally in a non-corroding, passive condition, but these conditions are not always achieved in practice, due to which corrosion of rebars takes place. This degradation has physical consequences, such as decreased ultimate strength and serviceability of engineering concrete structures. This work describes a laboratory test where GPR and SP geophysical techniques were used to detect and monitor the corrosion phenomena. The laboratory tests have been performed with several reinforced concrete samples. The concrete samples were partially submerged in water with a 5% sodium chloride (NaCl) solution. Therefore, an accelerated corrosion phenomenon has been produced by a direct current (DC) power supply along the rebar. The geophysical measurements were performed with a 2.0 GHz centre frequency GPR antenna along several parallel lines on the samples, always being the radar line perpendicular to the rebar axis. The GPR A-scan amplitude signals were elaborated with the Hilbert Transform approach, observing the envelope variations due to the progress of the steel rebar corrosion in each concrete sample. Moreover, Self-Potential acquisitions were carried out on the surface of the concrete sample at the beginning and end of the experiments. Each technique provided specific information, but a data integration method used in the operating system will further improve the overall quality of diagnosis. The collected data were used for an integrated detection approach useful to observe the corrosion evolution along the reinforcement bar. These first laboratory results highlight how the GPR should give a quantitative contribution to the deterioration of reinforced concrete structure.

The impact of non-uniformity and resistivity on the homogenised corrosion parameters of rebars in concrete – a circuit model analysis

ABSTRACT When rebar corrosion parameters are characterised from an electrochemical polarisation curve, the non-uniform rebar surface conditions need to be considered. In this research, a circuit model was developed to simulate the polarisation behaviour of rebar in concrete. It is found that the resistivity of concrete leads to non-uniform potential on the rebar, which causes the polarisation curve of the entire rebar to deviate from the Butler–Volmer kinetics. This, in turn, leads to an overestimation of the Tafel constants and the corrosion current density. Such deviations are more pronounced with higher concrete resistivity, especially when the active and passive rebar surfaces have a similar area ratio. The study recommends using potentiodynamic scans of representative reinforced concrete samples of the field conditions or the calculated parameters using an averaging technique, such as the proposed circuit model, to obtain accurate E-I curves or parameters for electrochemical modelling and corrosion rate prediction.

Experimental investigations of bond behavior of double-row spliced rebars in Ultra-High Performance Concrete (UHPC)

The paper aims to evaluate the bond behavior of spliced rebars in Ultra-High Performance Concrete (UHPC). A total of 27 double-row spliced specimens were prepared and tested under direct tension where the test variables covered bar diameter (14 mm and 25 mm) and splice length (2db, 4db, 6db and 8db). The failure mode, crack pattern, bond-slip relationship, bond strength, and bond stress distribution were determined and discussed. Three failure modes including rebar pullout, rebar rupture and UHPC splitting were observed. Owing to the bridge action of steel fibre in the post-cracking phase, the splitting failure was ductile. The bond strength decreased as the splice length and bar diameter increased. For db of 14 mm, the bond strength of specimens with splice lengths of 4db, 6db and 8db dropped by 30.9 %, 40.6 % and 50.1 % than that with a splice length of 2db, respectively. Under various splice lengths, the bond stress presented uniform distribution, single peak distribution and bimodal distribution profiles. Moreover, the design recommendation for the critical splice length of rebars in UHPC was presented and compared with the current specifications.

Effects of cracks on chloride‐induced corrosion initiation and propagation of carbon and stainless steel rebar

AbstractCurrent durability design models for reinforced concrete structures in chloride‐contaminated environments do not consider the effects of cracks, which in practice are almost inevitable. Literature reports controversial results on corrosion propagation time of carbon steel (CS) in cracked concrete, while fewer information can be found on stainless steel (SS) rebar, which can be employed as additional protection strategy. In this experimental study, corrosion initiation and propagation of CS and SS rebar in uncracked and cracked concrete are presented. Prismatic specimens, reinforced with CS and 304L SS bars were subjected to a loading procedure to induce longitudinal micro‐cracks and exposed to a 3.5% NaCl solution for more than 2 years. Corrosion was monitored with electrochemical techniques and at the end of exposure corrosive attacks were observed. Results demonstrate the fundamental contribution of micro‐cracks in accelerating corrosion phenomena for CS, while SS is still in passive conditions also in cracked concrete.

