Epoxy-coated Rebar Research Articles

Improving the impermeability of cement/epoxy coating interface by g-C3N5: A molecular dynamics study

The accumulation of chloride that penetrates through the concrete cover from the ambient environment is the primary factor contributing to the interfacial degradation between concrete and epoxy-coated steel rebar. In this study, a nitrogen-rich carbon nitride (g-C3N5) modified epoxy (EP) coating is proposed to enhance the impermeability of the concrete/epoxy interface. The local structure, dynamic characteristics, and impermeability mechanism of g-C3N5 inserted into the interface of concrete/epoxy coating during the penetration of NaCl solution are studied using the molecular dynamics method. It is found that the insertion of g-C3N5 at the concrete/epoxy interface effectively slows down the penetration of NaCl solution. The g-C3N5 nanosheets block the C-S-H channel, and the water molecules form hydrogen bonds with the nitrogen and oxygen-containing groups in the g-C3N5 grafted with oxygen-containing functional groups (g-C3N5-COOH), significantly inhibiting the movement of water molecules. The oxygen-containing functional groups on g-C3N5-COOH form hydrogen bonds with the non-bridging oxygen on the surface of C-S-H and the oxygen in EP, respectively. This enhances the interaction of the C-S-H/epoxy interface and reduces the degree of interfacial peeling. The impermeability mechanism of the C-S-H/epoxy interface and the capture of corrosive particles can offer molecular insights into the interface design of cement/organic coatings.

Eccentric compression behavior of partially CFRP wrapped seawater sea-sand concrete columns reinforced with epoxy-coated rebars

The combined use of seawater sea-sand concrete (SSC), epoxy-coated rebar (ECR) and fiber-reinforced polymer (FRP) can achieve significant economic and environmental benefits in coastal infrastructure constructions. Thus, this paper first presents an experimental and analytical study on the eccentric compression behavior of partially carbon FRP (CFRP) wrapped SSC columns reinforced with ECR. The effects of load eccentricities, thickness of CFRP strips, clear spacing ratios, and slenderness ratios were comprehensively analyzed. Test results show that as the eccentricity increased from 60 mm to 120 mm, the increment of load capacity of partially CFRP wrapped columns reduced by 27.6 % to 17.1 %. Moreover, a larger lateral deflection was detected for the specimens with a relatively high slenderness ratio, which results in an obvious second-order effect and further aggravates the nonlinearity of axial load-bending curves, especially for the specimens under a small eccentricity. In addition, an eccentricity-dependent stress-strain model for concrete was developed under FRP strip-steel hoop composite confinement, and the lateral deflection formula of eccentrically loaded columns was also derived based on force equilibrium analysis. Finally, a new theoretical formula incorporating the effect of the slenderness ratio was also presented for the determination of load and moment capacity of the partially CFRP wrapped columns based on section analysis. By comparing with the test results, the developed model exhibits satisfactory accuracy.

Bond Strength of Reinforcing Steel Bars in Self-Consolidating Concrete

This paper presents an experimental investigation of the bond strength of reinforcing steel bars in tension in self-consolidating concrete (SCC). The effects of the reinforcing bar’s location, orientation, size, and coating on the bond strength with SCC were studied and compared to those with conventionally vibrated concrete (CVC). Several SCC mixtures were developed to cover a wide range of applications/components and material types. The fresh properties of the SCC mixtures were determined to evaluate their filling ability, passing ability and stability. Two hundred and thirty-four pull-out tests of rebars embedded in cubes, wall panels and slabs were conducted. Almost half of the tests were conducted to evaluate the bond with SCC and the other half with CVC. Load–slippage relationships were measured for each test. Pull-out test results were analyzed, and the bond strength was reported in two values: critical strength, which corresponds to slippage of 0.01 in. *0.25 mm); and ultimate strength, which corresponds to the maximum load. The critical strength of SCC and CVC were compared against the ACI 318-19 provisions and comparisons between the ultimate strength of SCC and CVC were conducted. The comparisons indicated that SCC has lower bond strength with vertical rebars than CVC, and a 1.3 development length modification factor is recommended. A similar conclusion applies to epoxy-coated and large diameter rebars. Also, SCC with high slump flow has shown a less top-bar effect than that of CVC.

