Pull-out Specimens Research Articles

Bond performance of fiber reinforced polymer bars in normal- and high-strength concrete

The structural performance of reinforced concrete (RC) members depends on the bond between the reinforcing bars and surrounding concrete. Unlike steel bars, fiber-reinforced polymer (FRP) bars are manufactured with different fiber types (glass, basalt, carbon, and aramid) and have different mechanical properties and surface configurations (sand-coated, deformed, grooved, sand-coated over helical wrapping). These differences impact the bond performance between the FRP bars and concrete. This paper investigates the bond performance of new generation and different FRP bars embedded in concrete. A total of 87 pullout specimens were constructed and tested until failure. The test results are presented and discussed. The test parameters include (i) fiber type (glass or carbon), (ii) surface configuration (sand-coated, deformed, or grooved), (iii) No. 4 to No. 8 (13 to 25.4 mm diameter) bar diameters), and (iv) concrete strength (normal- or high-strength concrete: NSC or HSC). Specimens with deformed 10 M or 15 M steel bars were also fabricated as controls and tested for comparison. The embedment length and block dimensions were also considered to ensure pullout-failure mode. The test results reveal that increasing the bar diameter generally reduced the bond strength of the FRP bars, while the bar diameter had insignificant impact on the steel bars. There was a positive relationship between the concrete compressive strength and the bond strength gained. The anticipated failure modes with the high concrete strength were at the fiber resin interface due to the high confinement generated by high-strength concrete. With the lower strength, failure usually occurred at the resin–concrete interface. In addition, the test results were used to assess different analytical models for bond stress-slip relationships.

Influence of bond test methods on the bond performance between reinforcing bars and concrete

The bond strength between reinforcing bars and concrete is critical to structural performance for reinforced concrete structures. As bond strength is affected by the stress field, a beam test is recommended to evaluate the bond strength. However, the beam test is somewhat complicated and time-consuming compared to the pull-out test. To investigate the influence of testmethodson the bond strength, databases including 598 existing beam test data and 197 existing pull-out test data were established. Based on existing beam test results and bond mechanism, a regression analysis was performed to propose the bond strength model. The proposed empirical equation can better meet the test phenomenon with less dispersion. Moreover, the empirical equation was directly applied to existing pull-out test results to evaluate the effect of test methods on bond strength. The results showed that the contributions of the development length-to-diameter ratio and restraint factor are consistent for the different test methods. However, the concrete stress field is significantly affected by the use of transverse bars and the test methods and results in various contributions of concrete strength. Besides, a unified bond strength equation was proposed using a strength conversion factor of concrete, which can be applied to beam and pull-out test specimens with ld/db⩾7. Additional tests were performed, which verified the prediction accuracy of the proposed unified model. Finally, based on the statistical analysis result, it can be inferred that the pull-out test method was still effective in evaluating the development length and bond strength in the concrete strength range of GB 50010–2010.

Experimental and numerical simulation of bond-slip in textile-reinforced concrete for multiple bond lengths

The rise in the use of lightweight and sustainable structural systems in the construction industry opened the chance to improve conventional construction methods. To produce a slender structural member, the use of textile in concrete, herein referred to as textile-reinforced concrete (TRC), has been explored. The textile used is primarily carbon, producing a lightweight and durable construction material. The TRC possesses vast possibilities in terms of its usage, however, identification of accurate bond-slip behaviour at the materials interface is one of the limitations that need to be addressed. Based on the literature, there are difficulties in determining the bond-slip relationship both experimentally and numerically, creating inconsistency in the results. This study aims to determine the bond-slip relation of TRC through pull-out tests and finite element analysis in order to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using pull-out specimens with different bond lengths of textile, i.e.; 20 mm, 40 mm, and 60 mm. A double-sided unsymmetrical test setup with equal clamp lengths is used for the experimental work. Using a tri-linear bond-slip interface relation, the numerical model is developed to establish the microscopic interface behaviour. The bond failure due to pull-out and rupture are observed in the pull-out test. Finally, the experimental results are compared with numerical modelling, and the results are in good agreement.

