Bond Performance Research Articles

Experimental research on the degradation law of the bond performance between steel bars and concrete with rust expansion cracking

Experimental research on the degradation law of the bond performance between steel bars and concrete with rust expansion cracking

Influence of the Elastic Modulus and Spiral Rib Appearance on the Resin Bonding Performance Based on an NPR Prestressed Bolt

Influence of the Elastic Modulus and Spiral Rib Appearance on the Resin Bonding Performance Based on an NPR Prestressed Bolt

Failure of the SRC under freeze- thaw cycles by the push-out tests

This paper explores the impact of freeze-thaw cycles, the thickness of the protective layer, embedment length, and volumetric hoop ratio on the bond performance at the SRC interface, assessed through freeze-thaw and push-out tests. Results from SEM indicated significant cracking in concrete exposed to freeze-thaw cycles, with an increase in both the number and diameter of pores. Despite significant damage to the concrete exterior, the interface exhibited considerably less deterioration. Following 200 freeze-thaw cycles, the specimens displayed a maximum crack depth of 2.3 mm and a porosity rate of 35.1 %. As the cycles progressed, the failure mode of specimens under push-out loading transitioned from splitting to interfacial shear failure. Notably, the length of cracks on the end surfaces was markedly reduced, and the majority of specimens exhibited minimal cracking on the side surfaces. Additionally, interfacial bond stress decreased progressively with the increasing number of cycles. The ultimate bond stress declined more rapidly than residual bond stress, with the rate of decrease stabilizing after surpassing 100 cycles. Enhancements in protective layer thickness, embedment length, and volumetric hoop ratio effectively mitigated the reductions in bond stress. Among these, the protective layer had the most significant impact, followed by the volumetric hoop ratio, while embedment length had the least influence. The study concludes with proposed formulas for calculating bond stress and slip eigenvalues after freeze-thaw cycles, integrating experimental results and theoretical analysis.

Influence of synthetic fibres on the bond performance of glass fibres reinforced polymers concrete: an experimental investigation and regression-based analysis

Influence of synthetic fibres on the bond performance of glass fibres reinforced polymers concrete: an experimental investigation and regression-based analysis

Enhancing bond strength prediction at UHPC-NC interface: A data-driven approach with augmentation and explainability

Existing concrete structures often have difficulty reaching their design service life due to aging, increased loads, and natural disasters, and they need to be repaired and strengthened or replaced. Ultra-high-performance concrete (UHPC), known for its ultra-high strength and excellent toughness, offers a promising solution for repairing and strengthening normal concrete (NC) structures. It is expected to be a viable solution when applied to the repair and strengthening of NC structures. A reliable interfacial bonding between the two materials (NC substrate and UHPC) determines the overall performance of this composite structure. In this study, a data-driven approach is proposed to predict the bond performance at the UHPC-NC interface as accurately as possible. To overcome the problem of limited experimental data, a data augmentation model is introduced, combining kernel density estimation (KDE) and tabular generative adversarial networks (TGAN). The optimal model is determined from six decision tree-based ensemble learning models applied to two strategies: "synthetic training - real testing" and "real training - real testing." Finally, a parametric analysis is performed using SHapley Additive exPlanations (SHAP) to elucidate the importance and sensitivity of different features related to bond strength. The findings illustrate that the suggested KDE-TGAN model effectively captures the distribution of the original dataset, enhancing both the accuracy and robustness of the bond strength prediction models. Furthermore, the model's ability to explain the importance and sensitivity of different features provides valuable insights into bond strength prediction. Thus, the proposed data augmentation model provides a reliable approach for modeling experimental data with small samples in structural engineering applications.

Study on the adhesive property of sludge-modified magnesium phosphate cement reinforcement coating for steel bars

The synergistic interaction inreinforced concrete systems originates from the strong bond between steel reinforcement and concrete, enabling them to collaborateunder load and optimize structural performance. This study applied various sludge-modified magnesium phosphate cement mixtures to the surfaces of plain round steel bars and ribbed steel bars to prepare steel-reinforced concrete specimens. The characterization of the bond performance of the sludge-modified magnesium phosphate cement reinforcement coating for steel bars and concrete was achieved through analyzing the failure modes, bond strength, and slip values of different groups. Microscopic analysis was performed using a scanning electron microscope. The results revealed that the primary failure mode of the steel-reinforced concrete specimens was steel bar pull-out, with some specimens exhibiting concrete splitting failure. Coating application on plain round steel bars increased bond strength, while on ribbed steel bars, it decreased bond strength. The application of the coating slightly reduced slip values to some extent.