Textured Epoxy-Coated Rebars: Physical, Structural, and Empirical Characterization

Although the traditional epoxy coating represents an effective corrosion protection system, it has the disadvantage of making bridge decks more susceptible to cracking. This phenomenon occurs because its smooth surface reduces the bond with the concrete and, therefore, increases the radial components of the force-transferring mechanism. To try to mitigate these problems, the Illinois Department of Transportation developed the textured epoxy-coated (TEC) reinforcement, which possesses a roughened surface and, in recent years, has been the subject of study at the University of Illinois Urbana-Champaign, in the U.S. Particularly, this experimental program explores, complements, and compares the physical and bond-slip characteristics of the TEC rebars developed hitherto. From the physical characterization, different parameters are measured on the textured surfaces to obtain a numerical comparison of each roughness type. Also, determining the adhesion strength and thickness of the textured coating reveals that it provides similar corrosion protection to the traditional approach while keeping its integrity on the steel substrate. The bond-slip characterization, in turn, was done using pull-out tests and, by combining these results with the microstructure examination of TEC bars, it is found that the absence of texture voids is related to the degradation of the slip resistance. Furthermore, through a finite element model, the development length of the TEC reinforcement is estimated and compared with the values calculated according to current standards. Finally, given the complexity of obtaining the surface parameters of the coating, an empirical, weight-based approach is developed for the TEC bars as a rapid method for assessing their roughness.

A comparative study on the microstructure, hardness and corrosion resistance of epoxy coated and plain rebars

Corrosion of steel rebars and susceptibility of reinforcement steel to chloride ion attacks are the two major problems for the construction industries and thereby a huge amount of money is spent to repair it. Epoxy coating on the steel rebars can be one cost-effective solution to alleviate the detrimental effects of corrosion in concrete structures. In the present research, plain and epoxy coated rebar (ECR) samples were chosen to study the correlation between microstructure, hardness and corrosion performance. The microstructures of the investigated thermomechanically treated (TMT) rebars primarily reveal tempered martensitic rings at the outer surface followed by a narrow bainitic transition zone in between along with a ferrite-pearlite microstructure at the inner core. The corrosion resistance of plain and epoxy-coated rebars in naturally aerated 3.5% NaCl and 1% HCl solutions were studied using gravimetric test, open circuit potential (OCP) test, and linear polarization monitoring techniques. It has been witnessed that the corrosion current (icorr) has been shifted towards lower values and polarization resistance (Rp) values are higher for ECR samples which is a clear indication of higher corrosion resistance of the ECRs than the plain rebars. Energy dispersive spectroscopy (EDS) analysis reveals the presence of iron hydroxides and iron oxides. However, x-Ray diffraction (XRD) analysis indicates the existence of various types of oxides, hydroxides, and oxy-hydroxides like iron chloride hydroxide [Fe2(OH)3Cl], goethite (α-FeO(OH)), lepidocrocite (γ-FeO(OH)), magnetite (Fe3O4) and bernalite [Fe(OH)3(H2O)0.25] in the epoxy coated rebar samples whereas, plain rebars indicate the presence of goethite (α-FeO(OH)), maghemite (γ-Fe2O3), magnetite (Fe3O4), hydrogoethite (Fe2O3.H2O), lepidocrocite (γ-FeO(OH)) and iron oxide (Fe21.34O32). All the experimental results confirm that ECR samples are more corrosion resistant under both acidic and saline environments.