Strain-based analysis of reinforced concrete pull-out tests under monotonic and repeated loading

This paper presents the results of an experimental campaign on standard pull-out specimens instrumented with refined strain measurement techniques. The quasi-continuous strain measurements allowed the derivation of experimentally substantiated local bond stress-slip relationships for static and repeated loading. It was shown that the force transfer between concrete and reinforcement along the bond length is not uniform and that redistribution occurs with increasing as well as repeated load. The variation of bond stresses along the bond length is of great importance for fatigue studies, as the fatigue damage depends on the level of the applied stress. In addition, the refined measurements revealed non-uniformities in the unloading behaviour. Thus, a slip reversal occurs mainly on the loaded side of the pull-out specimen. The experiments confirmed that the residual nominal bond strength after repeated loading does not significantly vary from the initial bond strength, and the redistribution capacity was identified as a possible cause. The comparison with the nominal bond-slip relationship obtained in a conventional test setup agreed well with the mean value of the refined measurements. However, local degradation processes, such as fatigue, cannot be investigated properly with conventional pull-out tests.

Experimental and analytical assessment of fatigue damage in reinforced concrete tension members

In this paper, the effects of bond deterioration due to fatigue loading on the structural response of reinforced concrete tension members are studied. A comprehensive experimental campaign on reinforced concrete ties and pull-out specimens was carried out under monotonic and repeated loading. The use of distributed fibre optical sensing to assess the local strains allowed the bond deterioration mechanism under repeated loading to be observed. Previously applied load cycles caused a reduction in tension stiffening for load levels below the maximum cyclic load but did not significantly influence the deformation behaviour of the member near the ultimate load. The bond stresses at the maximum cyclic load decreased fairly linearly with the logarithm of load cycles, with the most pronounced reduction in bond stresses near the cracks. At the minimum cyclic load, the bond stress distribution along the tie changed and bond stresses reversal occurred close to the cracks. This caused negative tension stiffening in some cases, i.e., the mean strains exceeded those occurring in a bare reinforcing bar at the same load. The mean steel stresses and the steel stress amplitudes between the cracks increased with the number of load cycles due to the gradual reduction of the concrete contribution and bond degradation. Bond degradation occurred linearly on a semi-logarithmic scale, as expected for the generated bond stresses, which were below the fatigue bond strength. The test results highlight that accounting for shrinkage-induced strains is essential for a realistic evaluation of tension stiffening and residual deformations in particular.Based on the experimental observations and previously developed models for monotonic and cyclic loading, two approaches were used to predict the response of reinforced concrete tension members under repeated loading: the Local Fatigue Damage Model (LFDM), based on the local bond stress-slip relationship, and the adapted Tension Chord Model (TCM) which assumes constant bond stresses and mean strains. The results of both approaches agree well with the test results at the maximum load but yielded less satisfactory predictions at the minimum loading level where only the LFDM was able to be applied successfully. Further research is required to validate the negative bond stresses occurring upon slip reversal in the LFDM and the reduction factor proposed in the adapted TCM.

Bond performance of CFRP bars embedded in UHPFRC incorporating orientation and content of steel fibers

The bond behavior of carbon fiber-reinforced polymer (CFRP) bars embedded in ultra-high-performance fiber-reinforced concrete (UHPFRC) is a pivotal factor affecting the performance of CFRP bar-reinforced UHPFRC structures. The present investigation delves into the bond performance of CFRP bars in UHPFRC by conducting tests on thirty-six pullout specimens. In these tests, the effects of steel fiber orientation, steel fiber content, and CFRP bar diameter were considered. The results revealed that specimens with 12 mm-diameter CFRP bars primarily failed in a splitting-pullout mode, whereas those with 10 mm- and 8 mm-diameter CFRP bars exhibited pullout failure. It was observed that specimens containing 45° oriented steel fibers have the maximum bond strength (∼35.30 MPa), as the cracks within UHPFRC were more effectively constrained. The bond strength was found to increase with an increase in steel fiber content, attributed to the improved cracking resistance of UHPFRC. The average bond strengths of specimens with fiber contents of 2% and 2.5% are respectively increased by 10.66% and 14.52% compared to those with a fiber content of 1.5%. The bond strength increases with the increase in CFRP bar diameter, owing to the greater rib height and rib height-to-inner diameter ratio of larger-diameter CFRP bars. Finally, a theoretical model was developed to predict the bond strength, with an average ratio of predicted results to experimental results of 0.93 and a standard deviation of 0.176.

