Search Results (50)

Pullout bond tests using specimens with an expansion-agent-filled pipe (EAFP) simulating the cracking due to rebar corrosion were conducted to evaluate the deterioration of bond behavior when the crack width is not uniformly distributed along the longitudinal direction. The primary specimens for the pullout test are designed with a bond length equal to 20 times the bar diameter. To investigate the distribution of bond stress along the rebar in detail, a bond analysis was performed using the local bond stress–slip model as a function of the induced crack width that is developed based on the pullout test of the specimens with a bond length of four times the rebar diameter. The EAFP simulation showed a tendency for larger crack widths at the free end, likely due to filling the expansion agent from the load-end side. From the results of the pullout bond test, as the induced crack width increases, the maximum bond stress decreases. The results of the bond analysis, assuming the five patterns of crack width distributions along the longitudinal direction, showed that the bond stress–slip curve is little affected by the difference in the crack width distribution. Within a bonded length up to 20 times the rebar diameter, the differences in crack width variations had little effect on the distribution of the local bond stress. It is possible to evaluate the bond behavior based on the average crack width. Full article

Natural sand (NS) is facing the problem of resource scarcity, while manufactured sand (MS) has become a favorable alternative resource due to its wide range of sources, superior performance, as well as economic and environmental protection. This study adopted MS to replace NS to prepare manufactured sand concrete (MSC). The water–cement ratio, replacement rate of MS, and stone powder content were systematically investigated for the damage evolution of rebar during bond–slip with MSC. Seven groups of specimens were tested using the center pull-out test to analyze the effects of different factors on the bond–slip characteristics (bond stress–slip curve, bond fracture energy, peak stress, and peak slip). Acoustic emission (AE) monitoring was also adopted to synchronously characterize the slip damage process of reinforced MSC. The results indicate that the water–cement ratio and replacement ratio of MS present significant influences on the bond strength of reinforced MSC, in which the smaller the water–cement ratio is, the stronger the bond strength of reinforced concrete. Further, the larger the replacement rate of MS is, the stronger the bond strength of reinforced concrete. The higher the stone powder content, the higher the bond strength, but the effect is small compared to the two variables mentioned above. In terms of AE, count and energy remain at low values in the first and middle stages, followed by larger values, proving that cracks were beginning to develop within the specimen, and then a very large signal and then splitting occurred. The information entropy is relatively stable in the first and middle stages of the test, then fluctuates with the generation of cracks, and finally fluctuates violently and then the specimen splits. The AE parameters are more active with an increasing water–cement ratio, while they are smoother with increases in the replacement rate of MS and stone powder content. Full article

There are many methods for evaluating the bond behavior between rebar and concrete. For certain experimental purposes, selecting the ideal method for testing the rebar–concrete bonding properties is often a controversial problem. The most representative single-end pull-out test method and the full-beam test method were applied in this work to conduct bonding tests between rebar and concrete. Considering the influence of the concrete strength, bonding length, stirrup, and rebar slotting, these two testing strategies are compared and analyzed in terms of the specimen failure mode, bonding strength, bond–slip curve, and rebar stress distribution. Suggestions are offered regarding the selection of an appropriate method for evaluating the bond behavior between rebar and concrete based on an comparative analysis of the two tested approaches. The results presented herein provide a basis for the preparation of relevant test method standards. Full article

The increasing demand for sustainable construction materials has driven the exploration of alternatives to traditional cement-based concrete. In this context, this study investigates a cement-less material, specifically an alkali-activated or geopolymer concrete (GPC), which presents potential environmental benefits. The material has been characterized with respect to both its fresh and hardened properties, providing groundwork for future structural applications. A key focus of the research is the bond behavior between GPC and reinforcing bars, including both steel and non-metallic fiber-reinforced polymer (FRP) bars. The use of non-metallic bars is particularly relevant as they offer the potential to enhance the durability of structures by mitigating issues such as corrosion. Current research lacks comprehensive studies on factors affecting stress transfer at the GPC-reinforcing bar interface, such as bar diameter, bond length, and surface finish. This study aims to expand knowledge on the bond between GPC and steel/FRP rebars through experimental and analytical approaches. The tests, which included different bar types and bond lengths, showed that GPC exhibited similar bond behavior with steel and ribbed glass FRP bars in terms of bond strength and stress-slip curves. The results indicate that GPC exhibits comparable bond strength and stress-slip behavior when reinforced with either steel or ribbed glass FRP bars. Full article