Evaluation of corrosion inhibition capability of graphene modified epoxy coatings on reinforcing bars in concrete

Corrosion of reinforced concrete structures is the one of the biggest problems faced by the construction industry, with billions of dollars spent annually on corrosion control strategies. Epoxy Coated Rebars (ECRs) have been reported to mitigate corrosion in Reinforced Concrete (RC) structures, but due to the inherent brittle nature of epoxy, its usage is limited. In this study we have proposed modified epoxy coatings on rebars using reduced graphene oxide (rGO) and graphene oxide (GO) along with carbon nanotubes (CNTs) and silane agents for improved ductility and corrosion inhibition properties. Hybrid mixture of CNTs and rGO/GO enhances the mechanical strength of the coating matrix whereas silane agents improve dispersion and bonding characteristics of nano fillers. Differently coated mild steel rebars with rGO/GO based coatings were subjected to accelerated impressed current corrosion. Performance of the coatings was evaluated by visual inspection, corrosion current, ultrasonic guided wave measurements, mass loss and residual tensile strength. Our results indicate that compared to rGO, GO in small proportion (0.4 wt% of epoxy resin) performs superior in corrosion inhibition. The GO/CNT nano composites could have potential application in the field of modified ECR reinforced concrete structures.

Electrochemical evaluation of epoxy-coated-rebar containing pH-responsive nanocapsules in simulated carbonated concrete pore solution

This study introduced an enhanced corrosion performance of an epoxy coated rebar (ECR) embedded with the nanocapsules containing triethanolamine (TEA) as the corrosion inhibitor. Electrochemical corrosion tests indicated a successful protection of the artificially defected area from the sample with encapsulated TEA coating, especially in the initial immersion period, indicating that there was a successful release of TEA from the embedded nanocapsules. A considerably lower surface current density of the encapsulated TEA coating also indicated that the electrochemical reactions were delayed which were further confirmed by surface micrographs that revealed a relatively less degraded artificial defect of the sample with the encapsulated TEA coating. The corrosion product analysis denoted that the inhibiting action has delayed the further oxidation of the exposed surface by having an enhanced barrier protection that helped to maintain a lower O/Fe ratio.

Influence of Microdefect Size on Corrosion Behavior of Epoxy-Coated Rebar for Application in Seawater-Mixed Concrete

Corrosion behavior of epoxy-coated rebar with different size of microdefects in uncarbonated/carbonated simulated pore solution (U/CSPS) of seawater concrete was investigated. Specimens in both solutions underwent two stages of corrosion, according to the electrochemical impedance spectroscopy (EIS) response. The initial stage was the extension of corrosion. The second stage was dominated by the diffusion process, due to the corrosion products blocking the defects and hindering the transportation of the reaction matter. Local electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET) measurements and the observation of corrosion products indicated that 50 μm might be the threshold, because the corrosion of specimens with defects bigger than 50 μm in diameter was significantly more severe. Crevice corrosion was identified to occur in the experiments. The corrosion products of specimens in USPS and CSPS were mainly Fe3O4 and FeOOH, respectively. α-FeOOH and β-FeOOH exhibited an anion ion-selective property in the corrosion process, which induced crevice corrosion in CSPS. In particular, it is contended herein that Fe3O4 has the cation ion-selective property to protect the substrate in USPS.

Review of Short-Term and Long-Term Bond Properties Between Epoxy-Coated Reinforcement and Concrete

Epoxy-coated rebars have been widely used to prevent steel corrosion problems in marine infrastructures of coastal cities. Based on the extensive studies on the bond behavior of epoxy-coated bars, the factors affecting the bond strength of epoxy-coated bars and the relative bond ratio, i.e., the bond strength ratio of epoxy-coated bars to uncoated bars were analyzed. The recommendations for the use of epoxy-coated bars are presented based on the evaluation of the calculated model of the bond strength in the current codes and specifications, which may provide some useful guidance for the widespread applications of epoxy-coated bars in the future.