Approximate Relationship for the Bond-Slip Using a Concrete Damage-Plastic Model

This paper presents an approximate multicontact model to study dynamic bond stress-slip based on the concrete damage-plastic model. To establish the bond stress-slip between rebar and concrete, an elastic-plastic steel cylinder contact element was used as the tube (ring contact element), and then, by reducing the bond strength, the amount of slip between rebar and concrete and its effect on concrete damage-plastic parameters were considered. When concrete cracks, the parameters of concrete cracking, the plasticity of rebar and concrete fracture, and the pull-out of rebar from concrete are used to consider the bond-slip relationship between rebar and concrete. Meanwhile, an external constraint in the cylinder model is taken into account. The bond strength calculated by the presented model is compared with the pull-out test specimen results, and the errors are generally within 15%. Finally, using the results obtained from the amount of slip in models, an approximate mathematical relationship between the slip of the rebar inside the concrete can be obtained in terms of the resistance of the ring contact element (instead of the concrete surrounding). This formula can be used to calculate the bond-slip rate of all the rebars of a structure. The results of the mentioned model using the ABAQUS software demonstrated that by reducing the strength of the ring contact element by 20%, slip increased by 4.2%. Also, with an 80% reduction in ring strength, the bond-slip rate increases by 45%. The proposed approximate relationship has reasonable accuracy and lower computational cost.

Interfacial bond behavior between ribbed CFRP bars and UHPFRC: Effects of anchorage length and cover thickness

Carbon fiber-reinforced polymer (CFRP) bars and ultra-high-performance fiber-reinforced concrete (UHPFRC) feature high strength, high elastic modulus, and excellent durability, which can be combined and applied to the high-load or corrosive environments. To comprehend the bond behavior between the ribbed CFRP bar and UHPFRC, 30 cubic specimens for axial pull-out tests and 12 cubic specimens for eccentric pull-out tests were tested in this study. The effects of CFRP bar diameter, anchorage length, and cover thickness on the bond behavior were investigated. The results indicated that three different failure modes, which were pull-out failure, splitting failure and splitting-pull-out failure, were detected. The delamination of fibers and resin in the specimens with pull-out failure caused interfacial bond failure between the ribbed CFRP bar and UHPFRC. The bond strength increased from 18.41 MPa to 36.41 MPa when the diameter increased from 10 mm to 12 mm, owing to the increase in the geometric ratios (concrete lug ratio and relative rib area) of the CFRP bar surface. Additionally, the increase of cover thickness was beneficial for improving the interfacial bond strength, and the critical cover thickness was about three times the bar diameter (3d). The residual stage of pull-out specimens still exhibited a high-stress level in the case of splitting failure owing to the fiber bridging effect of UHPFRC. Finally, a bond strength prediction model related to anchorage length, cover thickness, and the geometric ratio of CFRP bar surface was proposed.

Corrosion-Effected Bond Behavior between PVA-Fiber-Reinforced Concrete and Steel Rebar under Chloride Environment

Corrosion-effected bond behavior between polyvinyl-alcohol-fiber-reinforced concrete and steel rebar under a chloride environment is the experimental subject studied in the present work. Twenty-four pull-out specimens are designed and subjected firstly to an accelerated corrosion test. The effects of polyvinyl alcohol fibers on the cracking behavior, chloride penetration of concrete members and the corrosion loss of steel rebars during the corrosion test are discussed. After this, these corroded specimens are subjected to a pull-out test. The failure mode, the bond-slip curves and the typical bond-stress values are measured during the test. The effects of polyvinyl alcohol fibers and corrosion loss on bond behavior between polyvinyl-alcohol-fiber-reinforced concrete and steel rebar are clarified. Results show that the polyvinyl-alcohol-fiber-reinforced concrete exhibits worse resistance to corrosion damage than plain concrete. The cracking width, chloride penetration depth in concrete and the corrosion loss of steel rebar are more serious for the specimens with more polyvinyl alcohol fibers. The polyvinyl alcohol fibers also negatively affect bonding in ascending branches for both the specimens, but improve the bonding in descending branches after peak stress in the case of splitting. In the present test, the bond strength of corrosive specimens is increased slightly and then decreases gradually with the deepening of corrosion loss. The failures of specimens change from pull-out to splitting-pull-out as the corrosion time exceeds 30 days. Compared with uncorroded specimens, the maximum degradation of bond strength is about 50.1% when the corrosion is increased from 0% to 15%.

