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Pullout tests on geogrids have been regarded as the most direct way to investigate geogrid–soil interaction. In the pullout tests on geogrids, either static or dynamic load is commonly used for applying the vertical loads. In order to investigate the influence of static and dynamic load on pullout test results, pullout tests are carried out to analyze the mechanical response of geogrids and soils under static and dynamic load from the large-scale pullout tester. The results show that frequency and amplitude have significant effects on the pullout test results under the dynamic load. The interface cohesion and friction coefficients under dynamic loads are smaller than those under static loads. The reinforcement effect of geogrids is reduced by dynamic load. Therefore, the strength of geogrids should be reduced when quasi-static analysis is used for reinforced structures. Knockdown factor is recommended for the corresponding reduction. The investigation results of this study may provide scientific references for regulating the design method of reinforced structures. [ABSTRACT FROM AUTHOR]

Cracking is one of the most common distresses in asphalt pavement. Because asphalt concrete is relatively weak in tension, synthetic fibers have shown to increase its tensile strength and, therefore, reduce the chance of cracking. An approach was used in this study with the aim of evaluating the interaction between fibers and asphalt mastic and the fiber distribution in asphalt concrete. Three types of aramid fibers and two types of nylon fibers were used. A pullout test was used to determine the typical shear bond strength between fibers and the asphalt mastic. The bond strength obtained from the pullout test was then used to calculate the minimum fiber embedded length on each side of the crack in order for the fiber to reach its full capacity before being pulled out. Of course, increasing fiber length increases the chance of bridging cracks considering the random distribution of fibers in fiber-reinforced asphalt concrete (FRAC) and the random orientation of fibers relative to cracks. On the other hand, increasing fiber length may result in uneven distribution of fibers in the FRAC. Fiber extraction and recovery tests were then used to determine the dispersion of aramid fibers in the FRAC with different fiber lengths. The study showed that aramid fibers in the order of 20 mm would provide a good bond with the asphalt mastic and result in reasonable dispersion in the FRAC. The uniaxial fatigue test and flow number test were also performed on FRAC with different aramid fiber lengths. The 19-mm fibers also showed better performance test results than the 10- and 38-mm fibers. A similar length is recommended for the Nylon 1 fibers based on the bond properties only. Longer Nylon 2 fibers are recommended, but caution needs to be taken to avoid uneven fiber dispersion in the FRAC. [ABSTRACT FROM AUTHOR]

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract Bolt is an important connection in underground construction and monitoring its stress characteristics is essential to evaluate the effectiveness of bolt. The strain information collected along a rock bolt reveals the long‐term movement characteristics of rock mass, which greatly helps toward disaster prevention and risk warning. Grooving on the surface of a bolt and embedding an optical fiber is one of the main methods for monitoring the anchorage performance and stress distribution around the bolt in underground engineering. In this study, Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis (PPP‐BOTDA) technology is used to evaluate the stress, axial force, and shear stress distribution of the bolt under tensile load for different types (grooved and nongrooved) of bolts embedded in concrete with resin as anchoring agent. The results show that the PPP‐BOTDA sensor can be used to monitor the stress state of the bolt embedded in concrete with resin as anchoring agent when the bolt is subjected to a tensile force. However, the apparent stress value measured in this way is not the actual stress value of the bolt, but is an increased value caused due to the groove. The closer to the exposed end of the bolt, the greater is the deviation between the apparent stress value and the actual stress value of the bolt. Based on the monitoring results from this experimental study, a stress reduction calculation method is proposed, which can change the measured value into the actual stress of the bolt.

Even though steel bar is a conventional reinforcement in soil stabilization systems, the problem of corrosion of steel may lead to vast damages especially in aggressive environments. In the past decades, Fiber Reinforced Polymer (FRP) materials have offered an effective solution to overcome the corrosion problem. Despite numerous bond stress-displacement models for reinforcements in concrete, there is a lack of models for FRP nails in grout. In this paper, the usability of four bond stress models (Malvar, EPB, CMR and Soroushian) of reinforcements in concrete was evaluated to predict the bond stress of FRP nails in grout. For this purpose, the results of several experimental pullout tests were used to calibrate the reinforcement-concrete bond stress models and the constant parameters were obtained. To evaluate the accuracy of the calibrated models, four statistical criteria of R2, SSE, RMSE and MAPE have been also determined for each model. Results showed that Malvar model with R2 of 0.94 and MAPE of %21 was deemed suitable for the prediction of bond stress of GFRP nails while CMR model is not recommended.

