Bond-slip Behavior Research Articles

Unified Models for Bond Strength and Bond-Slip Response of Deformed Rebars in Cracked Concrete

Cracks in reinforced concrete structures pose a potential risk to their long-term stability and safety, necessitating an accurate analysis of the bond failure mechanism between the reinforcement and the cracked concrete. However, currently, there is a lack of comprehensive bond prediction models for the entire cracking stage, and limited understanding of the bond slip response. To address the aforementioned issues, an improved model incorporating internal pressure, crack width, and failure modes, aiming to provide a more precise estimation of the bond strength between deformed bars embedded in concrete under various cracked cases. The proposed model demonstrates superior performance in predicting cracked cases and failure modes. The performance of the proposed model in predicting cracked cases and failure modes is superior to existing models, as demonstrated by a comparative analysis. Additionally, a comprehensive model is proposed to analyze the bond-slip behavior in cracked concrete. This model introduces a bond reduction factor for cracks, aiming to determine the critical bond length required for bond strength.

Bond-Slip Behavior of Steel Bar and Recycled Steel Fibre-Reinforced Concrete

Bond-Slip Behavior of Steel Bar and Recycled Steel Fibre-Reinforced Concrete

Investigations on geopolymer-based seawater sea-sand high performance concrete slabs reinforced with basalt FRP bars under direct contact explosions

Adopting locally available raw materials like seawater and sea-sand in coastal areas and oceanic islands has facilitated meeting the demands of marine engineering. However, these raw materials contain corrosive elements that could threaten the steel reinforcement in concrete structures, thus non-corrosive fibre-reinforced polymer (FRP) bars are proposed. In the present study, the geopolymer-based seawater sea-sand high performance concrete (G-SHPC) slab reinforced with basalt FRP bars was designed to preliminarily evaluate its dynamic behaviour under contact explosions. Tests were conducted on three large-sized slabs with different TNT charge weights, including 0.8 kg, 1.6 kg and 2.2 kg. To complement the experimental investigation, a numerical simulation was then performed in ANSYS-DYNA. A Continuous Surface Cap (CSC) model was developed to accommodate the unique characteristics of G-SHPC. Two different blast modelling methods, including the Arbitrary Lagrangian-Eulerian (ALE) algorithm and a hybrid Finite-Element (FE) and Smooth Particle Hydrodynamics (SPH) algorithm, were examined to faithfully reproduce the contact explosion phenomena. The structural models considered the bond-slip behaviour, and three bond-slip models were compared. The numerical results obtained through the ALE algorithm and the beam-in-solid bond-slip model exhibited fair agreement with the test results, with a maximum error of less than 6.3%. A parametric study was further conducted to establish the damage identification diagram. Formulas based on empirical data were formulated to anticipate the damage degrees of G-SHPC slabs exposed to contact explosions.

Experimental study on the bond-slip behaviour between corroded bars and concrete

Pull-out tests were conducted to investigate the effects of corrosion of the both longitudinal bar on the bond-slip behaviour of reinforced concrete specimens. The main experimental variables include concrete strength (26.7 MPa, 37.7 MPa, 45.2 MPa) and expected corrosion rate (0%, 4%, 8%, 12%), with a total of 36 specimens fabricated. The results show that the relative bonding strength of specimens under different concrete strengths gradually decreases with increasing corrosion rate, but the higher the concrete strength is, the faster its degradation rate. Based on the experimental results of this work and the achievements of other scholars, a modified relative bonding strength degradation model is presented by accounting for the influence coefficient of concrete strength.

Study on Bond-slip Behavior between Non-uniformly Corroded Reinforcement and Concrete

In order to improve the stress concentration in concrete at steel nodes caused by zero thickness springs, the improved Spring2 nonlinear spring model from ABAQUS is used to simulate the bond-slip behavior between non-uniformly corroded reinforcement and concrete. Based on the collected test results with different stirrup spacing, fitting the influence coefficients of bond stress under stirrup corrosion. With the combination of a non-uniformly corroded rebar distribution model, the refined numerical simulation of the drawing process of reinforced concrete specimens was carried out using ABAQUS. The study shows that the improved nonlinear spring model is better than the zero thickness spring model in terms of computational accuracy and efficiency. The stirrup correction coefficient is approximately linear with the stirrup spacing; the bond-slip relationship considering the effect of stirrup spacing, has a better consistency with the relevant tests in the simulation of the pullout test. Weibull distribution for the fitting of non-uniform corrosion of reinforcement is more reasonable than Gumbel distribution.