Bond performance between recycled concrete and steel bar after high temperature

Abstract To investigate the influence of high temperatures on the bond performance of recycled concrete and steel bar, this article considers the influence of different concrete types (ordinary concrete and recycled concrete) and different temperatures (20, 100, 150, 200, 250, and 300°C) on the concrete compressive strength and the bond performance of concrete and steel bar. On this basis, the calculation formula of bond strength and bond slip between concrete and steel bar after the high temperature is established. The test results show that the concrete compressive strength presents a downward trend with the increase in temperature; the compressive strength loss of recycled concrete is higher than that of ordinary concrete; when the temperature reached 300°C, the compressive strength loss of ordinary concrete is 24.4%, while that of recycled concrete is 41.6%. The bond strength of pull-out specimens decreases with the increase of temperature, while the bond slip increases with the increase of temperature; the bond strength between recycled concrete and steel bar is lower than that between ordinary concrete and steel bar, while the bond slip between recycled concrete and steel bar is higher than that between ordinary concrete and steel bar. This article can provide a theoretical basis for the application of recycled concrete in high-temperature environment.

Bond behavior of recycled tyre steel fiber reinforced concrete and basalt fiber-reinforced polymer bars under static and fatigue loading conditions

Nowadays, there is a growing demand for the development of structures and construction materials from recycled or reused and renewable resources, in line with circular economy principles and the goal of sustainable development. The present study explores promising solutions for increasing the sustainability of concrete structures, through the application of basalt fibers reinforced polymer (BFRP) rebars, whose raw materials show an unlimited availability on earth, as well as recycled steel fibers from waste tyres (RTSF), for RTSF reinforced concrete structures with BFRP reinforcements. Three different types of self-compacting concretes with 1.1% fiber volume fractions of industrial and/or recycled steel fibers were developed, where 50% and 100% of the industrial steel fibers (ISF) weight was replaced by RTSF. Five different groups of pull-out specimens, with total number of 26 specimens, were fabricated to evaluate bond performance of BFRP rebar embedded in RTSF reinforced concrete. The understanding of the bond behaviour is critical to the effective design of reinforced concrete structures under both static and dynamic loadings. The influence of the type of reinforcement, dosage of the adopted RTSF, type of loading, and concrete flow direction on bond stress versus slip behavior, maximum bond stress, and failure mode are analysed and discussed. One of the main contributions of this research regards the understanding of the effect of RTSF orientation on bond performance obtained when BFRP rebars are pulled out from RTSF reinforced concrete. Compared to ISF, using RTSF for reinforcing concrete can increase the bond strength between BFRP rebars and fiber reinforced concrete up to 6.3% under static and 9.7% under fatigue loading regime. As the future research in this area, it is recommended to evaluate the long-term bond durability of BFRP reinforced FRC embedded in seawater, the environmental and economic feasibility of using BFRP and TRSF for reinforcing concrete structures, and fiber orientation and dispersion using image analysis and 3D visualization.

Simulation on pull-out performance of steel bar from 3D-printed concrete

In this study, a finite element (FE) model for the pull-out test was established and verified to examine the influence of printed concrete-to-concrete interfaces on the pull-out performance of steel bar from 3D-printed concrete. The stress transfer, debonding process, and failure mechanism of 3D-printed specimen were revealed by detailed interfacial stress analysis. Moreover, the effects of the interfacial bond strength, filament size, angle between the steel bar and the printing direction (α), and bond length on the pull-out performance were intensively investigated. The numerical results showed that the failure pattern changed from the conventional pull-out failure to interfacial bond failure induced by 3D-printed concrete-to-concrete interfaces. Compared with the pull-out specimen with α = 0°, the peak load of pull-out specimen with α = 90° increases by 9.6%, which became the weakest when angle α = 30°. Moreover, the failure mode was observed to be influenced by the relative strength of the interlayer and interstrip interfaces and their distributions.

Bond performance of the additional aluminum alloy ribs anchored CFRP bars in concrete under sustained loading

The novel additional aluminum alloy ribs (ARs) anchorage is a convenient and effective solution to improve the bond of FRP bars in concrete. Although the bond behavior between the ARs anchored FRP bars and concrete under the short-term loading has been recently investigated, its long-term behavior under sustained loading has yet been assessed. This paper aims to study the long-term bond behavior of both the unanchored and ARs anchored CFRP bars in concrete under sustained loading for a period of 380 days. 12 pull-out specimens were tested under sustained loading considering parameters including the bond length, sustained loading level, and the type of FRP bars. Results showed that the ARs anchored specimens effectively reduced the long-term slip by as much as 48.7%-52.5% compared to that of the referenced unanchored specimens due to an improved bond mechanism. In addition, an analytical model was proposed to predict the long-term end slip for both the unanchored and ARs anchored FRP bars in concrete.