Machine learning prediction method for the interface bond strength between fiber reinforced polymer bars and concrete based on multi-feature driven analysis

In severe service conditions, corrosion of reinforcement poses a significant challenge for concrete structures. Fiber reinforced polymer (FRP) materials, characterized by their low weight, high strength, and superior corrosion resistance, are effective in enhancing the durability of these structures. The interfacial bond performance between FRP bars and concrete is crucial for their synergistic action and is pivotal for the design and safety evaluation of FRP-reinforced concrete structures. This paper conducts a comprehensive analysis of factors including the material and mechanical properties of FRP bars, concrete mechanical properties, and bond length. Utilizing an exhaustive search strategy, it identifies the optimal characteristic parameters for assessing the bond strength between FRP bars and concrete. Subsequently, these parameters are integrated with four machine learning (ML) algorithms—DT, SVM, RF and XGB—to train the nonlinear mapping relationship between influencing factors and bond strength, proposing a unified and interpretable prediction method for the FRP bar-concrete interface bond strength. The model's predictive accuracy is then validated using a test dataset, and a comparative analysis is performed among the predictive models generated by the four ML algorithms, as well as against empirical calculation formulas. The findings indicate that the ML models offer superior predictive performance and accuracy over empirical formulas, with the XGB algorithm demonstrating the highest overall accuracy and best performance. Moreover, to address the black-box nature of ML algorithms, the SHAP method is employed to enhance the interpretability of the bond strength prediction process. The newly developed hybrid ML model holds promise as a novel approach for accurately assessing the bond strength at the FRP bar-concrete interface.

Degradation law of bond strength of reinforced concrete with corrosion-induced cracks and machine learning prediction model

During long term operation service, reinforced concrete (RC) structures are subjected to corrosive media such as chloride salts, which results in the degradation of interface bond performance, subsequently reducing the load bearing capacity and service life of the structures. To accurately assess the durability of RC structures in environments such as oceans and salt lakes, this study combines experimental methods with machine learning (ML) techniques to explore the degradation patterns and predictive models of bond performance under chloride salt corrosion. Accordingly, a series of central pull-out tests were conducted based on an electrochemical accelerated-dry-wet cycle corrosion regime to investigate the degradation patterns of bond performance between corroded steel bars and concrete under different corrosion degree and corrosion-induced crack widths. By comparatively analyzing the evolution patterns of cracks and the morphology of the steel bars in reinforced concrete specimens and their failure modes, and integrating the mechanical degradation mechanism with chemical and microscopic corrosion mechanisms, an in-depth analysis of the corrosion-induced degradation patterns at the bond interface was performed. The internal relationships between corrosion degree, corrosion-induced crack width and bond strength were discussed, and the variation patterns of bond strength with corrosion-induced crack width and corrosion degree were explored. Moreover, the bond strength patterns were analyzed from an energy perspective. The results indicate that bond strength and bond energy decrease with an increase in the corrosion-induced crack width of the concrete. Additionally, based on the experimental data from this study, ML predictive models for bond strength were established using corrosion-induced crack width as the control variable. The results show that the ML-based bond strength predictive models fit well with the experimental data, offering higher accuracy and reliability compared to traditional bond strength models. The research findings provide significant theoretical basis and practical guidance for safety assessment, maintenance, reinforcement, and full-life design of corroded RC structures.

Bond behaviour between near surface mounted CFRP and concrete members using magnetized bond agent under different temperature degrees

ABSTRACT In this investigation, the bond performance between CFRP and concrete in Near Surface Mounted (NSM) strengthening system using cementitious-based adhesive (CBA) was evaluated at different exposure temperatures. Two types of CBA were used (CBA-A and CBA-B) with and without magnetic water (MCBA-A and MCBA-B). Magnetic device with magnetic strength of 9000 Gauss was used to magnetise the water for 15 mins with a flow rate of 0.1 m3/hr. The bond efficiency was evaluated by performing single-lap shear tests for CFRP laminate embedded in concrete prisms as a near surface-mounted strengthening system. The bond between CFRP and concrete was tested under ambient and high temperatures. The heating regime involves the exposure of NSM CFRP/concrete samples to constant temperature (200°C) for 2 hrs, then the load was applied until failure. In comparison with control samples, an improvement of 40% in the load failure was achieved for specimens strengthened with CFRP using magnetised water in CBA. Within the MCBA samples, higher failure load was conducted for MCBA-B samples when compared with samples of MCBA-A since the latter contain primer in its compositions in which its properties deteriorate by high temperature. All tested samples showed similar failure pattern, which is slippage of CFRP.