Studying Steel-recycled Aggregate Concrete Bond–slip Behavior Using Digital Image Correlation

Studying Steel-recycled Aggregate Concrete Bond–slip Behavior Using Digital Image Correlation

The influence of steel fibers on the bond slip behavior between rebars and concrete: Experimental and analytical investigation

Present research brings a broad analysis on the influence of steel fibers on quasi-static and fatigue rebar pull out loading. The analysis covers the impact of fiber addition on diverse mechanical parameters, such as peak bond strength, stiffness and bond degradation under fatigue. A model previously developed for single fiber pull out in the literature was modified in order to study the bond response through analytical equations. The fiber reinforcement is responsible for providing post-crack resistance to the composite, raising the confinement around the interface and significantly increasing the peak bond strength. Moreover, by enhancing the bond strength, the addition of steel fibers could successfully increase fatigue life of cyclic pull out tests. Finally, the proposed model for rebar pull out from steel fiber reinforced concrete matrices successfully fitted the bond-slip behavior observed the experimental data. The model divided the bond-slip response in three distinct stages: elastic, nonlinear and dynamic.

Optimisation Investigation and Bond-Slip Behaviour of High Strength PVA-Engineered Geopolymer Composite (EGC) Cured in Ambient Temperatures

Engineered geopolymer composite (EGC) is becoming an uprising product in the civil industry as a substitute and solution for conventional geopolymer concrete (GPC) as GPC exhibits brittleness and has poor cracking resistance. In this paper, we explored high strength engineered geopolymer composite (EGC) made of polyvinyl alcohol (PVA) fibre and without coarse aggregate constituents characterised as high-performance geopolymer concrete. Varying alkaline solution to fly ash ratio (AL/FA) was investigated. Bond-slip behaviour and the mechanical properties, including compressive, tensile, and flexural strengths, were studied. PVA-EGC mix designs in this research was optimised using response surface methodology (RSM). Various parameters, including the amount of ground granulated blast slag (GGBS) and silica fume, were included in the parametric and optimisation study. Based on the RSM study, the use of quadratic studies found the responses to be well-fitted. Next, the optimised mix design was utilised for the casting of all the samples for the mechanical and bond-slip tests in this study. The main parameters of bonding behaviour include multiple embedment lengths (7 d, 10 d, 12 d and 15 d) and various sizes of rebar diameter used for pull-out tests. Moreover, the mechanical properties and bond behaviours of EGC were compared with those of conventional geopolymer concrete (GPC). The compressive strength of EGC and GPC at 28 days were designed to be similar for comparison purposes; however, EGC shows higher early compressive strength on day 1 compared to GPC. In addition, results indicate that EGC has superior mechanical properties and bond performance compared to GPC, where EGC is approximately 9 and 150% higher than GPC in terms of flexural and tensile strength, respectively. Pull-out tests showed that EGC samples exhibited higher ductility, as evidenced by the presence of multiple cracks before any exhibited failure in tension and flexure. Ductile failure modes, such as pull-out failure and pull-out splitting failure, are observed in EGC. In contrast, GPC specimens show brittle failure, such as splitting failure.

Study on mechanical properties of composite support structures in TBM tunnel under squeezing soft rock conditions

As more and more TBM tunnels are constructed under complex conditions such as high stress and fault fracture zones, large deformation disasters of squeezing soft surrounding rocks occur frequently. However, TBM method shows poor adaptability to major engineering challenges. Equipment damage, track deviation and support structures failure are widely observed. It is important to propose an effective support scheme and to fully clarifying the mechanical properties of the support structures in TBM tunnel. In this case, this paper aims to conduct laboratory and numerical tests considering steel–concrete interface bond-slip behavior so as to verify the effectiveness of the proposed support scheme. Thus, the quantitative relationship between arch type, arch spacing, longitudinal connection strength, concrete strength, steel fiber content, and tunnel surrounding rock deformation can be obtained. The research results show that the support scheme proposed in this paper shows good applicability for deformation control of TBM tunnels under squeezing soft rock conditions, which provides a reference for TBM tunnel support under squeezing soft rock conditions.