Abstract Longwall face fall in the open face area is one of the most difficult ground control problems in mining thick coal seams in China especially under difficult geological conditions. This paper has proposed a new flexible bolting and grouting technology for face support. The flexible support method includes face support using flexible coir ropes and face grouting with cement and accelerator mixtures. Numerical and laboratory studies of pullout tests are performed to further improve the flexible support performance including optimization of boreholes and flexible bolts diameters, and selection of grouting materials. The results show that (a) The optimized rope‐borehole diameter ratio is around 0.5 to ensure the best face reinforcement; (b) The grouting material (a mixture of ultrafine cement, mineral powder and sodium silicate) shows advantages of low cost, effective waste disposal, reduced setting time, and good pullout limit force and is recommended for industrial application with sodium silicate at a proportion of 10% by weight and mineral powder at 30%. The application of the new flexible bolting and grouting method in Chenmanzhuang mine shows improved face stability and reduced capital cost.

Geogrid-reinforced structures are extensively adopted in various engineering fields. At present, the influence of boundary conditions was not considered in design methods, bringing hidden dangers to the safety of the structure. In the current study, a series of pullout tests were carried out on high-density polyethylene (HDPE) geogrid-reinforced coarse sand. The magnitude and growth pattern of pullout resistance and the variation laws of interfacial shear strength indexes under four types of boundary conditions were analyzed. Additionally, the boundary reduction coefficient (BRC) was introduced to establish the relationship between rigid and flexible boundary for the design of the structure. The tests results showed that the boundary conditions cannot be ignored in the design of structures, especially in the front. When the normal loading was up to 120 kPa, the BRC-top and BRC-positive could be taken as 0.9 and 0.5, respectively, and verified by fitting results. The boundary conditions affected the pullout resistance, while the vertical loading corresponding to the maximum pullout resistance was not related to boundary conditions. Investigating the interaction of the geogrid–soil under different boundary conditions can help to improve the understanding of the behavior of reinforced soil structure, and to achieve a more efficient and economical design. [ABSTRACT FROM AUTHOR]

Featured Application: A potential application of the study is the use of the technology described in the construction of bridges, in particular for the construction of retaining structures within abutments. This study considered the possibility of using steel gabion baskets made of welded mesh for a soil-strengthening function. Examples of such applications are known for meshes made of wires with diameters from 6.3 to 12.7 mm and mesh openings from 125 to 225 mm. In the case of a welded grid, the pulling resistance of fine-grained soil consists of two factors: frictional resistance and bearing resistance. Therefore, for the purposes of this issue, a simplified laboratory pullout test was carried out with four types of welded steel grid (common in Europe) embedded in the fine sand. The geometry of the grid (opening size: 76.2 × 76.2 mm), the type of steel (low carbon steel, tensile strength from 500 to 700 MPa), the diameter of the wire (2.7–4.5 mm) and its cover (ZN + PVC or ZnAl) were taken into account during the analysis. It was unequivocally stated that as the stiffness of the steel grid itself increases, its strength increases during the pullout test, which is not so obvious in the case of popular steel woven meshes. In addition, it has been shown that steel welded meshes with wire diameters less than 6 mm are suitable for soil reinforcement in structures with gabion facing, and the determined apparent friction coefficient (μk = 0.39–1.47) takes values similar to the friction coefficient given in references for welded meshes of larger diameters. This is a positive premise for starting further research on the use of wires of smaller diameters for welded mesh production used as soil reinforcement. [ABSTRACT FROM AUTHOR]

