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The Alkali-silica reaction (ASR) is a deterioration phenomenon that causes undesirable expansion and cracking in hardened concrete. This reaction usually occurs between certain types of reactive aggregates and high-alkali cement and is reported in a notable number of reinforced concrete (RC) structures worldwide, for which assessing the residual performance is critical. Many of these structures employ hooked bars to provide anchorage, especially in their joint regions. This paper examines the pull-out behavior of hooked bars in RC beam-column joints affected by ASR to help assist with safety evaluation of RC structures impacted by this reaction. A set of 7 full-scale RC columns was fabricated with concrete containing reactive fine aggregates, which incorporated different hooked bar diameters and amounts of transverse reinforcement. The specimens were subjected to pull-out of their hooked bars either in control conditions or after curing in a relative humidity of 100 % and a temperature of 50°C for up to 303 days to achieve different levels of ASR-induced expansions. Results showed that up to an unrestrained uniaxial expansion level of 0.2 %, the ASR-affected hooked bars showed an increase by up to 22 % in their ultimate pull-out capacity but a notable reduction in their ductility. Despite distributed cracking in ASR-affected specimens, their failure mode was relatively similar to that in the control specimen and remained a combination of side and front failure. • Anchorage behavior of hooked reinforcing bars in concrete affected by alkali-silica reaction experimentally investigated. • Full-scale reinforced concrete columns fabricated with reactive concrete and tested. • Different bar diameters, transverse reinforcement volumes, and ASR expansion levels examined. • Effects of ASR on load-displacement behavior, cracking patterns, and ultimate pull-out strength evaluated. • Experimental results compared with pull-out capacities based on existing code and literature equations. [ABSTRACT FROM AUTHOR]

Quartz sand modified enamel (QSME) coating has been recently developed to improve both the corrosion resistance and bond strength of steel reinforcement in concrete structures. During the service life, earthquake may occur, but the bond behavior QSME-coated steel bars under the influence of seismic loading remains unknown. In this study, the bond performance of QSME-coated plain rebar under reversed cyclic loading is investigated. Cubic concrete specimens with different diameters and embedment length of steel bars, concrete strength, and coating type were prepared and tested, Acoustic emission (AE) signal was also collected during the pull-out tests. Results indicate that reversed cyclic loading intensify bond degradation compared to monotonic loading. QSME improves the bond strength of plain steel bar specimens to 2.94 and 5.03 times higher compared to uncoated ones under monotonic and cyclic loading, respectively. The bond strength of QSME-coated specimens under cyclic loading degrades as the number of loading cycles increases. QSME increases the energy dissipation of plain steel bars. The AE energy released from QSME-coated rebar specimens is higher than those of uncoated and enamel-coated specimens, which is attributed to enhanced interfacial friction and chemical adhesion. • QSME increases the bond strength of plain steel bars under reversed cyclic loading. • The bond strength decreases as the number of reversed loading cycle increases. • High concrete strength is beneficial to the bond strength of QSME-coated plain bars. • QSME increases the energy dissipation of plain steel bars. • More AE events are detected for QSME-coated plain steel bars during pull-out tests. [ABSTRACT FROM AUTHOR]

• Mode of failures in pull-out test of NS-modified SC-ECC. • RSM has been used to assess bond of NS-modified SC-ECC. • NS influences the bond strength. • RSM has been used to modeling bond strength. This paper analyses the bond behaviour of steel reinforcement bars in the matrix of nano-silica (NS)-modified self-consolidating engineered cementitious composites (SC-ECC). Presented first is the results of pull-out tests performed on three different diameters (12 mm, 16 mm, 20 mm) sizes of reinforcing steel bar embedded in the matrix. Subsequently, the results of the experiment are used in identifying the bond-slip relationship which explains the interactions between steel bars and matrix. A response surface methodology is applied to develop predictive models which are used to perform multi-objective optimization on bond-slip properties such as bond energy, bond slip and bond strength. Lastly, the experimental and predicted results obtained demonstrate that the developed models are suitable for the interpretation of the bond behaviour of steel bars embedded in the NS-modified cementitious matrix. [ABSTRACT FROM AUTHOR]

• Three distinct corrugation patterns (CR, CV, CT) are utilized in bamboo samples. • Theoretical bond model with high accuracy is proposed for 3 corrugated patterns. • V notch Corrugation showed the highest improvement of 85% compared to plain bamboo. • Corrugation showed 43% improvement than epoxy treated samples. In the quest for sustainable development and to address the challenges of urbanization, researchers are exploring alternative sources of materials for construction and bamboo has emerged as a promising alternative to steel reinforcement in concrete construction due to its impressive weight-to-strength ratio. The goal of the present work is to investigate the bond properties of three different corrugation patterns in surface-treated bamboo alongside non-corrugated and epoxy-treated bamboo samples through pull-out testing. Bamboo corrugation is advocated as an ingenious mechanism to foster a robust interlocking effect between bamboo and concrete, effectively bolstering cohesion and optimizing skin friction to amplify the overall bond strength significantly. The findings revealed significant improvements in bond strength for rectangular corrugation, V-notch corrugation, and trapezoidal corrugation patterns, with strength enhancements of 46%, 85%, and 81% respectively, compared to plain bamboo. Furthermore, a theoretical bond model was developed for each corrugation pattern, which has been successfully validated against the experimental results with a notable accuracy ranging from 78.7% to 95.6%. Finally, the theoretical model was suggested as a tool for estimating the bond between bamboo and concrete. These findings underscore the potential of using corrugated bamboo reinforcement as a sustainable solution for enhancing bond performance in concrete. [ABSTRACT FROM AUTHOR]