Models used to study the fracture process of concrete are often considered 2D, ignoring the influence of specimen width. However, during the fracture process in pre-cracked concrete beams, the crack length varies along the thickness direction, especially in reinforced concrete. To study the influence of specimen width on reinforced concrete fracture behavior, a 3D numerical method was used to simulate the crack propagation processes of lightly reinforced concrete beams based on Fracture Mechanics. Nonlinear spring elements with different stress-displacement constitutive laws were employed to characterize the softening behavior of concrete and the bond-slip behavior between the steel bars and concrete, respectively. It is assumed that the crack begins to propagate when the maximum stress intensity factor at the crack tip along the beam width reaches the initial fracture toughness of concrete. To verify the validity of the proposed method, the completed crack propagation processes of lightly reinforced concrete three-point bending notched beams were simulated, and the calculated load-crack mouth opening displacement curves showed a reasonable agreement with the experimental data. Moreover, the impact of the 2D reinforced concrete beam model on the crack propagation process was analyzed. The results indicate that at the initial loading stage, the external load P obtained from the 2D model is significantly larger than the result from the presented 3D model. Full article

Epoxy resin concrete, characterized by its superior mechanical properties, is frequently utilized for structural reinforcement and strengthening. However, its application in structural members remains limited. In this paper, the bond–slip behavior between steel reinforcement and epoxy resin concrete was investigated using a combination of experimental research and finite element analysis, with the objective of providing data support for substantiating the expanded use of epoxy resin concrete in structural members. The research methodology included 18 center-pullout tests and 14 finite element model calculations, focusing on the effects of variables such as epoxy resin concrete strength, steel reinforcement strength, steel reinforcement diameter and protective layer thickness on bond performance. The results reveal that the bond strength between epoxy resin concrete and steel reinforcement significantly surpasses that of ordinary concrete, being approximately 3.23 times higher given the equivalent strength level of the material; the improvement in the strength of both the epoxy resin concrete and steel reinforcement are observed to marginally increase the bond stress. Conversely, an increase in the diameter of the steel reinforcement and a reduction in the thickness of the protective layer of the concrete can lead to diminished bond stress and peak slip. Particularly, when the steel reinforcement strength is below 500 MPa, it tends to reach its yield strength and may even detach during the drawing process, indicating that the yielding of the steel reinforcement occurs before the loss of bond stress. In contrast, for a steel reinforcement strength exceeding 500 MPa, yielding does not precede bond stress loss, resulting in a distinct form of failure described as scraping plough type destruction. Compared to ordinary concrete, the peak of the epoxy resin concrete and steel reinforcement bond stress–slip curve is more pointed, indicating a rapid degradation to maximum bond stress and exhibiting a brittle nature. Overall, these peaks are sharper than those of ordinary concrete, indicating a rapid decline in bond stress post-peak, reflective of its brittle characteristics. Full article

Manufactured sand (MS), due to its wide availability and cost-effectiveness, is used as an alternative aggregate for quartz sand (QS) in ultra-high-performance concrete (UHPC) to prepare ultra-high-performance manufactured sand concrete (UHPMC). This study aims to assess the bond behavior of 600 MPa-grade, high-strength, hot-rolled ribbed bars (HRB 600) in UHPMC. Thirty specimens were designed for the pull-out tests, taking into account several feature parameters, including MS replacement ratio (0%, 50%, 100%), water–binder ratio (0.17, 0.19, 0.21), steel fiber content (0%, 1%, 2%), and anchorage length (2d, 3d, 4d, 5d). The effects of the feature parameters on the failure mode, bond stress–slip curves, bond strength, bond-slip mechanism, and constitutive model were analyzed and illustrated. The results reveal that the pull-out specimen of UHPMC exhibits three distinct failure modes: rebar pull-out failure, UHPMC splitting failure, and splitting-pull-out failure. The bond strength increases from 46.57 MPa to 56.92 MPa when the steel fiber content increases from 0% to 2%. Additionally, a decrease in anchoring length is beneficial for improving the bond strength; as the anchoring length increases from 2d to 5d, the bonding strength decreases by 35.84%. The bond strength increases with an increase in the MS replacement ratio. As for the water–binder ratio, the bond strength presents the highest value when the water–binder ratio is 0.17. In addition, a new bond-slip constitutive model applicable to UHPMC and HRB 600 rebar, considering the MS replacement ratio, the water–binder ratio, etc., is proposed, which presents favorable prediction accuracy. Full article