Bonding of Beech Wood to Mortar with a Novel Epoxy Hybrid-Adhesive: Performance in Dry and Wet Conditions

Composites made of timber and cementitious materials require a rigid connection to exploit their full composite action, which can be achieved by using full-surface adhesive bonding. In this work, we investigated a novel hybrid-adhesive system consisting of a silane-terminated polyurethane (STP) and epoxy resin for the bonding of beech wood timber to fresh mortar for use in timber-mortar composites (TMC). The mechanical performance and the influence of moisture on TMC produced by the wet-in-wet process (fresh mortar) was investigated and compared to the bonding of prefabricated mortar (prefab process). The STP-epoxy hybrid-adhesive showed a suitable bonding performance of beech wood to both, fresh mortar and precured mortar with median compression shear strengths of 4.57 MPa and 6.07 MPa, respectively. The fracture pattern showed the strength of the near-surface layer in the mortar, close to the adhesive, being often decisive for the bond performance. The same failure mode predominated in TMC beams after 3-point bending tests. The stability of the composite upon the influence of moisture is especially challenging when using beech wood due to its low dimensional stability. Thus, the moisture stability of the bond was investigated by compression shear tests after water immersion. It showed superior water stability compared to composites bonded with a pure epoxy resin. Nonetheless, a clear reduction in bond strength compared to the dry state was observed, with delamination of 25% of the wet-in-wet and 17 % of the prefab specimens during water immersion. Furthermore, it was seen that the adhesive waiting time played a decisive role in the wet-in-wet produced specimens influencing both, dry and wet shear strength.

An innovative strategy for improving ductility of seawater sea-sand engineered cementitious composites beam reinforced with GFRP bar

Seawater sea-sand engineered cementitious composites (SS-ECC) members with glass fiber reinforced polymer (GFRP) bars have inferior ductility due to the brittle nature of GFRP bars. In the current research, an enlarged head anchorage system (EHAS) was recommended to improve the ductility of GFRP bars reinforced SS-ECC beams. To explore the bond characteristics between SS-ECC and GFRP bars with EHAS, a total of 39 specimens were tested by pull-out loading. The influences of enlarged head shape, stirrup spacing and SS-ECC’s strength grade on the bond characteristics were experimentally investigated. GFRP longitudinal bars in specimens with EHAS presented rupture failure rather than anchorage failure. EHAS could effectively realize the slip hardening of GFRP bars in low strength SS-ECC, and ensure the reliable bond of GFRP bars in high strength SS-ECC. Additionally, the failure mechanism of specimens under pull-out loading was explored by finite element analysis (FEA). The pull-out resistance was mainly provided by EHAS in force transition stage and slip hardening stage. The influences of fiber reinforced polymer (FRP) bar type on the bond performance were investigated by FEA. EHAS could realize the slip-hardening behaviors of aramid, basalt and carbon FRP bars in normal strength SS-ECC. More importantly, to verify the effectiveness of the proposed ductility enhancement strategy, SS-ECC beams reinforced with GFRP bars were tested by four-point bending. These beams with different enlarged head shapes possessed excellent ductility and strong ultimate deformation capacity. It was recommended that low strength SS-ECC and GFRP bars with EHAS were jointly utilized to enhance the ductile performance of the beams.

Rheological and adhesive improvements of terminal blend rubberized asphalt via fumed silica nanoparticle modification

Due to the high degree of desulfurization and depolymerization of crumb rubber (CR) particles in terminal blend rubberized asphalt (TBRA), their elasticity and adhesive performance are insufficient. To address this, the study utilized low-cost fume silica nanoparticles (FSNPs) to enhance the elasticity and adhesive properties. TBRA binders with varying CR contents (30 %, 40 %, 50 %) were modified using different dosages of FSNPs (2 %, 4 %, 6 %). The microstructure of FSNPs was examined through TEM and SEM. Using a dynamic shear rheometer (DSR) test, contact angle test, and atomic force microscope (AFM) test, the effects of FSNPs on the rheological properties, surface energy, and adhesive properties of TBRA binders were evaluated. The results showed significant improvements in the deformation resistance and elasticity of the TBRA binders modified with FSNPs. This is attributed to the branched network structure of FSNPs, which notably enhances the binder's cohesion, thereby strengthening its resistance to shear deformation and improving elasticity. FSNPs effectively reduce the moisture sensitivity of TBRA, due to the hydrophilic hydroxyl groups on FSNPs being replaced by hydrophobic methyl groups (-CH3). The inadequate bonding performance of TBRA can be attributed to the high levels of extensively depolymerized and desulfurized CR particles, which reduce the cohesiveness of the binder. The addition of FSNPs, although it lowers the surface energy of TBRA binders, significantly enhances their cohesiveness due to the branched network structure, thereby improving their bond performance. AFM results indicate that FSNPs enhance the adhesive strength of the TBRA binder surface due to their high specific surface area, which provides more van der Waals forces and electrostatic interactions. For economic efficiency, an addition of 4 % is recommended for TB30, and 2 % for TB40 and TB50. At these specified concentrations, the bond strength of the TBRA binder can be increased by 45–55 %.