Investigation of Grouted Coupler Connection Details for Accelerated Bridge Construction

This paper presents a laboratory investigation on the performance of grouted rebar couplers with the connection details similar to those utilized on the precast concrete elements of the Keg Creek Bridge on US 6 in Iowa. The testing program consisted of a series of static load tests, a fatigue test, and evaluation of the chloride penetration resistance of laboratory specimens. The goal of this testing was to evaluate the ability of the grouted rebar couplers to develop flexural capacity at the joint between the precast elements as well as the durability of the connection. For structural load testing, seven full-scale specimens, each with #14 epoxy-coated rebars spliced by epoxy-coated grouted couplers, were fabricated and tested in three different loading cases: four-point bending, axial tension plus bending, and a cyclic test of the system in bending. The static load testing demonstrated that the applied axial load had a minimal effect on the formation of cracks and overall performance of the connection. When ultra-high performance concrete was used as a bedding grout, the initiation of crack was slightly delayed but no considerable improvement was observed in the magnitude of the crack width during loading or the crack closure on unloading. The results of the seventh specimen, tested in fatigue to 1 million cycles, showed little global displacement and crack width throughout the test, neither of which expanded measurably. No evidence of moisture or chloride penetration was detected at the grouted joint during the 6-month monitoring.

Variations in Velocity and Sensitivity of Electromagnetic Waves in Transmission Lines Configured in Model Piles with Necking Defects Containing Soils

This study investigates variations in the velocity and sensitivity of electromagnetic waves in transmission lines configured in defective model piles for the detection of necking defects containing soil. Experiments are performed with model piles containing defects filled with different materials, such as air, sands, and clay. Five different types of transmission lines are configured in model piles. The electromagnetic waves are generated and detected using a time domain reflectometer. The velocity of electromagnetic waves is highest when the defect is filled with air, and it decreases with an increase in the water content. The velocity is lowest when the defect is filled with clay. The sensitivity of transmission lines for detecting defects decreases with an increase in soil water contents. The transmission line with a single electrical wire and epoxy-coated rebar exhibits the highest sensitivity, followed by that with three and two parallel electrical wires. Transmission lines with a single electrical wire and uncoated rebar and those with two parallel electrical wires wrapped with a sheath exhibit poor sensitivity when the defect is filled with clay. This study demonstrates that electromagnetic waves can be effective tools for detecting necking defects with wet and conductive soils in bored piles.

An experimental study on corrosion initiative of infused reinforcing bar in concrete

Durability of concrete is the essential property for the lifespan of concrete structures. Rusting of steel is the major factor responsible for the loss of durability property. In order to study the corrosion behaviour of three types of reinforcing bars like Thermo-mechanically treated bar(TMT), Corrosion resistant steel (CRS), Epoxy coated rebar(ECR) were experimentally studied. The reinforcing bars having 12 mm diameter were infused in 300×300×75 mm size of concrete slab samples were kept under room temperature and certain samples are spraying with 3% of NaCl solution to attain a simulated marine exposure condition. There are various techniques including Open circuit potential (OCP), Linear polarisation resistance (LPR), Electrochemical impedance spectroscopy (EIS) are used to monitorize the corroding performance of samples. On analysing the results of the electrochemical studies, it could be inferred that the efficient rebar to withstand the corrosive nature by improving the life expectancy of the concrete structure.

Evaluation of corrosion inhibition and self healing capabilities of nanoclay and tung oil microencapsulated epoxy coatings on rebars in concrete

