Types Of Rebars Research Articles

Bond–slip behaviour of FRP-reinforced concrete beams

Flexural and bond–slip behaviour of fibre reinforced polymer (FRP)-reinforced concrete beams are investigated experimentally and numerically in this paper. Four-point bending tests are carried out to study the flexural and bond–slip behaviour of FRP-reinforced concrete beams reinforced with carbon FRP, glass FRP, and basalt FRP rebars with different surface conditions. The flexural and bond–slip behaviours of the test beams are also studied numerically by employing the recently developed finite element models with and without bond–slip effect. The results obtained from the numerical modelling agree very well with those obtained from experimental studies. Parametric study is carried out to investigate the effects of different rebar surfaces and rebar types on the structural behaviour of the FRP-reinforced concrete beams.

Bond degradation of glass fibre reinforced plastic bars in concrete subjected to tensile cyclic loads

An adequate bond between reinforcement and concrete is critical in ensuring the composite behaviour of a reinforced concrete structure. Although fibre reinforced plastic rebar–concrete bond behaviour under monotonic load has been studied by many researchers, little is known about its behaviour under repeated loads. In this study, a series of pull-out tests were performed to investigate the bond stress-slip behaviours under tensile cyclic loads at local slips greater than elastic range. Conventional reinforcing steel bars and two common types of glass fibre reinforced plastic bars, embedded in concrete with strength of 42 MPa, were tested under four different loading patterns (monotonic + 3 tensile cyclic load patterns), and the bond failure of each specimen was examined. The results indicate that the bond strengths of fibre reinforced plastic rebar, unlike steel rebar, can be affected by as much as 24% by tensile loading history. In addition, the analysis of the failure surfaces of the rebar after the tests showed that bond strength degradation of the glass fibre reinforced plastic rebar types considered in this study can be attributed to the degree of interlaminar failure.

Factors governing the fire response of concrete beams reinforced with FRP rebars

This paper presents results from a set of numerical studies on the influence of critical factors on the fire response of concrete beams reinforced with FRP rebars. The macroscopic finite element model used in the analysis accounts for high temperature properties of constitutive materials, realistic load and restraint conditions, as well as temperature induced slip between FRP rebars and concrete. The validity of the model is established by comparing predictions from numerical analysis with measured data in fire test. Results from parametric studies indicate that rebar type, concrete cover thickness, and fire scenario have significant influence on the fire response of concrete beams reinforced with FRP rebars, while the presence of axial restraint in the beam has moderate influence on fire resistance. These results from parametric studies are utilized to propose an optimum insulation scheme for enhancing the fire response of concrete beams reinforced with FRP rebars.

Durability of hybrid FRP reinforcing bars in concrete structures exposed to marine environments

To solve the brittle failure of existing FRP rebar, we developed hybrid FRP rebar that has more than 3% strain and plastic deformation like a steel reinforcement. So, the developed hybrid FRP rebar has emerged as one of the most promising and affordable solution to the brittle failure problem of existing FRP rebar in concrete structures. In this study, the durability of hybrid FRP rebar exposed to marine environments was evaluated. The performance degradation of three types of hybrid FRP rebar and one type of GFRP rebar were investigated after exposure to marine environment. Laboratory simulated a marine environment with solutions of NaCl, Na2SO4, and CaCl2, and repeated dry/wet and freeze/thaw cycles after immersion in salt water. Performance assessment was based on tensile strength, short beam tests, and bond tests. All test results showed high residual strength under the all condition. The experimental results confirm the desirable resistance of hybrid FRP rebar to marine environment.

Polyvinyl Alcohol Engineered Cementitious Composite (PVA-ECC) for the Interfacial Bond Behaviour of Glass Fibre Reinforced Polymer Bars (GFRP)

This paper presents experimental investigations of the interfacial bond behaviour of different types of rebar (steel, sand-coated GFRP, and helically-wrapped GFRP bars) and cementitious composites with and without polyvinyl alcohol (PVA) fibre. A total of 27 cubic specimens were prepared, and different PVA fibre volume fractions of 0%, 1% and 2% were added. The effects of PVA fibre on the compressive strength and interfacial bond strength were not significant. However, PVA fibre in engineered cementitious composites apparently changed the failure mechanisms during the pullout of both the steel and the helically-wrapped GFRP bars. The increase in PVA fibre volume fraction significantly improved the ductility of the matrix. Specifically, the helically-wrapped GFRP bar demonstrated the greatest improvement in ductility, while the sand-coated GFRP bar resulted in frictional pullout of the rebar due to the complete slip failure of the resin, regardless of the fibre content. Finally, the application of PVA-ECC to the helically-wrapped GFRP bar was found to be effective as replacement for steel rebar with respect to the ductility of the interfacial bond.