Corrosion failure analysis of interfacial bond performance in circular seawater sea-sand concrete encased weathering steel structures

This paper investigated the bond-slip behavior of circular seawater sea-sand concrete encased weathering steel (CSSCEWS) structures after chloride-induced corrosion. Electrochemical corrosion tests and push-out tests were conducted on fifteen designed CSSCEWS specimens. The results revealed that the corrosion ratio and steel section type distinctly influenced the interfacial bond performance. Both the ultimate and residual bond strengths decreased with the increase of the corrosion ratio, and the decline rate slowed down gradually. Compared to the uncorroded specimens, the average damage ratio of the ultimate strength of the specimens with a corrosion ratio of 8% is 25.9%, while the average damage ratio of the residual strength is 49.1%. The bond toughness continuously decreased with prolonged corrosion, while the bond stiffness and energy dissipation index first increased and then decreased. Additionally, formulas for calculating the corroded bond strengths of CSSCEWS specimens were proposed. Considering the strength damage due to corrosion and the stiffness damage due to slip, a three-stage bond-slip constitutive model was proposed. Finally, this model was applied to the nonlinear spring elements in finite element modeling to effectively simulate the interfacial bond behavior during the loading of corroded CSSCEWS specimens.

Influence of mechanical anchors on bond performance of fiber fabric-steel joints

This study proposes an experimental model for anchor reinforcement and conducts uniaxial static tensile tests. The influence of anchor reinforcement on the failure mode of specimens is revealed. This includes the effects of bond length, number of layers, and types of fiber fabric under anchor reinforcement on the ultimate bearing capacity and bond-slip curve. The results demonstrate that anchors can effectively increase the ultimate bearing capacity of the test specimens. There are differences in bond-slip behavior between the anchors near the free end and the joint end. Higher stresses are experienced near the joint end. The use of anchor reinforcement can significantly enhance the load-bearing capacity of multi-layer carbon fiber specimens. Increasing the number of anchors and reducing the distance between the anchor and the joint end can further improve the stiffness of the specimens. A finite element model is established using ANSYS, which agrees well with the experimental results and parameterized analysis results reveal a linear increase in load-bearing capacity and stiffness with higher anchor bolt preload, achieving an 84.42 % increase at 11kN. Increased preload enhances friction at the carbon fiber-steel interface, reducing deformation. Similarly, expanding anchor width from 9 mm to 39 mm improves load-bearing capacity by 54.28 %, with larger anchors significantly boosting stiffness and bonding performance, which can be used to predict the mechanical properties of fiber fabric-steel reinforced by anchors.

Durability Properties of Steel Textiles and Bonding Properties at the Interface of Steel Textiles with Reinforced Mortar-Reinforced Concrete Systems.

Aging and deterioration of building structures have been persistent concerns in the field of engineering. To address these challenges while supporting modern green and sustainable development goals, this study introduces an innovative reinforcement system that employs steel textiles as the primary reinforcing material. The steel textiles were engineered by optimizing the compatibility between steel fibers and a hot melt adhesive (HMA). These textiles were then used to reinforce concrete structures, creating a steel textile-reinforced mortar (STRM)-reinforced concrete system. The study also examined the durability of the steel textiles and the interfacial bonding performance within the STRM-reinforced concrete system. The results showed that the compatibility between steel fibers and ethylene vinyl acetate copolymer (HMA-2) is better, and the steel textiles prepared with it have superior hydrothermal and corrosion resistance. After the system had been maintained for 28 days, the overall flexural strength of the STRM-reinforced concrete system was increased by 100.03%, the interfacial shear load by 49.54%, the interfacial shear stiffness by 61.2%, and the positive tensile bond performance by 26.1%. This proves that STRM has a good reinforcement effect on the concrete reinforcement system.