Highlights • Heat-rain test is realised most effective test to find out durability problem of BRC. • Aim is to eliminate accumulation of hydration products on fibre surface in BRC, BFRC. • Positive effect of pozzolanic admixtures on strength-strain degradation is addressed. • Results after standard curing and aging tests reveal most effective additive is metakaolin. • High reactivity of Al 2 O 3 and fineness largely prevent accumulations on fibre. Abstract In this study, the effects of pozzolanic admixtures (ground granulated blast furnace slag, nano-clay, metakaolin) are investigated in chopped basalt fibre cementitious composites (BRC). First, the variations in compressive strengths and flexural characteristics during 3, 7, 28, 56, 90 and 120-day curing periods are addressed. Afterwards, most importantly, the degradation in the flexural performance during aging tests (freeze-thaw test, heat-rain test) are focused. The main aim is considerably to save the pull-out behaviour of BRC, even when exposed to harsh atmospheric conditions. All the test results are compared with control specimens (100% cement). The results arising from the experiments including metakaolin are promising to enhance the durability performance of BRC. The implications in this experimental study are valid for basalt fibre reinforced concrete (BFRC) subjected to those atmospheric conditions as well. [ABSTRACT FROM AUTHOR]

Grouted dowel connections are widely used to resist tension induced by in-plane straining actions and to provide ductility to precast concrete load bearing wall structures. Yet, such connections have not yet been duly investigated. Current design code and standard provisions treat it similar to a simple bar-in-concrete detail. The present study reports the findings of 22 full-scale tests undertaken to examine the bond behaviour of grouted connections under monotonic tensile loading. The examined test parameters included the bar embedment length, bar material and corrugated duct. Results indicate that grouted connections behave quite differently from the bar-in-concrete model assumed in design codes, primarily due to the confinement mechanism of the duct, which provides restraint to lateral expansion of the grout. Varying the embedment length seemed to affect both the bond stress and slip, but did not influence the failure mechanism of the connections. The experimental results were used to calibrate two well-known bond-slip analytical treatments, predictions of which appear to be in good agreement with experimental results. The experimental and analytical findings provide an enhanced understanding on the behaviour of such connections, highlighting the need for revisions in future relevant design code provisions. [ABSTRACT FROM AUTHOR]

For the corroded reinforced concrete (RC) members repaired using steel fiber reinforced concrete (SFRC), bonding between corroded rebar and SFRC greatly affected the mechanical performance of repaired members. In the present paper, the central pull-out tests were carried out to investigate the bond behavior of SFRC and pre-corroded steel bar obtained in concrete specimens. The varied parameters included corrosion ratio and cover thickness to rebar diameter ratio ( c/d ). The experimental results revealed that the confinement and bridging action of fiber can improve the bond strength and transform the failure mode from splitting to pull-out or combined splitting and pull-out. Bond strength decreased with increasing corrosion ratio and decreasing c/d , whereas the residual bond strength remained no less than that of non-corroded rebar especially for specimens with a small c/d . Bond strength degradation, bond toughness variation and bond-slip descending behaviors with corrosion ratio were correlated to c / d and failing mode. A modified bond strength model considering the coupling effect of corrosion and c / d was proposed, and the calculated strength agreed well with the tested. [ABSTRACT FROM AUTHOR]

The success of Fiber Reinforced Polymers (FRP) strengthening methodologies for reinforcing concrete structures is highly related to the interfacial bond properties between reinforcement and concrete, which depends upon a number of parameters. Several studies were carried out investigating the short-term bond behavior of Near Surface Mounted (NSM) FRP strengthening systems. However, there has been only limited investigation of its long-term behavior resulting in a significant lack of available experimental data about this relevant aspect. The bond performance of the materials involved in the NSM FRP strengthening system (FRP, adhesive and concrete), due to its nature, is susceptible to be affected by both the sustained loading and environmental conditions. In this study, bond of NSM Carbon FRP (CFRP) laminates in concrete was investigated experimentally using pull-out tests. The experimental program consisted of both short-term tests, in which the load was applied monotonically up to failure, and long-term tests in which different levels of sustained loading were applied. The specimens were tested under sustained loading using bonded length, adhesive thickness and sustained loading level as the main parameters of the study. Results in terms of slip evolution with time are presented to explore the effects of the studied parameters on the long-term bond behavior between NSM CFRP laminates and concrete. Moreover, an analytical procedure to predict the slip variation versus time is proposed and compared to experimental results. [ABSTRACT FROM AUTHOR]

The authors have recently proposed an innovative connector system that consists on a Glass Fibre Reinforced Polymer (GFRP) perforated plate that is embedded into Steel Fibre Reinforced Self-Compacting Concrete (SFRSCC) layers. The connection is strongly based in the mechanical interlock assured by the dowels originated from the SFRSCC passing through the holes opened on the GFRP plates. In this study, an analytical framework to evaluate the load capacity of the connections when loaded transversally was developed based on experimental pull-out tests presented in the companion paper (Part I). For a better understanding of the mechanical behaviour of the connections and to allow to make estimations of the load capacity of connection when it is conditioned by the rupture of the connector itself, pull-out pin-bearing tests with single-hole plates were executed to assess the effect of the type of GFRP on the strain distribution in the vicinity of the holes until the failure, as well as the estimated failure modes and load capacities of the connections. [ABSTRACT FROM AUTHOR]