Corrosion of civil infrastructure is the biggest challenge faced by the construction industry worldwide and billions of dollars are spent for its repair and rehabilitation. One of the methods to mitigate the effects of corrosion is the use of Epoxy Coated Rebars (ECR) in concrete. But epoxy coatings are inherently brittle and susceptible to crack initiation and propagation. Thus, to further improve their efficiency in inhibiting corrosion, modifications in the epoxy coatings have to be done. In the present study, it is suggested to modify epoxy coatings by adding nano-clay and tung oil microcapsules. To measure the effectiveness of these coatings to corrosion inhibition, non-destructive monitoring has been done using electrochemical current measurements and ultrasonic guided wave propagation characteristics while the coated rebars are subjected to impressed current accelerated corrosion. The corrosion introduces non-uniform and localized pits in the rebars and disturbs the path of the propagating guided waves through it by mode conversions and scattering which results in drop in transmitted guided wave signal strengths. Nano dispersion of clay in epoxy not only increase of toughness, tensile and flexural properties of the epoxy but leads to torturing of the path for moisture progression. Lastly, the hydrophobic nature of modified clays will aid in reducing progression of water molecules. This was successfully illustrated by very small corrosion current values and small rate of drop in ultrasonic guided wave voltage signals as compared to plain epoxy coated rebars. On the other hand, tung oil microcapsules in Urea-formaldehyde (UF) shells prepared by in-situ polymerization improves the self-healing ability and adhesion strength of capsule embedded coatings and act as self-healing agents. Tung-oil micro-encapsulated coatings perform the best in terms to corrosion resistance as well as bonding with surrounding concrete. The drop in voltage amplitudes as well as the rate of voltage drop with increasing corrosion exposure is very nominal and insignificant. It points towards remarkable inhibition of corrosion offered by self-healing tung oil microcapsules to corrosion damage.

Corrosion performance of mild steel and epoxy coated rebar in concrete under simulated harsh environment

PurposeThe purpose of this paper is to present the results of a two-year long study carried out in order to evaluate the corrosion performance of mild steel bare bars (BB) and epoxy-coated rebar (ECR) in concrete under a simulated harsh environment of chlorides.Design/methodology/approachThe blocks are subjected to Southern Exposure testing. The electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and Tafel plot are performed to measure the polarization resistance and corrosion current densities of these rebars. Knife-peel test was performed to assess the adhesion between epoxy and underlying steel after two years of exposure.FindingsMild steel BB showed a high corrosion current density of 1.24 µA/ cm2 in Tafel plots and a very low polarization resistance of 4.5 kΩ cm2 in LPR technique, whereas very high charge transfer resistance of 1672 and 1675 kΩ cm2 is observed on ECR and ECR with controlled damage (ECRCD), through EIS technique, respectively. EIS is observed to be a suitable tool to detect the defects in epoxy coatings. After two years of immersion in 3.89 percent NaCl− solution, the mild steel BB were severely corroded and a considerable weight loss was observed, whereas under heavy chloride attack, ECR showed no deterioration of epoxy coating and neither any corrosion of underlying steel. Results of this study show that the durability of reinforced concrete (RC) structures with respect to corrosion could be enhanced by using ECR, especially in harsh climatic conditions.Originality/valueThe corrosion performance of mild steel and ECR in concrete under a simulating splash zone environment is evaluated. EIS was used to evaluate the health of epoxy and corrosion state of underneath steel rebars. EIS was able to detect the defects in epoxy. The durability of RC structures could be enhanced in harsh climate regions by using ECR.