The key to modeling the interlocking of geogrid-reinforced ballast is considering both the continuous deformation characteristics of the geogrid and the discontinuity of the ballast particles. For this purpose, pullout tests using biaxial and triaxial geogrids were simulated using the coupled discrete element method (DEM) and finite difference method (FDM). In this coupled model, two real-shaped geogrid models with square and triangular apertures were established using the solid element in FLAC3D. Meanwhile, simplified shaped clumps were used to represent the ballast using PFC3D. The calibration test simulation showed that the accurately formed geogrid model can reproduce the deformation and strength characteristics of a geogrid. The pullout simulation results show that the DEM-FDM method can well predict the relationship between pullout force and displacement, which is more accurate than the DEM method. For ballast particles of 40 mm in size, both the experiment and simulation results showed that the triaxial geogrid of 75 mm is better than the 65-mm biaxial geogrid. In addition, the DEM-FDM method can study the interaction mechanism between the particles and the geogrid from a microscopic view, and also reveal the similar deformation behavior of the geogrid in the pullout process. Therefore, the DEM-FDM coupled method can not only investigate the interlocking mechanism between the ballast and particles but can also provide a great method for evaluating the performance of different types of geogrids. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Near-surface-mounted (NSM) fiber-reinforced polymer (FRP) is a strengthening method for reinforced concrete (RC) structures that relies on the bond between FRP strip/rod embedded in an epoxy-filled saw-cut groove and the concrete substrate. The bond stress is known to relate to the slip along their interface. This paper aims to propose a technique for modeling the bond between NSM FRP and concrete for the specimens, in which failure occurred at the concrete-adhesive or adhesive-FRP interface, or by rupture of the FRP, using the finite element (FE) method. The FE analysis is more accurate in predicting the bond capacity of the joint and simple to use for modeling the interactions in comparison to the existing bond models. The proposal uses a three-dimensional (3-D) FE model, and simulation results are verified by the experimental results of direct pullout tests of 25 specimens done by the other researchers. The form of the bond stress-slip curve considered in the proposed model is bilinear. A comparison of the strain distribution along the bond length at different loading stages with available experimental values showed that the proposed model accurately predicts this distribution. A parametric study on the initial stiffness of the bond stress-slip curve revealed that a value of 10 times the epoxy elastic modulus (Ee) to the thickness of the epoxy layer between FRP and concrete (te) is appropriate. In addition, a parametric study on bond length disclosed that the developed model can capture effective bond length--that is, the length beyond which bond strength no longer increases. [ABSTRACT FROM AUTHOR]

The growing concern about the limitation of non-renewable resources has brought a focus on the development of environmentally sustainable and biodegradable composite materials. In this context, a trend in the development of natural fibers used as a reinforcement in composites is ever-increasing. In this work, for the first-time, fibers extracted from the seven-islands-sedge plant (Cyperus malaccensis) have been characterized by X-ray diffraction (XRD) to calculate the crystallinity index and the microfibrillar angle (MFA). Also, an evaluation of the ultimate tensile strength by diameter intervals has been investigated and statistically analyzed by both the Weibull method and the analysis of variance (ANOVA). Moreover, the maximum deformation and tensile modulus have been found from the data acquired. Pullout tests have been conducted to investigate the critical length and interfacial strength when sedge fibers, are incorporated into epoxy resin matrix. Microstructure analysis by scanning electron microscopy (SEM) was performed to observe the mechanism responsible for causing rupture of the fiber as well as the effective fiber interfacial adhesion to the epoxy matrix.

In this work, the effect of high temperature on the bond behavior between Recycled Asphalt Pavement (RAP) concrete and Fiber Reinforced Polymer (FRP) was studied. The use of RAP in concrete construction has been developed and utilized recently due to its various economic and environmental features. Nevertheless, very few studies have examined the bonding performance and failure mode between RAP concrete and FRP. A total of 46 asphalt pavement concrete specimens with three different concrete compressive strength were cast and tested under pullout test. The specimens were prepared using different RAP aggregate content and were subjected to elevated temperatures within a range from 23 °C to 600 °C. The heat damaged specimens were repaired using two Near-Surface Mounted Carbon Fiber Reinforced Polymer (NSM-CFRP) strips spaced at 50 mm with three different bonded lengths. According to the experimental results of the pullout test, RAP concrete specimens showed lower bonding strength and slippage than Natural Aggregate (NA) concrete specimens. Furthermore, specimens exposed to elevated temperatures showed a significant decrease in bonding strength and a significant increase in slippage. Results also indicated that as the temperature increased, specimens with high RAP aggregate content failed at higher slippage compared to specimens with low RAP aggregate content with the same compressive strength. Moreover, the relationships between bond load and strain of (CFRP) strips were established and discussed in the results. The failure mode in all specimens was concrete separation.