Bond behaviour of deformed reinforcing bars in ultrahigh-performance fibre RC

In reinforced concrete (RC) structural systems, the use of ultrahigh-performance fibre RC (UHPFRC) as an alternative to ordinary concrete is promising, especially in critical locations, such as wet joints between prefabricated members. To better understand and guide the construction practice of reinforced UHPFRC members, 28 pull-out specimens were tested to investigate the bond performance of steel bars embedded in UHPFRC. The influences of embedment length and bar diameter were analysed and discussed. Owing to the high cracking resistance of UHPFRC, no crack formation or splitting failure was found during the test. It is concluded that the bond development and deterioration process of steel bars in UHPFRC are fundamentally similar to those observed in ordinary concrete except for the higher initial bond stiffness and peak bond strength. Moreover, formulae for calculating normalised bond strength and residual bond strength are proposed, and an analytical model for bond stress–slip response has been developed accordingly, based on a modification of the model recommended by fib Model Code 2010. Finally, suitable anchorage lengths of deformed steel bars in UHPFRC are discussed and suggested.

Pullout behaviors of basalt fiber-reinforced polymer bars with mechanical anchorages for concrete structures exposed to seawater

This study presents an investigation of the pullout behaviors of basalt fiber-reinforced polymer (BFRP) bars with mechanical anchorages in concrete exposed to seawater. A total of forty-eight pullout specimens were prepared. Three types of mechanical anchorages that can be flexibly assembled on FRP bars, that is, additional straight bar, additional hook, and composite head, were adopted. The experimental variables comprised the anchorage type, conditioning temperature, and conditioning duration. The maximum pullout load (Pmax) and corresponding slip (smax), and the plateau length at the peak (lp) and slope of the descending branch (kd) of the load-slip curves, were evaluated and discussed. The results show that mechanical anchorages contribute to significant increases in the lp and decreases in the kd. Furthermore, the composite head achieves 32 % and 10 % increases in Pmax and lp respectively, and 20 % and 36 % decreases in smax and kd respectively, compared with the other two types of anchorages. After conditioning in seawater, the specimens with composite heads exhibit no significant degradation in their pullout behaviors, which indicates the effectiveness of the composite head in the protection against corrosive media. These results demonstrate the application prospects of a composite-head mechanical anchorage for FRP reinforcement in concrete structures constructed in the marine environment.

Bond behavior between steel bar and concrete considering cryogenic temperatures and confinement

Reinforced concrete (RC) structures exposed to cryogenic temperature environment, the bond performance of rebar-concrete is related to the characteristics of concrete material and rebar. The mechanical characteristics of concrete material and rebar vary greatly at cryogenic temperatures. To illustrate the bond behavior of rebar-concrete at cryogenic temperatures, the pull-out specimens were simulated focusing on the coupling effects of cryogenic temperatures and confinements on the bond behavior. The model considers the surface characteristics of deformed reinforcement and the cryogenic temperature effects on the mechanical characteristics of materials. The confinements were applied to the specimens by carbon fiber-reinforced polymer (CFRP) and stirrup respectively, and the temperature ranges from 20 °C to − 120 °C. The effects of thickness diameter ratio (c/d), and confinements on the bond behavior at cryogenic temperatures were discussed. The results showed that at cryogenic temperatures, the failure modes are similar to those at 20 °C for the specimens with c/d ≤ 3.75. However, for the specimen with c/d = 4.0, the specimen at − 120 °C exhibits splitting failure due to the increase of brittleness. The bond strength at cryogenic temperatures is improved with the increasing c/d. The effects of confinements on the failure modes are small, but the bond strength is improved by the CFRP confinements and stirrup confinements. According to the numerical data, the developed bond strength model and bond stress-slip model considering the effects of confinements could provide better predictions of the bond behavior at cryogenic temperatures.