Due to their excellent ductility and crack-control ability, engineered cementitious composites (ECCs) combined with shaped steel can produce steel-reinforced engineering cementitious composite (SRECC) structures which exhibit significant advantages in prefabricated buildings. The interface bond behavior is the base for the cooperative working performance of the shaped steel and ECC. This study included push-out tests of one ordinary concrete control specimen and ten ECC specimens. The various parameters were the ECC compressive strength, fiber volume content, cover thickness, and the embedded length of shaped steel. The bond stress–slip curves at the loading and free end were obtained, and the effects of various parameters on the characteristic points of curves were analyzed. The results indicated that the ordinary concrete specimen failed in brittle splitting, with the cracks completely penetrating the surface of the specimen. Due to the fiber-bridging effect in ECCs effectively preventing the development and extension of cracks, the shaped steel at the free end was obviously pushed out, and the surrounding matrix maintained good integrity after testing finished. For ECC specimens, bond or splitting-bond failure occurred, exhibiting outstanding ductility. Compared with the ordinary concrete specimen, the standard ultimate and residual bond strength of ECC specimens improved by 37.9% and 27.4%, respectively. Besides the increase in ECC compressive strength, the fiber volume content and cover thickness had a significant positive influence on the ultimate and residual bond strength, whereas the effect of the embedded length was the opposite. Finally, the calculation equations of characteristic bond strength were proposed, and the calculated values matched well with the experimental values. Full article

Reinforced concrete structures play a pivotal role in island and reef engineering projects. Given the resource constraints typical of island regions, substituting traditional manufactured sand aggregate with reef limestone not only reduces reliance on river sand but also addresses the issue of disposing of waste reef limestone slag generated during excavation. However, the performance characteristics of reef limestone concrete, particularly its bond strength with reinforcing steel, warrant further investigation. This is particularly true for the bond–slip behavior of the reinforcement. This study aims to elucidate the effects of various parameters on the bond performance between steel and reef limestone concrete through central pullout tests. These parameters include the type and diameter of the reinforcement, bond length, and loading rate. The investigation encompasses the analysis of load–slip curves, bond failure modes, and variations in bond stress. Additionally, using the Abaqus software, a numerical simulation was conducted to analyze the mesoscopic stress characteristics, thereby revealing the mechanisms of bond formation and failure modes between steel reinforcement and reef limestone concrete. The results indicate that the bond–slip curve for reef limestone concrete reinforced with ribbed rebars and Glass Fiber-Reinforced Polymer (GFRP) rebars can be broadly categorized into four phases: minor slip, slip, decline, and residual, with the residual phase exhibiting a wave-like pattern. The predominant failure modes in reef limestone concrete are either pulling out or splitting. The bond stress in reef limestone concrete decreases with an increase in rebar diameter and bond length; conversely, it increases with the loading rate, although the ultimate slip decreases. The mesoscopic failure characteristics of reinforced reef limestone concrete, as simulated in Abaqus, are consistent with the experimental outcomes. Full article

The use of Fabric-Reinforced Cementitious Matrix (FRCM) systems is an innovative method for strengthening structures, particularly masonry, while addressing environmental and economic concerns. Despite their widespread use, characterizing FRCM composites poses challenges due to their complex mechanical behavior and considerable variability in properties. The available standardized testing methods exhibit some inconsistencies, underscoring the need for reliable characterization procedures. This paper presents an experimental study on the bond behavior between FRCM materials and calcarenite stone using a non-standard setup for double shear bond tests. Different FRCM systems are considered, varying the matrix composition and fabric nature. The experimental results are evaluated in terms of maximum stress, slip and data dispersion, alongside comparisons with double shear tests on larger samples and single-lap shear. These findings provide insights into how the mortar nature influences the stress-slip curves, strength, ductility and failure modes. The experimental study demonstrates the repeatability and robustness, particularly in terms of peak strength, of the non-standard setup configuration utilized in the study. The study highlights the importance of reliable characterization procedures for FRCM materials, especially in bond behavior assessments, emphasizing the need for further research to enhance our understanding of their application in structural reinforcement. Full article

Half-grouted sleeve connectors are a primary method for connecting rebar in prefabricated concrete structures. However, due to limitations in the construction environment, all kinds of grouting defects are inevitable, especially grouting voids. Additionally, fire disasters, among the most common types of disasters, significantly threaten the structural performance and safety of these prefabricated structures. Therefore, it is imperative to determine the mechanical properties of half-grouted sleeve connectors with grouting voids after high temperatures. This study designed and prepared 48 groups of half-grouted sleeve specimens with different grouting voids and defect locations. These specimens were heated to the specified temperature (25 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C), followed by unidirectional tensile testing after natural cooling. The experimental results showed that rebar fracture failure and rebar pulled-out failure were the failure modes of specimens. With the increase in temperature, bearing capacity, safety factor and ductility coefficient of specimens all decreased. When the temperature was lower than 400 °C, the specimen with void length less than twice the diameter of the rebar (i.e., 2d) had sufficient connection performance. For specimens with the same total void lengths, the bearing capacity of discrete voids is lower than concentrate voids at the same temperature. The load-displacement curve, safety coefficient, ductility coefficient and grey correlation degree of half-grouted sleeve specimens with grouting voids at different temperatures are analyzed and discussed, and the bond stress slip constitutive model is given. Grouting defects have greater influence on specimens after grey correlation analysis. Findings from this study provide valuable references for the safety performance evaluation of prefabricated structures with half-grouted sleeve connectors after exposure to fire. Full article