Bond stress–slip behaviour of two common GFRP rebar types with pullout failure

Numerous studies on fibre reinforced plastic (FRP) rebar–concrete bond behaviour have been carried out by many researchers. However, most of the reported works have focused on the ascending part of bond–slip behaviour, especially the maximum bond stress and corresponding slip values. Fewer efforts have been made to explore the post-peak bond–slip behaviour of FRP rebars in concrete. In this study, a series of pullout tests was performed to investigate the bond stress–slip behaviour of glass fibre reinforced plastic (GFRP) bars in concrete failed by pullout under monotonic load. The test specimens were prepared using two common types of GFRP rebars (helically wrapped and sand coated) with three different concrete strengths (25, 40 and 70 MPa). The results showed quite different pre- and post-peak bond–slip behaviours for the two GFRP types. Based on an analysis of the experimental data from this study and additional data from a literature review, simple model equations to predict the bond stress–slip behaviour for the two GFRP rebar types are suggested. The predicted bond–slip curves showed good agreement with the test results.

Corrosion behavior of epoxy/zinc duplex coated rebar embedded in concrete in ocean environment

The corrosion behavior of epoxy/zinc duplex coated rebar embedded in concrete is evaluated comparing with the black steel, galvanized and epoxy coated rebars for a long term in ocean environment. The effect of mechanical damages of epoxy coatings on the corrosion protection is examined. The epoxy coated and epoxy/zinc duplex coated rebars show the higher anti-corrosion performance than other types of rebars. However, once the epoxy coating is mechanically damaged, the more serious corrosion may occur in the damaged area of epoxy coated rebar in concrete. The epoxy/zinc duplex coating remains a good corrosion protection to steel in concrete even when suffering from some mechanical damages.

Estimation of compressive strength based on Pull-Out bond test results for on-site concrete quality control

Quality control of structural concrete has been conducted for several decades based mainly on the results of axial compression tests. This kind of test, although widely used, is not exempt from errors and has some considerable drawbacks that may affect its reliability, such as the need for appropriate and careful specimen conditioning and adoption of adequate capping techniques. For these reasons, it would be useful to have complementary or alternative ways to check compressive strength, in order to improve concrete quality control. The use of a bond test to monitor concrete strength is being proposed by an international group of researchers from France, Tunisia and Brazil as a potential means to this end. Given the fact that the link between bond resistance and concrete strength is already well established, this type of test seems to be a viable alternative to traditional methods. Nonetheless, to check if the underlying principle is sound when used in different circumstances, the group has been gathering data from several studies conducted by different researchers in various countries, with distinct concretes and rebar types. An analysis of the data collected shows that there is a clear and strong correlation between bond resistance and compressive strength, no matter the influence of other variables. This result validates the basic idea of using an Appropriate Pull-Out (APULOT) bond test to assess concrete strength. If the general principle is valid for random data obtained from different studies, the definition of a clear and appropriate test will probably lead to the reduction of experimental noise and increase the precision of the strength estimates obtained using this method.

Flexural capacity of one-way GFRP concrete slabs

The objective of the reported study was to investigate and evaluate the behaviour of one-way concrete slabs reinforced with glass-fibre-reinforced polymer (GFRP) rebars under distributed and line loads. A fibre-reinforced polymer (FRP) composite made with resin-impregnated continuous fibres is considered a promising alternative to traditional steel reinforcement. The experimental programme used eight GFRP concrete slabs to study the type of rebar (steel and GFRP), strength of concrete (25 and 45 MPa), reinforcement ratio and type of loading (distributed and line) loads. The results from a series of tests showed that strains of GFRP rebars are generally larger than those of steel rebars, increasing the ratios of the GFRP rebars led to an increase in ultimate flexural strength and increasing the concrete strength of the slabs led to an increase in slab rigidity, which improves flexural capacity. Furthermore, it was found that failure of slabs reinforced with GFRP rebars occurred by crushing and end slip of GFRP rebars must be prevented by using additional bars beyond the supports.

AFRP rebar로 보강된 콘크리트 깊은보의 전단강도

This study carried out a shear experiment on concrete deep beam reinforced AFRP to investigate the shear strength of deep beam. The test was conducted on 8 specimens, and the variables were shear span ratio, reinforcement ratio, effective depth, and rebar type. We compared shear strength using ACI 318-08 STM with proposed equations that considered arching action according to shear span ratio. As a result, it was found that shear strength of deep beam reinforced AFRP rebar presented higher shear strength than steel rebar. ACI STM`s predictions are more accurate than other predicting equations, and thus this research proposed model versus effective compressive strength of the concrete strut that considered strut size effect based on test results. The predictions obtained using the proposed model are in better agreement than previous equations and codes.