Inhibition Mechanism of Oxalhydrazide on Reinforcing Steel in Pore Solution Contaminated by 3.5%NaCl - Experimental and Theoretical Study

Concrete is one among the most consumed materials on the planet secondary to water. However, the degradation of concrete happens due to the corrosion of reinforcement. Although the pore solution of concrete is alkaline, the corrosion of rebars in concrete is triggered due to aggressive ions like chlorides entering the concrete. The most common method of corrosion inhibition is by utilising corrosion inhibitors which when added to the concrete stays in the pore solution and prevents the corrosion of surface of rebars from aggressive ions. Although there are number of inhibitors, the rise in corrosion deterioration demands the need for new potential inhibitors which are highly effective in different aggressive environments. This study is based on the corrosion of rebars in simulated concrete pore solution in the presence of 3.5% NaCl with oxalhydrazide as the potential inhibiting material. The corrosion behaviour of rebar is obtained by electrochemical studies using EIS and potentiodynamic polarization and theoretically analysed employing molecular mechanics and molecular dynamics simulations. The experimental results revealed that the inhibitor is effective in reducing the corrosion and the values of binding energy of the inhibitors on rebar surface also go well with the experimental results. Oxalhydrazide is found effective in minimizing the attack of chloride ion on rebar in pore solution.

Effect of GFRP rebars and polypropylene fibers on flexural strength in high-performance concrete beams with glass powder and microsilica

Considering the benefits of GFRP rebars and their lighter weight compared to steel rebars and the sustainability of polypropylene fibers, GFRP rebars and polypropylene fibers are investigated as sustainable materials replacements for steel rebars in high-performance concrete (HPC). This study employs micro silica (10 wt % of cement) and wastes glass powder (25 wt % of fine grains) to increase the concrete's strength and achieve HPC. There are four compression specimens and six flexural specimens created. The flexural specimens comprise those without reinforcing bars, those with steel reinforcing bars, those with GFRP reinforcing bars, and those with a hybrid usage of GFRP reinforcing bars with varying fiber ratios. Utilizing only GFRP reinforcing bars produces concrete beams with a lower flexural strength than using steel reinforcing bars. Simultaneous usage of 1.5 % polypropylene fibers and GFRP rebars achieves the same flexural strength as steel rebars while decreasing the beam's weight by about 4 % and minimizing preparation costs and CO2 emissions. The addition of 0.5 % polypropylene fiber enhanced the flexural strength of concrete reinforced with GFRP rebars by about 6 %, while the addition of 1.5 % fiber increased the compressive strength by 20 %. Glass, micro silica, fibers, and rebars are among the sustainable materials employed in this study. Consequently, the use of GFRP reinforcing bars decreases CO2 emissions by 43 %. Additionally, employing micro silica at 10 wt % of cement decreases CO2 emissions by 95,4 kg per ton of cement.

Effect of concrete workability on bond properties of steel rebar in pre-cracked concrete

Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm.

Muography for Inspection of Civil Structures

Aging infrastructure is a threatening issue throughout the world. Long exposure to oxygen and moisture causes premature corrosion of reinforced concrete structures leading to the collapse of the structures. As a consequence, real-time monitoring of civil structures for rust becomes critical in avoiding mishaps. Muon scattering tomography is a non-destructive, non-invasive technique which has shown impressive results in 3D imaging of civil structures. This paper explores the application of advanced machine learning techniques in identifying a rusted reinforced concrete rebar using muon scattering tomography. To achieve this, we have simulated the performance of an imaging prototype setup, designed to carry out muon scattering tomography, to precisely measure the rust percentage in a rusted rebar. We have produced a 2D image based on the projected 3D scattering vertices of the muons and used the scattering vertex density and average deviation angle per pixel as the distinguishing parameter for the analysis. A filtering algorithm, namely the Pattern Recognition Method, has been employed to eliminate background noise. Since this problem boils down to whether or not the material being analyzed is rust, i.e., a classification problem, we have adopted the well-known machine learning algorithm Support Vector Machine to identify rust in the rusted reinforced cement concrete structure. It was observed that the trained model could easily identify 30% of rust in the structure with a nominal exposure of 30 days within a small error range of 7.3%.