This paper presents an extensive experimental work on various factors related to the construction conditions that affect the strength of post installed bonded anchors in concrete. The strength of the anchors was evaluated in conventional and self-compacting concrete. Two walls, 2 m high, one of conventional vibrated concrete (VC) and the other of self-compacting concrete (SCC) were built. In each of the walls, 175 anchors of 20 mm rebars were installed. The variables considered for each concrete block were the type of drilling machine used for drilling the hole, type of filling material, moisture conditions of the hole during installation, cleanliness of the hole, and installation direction. A detailed statistical analysis was used to evaluate the influence of the considered variables on the anchors ultimate capacity and slippage of the rebar at service level. The results show that the installation conditions significantly affect the strength of the anchors. The type of drilling machine has a major impact on the anchor strength, while the drill diameter had no significant impact on the results. [ABSTRACT FROM AUTHOR]

• Telescopic failure becomes more pronounced with longer embedment lengths. • The matrix imprint resulting from the embedded yarn provides pull-out resistance. • The presence of filament fragments increases pull-out resistance. • X-ray CT scans on the matrix, post-pull-out, highlight the bottleneck effect. Textile-reinforced concrete (TRC) offers a solution to the drawback associated with the production of cement and its use in construction. It also promotes the design of concrete in a post-cracking stage as the yarns bridge cracks once the concrete fails in tension. The pull-out behaviour of TRC has and still receives considerable attention to progress its use, but the full extent and types of mechanisms associated with the pull-out is not yet fully understood. This research sets out to investigate the pull-out mechanism when considering various embedment lengths, as well as employing the use of X-ray computed tomography and scanning electronic microscope imaging on the post-pull-out elements. The study identified a bottleneck mechanism, resulting from the undulating imprint the warp yarn produces, which improves the pull-out resistance of yarns. Additionally, the latter mentioned mechanism is also enhanced by the effect of congestion caused by filament debris, resulting from the telescopic failure. [ABSTRACT FROM AUTHOR]

Large-diameter anchors are one of the important connection components in the reinforcement of industrial facilities. In the present study, a finite element (FE) model of large-diameter post-installed anchor system is appropriately established to investigate its pull-out performance and failure modes observed in the prototype experiments. The applicability of the proposed model is discussed through comparison of its results with experimental results (e.g., in terms of the ultimate load, corresponding displacement, and failure modes), and the parametric sensitivity based on the numerical results is studied. The results showed that the pull-out behavior could be well simulated using the proposed model. The progressive failure evolution process of the large-diameter anchor can be revealed by computational load–displacement curves. Thus, the proposed model of a large-diameter post-installed anchor can enable reliable design of anchor systems for industrial reinforcements. [ABSTRACT FROM AUTHOR]

Reinforcing concrete with steel fibres has been proven being able to improve the properties of concrete such as strain capacity, impact resistance, energy absorption and tensile strength because the discrete steel fibres act as dispersed reinforcement in mitigating crack propagation. A number of laboratory tests in recent years have indicated the superiority of spiral geometry of steel fibres as compared to other fibre types in terms of ductility, crack controllability, dynamic strengths and energy absorption. Understanding fibres’ pull-out behaviour is essential to evaluate the properties of steel fibre reinforced concrete (SFRC). The pull-out behaviour of straight, hooked-end and twisted steel fibres have been investigated by many researchers. However, there has been no study that focuses on pull-out behaviour of spiral fibres in the literature yet. The pull-out behaviour of steel fibre with spiral geometry from concrete matrix is experimentally investigated in the present study. In addition, steel fibres with hooked ends were also prepared and tested for comparison. The spiral fibres with various geometric characteristics such as pitch length, embedment length and coil diameter were pulled out from concrete matrix at different rates. Test results showed several peak loads before reaching a final maximum pull-out force. Based on the experimental results, the influences of embedment length, pull-out rate, coil diameter and pitch length were investigated. Through analysing the testing results, combining hooked-end fibres and spiral fibres was proposed as a hybrid steel fibre reinforcement technique in order to further improve the performance of SFRC materials and structures. Laboratory tests in this study proved the effectiveness of this technique in enhancing the capacity of the reinforced concrete structure. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of a low elevated temperature on the mechanical behavior of steel B500B rebars and T15.2 prestressing wires in nuclear containment structures. Tensile tests were carried out to evaluate the evolution of mechanical properties during heating. The bond between concrete and rebars was also studied and relaxation tests on prestressing wires have been done. Between 20 °C and 140 °C, the mechanical behavior of rebars and tendons exhibited no major deteriorations. However, a high decrease of the ultimate bond was observed for pull-out tests. Concerning relaxation tests, the temperature tends to significantly increase the relaxation rate. [ABSTRACT FROM AUTHOR]

• Sixty-four FRLWAC bond-slip specimens are exposed to high temperatures and tested. • Test parameters are concrete cover, temperature exposures and steel fibre content. • High temperature exposure shifted failure mode from pull-out to splitting failure. • Steel fibre addition prevented brittle splitting failure from occurring. • Semi-analytical bond-slip model that considers different failure modes is proposed. This paper presents an experimental investigation of the bond-slip behaviour of reinforcing bars in fibre-reinforced lightweight aggregate concrete (FRLWAC) at ambient and elevated temperatures. Sixty-four bond-slip specimens with four target temperature exposures, two concrete covers and four steel fibre contents were tested to failure. The experimental results showed that exposure to elevated temperature shifted failure pattern from more ductile pull-out to brittle splitting modes, and reduced the peak bond strength and toughness of bond-slip behaviour. Scanning electron microscope (SEM) images of the concrete-steel interface showed that thermal mismatch induced microcracks contributed to degradation of bond strength, in addition to temperature induced degradation of concrete materials. The temperature exposure also negated beneficial effect of concrete cover in enhancing bond behaviour. Addition of steel fibre helped in preventing brittle failure mode, enhancing bond strength in specimens with small concrete cover and improving the post-peak bond-slip behaviour at all target temperatures. A simple semi-analytical bond-slip model that considers different failure modes and incorporates fibre-reinforced concrete tensile behaviour from Swedish Code SS 812310 was proposed and validated based on the test results in this study. [ABSTRACT FROM AUTHOR]