Flexural Characteristics of Concrete Beams Reinforced with a New Type of GFRP Bar

Beam tests were conducted to investigate the characteristics of a newly developed type of glass fibre-reinforced polymer (GFRP) rebar as reinforcement in flexural concrete members. Nine beams over-reinforced with different types of rebar, and with varying reinforcement ratios and depths of concrete cover, were monotonically loaded up to failure. Results were characterised by failure mode, moment–curvature, flexural capacity, load–deflection, and crack width. The test results were compared with the theoretical model and the American Concrete Institute design guide, which showed that the performance of the newly- developed GFRP rebar was comparable to commercially available GFRP rebars. In addition, a theoretical model for moment–curvature and an equation for predicting the flexural capacity of the beams with multiple layers of GFRP rebar are presented, based on the experimental observations.

Effective Surface Deformation Height and Bond Rigidity of GFRP Reinforcing Bars with Ribs

This study focuses on the evaluation of the surface deformation height of ribbed type of GFRP rebars. The bond behaviour of ribbed type of GFRP rebar is investigated in terms of the effective deformation height and bond rigidity, both experimentally and numerically. Pullout tests on ribbed type GFRP rebars embedded in concrete have been conducted to obtain an accurate bond stress-slip law and also to closely observe the state of the surface of pulled-out rebars at failure, in order to categorise accurately the mode of failure. In the pullout tests, the high temperature regime is particularly considered. In addition, finite element (FE) simulations of the specimens subjected to pullout tests are developed. From the FE analyses and the experiments, the effective surface deformation height and bond rigidity of the GFRP rebar with ribs was determined. The numerical results were substantiated by the experimental findings and good agreement was observed. Moreover, adding milled glass fibres in the surface deformations could not increase the effective surface deformation height and bond rigidity of the rebar; however, it seems to improve the bond strength because increasing the proportion of milled glass fibres improves the connections between the core and rib section.

Performance evaluation of rebar in chloride contaminated concrete by corrosion rate

The presence of chloride ions in reinforced concrete (RC) plays a major role in reinforcement corrosion and hence for the durability and service life of RC structures. With growing concern towards the deterioration of reinforced concrete structures, the use of electrochemical techniques for their performance evaluation has become an important topic of durability study. This paper illustrates the findings of an experimental investigation carried out on large number of specimens for evaluating the performance of different types of rebar in chloride contaminated concrete made with different types of cement through different corrosion rate techniques. The specimens were prepared with three types of cement and three types of steel. From the results of corrosion rate, it was observed that the values of corrosion rate obtained by linear polarization resistance (LPR) technique with guard ring arrangement were in close agreement with those obtained by gravimetric method. On the other hand the corrosion rate values obtained by AC impedance spectroscopy were slightly lower than those obtained by LPR measurement. Further, correlations between different corrosion rate techniques were also obtained. From the results of analysis of variance (ANOVA), it was observed that chloride content has the strongest effect on corrosion rate as compared to other factors.

Design recommendations for bond between GFRP/steel wire composite rebars and concrete

Due to significant advantages over GFRP rebars, namely high tensile strength, high elastic modulus, and good ductile properties, GFRP/steel wire composite rebars offer a superior alternative to ordinary steel rebars. However, experimental researches on this new type of rebar have been limited, especially those on the bond performance. This research is designed to investigate the bond behavior between GFRP/steel wire composite rebars and concrete. According to American Concrete Institute (ACI) code, a total of 180 pull-out specimens were tested under monotonic static loading conditions. The test parameters were the rebar rib spacing, rebar diameter, embedded length, concrete compressive strength, concrete cover thickness, and concrete cast depth. Based on the numerical analysis of the test results, new criteria for acceptable bond performance of GFRP/steel wire composite rebars to concrete were developed. Designed recommendations for the modification factor of concrete cover thickness, the modification factor of concrete cast depth, and the critical value of bond slip at both free and loaded ends were derived. The calculation formula of bond strength and the basic development length were proposed, and the calculation principle of development length of concrete structures reinforced with GFRP/steel wire composite rebars was suggested.

Bond strength improvement of GFRP rebars with different rib geometries

Based on the Canadian Standards Association (CSA) criteria, 105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube, with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type, rebar component, rebar diameter, rebar surface texture, rib height, rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%∼35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type, rebar diameter, rebar surface texture, rib height, rib spacing and rib width. Using the results, design recommendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics, which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter, and that the optimal rib height is 6% of the rebar diameter.