Experimental and Numerical Assessment of Bonding Between Geopolymer Concrete and CFRP Sheet Using NSM Techniques

Abstract Geopolymer concrete is a new concrete technology that emerged as an alternative to conventional concrete by replacing traditional Portland cement with geopolymer binders. Strengthening of concrete structures using CFRP composites has become an essential technique last decades. Most of the studies were conducted on conventional concrete of Portland cement. In this research, an experimental and finite element analysis has been conducted to assess the bonding properties between geopolymer concrete substrate and CFRP composites using near-surface mounted strengthening system. The program consisted of concrete prisms bonded with NSM CFRP laminate and tested using single-lap shear test set-up with different bond lengths. Bond-slip behaviour has also been evaluated. The experimental results exhibited significant bonding properties, achieving an average bonding stress between 8.97 and 15.58 relative to the bonding length. The numerical analysis showed comparable results and a good correlation with that of experimental work.

Influences of the bond-slip on the flexural performance of CFRP plate-strengthened damaged steel beams with intermediate debonding: A numerical study

The interfacial intermediate debonding between the steel beam and CFRP (carbon-fiber-reinforced polymer) is a considerable issue for a CFRP plate-strengthened damaged steel beam. The interfacial bond-slip property determines the interfacial debonding and thus affects the strengthening efficiency. To comprehend the influence laws of the bond-slip behavior, this study conducted a finite element (FE) modelling to assess the strengthening efficiency of the damaged steel beam using CFRP plates. The triangular and trapezoidal cohesive zone models were considered in parametric investigations. The comparisons of FE and experimental results verify the developed FE models. The FE modelling shows that the interfacial fracture energy is the most important bond-slip parameter affecting the flexural strengthening efficiency, relative to the maximum bond stress, elastic and plastic slips. The flexural capacity, ultimate deflection, and debonding load of the damaged steel beam are significantly increased with an increase in the interfacial fracture energy. However, changing the maximum bond stress, elastic slip or plastic slip only produce a minor influence under the same interfacial fracture energy. The selection of the adhesive type is critical for strengthening the damaged steel beam using CFRP plates. In this study, the debonding load, flexural capacity, and ultimate deflection are increased by 75.0%, 51.0%, and 131.1%, respectively, when Araldite-2015 adhesive with the trapezoidal bond-slip model is used instead of Sikadur-30 adhesive with the triangular bond-slip model. Moreover, the debonding load and flexural capacity are hardly increased but the ductility can be considerably improved with an increasing CFRP plate length.

Influence of Corrosion on the Bond–Slip Behaviour between Corroded Bars and Concrete

Pull-out tests were conducted to investigate the effects of corrosion of both the longitudinal bars and stirrups on the bond slip behaviour of reinforced concrete specimens. The main experimental variables include concrete strength (26.7 MPa, 37.7 MPa and 45.2 MPa) and expected corrosion loss (0%, 4%, 8% and 12%), with a total of 63 specimens fabricated. The results show that the relative bonding strength of specimens under different concrete strengths gradually decreases with increasing corrosion loss, but the higher the concrete strength is, the faster its degradation rate. The influence of stirrup corrosion on the peak slip can be ignored, but it will further aggravate the degradation of the bonding strength of the specimens. This reduction in bonding strength is linearly related to the stirrup corrosion loss. Based on the experimental results of this work and the achievements of other scholars, a modified relative bonding strength degradation model and a bond–slipbond–slip constitutive model of corroded reinforced concrete are presented by accounting for the influence coefficient of concrete strength. The results show that the constitutive model is in good agreement with the relevant experimental results.