Passivation and Depassivation Behavior of Zinc in Concrete

Steel rebar in concrete structure is in a passive state due to high pH in sound concrete. However, depassivation takes place by neutralization of concrete due to CO2 gas and penetration of chloride through the concrete. To extend the life time of concrete structure, it is of great importance to examine the degradation of concrete and corrosion of steel rebar. Recently, hot-dip galvanized steel rebar and epoxy-coated rebar are being used. They are expected for long durability. For the galvanized steel rebar, it has been reported [1] that zinc becomes passive by formation of Ca(Zn(OH)3)2・2H2O in simulated concrete solutions, although zinc generally corrodes in high alkaline solutions. In this study, passivation and depassivation behavior of zinc has been investigated in simulated concrete solutions, and fresh concrete. Special attention has been paid to effect of mass transfer in the concrete on the passivation and depassivation. Difference from carbon steel in passivation and depassivation was also discussed. A pure zinc plate and carbon steel plate were used as the specimens, and they were buried in epoxy resin as working electrodes. Two test solutions of a saturated Ca(OH)2 solution (pH12.5) and fresh mortar (water: cement: sand = 0.6:1:2) simulating concrete environment were employed. To determine a critical chloride concentration for the depassivation, NaCl was added into the test solutions and mortar. EIS was measured at certain intervals of the test, and Ecorr was continuously measured. To characterize the corrosion products, the surface and the cross-section were observed by SEM, and elemental analysis was conducted by EDX. The corrosion products were identified by XRD. The corrosion potential of zinc gradually shifted in positive direction, and reached around -0.5 V vs. SSE after 400 h in a saturated Ca(OH)2 solution. On the other hand, in a fresh mortar, it jumped up to about -0.5 V after 20 h. The charge transfer resistance (R ct) of zinc in the Ca(OH)2 solution and mortar was in the other of 106 Ω∙cm2 after the positive shift to -0.5 V in the both solutions. Since the R ct value was comparable to that of carbon steel in the same solutions, the zinc surface was passivated in the both solutions. The different time to passivation could be attributed to the difference of mass transfer of dissolved zinc ions. A compact Ca(Zn(OH)3)2∙2H2O film was observed in the whole surface of the passivated zinc. The passivation might occur due to highly protective Ca(Zn(OH)3)2∙2H2O film. On the other hand, in Ca(OH)2 solution at pH10.5, the R ct of zinc was about 104 Ω∙cm2, where porous ZnO was observed on the surface. In the presence of chloride, zinc and carbon steel were depassivated in the saturated Ca(OH)2 solution at pH12.5, when chloride was increased by 0.05 M. On the other hand, zinc and carbon steel were passivated in the fresh mortar containing 0.05 M NaCl. The film of Ca(Zn(OH)3)2∙2H2O was detected on the zinc surface in the mortar containing 0.05 M NaCl. They were depassivated in the fresh mortar when NaCl was higher than 0.5 M. A critical chloride concentration for the depassivation in the mortar was much higher than in mortar. This might be attributed to the difference of mass transfer. The threshold of chloride concentration for the depassivation of zinc in mortar (pH12.5) was almost same as that of carbon steel. Reference[1] Z.Q.Tan et al.,Corr. Sci., 50(2008),2512

Corrosion Behavior of Epoxy-Coated Rebar with Pinhole Defect in Seawater Concrete

Experiments were carried out to investigate the corrosion behavior of epoxy-coated rebar (ECR) with pinhole defect (diameter in hundreds of microns) immersed in the uncarbonated/carbonated simulated pore solution (SPS) of seawater concrete. Corrosion behavior was analyzed by electrochemical impedance spectroscopy. The composition and morphology of corrosion products were characterized by X-ray diffraction, energy-dispersive spectrometry and scanning electron microscopy. Meanwhile, oxide film produced by preheating before spray coating was investigated by X-ray photoelectron spectroscopy and Mott–Schottky technology. Results indicated that corrosion behavior of ECR with pinhole defect exhibited three stages when immersed in the uncarbonated/carbonated SPS. In the initial stage, steel in defect was passivated when exposed in the uncarbonated SPS and corroded when exposed in the carbonated SPS, due to competitive adsorption between chloride and hydroxyl ions. In the second stage, the oxide film under coating reconstituted (the thickness and defects density decreasing) in the uncarbonated SPS, which was caused by the synergy between high hydroxide and chloride activity, while in the carbonated SPS, crevice corrosion happened under the coating around pinhole, because of the different oxygen concentrations cell at the coating/steel interface. In the third stage, localized corrosion occurred under the coating around the pinhole in the uncarbonated SPS, which was probably induced by ion diffusion at the nano-scale coating/steel interface. The corrosion products adjacent to the defects were re-oxidized from FeCl2·4H2O and Fe2(OH)3Cl to Fe2O3·H2O, and the corrosion area was expanded outward in the carbonated SPS.