Increasing the adhesion efficiency between the fiber and the concrete, in fiber reinforced concrete members, might be obtained by enhancing the properties of the concrete mixture using several parameters such as cement weight, water to cement ratio, grading curve of aggregates and admixtures, or by apply some changes on the fiber parameters such as the aspect ratio (l/d) or the outer roughness or the embedded length and the diameter value. Laboratory experiments lead to the fact that the use of smooth and straight steel fiber, in fiber reinforced concrete, produces weak bond strength between the fiber and the concrete. Therefore, to obtain better bond strength it is necessary to increase the total length of the fiber, which may cause unacceptable workability. Accordingly, it could be developed a new form of fiber has larger supporting region using the corrugated fiber shape. In this paper, the performance of this corrugated form will be monitored through new shear lag model to extract the traction separation relations between the corrugated fiber and the concrete matrix, as well as an experimental study using different values of embedded length of the fiber, in addition to several computer simulations which will be created using a finite element model and applying same dimensions and forces which are used in the laboratory experimental procedure. Through the results of nonlinear analysis of the computer simulations, the distribution of stresses in different directions for each of the concrete and the fiber can be shown, then the evolution of the bond strength between the fiber and the concrete can be monitored as an actual result of applying the corrugated shape. [ABSTRACT FROM AUTHOR]

An attempt was made to drift nanoalumina particles into concrete pores through electrokinetic treatment. An external electric current (current density = 3 A/m 2 ) was applied for 3 and 15 days in reinforced concrete blocks toward steel reinforcement and microstructural characterizations (i.e. morphology observation and porosity analysis) were performed on concrete fragments of different depth from exposure surface. The morphology observation evidenced transport of nanoalumina from the exposure surface even reaching the rebar-concrete interface (up to 25–30 mm, in 15 days treatment). The porosity analysis of treated samples revealed that reduction of porosity of rebar interface was more pronounced as compared to the exposure surface and the treatment for 15 days was more beneficial for porosity refinement than treatment for 3 days. Effects of the electrokinetic NA treatment on strength of rebar-concrete interface were evaluated through pull-out test. The results showed that by increasing current density, bond strength of rebar-concrete interface increased. [ABSTRACT FROM AUTHOR]

Glass Fiber Reinforced Polymer (GFRP) rebars have great potential for applications in concrete structures under corrosive environment. The bond behavior between GFRP rebar and concrete needs to be understood for such applications. This paper presents a new method for improving the bond behavior using Calcium Sulfoaluminate (CSA). CSA has an expansive effect when added to the concrete mixture. It is proposed to embed the GFRP rebar in the fresh expansive concrete which is encased by the surrounding hardened concrete. When the fresh expansive concrete gradually becomes hardened, the expansion is restrained by the surrounding concrete, resulting in confining pressure on the GFRP rebar. To validate the proposed method, experimental pull-out tests were conducted to quantify the improved bond behavior between GFRP rebar and concrete. Steel rebar pull-out test was also carried out for comparison purpose. The experimental results were reported including failure modes, ultimate pull-out capacities and bond-slip responses. It was found that the bond behavior between GFRP rebar and surrounding concrete was greatly improved using the proposed method. [ABSTRACT FROM AUTHOR]

The effects of material properties on bond strength between reinforcing bar and concrete exposed to high temperatures are investigated extensively using modified pullout tests. The specimen parameters include various bar diameters, rebar grades and concrete strengths. Three different concrete cubes with compressive strengths of 20, 34 and 44 MPa, 12, 16 and 20 mm rebar diameters and S220a, S420a and S500a rebar grades were utilized for the tests. In the experimental study, the tests were conducted on 150/300 cylinder specimens in which rebars are embedded vertically exposed to high temperatures (100, 200, 400, 600 and 800 °C) and cooled down. Furthermore, 150 mm cube and 100/100/300 mm prism specimens were used to determine compressive and flexural strength of concrete. Bond strengths of these specimens were compared with each other and then with unheated specimens at 20 °C. Experimental results indicated that residual bond strength between reinforcing bar and concrete decreases with increasing temperature. The first severe bond strength loss was observed for grade S220a at the range of 200–400 °C and for grade S420a and S500a at the range of 400–600 °C. The residual compressive strength is in tendency with the residual bond strength of S420a and S500a whereas the residual flexural strength corresponds agrees with the residual bond strength of S220a. [ABSTRACT FROM AUTHOR]

This experimental study assesses the bond performance of recycled aggregate concretes (RAC) with embedded uncorroded and corroded steel bars. The RAC were produced using 20%, 50% and 100% of coarse recycled aggregates obtained from the crushing of waste 40 MPa compressive strength concrete. Three degrees of corrosion were reached on the steel bars. The uncorroded RAC specimens presented a comparable bond strength to that of conventional concrete (CC). Low corroded RAC specimens presented better bond performance and later superficial cracking when compared to those of CC. At a higher corrosion degree, all concretes presented a similar bond capacity. The ultimate bond strength estimation models used for CC were adequate for its prediction on RAC. [ABSTRACT FROM AUTHOR]