Pullout behavior of recycled macro fibers in the cementitious matrix: Analytical model and experimental validation

A novel mechanical recycling method has been recently developed in the authors’ group for processing waste glass fiber-reinforced polymer (GFRP) composites into macro fibers, which are then incorporated into concrete to produce green fiber-reinforced concrete (FRC). The present study has been conducted for facilitating the characterization of the tensile properties of macro fiber reinforced concrete (MFRC). A trilinear bond-slip model based on the shear-lag theory has first been refined by introducing a slip coefficient to consider different slip behaviors at the final pullout stages. Such a refined trilinear bond-slip model is suitable for describing the bond-slip behavior of the recycled macro fibers embedded in the cementitious matrix. The bond parameters are obtained through an inverse analysis, in which an improved particle swarm optimization algorithm (PSO) is used. The predicted force-end slip curves are compared with the pullout test results, and a good agreement is observed counterparts with the integral absolute error (IAE) ranging from 3.05% to 5.52%, demonstrating the feasibility of the proposed analytical model. A parametric study is finally conducted to examine the sensitivity of different parameters including the fiber geometries and bond properties on the pullout behavior of the macro fibers.

Influence of activation temperature and prestress on behavior of Fe-SMA bonded joints

The prestressed strengthening of structures via use of bonded iron-based shape memory alloys (Fe-SMAs) has proven promising, albeit with concerns regarding the temperature dependency of the adhesive properties. In this study, the effect of activation temperature and generated prestress are investigated experimentally. Six Fe-SMA-to-steel adhesively bonded joints, comprising different Fe-SMA strips (non-prestrained and prestrained) and activation strategies (full activation and partial activation), were prepared, activated via electrical resistance heating, and tested under quasi-static loading. It is found that the bond–slip behavior of a joint with activation can be modeled by that of an equivalent non-activated joint. The generated prestress influences the full-range behavior by raising the base tensile stress level of the Fe-SMA strip, with negligible effects on further aspects of the full-range behavior. With the increasing activation temperature, the fracture energy is initially increased and eventually reduced, while the bond capacity and effective bond length are retained almost constant.

Generalised analytical solutions for linear and non-linear bond–slip models for externally bonded FRP to a concrete substrate

This article presents a set of novel analytical derivations from generalised bond–slip models using first principles, which can be used to predict experimental outcomes, including maximum load resistance, load-slip response, and strain throughout the bonded length. The generalised bond–slip models are constructed in a way that can be translated into various shapes, including linear, nonlinear and exponential forms, all of which have been used in the literature to explain the bond–slip behaviour of epoxy-bonded FRP on concrete. When the prerequisites for the derivations are satisfied, as demonstrated in this paper, a comprehensive validation of a bond–slip model is possible. Furthermore, the transformability of the generalised bond–slip models and the analytical nature of the derivations also allowed for the comparison of several bond–slip models simultaneously.

Bond-Slip Behaviors Between BFRP Bar and Ecological High Ductility Concrete Using the Beam Test

To better understand the design parameters of bridge deck link slab made by basalt fiber reinforced polymer (BFRP) bar and ecological high ductility concrete (Eco-HDC), the bond behaviors of BFRP bar embedded in Eco-HDC using beam test based on RILEM standard were studied. The beam specimens had variable factors namely diameter of BFRP bar, embedment length and cover thickness. The results indicate that most beam specimens display a failure mode of BFRP bar pulled out with specimen splitting. Besides, with the increase of diameter and embedment length, the bond strength decreases. While as the cover thickness increases, the bond strength and first bond stress show an increasing trend. The free end slip increases as the embedment length or cover thickness increases. In addition, the strain at loaded end is larger than that at free end as the load increases. Moreover, the formulas of bond strength and peak slip are proposed based on the test data of specimens. At last, embedment length and cover thickness of BFRP bar in the bridge deck link slab are recommended.