A comparative study on strength, bond-slip performance and microstructure of geopolymer/ordinary recycled brick aggregate concrete

Geopolymer recycled brick aggregate concrete (GRBC), which is a new kind of sustainable eco-friendly material, has the potential to be widely used in engineering applications. However, little research has been done on its basic mechanical properties and microstructures. Accordingly, a series of tests such as uniaxial compressive test, splitting tensile test and pull-out test were carried out in this paper. Taking recycled brick aggregate (RBA) replacement ratio (0%, 25%, 50%, 75% and 100%) as the main variable, 60 cubes and 40 pull-out specimens with steel bars were fabricated and tested. The compressive strength, tensile strength and bond-slip performance of GRBC were investigated and compared with the ordinary recycled brick aggregate concrete (ORBC). The analysis using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) was conducted to study the microstructure characteristics of GRBC and ORBC. The results show that the compressive strength, splitting tensile strength and bond strength between concrete and steel bar decrease with the increase of RBA replacement ratio, and the decrease rate of GRBC is faster than that of ORBC. For GRBC, when RBA replacement ratio varies from 0% to 50% and 100%, the compressive strengths decrease by 32.25% and 57.49%, respectively; the splitting tensile strengths decrease by 33.11% and 53.20%, respectively; while the bond strengths decrease by 19.91%–28.11% and 46.32%–49.63%, respectively, depending on different bond length. ORBC pull-out specimen is more prone to splitting failure than GRBC specimen. The aluminosilicate gel formed by the hydration of geopolymer matrix has a denser structure than the gel of ordinary concrete matrix. Incorporating the RBA results in the failure order change in weakness of GRBC and ORBC, and the failure of interfacial transition zone (ITZ) between matrix and aggregate is transformed into the failure of RBA.

Optimization of test method for bond performance between steel bar and concrete

The optimization device for the pullout test was designed by mechanical principle. The influence of specimen type on the accuracy of bond performance was studied by test and simulation analysis. Results show that the optimized device improves test accuracy, especially the loading end slip. The circular section specimen has better mechanical performance, more uniform and stable strain variation, and better regularity, which is the preferred section of pullout specimens. The concrete strain distribution does not meet the plane section assumption along the protective layer thickness. In addition, a more practical method for calculating bond stress is proposed.

Bond Strength between Recycled Concrete and Rebar under Stirrup Constraint after Freeze-thaw Cycles

In cold regions, freeze-thaw (F-T) damage is the main detriment to the durability of reinforced concrete structures, which will reduce the bond performance between concrete and rebar, and then adversely affect the bearing capacity and stiffness of structures. In this study, 21 groups of tests were performed to analyze the effects of the number of F-T cycles, volume stirrup ratio, and replacement percentage of recycled aggregate on the bond performance between recycled aggregate concrete and deformed rebar. The stirrup stress during the pulling process was measured using strain gauges attached to the stirrup surface, and the contribution of the stirrup to the bond strength was analyzed. The results showed that the F-T damage and stirrup constraints could affect the failure mode, the bond strength and the peak slip of pullout specimen. The failure mode of specimen with stirrups could be determined by splitting angle index. The indirect contribution of stirrup accounts for 14–25% of the bond strength and increases with the increase in F-T damage. The full bond-slip curve was obtained by fitting four parameters including splitting tensile strength, constraint coefficient, splitting angle index and brittleness index.

Effect of magnesium phosphate cement mortar coating on strand bond behaviour

Surface coating on prestressing strand is an effective and economic measure to prevent pre-tensioned prestressed concrete structures from corrosion. The effects of magnesium phosphate cement (MPC) mortar coating on the strand bond behaviour are investigated experimentally in the present paper. Ten pull-out specimens with different MPC mortar coating thickness are designed to study the effect of coating thickness or thickness ratio on the bond failure mode, bond strength and force-slip response. Experimental results demonstrate that the bond failure mode changes from pull-out failure accompanied with strand rotation to cover splitting failure when coating thickness and thickness ratio exceed 10 mm and 0.15, respectively. Compared with the uncoated and epoxy coated control specimens, coating thickness ranging from 25 mm to 35 mm or thickness ratio ranging from 0.37 to 0.52 contributes the most to the increase of bond strength and stiffness. Beyond that range, the facilitation in both bond strength and stiffness gradually decreases. Besides, an analytical model, which considers the composite cover confinement provided by the coating and concrete, is proposed to reproduce the bond strength evolution. Comparison of experimental and prediction results show that the proposed model can be used to reasonably evaluate the bond strength.