The soil reinforcement by geosynthetics has been extensively applied in covers and liners of landfills. The stability of this structure is especially dependent on the effectiveness of the anchorages holding the geosynthetic sheets. The simple run-out and L-shaped anchorages are the two most commonly used approaches. For increasing the available knowledge of the anchorage system behavior, experimental studies have been conducted. This paper shows the results of the experimental analysis that are based on the results of large-scale pullout apparatus on geogrid embedded in simple run-out and L-shaped anchorage in two modes (fixed length and fixed space). The influence of different geometric parameters of the trench on the behavior of the geogrid is also examined. Based on the results, the values of pullout force were approximately 69% and 196% higher in the case of the fixed length mode and the fixed space mode, in the respective order, compared to the simple run-out anchorage. In the L-shaped anchorage, it is observed that for the initial length (L) constant, the mode is optimized with a small value of the geogrid rear heel length (B) and a greater value of the depth of the buried geogrid (D) when D+B is constant. • The L-shaped anchorage capacity of the geogrid was investigated by the pullout test. • The fixed space mode has shown the best performance of the anchorage system. • The pullout force of the anchorage increased with the increase of the depth of the buried geogrid. • The increased initial length does not have a significant positive effect on the pullout force. • The most optimal anchorage was created with a lower heel length and greater buried depth of the geogrid. [ABSTRACT FROM AUTHOR]

The use of bundled bars in highly loaded concrete members instead of individual bars can reduce or even avoid reinforcement congestion, allowing easier placing and compaction of concrete, since bundles (with two or more side‐by‐side bars) are less obstructive to fresh‐concrete flow. However, there is still a lack in knowledge of the fundamental phenomena related to the bond behavior of bars in bundles. Therefore, design code rules for anchorages and splices differ significantly among International Standards (Eurocode 2, fib Model Code 2010, and ACI 318–19). The present paper reports the results of more than 100 pullout tests with short embedded length with the aim of comparing the local bond behavior of bundles with that of corresponding notional individual bars. Among the three criteria usually introduced to compare bundled and individual bars, based on the concepts of "equivalent sectional area," and "minimum or maximum sectional perimeter," the first and the second are introduced in this paper. Experimental results show that both criteria are suitable methods for evaluating the bearing capacity of bundled bar anchorages, even if equivalent area criterion seems to be slightly more conservative. The experimental results provide also information on the bursting forces generated by the wedge action of the ribs which clearly increases with bar diameter. Finally, experimental results are compared with design rules for anchorage strength of bundled bars as prescribed by fib‐Model Code 2010. [ABSTRACT FROM AUTHOR]

For most of the structural solutions, the construction industry in Brazil is based on the use of conventional reinforced concrete elements composed of concrete and steel bars. However, problems related to this traditional structural system, such as the corrosion of metallic bars exposed to aggressiveness environments, motivate the study of new materials to be used as a replacement of conventional bars. In this context, FRP (Fiber Reinforced Polymers) bars can be viable due to their good mechanical properties and resistance to aggressive environmental agents. Thus, the main objective of this paper was the evaluation of the bond stress of GFRP bars using pullout tests. Thus, twenty specimens were analyzed with two concrete compressive strengths of 30 MPa and 60 MPa and two different GFRP bar diameters of 9.5 and 16.0 mm. According to the test results, it was verified a high variability of the adhesion between the GFRP bar and the concrete. Concerning the statistical analysis of pullout tests performed and considering the methodology proposed to analyze the quality control, the variation coefficient varied from 13.71% to 20.17%, classifying the pullout tests performed as medium or poor. These results demonstrate that the response of the GFRP bars obtained in the pullout tests was not reliable, demonstrating the need for new research to obtain adhesion coefficients and anchoring lengths for use in structural designs with such materials. [ABSTRACT FROM AUTHOR]