• Pull-out performance of PBLs shallowly embedded in high strength concrete is studied. • Concrete breakout dominates the failure of shallowly embedded PBLs under pull-out load. • Increasing embedded depth significantly increases pull-out resistance of shallowly embedded PBLs. • Proposed analytical model accurately predicts pull-out resistance of shallowly embedded PBLs. Perfobond rib connectors (PBLs) used in steel high-strength concrete composite pylons of cable-bearing bridges are subjected to considerable pull-out forces caused by the local buckling tendency of the steel panels. In order to investigate the pull-out performance of PBLs embedded in high-strength concrete, an experimental study was conducted with twelve single-hole PBL specimens constructed of concrete with a cubic compressive strength of 80 MPa. The test results indicate that the failure of shallowly embedded PBLs was dominated by the concrete breakout. Then a numerical investigation was conducted using the validated finite element method to figure out the failure mechanism of the shallowly embedded PBLs, followed by a parametric study to identify the sensible parameters concerning the pull-out resistance. The numerical results show that increasing the embedded depth, concrete strength, and rib hole diameter can increase the pull-out resistance of the PBLs with an embedded depth smaller than 140 mm. In contrast, the thickness of perforated ribs exhibits a negligible impact on the pull-out resistance. It is recommended that the transverse rebar diameter should not exceed the difference between the rib hole diameter and the maximum coarse aggregate particle size of the concrete to avoid the possible decrease in the concrete strength near the rib hole. Finally, a concrete breakout model was developed to predict the pull-out resistance of PBLs shallowly embedded in high strength concrete with reasonable accuracy. [ABSTRACT FROM AUTHOR]

Even though limited to the outer concrete layer of structures, pull-out tests have been proved to be a reliable technique for the in situ estimation of concrete strength. The most studied post-installed wedge anchor, the CAPO test, is not widely used due to some complexity in its use. A simplified procedure, resembling the CAPO test, the Zykon technology, has been used in Italy for more than 20 years with substantially unsatisfactory results, mainly for tensile stress states and for high stress gradients. In both the cases, the calibrations curve, relating the pull-out load to concrete strength, is related to unstressed concrete, which is troublesome when applied to in-service structures, i.e. with not vanishing stress states. A new post-installed wedge anchor is discussed in this paper that, based on a careful choice of all the technical details, has been proved to be reliable for all stress states since: (i) the drilling and expansion procedure avoids much of the uncertainties that affect the commonly used procedure; (ii) the calibration of the procedure has been performed on 6 classes of concrete and considering 5 different stress distributions (medium and low compression, vanishing stress states, compressive and tensile stresses with strong gradients). The correlation curves are nonlinear, as for pre-installed inserts, and depend on the stress state, with statistical scattering never exceeding 7–8% of the average values. A theoretical analysis fits rather well the test data and provides explanation to several aspects of pull-out tests. [ABSTRACT FROM AUTHOR]

The bond between steel and concrete has a profound influence on the structural behaviour of reinforced concrete structures in both service and ultimate conditions. In the present work, bond–slip behaviour between steel and concrete has been analysed in the presence of corrosion of a steel reinforcing bar. The results of pull-out RILEM type tests are presented. The tests have been performed on specimens with and without confinement in the presence of an increasing level of corrosion up to 20% of mass loss. Corrosion has been induced by means of an electrochemical procedure with a current density of 200 μA/cm 2 . The local bond–slip curve between the steel and concrete, in the presence of a short embedment length between the two materials, has been obtained. The results show the influence of the corrosion level and the presence of confinement in terms of the bond–slip response. [ABSTRACT FROM AUTHOR]

• This review article helps to summarize the interaction between the steel rebars and concrete. • The various equations and models developed by many researchers and codes are discussed. • The ANN predicts the interaction between rebar and concrete in a relatively short time with low error rates. • The introduction of ANN model can save time, reduce the material wastage thereby reduce the construction cost. The reinforcement of concrete with steel results in stress transfer from steel to concrete and hence it becomes essential to understand the bond and anchorage behaviour of concrete. A strong bond between the steel reinforcement and concrete is a major contributing factor to the durability of reinforced concrete structures. This article focusses on reviewing the bond strength of concrete with steel rebars considering various parameters such as compressive strength, diameter of the bar, concrete cover, bar geometry and anchorage length using pull-out and beam bond tests. The role of artificial neural networks (ANN) in predicting the bond strength of concrete using these parameters is also discussed. Various international codes and literature discussing the pull-out and beam bond tests have provided a better understanding of the bond properties of concrete. [ABSTRACT FROM AUTHOR]

Highlights: [•] The concrete–steel bond of LWC is characterized for different failure mechanisms. [•] In splitting, the bond strength of LWC was 70% that of normal concrete. [•] The bond strength of LWC can be more than twice that of NWC of equal compressive strength. [•] It has been shown that the normative expressions proposed for LWC may be too unrealistic. [•] A new approach for estimating the LWC bond strength has been suggested. [ABSTRACT FROM AUTHOR]

Highlights: [•] The pull-out response of grouted FRP rods in steel tubes is analytically modeled. [•] The interfacial bond-slip model is incorporated into the analysis. [•] Different boundary conditions are considered in the analysis. [•] The solutions can be applied to the problem of FRP rods embedded in rock. [Copyright &y& Elsevier]