Bond Strength Properties of GFRP and CFRP according to Concrete Strength

Reinforced concrete is the most commonly used material in the construction industry. However, one disadvantage of reinforced concrete is that environmental factors cause materials to penetrate the concrete and cause steel bar corrosion. Rebar corrosion increases its volume significantly by approximately 3–6 times, which lowers concrete–rebar adhesion. This severely affects the serviceability and durability of concrete structures. The economic and social impacts of such deterioration are extremely large. To reduce corrosion, glass fiber-reinforced plastics (GFRP) and carbon fiber-reinforced plastics (CFRP) can be applied to concrete. The rebar–concrete bond strength is an important factor to be considered while applying GFRP and CFRP. Thus, we experimentally investigated the adhesion strength of GFRP and CFRP in relation to the strength of concrete and water–cement ratio according to ASTM C 234 to correlate the data for the development of GFRP and CFRP as substitutes for deformed reinforcing bars. The results showed that a lower water–cement ratio yielded higher compressive strength and bond strength; the bond strength of GFRP was approximately 23% lower than that of CFRP. The coating of the rebar surface required for GFRP and CFRP application in reinforced concrete structures ought to be investigated in the future.

Bond-slip relationship of rebar in lightweight aggregate concrete

This paper presents the bond-slip relationship of deformed rebar in lightweight aggregate concrete (LWAC) considering the effect of additional embedded bars around the centric bar. Twelve groups of specimens considering the amount of embedded rebar, deployments, rebar diameters, and concrete types were constructed. The test results indicate that the additional embedded bars alter the bond-slip relationship and failure modes, which the proposed strut mechanism between rebars can illustrate. Next, an analytical solution for bond strength was derived based on a proposed strut mechanism and the thick-walled theory. A modified bond stress-slip model was then developed for LWAC by incorporating the proposed bond-strength equations, which were found to give a good prediction of the experimental results.

Bond Properties of Deformed Rebar in Frost-Damaged Recycled Coarse Aggregate Concrete under Repeated Loading

The bond properties of deformed rebar in frost-damaged recycled coarse aggregate concrete (RAC) under repeated loading (R-L) was studied. It is found that the bond failure modes of specimens for R-L is similar to that for monotonic loading (M-L), whereas the crack width for R-L is larger than that for M-L. The bond strength has a tendency to decrease after frost damage, whereas the peak slip has a tendency to increase, whether under R-L or M-L. The bond strength under R-L is lower than that under M-L, whereas the peak slip under R-L is higher than that under M-L. The experimental results of the pullout specimens in water are contrasted with that in salt solution. Through contrasting research, the frost-damage resistance coefficient and the R-L resistance coefficient in salt solution are lower than that in water, whereas the rebar slip in salt solution is higher than that in water. An ultimate bond strength calculation expression of deformed rebar in frost-damaged RAC under R-L is presented.

Effect of the Current and Pressure on Weld Strength for IBS Rebar Machine

The increase of population results to the increase of housing in Malaysia. One of the technologies of building houses is using the technique of prefabrication by manufacturing the walls, roof and pillars in factory and assembling the part at the construction site. This research is to study the effect of pressure and time on weld strength of IBS Rebar. In conducting the study, the data for the parameter was collected from the IBS fabrication site in Mahligai Idaman in Kota Bharu, Kelantan. The machine used spot weld to joint the concrete rebar together to make the structure of prefab. The parameter that were taken for this study are current and pressure. The result showed the effect of current and pressure to Ultimate Tensile Stress and Young Modulus. These result suggest that the effect of current and pressure significantly affect the strength of the weldment of the spot weld. On this basis, the parameter of current and pressure need to be account when run the IBS rebar machine.

Anchorage behavior of Fe-SMA rebars Post-Installed into concrete

The unique self-prestressing behavior exhibited by Iron-based shape memory alloys (Fe-SMAs) coupled with the ease of application makes them suitable for numerous structural applications requiring post-installed reinforcement. However, the practical realization of Fe-SMA rebars as post-installed reinforcement systems entails an understanding of their bond behavior with concrete to ensure the use of adequate anchorage length for prestress transfer and prevention of premature failure. The bond behavior of cast-in-place and near-surface mounted Fe-SMA rebars with concrete has been investigated in detail in a few recent studies. However, no study has so far investigated the bond behavior of Fe-SMA rebars post-installed into concrete. To address this important knowledge gap, this paper presents an extensive experimental campaign aimed at evaluating the anchorage of post-installed Fe-SMA rebars in concrete. The experimental campaign comprised 23 specimens, with the variable parameters of the study including the bond length, state of Fe-SMA rebar (non-activated or activated), drill-hole size, strength of the adjacent concrete, type of rebar (plain, threaded, or deformed), and the type of loading history (monotonic or cyclic). The experimental results showed that for bond lengths ≥ 5db, the ribbed Fe-SMA rebars primarily fail in a pull-out failure mode and exhibit large inelastic rebar strains and load capacity at bond failure. The paper is concluded with the comparison of anchorage length predictions of conventional design models with the results of the current experimental testing campaign. The comparison demonstrates that the anchorage length recommendations of existing design standards are generally conservative for Fe-SMA rebars.