Bond behavior of epoxy-coated rebar in ultra-high performance concrete

The bond behavior of epoxy-coated rebar embedded in two different ultra-high performance concrete (UHPC) mixtures is experimentally investigated by a uniaxial pullout test, and the effect of embedment length, side cover, and mixture type on the bond stress-slip relationship is predicted using a double-phase analytical model. The bond mechanism and failure modes of rebar in UHPC are similar to those observed in normal concrete. The embedment length and side cover have significant influence on the bond behavior of epoxy-coated rebar in UHPC, and more drastic bond stress hardening and softening are observed for the case of larger embedment length and side cover. Two UHPC mixtures exhibit comparable bond strength and critical development length because they have close mechanical properties gained at test age. The adopted analytical model matches well with the experimental bond-slip response of epoxy-coated rebar in UHPC, and both the characteristic parameters in the model show an increasing trend when more dramatic hardening and softening of bond stress exhibit.

The effect of heating and cooling on the bond strength between concrete and steel reinforcement bars with and without epoxy coating

The purpose of this study is to investigate the temperature effects on the bond strength between concrete and steel reinforcement bars. For two different steel bars (epoxy-coated and uncoated bars), three experimental parameters (heating rate, target temperature, and cooling condition) are examined. At a target temperature of 200 °C, the epoxy-coated rebar has much higher bond strength than the uncoated rebar. However, in the specimens exposed to target temperatures higher than 200 °C, the test results show that the epoxy coated rebar has less bond strength than the uncoated rebar. Also, the test results demonstrated that as the heating rate and target temperature increase the bond strength decreases. The cooling method does not affect the ultimate bond stress of the specimens using uncoated rebar very much but can greatly affect specimens that contained epoxy coated rebar. A more in-depth study can be considered regarding the cooling effect on the bond strength.

Pull-out bond strength and flexural load test of concrete beam with ethylene-vinyl acetate–modified cement slurry-coated rebar

A study has been conducted on a bond strength test of ethylene-vinyl acetate–modified ultra-high early strength cement slurry–coated rebar embedded in concrete and did a flexural loading test with the aim to verifying the feasibility of early strength cement slurry–coated rebar as a replacement for epoxy-coated rebar. Pull-out bond properties of the early strength cement slurry–coated rebar embedded in concrete with a 28-day compressive strength of 27 MPa depending on the coating thicknesses, curing ages, and polymer–cement ratios were experimentally investigated and mutually compared with two respective references consisting of a plain steel rebar and an epoxy-coated one. The effects of the uncoated, early strength cement slurry–coated, or epoxy-coated rebar embedded in a concrete beam with dimensions of 250, 350, and 3000 mm for the depth, height, and length, respectively, on the flexural loading capacity were investigated. From the results of this study, it was concluded that the early strength cement slurry–coated rebar with a coating thickness of 100 µm, and a curing time of 7 days could be competitive enough to replace epoxy-coated rebar based on the bond strength and flexural loading test results.

Protection of Steel Rebar in Salt-Contaminated Cement Mortar Using Epoxy Nanocomposite Coatings

Epoxy reinforced with two kinds of nanoparticles dealing with nano-SiO2 and nano-Fe2O3 was coated on steel rebar embedded in a chloride contaminated cement mortar. NaCl was added to the fresh Portland cement paste (at 0.3% and 0.5% by weight of cement) to simulate the chloride contamination at the critical level. The effect of incorporating nanoparticles on the corrosion resistance of epoxy-coated steel rebar was investigated by linear potentiodynamic polarization and electrochemical impedance spectroscopy. For the 0.3 wt.% chloride mortars, the electrochemical monitoring of the coated steel rebars during immersion for 56 days in 0.1 M NaOH solutions suggested the beneficial role of nano-Fe2O3 particles in significantly improving the corrosion resistance of the epoxy-coated rebar. After 56 days of immersion, the nano-Fe2O3 reduced the corrosion current of epoxy-coated rebar by a factor of 7.9. When the chloride concentration in the cement mortar was 0.5 wt.%, the incorporation of nanoparticles into the epoxy matrix did not enhance the corrosion resistance of epoxy coating for the rebar. At this critical level, chloride ions initiated rebar corrosion through nanoparticles at the epoxy/rebar interface.