Highlights: [•] The effect of ASR on steel fiber–matrix bond characteristics has been investigated in this research. [•] ASR gel congestion in fiber–matrix interface increased the pull-out load and debonding toughness significantly. [•] Supplementary cementing materials reduced the ASR expansion and mechanical strength loss. [•] SEM analysis revealed that the ASR products filled the fiber–matrix interface with different morphology. [Copyright &y& Elsevier]

Abstract: Experimental research that shows the improvement in structural behavior of concrete with the addition of fibers has been developed in the last years. Fibers control cracking and thus increase concrete toughness and ductility. Much effort has been devoted in the last decade to model this material. A simple homogenization approach based on a modified mixture theory is proposed in this paper to model Steel Fiber Reinforced Concrete (SFRC). The proposed and calibrated model takes information from the micro-scale to model the macro-scale. SFRC is considered as a composite material composed by concrete matrix and fibers. Concrete is modeled with an elastoplastic model and steel fibers are considered as orthotropic elastoplastic inclusions that can debond and slip from the matrix. In order to include this inelastic phenomenon without explicitly modeling interface, constitutive equations of fibers are modified including information from the debonding–slipping phenomena. The model requires concrete properties, fibers material, geometry, distribution and orientation as input data. The fibers bond–slip behavior is automatically derived from concrete properties and fibers geometry or it can be alternatively obtained from pull out tests. As illustration, the tension response of SFRC with different fiber contents is numerically simulated. The model is verified with the results of bending tests of beams extracted from a SFRC slab that present different fibers distribution due to the slab casting process. Comparisons with other numerical approaches modeling SFRC as an equivalent homogeneous material are also included in the paper. [Copyright &y& Elsevier]

Abstract: Slurry Infiltrated Fiber Concrete (SIFCON) is a special type of steel fiber-reinforced cement composite which has superior mechanical properties such as compressive, tensile, shear and flexural strengths with extraordinary toughness values. In this experimental study, the effect of mix proportions of SIFCON matrix (slurry), curing conditions, aspect ratio of steel fiber, embedded length and fiber type on the single fiber pull-out behavior from SIFCON matrix was investigated. Test results indicated that fiber type, embedded length of fiber, curing conditions, fiber end condition, and matrix strength has a considerable effect on fiber–matrix bond. Increasing the diameter of the fiber and improving the curing conditions increased matrix–fiber bond. In addition, increasing bond strength was observed with increasing strength of SIFCON matrix. The pull-out toughness increased by increasing embedded length of fiber. It has been observed that hooked end fibers have shown better interface bond compared to the smooth fibers. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an experimental study investigating the effects of steel fibers on the mechanical properties of concrete and the enhancement of bond strength of prestressing strands in steel fiber reinforced concrete (SFRC). The first part of the experimental program consisted of compression, tension and flexural tests on SFRC. Two types of steel fibers with 30mm and 60mm fiber lengths were used with five different fiber contents. The second part of the study consisted of simple pull-out tests on 12.7mm and 15.2mm diameter seven-wire untensioned prestressing strands embedded in concrete blocks. The pull-out tests were conducted with two different fiber lengths and five different fiber contents for each strand diameter. The steel fibers were observed to improve the pull-out resistance of strands by controlling the crack growth inside concrete blocks. [Copyright &y& Elsevier]

Abstract: The present study occupies with the characterization of the fracture process of steel fibre reinforced concrete. Different acoustic emission indices are correlated with the accumulation of damage and the type of source. The amplitude distribution of the acquired signals is very sensitive to micro-cracking, while individual mechanisms like matrix cracking and fibre pull-out can be distinguished by the average frequency of the corresponding signals which exhibits a severe decrease at the moment of main. As a result, acoustic emission can be used as a warning against the failure of this material while the broadband transducers can be used to characterize the different damage mechanisms. [Copyright &y& Elsevier]

• A two-phase experimental program is conducted to investigate anchorage performance of GCDC. • A reasonable anchorage length and duct-to-rebar diameter ratio is recommended for GCDC. • The bond-slip constitutive model considering nonuniform bond-stress distribution is developed. • The finite element model based on proposed bond-slip constitutive relationship is established. The grouted corrugated duct connection (GCDC) has wide applications in column-to-cap beam and column-to-footing joint of precast bridges. The anchorage performance of GCDC has received more attention due to the lack of understanding. In this study, a two-phase experimental program was conducted to investigate the anchorage performance of GCDC. The pull-out tests of 40 specimens in Phase Ⅰ mainly focused on the effects of various factors on anchorage requirement of GCDC, in which factors such as anchorage length, duct-to-rebar diameter ratio were considered. Test results indicate that the failure modes of GCDC and the proposed equivalent bond stiffness are mainly governed by the anchorage length and duct-to-rebar diameter ratio. The anchorage length of 10–15 times rebar diameter and duct-to-rebar diameter ratio of 2.5–3.5 are recommended to ensure bond strength. In Phase Ⅱ, 40 design specimens were pulled out to investigate the bond-slip constitutive relationship of GCDC. The variation law of ultimate bond strength was analyzed with the variation of the anchorage length and duct-to-rebar diameter ratio. Based on experimental results, basic bond stress-slip relationship and bond stress distribution function were obtained through curve fitting, which were in good agreement with test results. Finally, the comprehensive bond-slip constitutive model incorporating location function was developed. The refined finite element model considering bond-slip constitutive relationship was established to investigate and verify the pull-out test results. Therefore, the anchorage requirement recommended can provide reference for the selection of anchorage length duct-to-rebar diameter ratio for engineering application of GCDC. Furthermore, the bond-slip constitutive model developed is the theoretical basis for finite element analysis of GCDC. [ABSTRACT FROM AUTHOR]