Experimental study and reliability-based analyses on the bond performance of high-strength and corrosion-resistant rebar in concrete

In this paper, the influence of concrete strength, diameter, cover thickness, anchorage length, and stirrups ratio on the bonding performance of the HSCR rebar in concrete are experimentally investigated. A nonlinear FE model for simulating the bond performance between HSCR and concrete is established and validated, and the influencing parameters are parametrically investigated. Moreover, the applicability of the ultimate bond strength model for HSCR-concrete is comparatively discussed, and a new model is proposed and validated to give relatively accurate prediction. Based on the proposed model, the anchorage reliability analysis is conducted, the influencing parameters as well as their variation on the reliability of bond strength are discussed, and the reliable anchorage length is recommended.

A new method and device for detecting rebars in concrete based on capacitance

This study aims at developing a convenient and efficient rebar detection method based on capacitance that can be used to precisely locate the state (i.e., diameter and position) of the rebars in concrete. Finite element analysis was used to optimize the electrode of the capacitive sensor and verify that using the developed capacitive sensor to detect rebar in concrete is feasible and reliable. Based on the detected capacitance, the position of the rebar in concrete can be located. The relationships among capacitance, rebar diameter, and cover thickness are explored. Both the peak value and the peak area of capacitance evolve linearly with rebar diameter and exponentially with cover thickness. The 3D diagrams among the capacitance peak value, peak area, and rebar diameter or cover thickness are established in this research. The experimental result agrees well with the numerical results, which verifies the reliability of the capacitive sensor and detection methods established.

Investigating the Bond Strength of FRP Rebars in Concrete under High Temperature Using Gene-Expression Programming Model.

In recent times, the use of fibre-reinforced plastic (FRP) has increased in reinforcing concrete structures. The bond strength of FRP rebars is one of the most significant parameters for characterising the overall efficacy of the concrete structures reinforced with FRP. However, in cases of elevated temperature, the bond of FRP-reinforced concrete can deteriorate depending on a number of factors, including the type of FRP bars used, its diameter, surface form, anchorage length, concrete strength, and cover thickness. Hence, accurate quantification of FRP rebars in concrete is of paramount importance, especially at high temperatures. In this study, an artificial intelligence (AI)-based genetic-expression programming (GEP) method was used to predict the bond strength of FRP rebars in concrete at high temperatures. In order to predict the bond strength, we used failure mode temperature, fibre type, bar surface, bar diameter, anchorage length, compressive strength, and cover-to-diameter ratio as input parameters. The experimental dataset of 146 tests at various elevated temperatures were established for training and validating the model. A total of 70% of the data was used for training the model and remaining 30% was used for validation. Various statistical indices such as correlation coefficient (R), the mean absolute error (MAE), and the root-mean-square error (RMSE) were used to assess the predictive veracity of the GEP model. After the trials, the optimum hyperparameters were 150, 8, and 4 as number of chromosomes, head size and number of genes, respectively. Different genetic factors, such as the number of chromosomes, the size of the head, and the number of genes, were evaluated in eleven separate trials. The results as obtained from the rigorous statistical analysis and parametric study show that the developed GEP model is robust and can predict the bond strength of FRP rebars in concrete under high temperature with reasonable accuracy (i.e., R, RMSE and MAE 0.941, 2.087, and 1.620, and 0.935, 2.370, and 2.046, respectively, for training and validation). More importantly, based on the FRP properties, the model has been translated into traceable mathematical formulation for easy calculations.

Bond-slip Behaviour of Deformed Rebars in Normal and High Strength Concrete at Elevated Temperature-a review

ABSTRACT A comprehensive review is undertaken in this study in order to determine the bond-slip behaviour of deformed rebars in normal and high strength concrete at elevated temperatures. The experimental as well as numerical works are reviewed, and the effect of different parametric variations on bond-slip behaviour at elevated temperatures is reviewed.