Steel-strip reinforced earth walls stabilize through the pullout resistance of the reinforcements. Soil dilation during the pullout of ribbed reinforcements may contribute to the evolution of pullout resistance; however, few studies have clarified this mechanism by investigating how soils behave with increasing pullout displacement. The ribs of the reinforcements enhance the pullout resistance, although the influence of the rib dimensions on the evolution of pullout resistance with increasing pullout displacement has not been sufficiently revealed. In the present study, a triaxial pullout apparatus is developed and pullout tests are conducted using ribbed reinforcements with different rib-inclination angles under isotropic stress. The displacement and strain fields in the soils during the pullout of the reinforcements are investigated by X-ray micro CT and a digital image correlation technique. It is found that larger rib-inclination angles provide higher pullout resistance at an early stage of the pullout because of the higher bearing resistance related to the more significant soil densification above the ribs. With increasing pullout displacement, the reinforcements with different rib-inclination angles come to behave as almost one in the same since a rigid soil wedge related to the passive soil failure is generated above the ribs. This tendency results in similar soil deformation characteristics and pullout resistance levels for every reinforcement beyond the soil failure state, although the rib-inclination angles are different. [ABSTRACT FROM AUTHOR]

The study presents the experimental investigation of bond performance of normal and high-strength geopolymer concrete and Glass Fibre Reinforced Polymer (GFRP) bars. The effects of bar diameters, embedment lengths, and concrete grades on maximum pullout load and failure characteristics are investigated. When the adhesive and residual strengths of GFRP bond specimens were compared to steel specimens, the former demonstrated remarkable performance despite having differing surface properties. An energy-based equivalent bond strength approach is proposed to examine pre-peak bond performance, which demonstrating that the decreasing rate of strength is faster for higher diameter and embedment, showing a drop in bond performance. Pullout failure was noted in smaller diameter bond specimens, where the shear strength between the ribs and the GFRP bar controlled the bond strength. Concrete split failure occurs for 12 mm specimens with embedment lengths greater than 5d in both GPC40 and GPC60. Specimens with 16 mm, excluding G-16-5d-60, demonstrated concrete split failure for all embedment lengths and concrete grades; bond strength is determined by the concrete shear strength. Enhancing the concrete's compressive strength has a beneficial impact on the bond strength as it increases ranging, from 14.57 to 32.12%. Analytical models such as mBPE and CMR were employed to derive the mathematical expression for the bond stress versus slip curve. It was found that the curves of CMR model were typically closer to experimental curves than the mBPE model. • Bond performance of the GFRP bar with normal and high-strength geopolymer concrete is studied. • Effect of bar diameter, embedment length, and compressive strength of concrete on bond performance is investigated. • Existing analytical model are compared with the experimental results. • Energy-based equivalent bond strength is proposed to study the bond performance. [ABSTRACT FROM AUTHOR]

• Results show that resin annulus thickness is closely related to shear stress distribution in the resin annulus. • Uneven thickness of resin annulus significantly influences anchorage performance of the cable bolt. • A resin annulus thickness uniformity guarantee device has been developed to improve the thickness uniformity of the resin annulus. Resin grouted cable bolts are widely used in the control of surrounding rock in underground engineering such as roadways and tunnels. This study conducted theoretical analysis and laboratory experiments to investigate the influence mechanism and characteristics of the uneven thickness of the resin annulus on the anchorage performance of the cable bolt, and developed an effective method for controlling the uneven thickness. The theoretical analysis of the shear stress distribution in the resin annulus under tension revealed that, when the thickness of the resin annulus is uniform, the shear stress in the resin annulus and interface around the cable bolt has balanced distribution overall. When the resin annulus thickness is uneven, the shear stress level is higher in the thinner area compared with the thicker area of the resin annulus. The pullout test results for cable bolt specimens anchored with different resin annulus thicknesses reveal that, as the thickness uniformity of the resin annulus decreases, the pullout load of the anchored specimen decreases to different degrees. According to the structure of the cable bolt and the resin anchoring construction characteristics, the resin annulus thickness uniformity guarantee device (RATUGD) was designed. The results obtained by a device working effect experiment reveal that the RATUGD can significantly improve the thickness uniformity of the resin annulus, and the pullout resistance of the anchored specimen is also ensured when the device is used. This study elucidated the influence mechanism of an uneven resin annulus on the anchoring performance of a cable bolt to a certain extent. Additionally, technology that ensures the resin annulus uniformity is proposed to further ensure and enhance the support effect of a resin grouted cable bolt on the surrounding rock of underground engineering such as roadways and tunnels. [ABSTRACT FROM AUTHOR]