• Aromatic and saturate are agglomerated near SWCNT, followed by resin and asphaltene. • Van der Waals energy dominates interfacial interactions between CNTs and asphalt. • MWCNTs are more appropriate to be embedded into asphalt. • The addition of MWCNT to asphalt significantly increases aggregate-asphalt adhesion ability. In this work, a comprehensive study has been conducted on the interfacial contact behavior of carbon nanotubes (CNTs) and asphalt binders as well as the influence of multi-walled carbon nanotubes (MWCNTs) embedded into asphalt on the adhesion ability of asphalt on aggregate surface at atomic scale. CNT/asphalt composite and asphalt-aggregate interface models were investigated by molecular dynamics (MD) simulations to evaluate the molecular interactions of materials. The interfacial adhesion characteristics of functionalized single-walled carbon nanotubes (SWCNTs) and MWCNTs with asphalt binders were investigated by performing pull-out simulations and the interactions of SWCNTs and asphalt components were analyzed. The obtained results showed that asphalt components with low molecular weight were more easily adsorbed by SWCNTs than higher weight components. For CNTs/asphalt composite model, Van der Waals (VdW) energy is much higher than electrostatic energy accounting for a great portion of interaction energy. Although functional groups on the surface of CNTs can increase interfacial interaction, this increase is far less than the enhancement of interaction energy and interfacial shear stress between MWCNTs and asphalt binders. Therefore, MWCNTs are regarded as a better additive to be inserted into asphalt binders to enhance the interfacial adhesion of CNTs/asphalt composites. In addition, the results of adhesion energy change of asphalt-aggregate interface models indicated that MWCNT addition into asphalt significantly increased the adhesion ability of asphalt on aggregate surface (especially for alkaline aggregates). [ABSTRACT FROM AUTHOR]

• Fibre optic measurements were performed on near-surface-mounted memory-steel bars. • Decrease in bar stiffness led to a changed behaviour in active bond length. • An active bond length after prestressing of 200 mm was determined. • Post-processing of distributed strain delivered distributed stress and slip curves. • Novel fiber optic strain measurements delivered bond-slip law parameters. Near-surface-mounted (NSM) iron-based shape memory alloy (memory-steel) bars represent a novel type of reinforcement for prestressed strengthening of concrete structures. To examine the bond behaviour of these embedded reinforcements in detail, fibre optic (FO) methods can be used. In this study, distributed FO strain measurements were performed in small-scale bond experiments and large-scale structural experiments using prestressed and non-prestressed NSM memory-steel bars. The experiments demonstrated the FO measurement technique's feasibility on memory-steel bars, provided insights into the complex strain profiles before and after prestressing, and revealed the active bond lengths. When the memory-steel bar was subjected to an external load, a reduction in the bar's stiffness resulted in an increase in active bond length. The results furthermore highlighted the importance of rigid bar fixations to avoid prestress loss. The obtained strain distributions were also processed to calculate the distributed slip and axial bar stress, and to investigate the parameters of three different bond shear stress–slip laws (BSSLs). A linear increasing BSSL with a nonlinear bar stiffness led to a realistic calculation of the axial stress in the bar, while resulting in acceptable slip and strain. The implementation of a constant Young's modulus consistently overestimated the axial bar stress. [ABSTRACT FROM AUTHOR]

• Bond behaviour of FRP bars having 13 different surface configurations is studied. • Defining surface factors based solely on surface category is not supported by test results. • Bond strength increases with concrete strength even above f c = 30 MPa. • Bond strength of FRP bars increased compared to literature, FRP bars improved by time. • New test method was developed, the direct tension pull-out test. This paper presents an extensive experimental study of the effect of surface characteristics on the bond behaviour of Fibre Reinforced Polymer (FRP) bars in concrete. A wide range of commercially available FRP bars with different surface profiles (total of 13 different surface configurations) were involved. For comparison, ribbed steel bars were used. To investigate whether the effect of surface characteristics is in interaction with other factors, further parameters were included in the study such as concrete compressive strength (35 and 66 MPa), bar diameter (6 to 12 mm) and test type (pull-out [P-O] and direct tension [DT] pull-out). This resulted a total of 200 P-O and 38 DT tests. DT test method was developed by the authors based on a similar test setup from the literature. Surface finish of the investigated FRP bars include sand coated (SC), helically wrapped (HW), helically wrapped and sand coated (HWSC), indented (In) and ribbed (Rb). Most of the applied bars are Glass FRP (GFRP), however, due to the similar physical and mechanical properties Basalt FRP (BFRP) bars were used as well. The bond behaviour of the bars was evaluated by bond strength, bond stress-slip relationship, representative bond stresses and failure mode. It was found that the bond strength as well as bond stress-slip behaviour and failure mode vary considerably depending on surface characteristics. Furthermore, even within the same surface category the bond strength difference can be significant (e.g., SC surface with different sand fineness). The concrete strength influences the bond strength even if it is higher than the limit stated in literature (approximately 30 MPa). Furthermore, the bond strength results of all FRP bars were consistently higher than those of steel bars. The highest slip value to reach the bond strength was observed for HW FRP bars, while the lowest for SC bars. Some results reported in this paper considerably differ from those previously reported in other papers based on testing similar bars. The difference, in terms of bond strength, can be explained by the alteration of surface configuration, the improvements in material properties and fabrication processes. Finally, the test setup was found to affect the measurable bond strength. [ABSTRACT FROM AUTHOR]