Interfacial bond strength of glass fiber reinforced polymer bars in high-strength concrete

This paper presents the results of an experimental study on the interfacial bond strength of glass fiber reinforced polymer (GFRP) bars in high-strength concrete cube. The experimental program consisted of testing 54 concrete cube specimens prepared according to CSA S802-02 standard. Two main parameters were considered in the experimental investigation: the compressive strength of concrete (from 25.6 MPa to 92.4 MPa) and the type of rebar (steel, sand-coated GFRP, and helically wrapped GFRP). The test results showed that the interfacial bond strength of the GFRP bars increased as the compressive strength of concrete increased. However, the increasing rate of the bond strength of the GFRP bars with respect to the concrete strength was much smaller than that of the steel bars. The concrete specimens were sawn in half after the test for a closer investigation of the actual mode of bond failure. Visual examination of the specimens showed that bond failure of the steel bar was caused by concrete crushing against the face of the ribs, while bond failure of the GFRP bars occurred not only in the concrete but also in the bars by delamination of the resin-rich outer layer from the fiber core. The average area of the delaminated resin-rich layer of the GFRP bar increased with increasing compressive strength of concrete.

Realistic Bond Strength of FRP Rebars in NSC from Beam Specimens

The bond strength of reinforcing bars in concrete is a prerequisite for the evaluation of the development length in reinforced concrete structures. This study concerns these phenomena for fiber reinforced polymer (FRP) rebars in normal strength concrete (NSC). Three different types of rebars were tested using the beam specimen: Carbon, glass, and steel. This involved a total of 26 beam specimens containing 10, 16, and 19 mm rebars. The test embedment lengths were 10, 15, and 20 times the rebar diameter ( db ) . For each rebar tested, the results concern load deflection curves, bond stress-slip responses, and the mode of failure. The results showed that the bond strength of a FRP rebar is, generally, lower than that of steel rebar. Based on this and previous research, proposals for the average bond strength and for the development length of straight FRP rebars under tension in NSC are made.

Experimental characterization of the bond performance of a new type of glass fibre-reinforced polymer rebar for application in concrete structures

This paper presents experimental results obtained from direct pull-out tests of commonly used and a new type of glass fibre-reinforced polymer (GFRP) rebar. The new GFRP rebar, developed by the authors, has a surface structure composed of milled glass fibres and epoxy resin, and its appearance resembles that of ordinary steel rebar. The effects of surface type and increased amounts of milled glass fibres in each rib on bonding with concrete were investigated to characterize the bond performance of the new type of GFRP rebar. The results indicated that the new type of GFRP rebar performed better with a higher bond strength to concrete compared with other tested types of GFRP rebar. Moreover, the rib bearing resistance and energy absorption appeared to increase with increased milled glass fibre in the ribs, which dominated the overall bond behaviour.

Tests on reinforced-concrete-filled, fiber-reinforced-polymer circular tubes of different shear spans

This study examines the shear behavior of concrete-filled glass-fiber-reinforced-polymer (GFRP) tubes (CFFTs) reinforced with either steel or fiber-reinforced-polymer (FRP) longitudinal rebar. To evaluate the contribution of the GFRP tubes, control specimens with and without steel spirals, instead of the tubes, were also tested. Shear span-to-depth ratios (a/D) of 1 and 2 were considered in 14 three-point bending tests. CFFT specimens with a/D = 1 failed in shear by diagonal tension failure of the concrete core and tube, whereas those with a/D = 2 failed mostly in flexure. Control specimens failed in shear at both a/D = 1 and a/D = 2. The shear strength of CFFT beams was substantially higher than that of control specimens but was dependent on rebar type and size. Some slip occurred between the concrete core and both the GFRP tube and the rebar. It is concluded that shear failure may occur in reinforced CFFTs at a/D ≤ 2. Despite the shear failure of steel-reinforced CFFTs at a/D = 1, the measured moments at failure were only 9% lower than their respective ultimate flexural strengths. A simplified strut-and-tie model was developed, and it showed reasonable agreement with experimental results.Key words: concrete-filled glass-fiber-reinforced-polymer tube (CFFT), concrete-filled, fiber-reinforced polymer (FRP), rebar, shear span, shear strength, tube, strut-and-tie model.

Corrosion Resistance of Cr-Bearing Rebar to Macrocell Corrosion Environment Induced by Localized Carbonation

Artificial cracks were made in the cover concrete of specimens embedding ten types of steel rebars of different Cr contents. The research aims for developing Cr-bearing steel rebars resistant to macrocell corrosion environments induced by cracking in cover concrete. The cracks were subjected to intensive penetration of carbon dioxide (carbonation specimens) to form macrocells. The carbonation specimens were then treated with accelerated corrosion curing, during which current macrocell corrosion density was measured. The corrosion area and loss from corrosion were also measured at the end of 105 cycles of this accelerated curing. The results of the study showed that Cr-bearing steel with Cr content of 5% or more suppressed corrosion in a macrocell corrosion environment induced by the differences in the pH values due to carbonation of cracked parts. Cr-bearing steels with Cr content of 7% or more are proven to possess excellent corrosion resistance.