Dressing Mechanism and Evaluations of Grinding Performance with Porous cBN Grinding Wheels

Cubic boron nitride (cBN) grinding wheels play a pivotal role in precision machining, serving as indispensable tools for achieving exceptional surface quality. Ensuring the sharpness of cBN grains and optimizing the grinding wheel's chip storage capacity are critical factors. This paper presents a study on the metal-bonded segments and single cBN grain samples using the vacuum sintering method. It investigates the impact of blasting parameters—specifically silicon carbide (SiC) abrasive size, blasting distance, and blasting time—on the erosive wear characteristics of both the metal bond and abrasive. The findings indicate that the abrasive size and blasting distance significantly affect the erosive wear performance of the metal bond. Following a comprehensive analysis of the material removal rate of the metal bond and the erosive wear condition of cBN grains, optimal parameters for the working layer are determined: a blasting distance of 60 mm, a blasting time of 15 s, and SiC particle size of 100#. Furthermore, an advanced simulation model investigates the dressing process of abrasive blasting, revealing that the metal bond effectively inhibits crack propagation within cBN abrasive grains, thereby enhancing fracture toughness and impact resistance. Additionally, a comparative analysis is conducted between the grinding performance of porous cBN grinding wheels and vitrified cBN grinding wheels. The results demonstrate that using porous cBN grinding wheels significantly reduces grinding force, temperature, and chip adhesion, thereby enhancing the surface quality of the workpiece.

Study on bonding properties and constitutive model of steel bar and nano-SiO2 reinforced recycled aggregate concrete

Optimizing design and ensuring the structural safety of recycled aggregate concrete (RAC) structures requires a thorough understanding of the bond-slip mechanism between steel bars and RAC. Previous studies have demonstrated the significant enhancement of the microscopic properties of RAC and its bond with steel bars due to nano-SiO2. However, the structural bonding mechanism between the steel bar and nano-SiO2-enhanced RAC remains unclear. Therefore, this study investigates the influence of nano-SiO2 on the bond performance between RAC and steel bars, elucidating the enhancement mechanism through microscopic techniques. Additionally, various factors affecting the bond-slip performance of RAC specimens are analyzed, leading to establishing a multifactorial coupling formula considering thickness-to-diameter ratio, concrete strength, and relative anchorage length. Furthermore, slip index correction formulas and a constitutive model are developed, considering these factors. Acoustic emission (AE) technology monitors the bonding process, clarifying the evolution of AE digital signals and bond damage history. Employing the finite element method, a numerical model of bond-slip behavior is established, revealing specimens' changing bond strength and failure modes. Experimental results indicate that increasing nano-SiO2 content reduces structural porosity, leading to denser and more homogeneous microstructures, thereby enhancing RAC's mechanical properties and bonding performance. Moreover, AE techniques effectively monitor bond damage at different stages. Finally, a bond-slip constitutive model is proposed for steel bar and nano-SiO2 reinforced RAC, offering insights for numerical calculations and engineering designs.

Cyclic bond behavior and bond stress – slip model of steel strands in steel fiber reinforced concrete

To study the bond performance of steel strands in steel fiber reinforced concrete (SFRC), bonding tests under monotonic and cyclic loads were performed on the specimens with different steel fiber volume fractions (SFVFs), bond lengths, nominal diameters of steel strands and SFRC strengths. The results showed that the relative rotation between the steel strand and SFRC occurred when the steel strands were vertically pulled out from SFRC due to the smooth and continuous helical shape of the steel strands. For the specimens with the same parameters, the maximum bond stress under cyclic load decreased by 1.67–22.88 % than that under monotonic load. The maximum bond stress under cyclic load increased with the increasing SFVFs or SFRC strength. Notably, the maximum bond stress under cyclic load also increased with the increasing bond length or diameter of steel strands, significantly different from that of ordinary ribbed steel bars and FRP bars. The cumulative energy dissipation (CED) of bond specimens increased with the diameter of steel strands and SFRC strength. Besides, the SFVFs had a positive effect on the CED, but simultaneously increasing diameter of steel strands would weaken the positive effect of SFVFs, and simultaneously increasing bond length had no obvious on the CED. Finally, a bond stress – slip model of steel strands in SFRC was established, suitable for calculating bond stress – slip curves under random and complicated loading schemes. By comparing the calculation and test results of bond stress – slip curves, it was proved that the proposed model had an acceptable accuracy and could describe the influence laws of SFVF, bond length, nominal diameter of steel strand and SFRC strength well.

Improvements in Global Bond Portfolio Risk Management and Performance by Hedging the Components of Total Risk with Derivatives

Improvements in Global Bond Portfolio Risk Management and Performance by Hedging the Components of Total Risk with Derivatives

Experimental and Analytical Study of Tensile and Bond Performances of Glass Fabric Reinforced Cementitious Matrix for Retrofit Applications on Concrete Surfaces

Experimental and Analytical Study of Tensile and Bond Performances of Glass Fabric Reinforced Cementitious Matrix for Retrofit Applications on Concrete Surfaces