• 70 Pullout bond tests with GFRP bars in conventional or seawater-mixed concrete. • Detailed comparison of peak bond strength and bond-slip response. • One-way ANOVA tests were conducted to compare the results. • No statistically significant reduction in bond strength using seawater concrete. Portland Cement Concrete (PCC) is the most used construction material worldwide and its use is expected to increase in the future. PCC intensively uses two main natural resources, namely aggregates and fresh water. The concrete industry consumes about 2 billion tons of potable water annually. Due to climate change, rapid population growth, and industrial activity, there is a scarcity of fresh water; by 2025 more than half of the world's population will be living in water-stressed areas. In contrast, there is abundant seawater in the world, which represents about 97.5% of the total Earth's water. However, the incorporation of seawater in PCC is a complex problem because the sulfate ions can affect the microstructure durability and the chloride ions can accelerate reinforcing steel corrosion, which can compromise the structural integrity. Glass Fiber Reinforced Polymer (GFRP) bars may be used as an alternative reinforcing material to avoid corrosion. This paper assesses the bond strength of two types of GFRP bars with either a sand-coating or spiral grooves using a standard pullout test. Control samples were prepared using concrete made with potable water and compared with companion specimens made with seawater. Parallel experimental programs were carried out in Chile and Canada, with a total of 70 test specimens. The results suggest that there is no statistically significant difference in the short-term (28 day) bond strength of GFRP bars in seawater concrete compared to normal concrete. [ABSTRACT FROM AUTHOR]

• The effect of a highly thixotropic material on the bond strength was investigated. • The effects of the printing method on the bond strength were studied. • A highly thixotropic printed material generated a strong bond with steel bars. • Non-printed samples gave better pull-out resistance and higher stiffness. • 3D printed parallel samples outperformed the perpendicular ones. Digital construction of concrete elements using 3D printing technology has been undergoing an exponential growth in terms of research activities and demonstration projects. Though, most researches focused on the behavior of the cementitious materials used in 3D printing, without deeply immersing in the reinforcement of printed elements. In this paper, a detailed experimental program is presented to characterize the quality of the bond developed between concrete and steel bars through a series of pull-out tests. These tests are performed over printed and non-printed samples as well. When printed, the layers orientation, whether parallel or perpendicular to the steel bar is taken into consideration. Hence, it was found that a highly thixotropic material did not undermine the developed bond between printed concrete and rebar. In addition, vibrated concrete (non-printed) gave better resistance to pull-out stresses succeeded by the parallel then the perpendicular samples. Yet, the overall performance of 3D printed concrete in terms of the bond generated with steel could be rated as satisfactory. [ABSTRACT FROM AUTHOR]

• Flexural strength of unreinforced rammed earth (URE) is low. Reinforcing RE structural components improves the same. • Present study examined the bond between rebar and cement stabilised rammed earth (CSRE). • Pullout bond strength and bond force-slip relationships were established. • Dry density of RE, rebar diameter and type of reinforcement greatly influence the pullout bond strength of rebars in CSRE. • Ribbed rebars develop good bond strength with the CSRE matrix. Rammed earth construction involves compacting processed soil in progressive layers inside a rigid formwork. Rammed earth structural elements experience bending stresses under lateral loads such as wind and earthquake loads. The flexural strength of cement stabilised rammed earth (CSRE) walls is low. Reinforcing the rammed earth will improve the flexural strength of rammed earth to resist lateral loads. There is hardly any information on the bond strength of rebars embedded in CSRE matrix. There is a need to examine the bond developed between rebar and CSRE matrix. This paper focuses on determining the bond strength between rebar and CSRE; establish bond force – slip relationships for reinforced CSRE. The variables considered in the study included two dry densities (1800 and 1900 kg/m3), two cement contents (7% and 10%) and three types of rebars. The CSRE cubes embedded with different types of rebars were tested for pullout loading under two testing conditions (dry and wet). The bond strength of rebars in CSRE matrix was found to be greatly influenced by the dry density of the CSRE and the type of reinforcement. The bond strength of deformed rebars is higher than the plain rebars irrespective of the specimen density. [ABSTRACT FROM AUTHOR]

• The effect of the Printing Method on the Pull-Out Strength was investigated. • Printing over an actual steel bar is feasible and effective. • Printed elements almost give the same pull-out strength as for non-printed ones. • The layers direction do not majorly affect the Pull-out strength. • A printable material always generate a strong link with steel. 3D Printing of Concrete is gaining more attention with time as an alternative method for construction for its high degree of freedom. Until now, most of 3D printed elements are pre-printed then moved to their designated locations. The most practical method for moving printed elements is lifting them by means of implemented anchors. However, due to the nature of this construction method, it does not allow for any type of vibration, also due to the use of a special type of concrete mix, that do not flow by itself, there are still a lot of queries concerning the adherence of concrete with steel bars. The objective of this paper is to characterize the bond between steel and printed mortars as a function of mortar's workability and printing method. Pull-out tests of an 8 mm steel bar embedded in either printed or non-printed mortars of varying workability have been performed after 3 days of casting. It is found that the workability of the ink does not affect the pull-out strength, neither the printing method nor layers direction affect the pull-out strength in respect to the steel bar. [ABSTRACT FROM AUTHOR]