Effect of matrix self-healing on the bond-slip behavior of micro steel fibers in ultra-high-performance concrete

This study investigates the bond-slip behavior of micro steel fibers embedded into an Ultra-High-Performance Concrete (UHPC) matrix as affected by the self-healing of the same matrix in different exposure conditions. The UHPC matrix contains a crystalline admixture as a promoter of the autogenous self-healing specially added to enhance the durability in the cracked state. For the aforesaid purpose, some samples were partially pre-damaged with controlled preload (fiber pre-slip at different levels) and subjected to one-month exposure in 3.5% NaCl aqueous solution and in tap water to study the fiber corrosion, if any, and the effects of self-healing; after that, they were subjected to a pull-out test, to be compared with the behavior of analogous non-pre-slipped samples undergoing the same curing history. Moreover, some samples were cured in the chloride solution, intended to simulate a marine environment, to study the effect of marine curing on the pull-out behavior of steel fiber. The steel fiber corrosion and self-healing products attached to the surface of the steel fiber were analyzed via Scanning Electron Microscopy (SEM), and Energy -Dispersive Spectroscopy (EDS). The results indicate that the newly healed particles formed on the highly damaged fiber-matrix interface significantly enhance the friction phase of the bond-slip behavior and result in a significant residual capacity compared to non-pre-slipped specimens. On the other hand, the self-healing effect in specimens subjected to low damage pre-slip contributed more to the chemical adhesion region of the bond-slip behavior. Owning to the dense microstructure of the matrix, curing in 3.5% NaCl aqueous solution was not found to significantly affect the pull-out resistance as compared to the samples cured in tap water.

Pull-out behaviour of steel fibres embedded in ultra-high-performance concrete after exposure to high temperatures

The paper examined the bond-slip behaviour of steel fibres embedded in ultra-high-performance concrete (UHPC) after exposure to elevated temperatures. Different types of steel fibres were cast into the halved UHPC dog-bone-shaped samples, including straight fibres, three types of hooked-end fibres and corrugated fibres. The bond response was investigated through single fibre pull-out tests on the samples unheated and heated to 200, 400 and 600 °C. In addition, the effects of polypropylene (PP) fibre addition and heating rate on steel fibre’s bond behaviour were also investigated. The results revealed an increase in bond strength when the straight and hooked-end fibre samples were heated to 200 °C, while the bond strength of the corrugated fibre decreased at the same temperature. Bond strength reductions were observed at higher temperatures. In addition, the straight fibres led to the lowest pull-out resistance as both the hooked-end and the corrugated fibres significantly enhanced the bond strength. With the hooked-end or corrugated fibres, the failure mode gradually shifted from pull-out failure to fibre rupture. Besides, adding PP fibres increased the bond strength of straight fibres at 400 °C but reduced the bond strengths of hooked-end fibres at ambient and high temperatures. High heating rate also led to a greater bond strength for the straight fibres at 200 °C and 400 °C.

Bond-Slip Behavior between Deformed Rebar and Concrete at Cryogenic Temperatures

Bond-Slip Behavior between Deformed Rebar and Concrete at Cryogenic Temperatures

Experimental and numerical simulation of pull-out response in textile-reinforced concrete

Textile-reinforced concrete (TRC) is a construction material that uses continuous fibres such as carbon to create a lightweight and durable structural system. Even though TRC possesses vast possibilities in terms of its usage, identification of bond-slip behaviour at the material 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 pullout tests and validated through finite element analysis to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using a double-sided pullout test setup with different bond lengths of textile, namely 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm. It was noticed that in short bond specimens (20 mm, 30 mm, and 40 mm), the phenomena of pullout failure were due to weakened bond at the interface until pre-peak, followed by complete loss of adhesive bond due to debonding of fibre. However, for the specimens with longer bond lengths (50 mm and 60 mm), rupture of the textile leading to a sudden loss of bond capacity was observed. Additionally, the general fibre pullout phenomenon curve was used to explain the debonding process. Using a calibrated tri-linear bond-slip interface relation, the numerical model was developed to simulate the pull-out response of fibre. The numerical model was able to reproduce experimental results, including maximum load, post-peak behaviour, and interfacial slip. The difference of maximum shear stress between pull-out tests and numerical modelling was within 2 % while the slip difference was between 4 and 31 % for different bond lengths. However, for longer bond lengths, the fibre failure mode was due to pullout instead of rupture, unlike the experimental results.