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. Geometric parameters significantly influence the performance of the bond between ribbed FRP bars and SSC, thereby affecting the mechanical properties of the concrete structures. In this study, the performance of the bond between ribbed (i.e., with fiber wrapping) basalt-fiber-reinforced polymer (BFRP) bars and SSC was investigated through pull-out tests that considered rib geometry and SSC strength. The results demonstrated that an increase in rib and dent widths reduced the bond stiffness, while an increase in rib height and SSC strength gradually increased the bond stiffness and strength. Additionally, the bond stiffness and bond strength were relatively low because the surface fiber bundles buffered the mechanical interlocking force between the BFRP ribs and the concrete, resulting in plastic bond failure during the loading process. Furthermore, the adhesion of the fiber bundles to the surface of the BFRP bars also influenced bond performance, with higher adhesion leading to greater bond stiffness and strength. Full article

The bonding properties between rubber granule–basalt fiber composite modified concrete (RBFC) and rebar greatly impact the load-carrying capacity, stiffness, and crack development of RBFC structures. In this paper, the effects of rebar diameter, bonding length, and concrete type on the bonding properties between RBFC and rebar were investigated using center pull-out tests. The bond stress–slip curve as well as the bond strength and its influencing factors were discussed in detail, and a semi-theoretical and semi-empirical model of RBFC with rebar was established. According to the findings, when rubber granules were added to concrete, its bond strength with rebar decreased. At a dosage of 5%, the bond strength was reduced by approximately 4% compared to ordinary concrete (OC) under the same conditions. It was shown that the addition of small amounts of rubber granules did not significantly reduce the bond strength. On the other hand, the incorporation of an appropriate amount of basalt fibers had a positive effect on the bond strength. An admixture of 4.56 Kg/m³ of fibers increased the bond strength by 3% compared to OC under the same conditions. The bond strength of RBFC with these two additions was improved by approximately 2% compared to OC under the same conditions. When the bonding length was 60 to 100 mm, the ultimate bond strength decreased with increasing bonding lengths. The bond strength decreased by 13.91–16.72% for every 20 mm increase in bonding length. When the rebar diameter was 12 to 16 mm, the ultimate bond stress decreased as the rebar diameter increased. The bond strength decreased by 3.96–5.94% for every 2 mm increase in rebar diameter. The segmental bond–slip constitutive model between RBFC and rebar, established using the results of the center pull-out test, can provide a reference basis for engineering applications of RBFC. Full article

The utilization of fiber-reinforced polymer (FRP) composites for building reinforcement has gained widespread acceptance. However, the bond behavior between externally applied composites and strengthened substrates, which are crucial for system efficacy, has primarily focused on flat surfaces. Yet, the challenge of curved substrates, common in masonry arches and vaults, remains less explored. This study introduces a classical analytical model addressing the bond behavior between FRP plates and curved substrates. This classical approach is structured upon a simplified model that concentrates all the non-linearities of the FRP–substrate interface. The interface is described through a universal multi-linear stress–slip relationship, with the influence of the curved substrate being considered by the normal stress that impacts the interface law. Closed-form solutions for distinct bond-slip law stages are derived and verified against the previous study. Through comparisons with existing experimental data and simulations, this approach is able to predict the maximum load, the trends of the global load-slip curves, and give insights into detailed local behavior. Additionally, the exploration of employing neural networks for determining the interface law exhibits promising outcomes. Full article

Ultra-high-performance concrete (UHPC)-filled duct connection is an innovative solution for joining assembled structures, in which the anchorage performance of the rebar and UHPC filled in bellows plays a critical role in determining the overall connection effectiveness. To establish a reliable anchorage length and a bond–slip relationship between rebar and UHPC within a bellow, a total of 16 specimens were conducted, and pullout tests were carried out. Two parameters were considered, including the diameter ratio (D/d), representing the proportion of the diameter of the bellow D to the diameter of the steel bar d, and anchorage length (L). By analyzing the failure modes, load versus deflection curves, and steel strain data, the influences of the diameter ratio and anchorage length on the anchorage performance were discussed. The test results showed that the failure mode changed from rebar pullout to rebar breakage as the anchorage length increased from 3 d to over 10 d. The reliable anchorage length of the rebar was recommended to be at least 10 d with a diameter ratio (D/d) of 2.4. Moreover, a fitting bond–slip model was proposed based on the experimental bond–slip curves between the rebar and UHPC interface within the bellows with high precision. These findings constitute a crucial basis for the comprehensive stress analysis of assembled structures connected using UHPC grouted in bellows. Full article