One of the most serious problems of reinforced concrete structures is corrosion of embedded reinforcing steel bars especially in aggressive environments. To control steel corrosion, several approaches have been followed but do not introduce 100% corrosion resistance and guaranteed longterm performance. Glass Fiber Reinforced Polymer (GFRP) bars are considered to be an ideal alternative to overcome corrosion problem in steel bars because of their high corrosion resistance. This paper discusses the main topics related to the use of GFRP bars as reinforcement in structural reinforced concrete applications and presents an overview to the available literature especially in GFRP bond behavior. The main conclusions are: standardizing the manufacturing process of GFRP bars are needed in order to limit the contradictory results of their performances due to the high differences in the products characteristics, and that the available design guidelines have much conservative equations, so they are recommended to be revised to be more practical.

This paper presents the results of an experiment study and suggests a theoretical formulation for the bond behavior of reinforced fly ash-based geopolymer concrete. Three grades (20 MPa, 30 MPa and 40 MPa) of a geopolymer concrete along with three reinforcement diameters (12, 16, and 20 mm) were selected for experimental work. The bond behavior of the reinforced geopolymer concrete is determined using pullout test, finite element analysis (FEA), and theoretical work. The test data indicated that the bond strength of reinforced fly ash-based geopolymer concrete increases about 1.97 to 2.56 times with the increase of compressive strength from 20.33 MPa to 41.12 MPa. For grade 30 MPa and 40 MPa specimens, the concrete cover to diameter ratio (c/db) increased up to 4.19 resulted in the increase of bond strength. Then, the bond strength decreases with the increase of the c/db ratio from 4.19 to 5.75, while grade 20 MPa specimens is vice versa. The bond-slip relations between the reinforcement and geopolymer concrete determined from FEA is in good agreement with experimental results. The coefficient of variation (CoV) is only 0.01. However, this behavior is quite different from the data calculated by the fib model.

Considering the random orientation and distribution of steel fibers in concrete, the synergistic reinforcement of steel fibers on concrete is much complex than the bond of single fiber. It is meaningful to study the bond behavior of steel fiber during many actions. With the inclination angle of steel fiber to pullout direction and the fiber spacing as main factors, this paper carried out fifteen groups of pullout tests for hook-end steel fiber embedded in manufactured sand mortar. The inclination angle ranged from 0 to 60°, and the fiber spacing ranged from 3.5 mm to 21.2 mm. The characteristic pullout load-slip (PL-S) curve of steel fibers are given out after treating the original complete curves of each group test. The values of key points featured the debonding, peak and residual pullout loads and slips are determined from the characteristic PL-S curves. Based on a multi-index synthetical evaluation method, the nominal debonding strength, bond strength, residual bond strength and the debonding work, slipping work, and pullout work, as well as the debonding energy ratio, slipping energy ratio, and pullout energy ratio are analyzed. Results indicate that the bond performance represented by above indexes changes with the inclination angle and spacing of steel fibers. Except for the bond mechanism performing the same as aligned steel fibers by pullout test, the bond is dominated by the resistance of mortar to peeling off near pullout surface and scraping along pullout direction. When the inclination angle is over 15° or 30°, the bond performance is generally decreased, due to the peeling off of mortar on surface of transversal section with a certain depth. When the fiber spacing is over than 5 mm, the bond performance becomes worst due to the scraping out of mortar along with the slip of steel fibers.

Coir-fiber-reinforced epoxy resin composites are an environmentally friendly material, and the use of coir fibers improves the mechanical properties of epoxy resin. In order to improve the interfacial adhesion between coir fibers and the epoxy resin matrix, microwave treatment, alkali treatment, acetic anhydride modification, 3-aminopropyltriethoxysilane modification and their reasonable combination method treatments were carried out on coir fibers, respectively. Scanning electron microscopy (SEM), Fourier transform-infrared (FTIR) and X-ray diffraction (XRD) were used to analyze the effects of the different treatments on the characteristics of the coir fibers, and single-fiber pullout tests were performed on the pullout specimens made from the above coir fibers. The results calculated by the proposed estimation method show that the combination method of alkali treatment and 3-aminopropyltriethoxysilane surface modification could better enhance the interfacial bonding ability between coir fibers and epoxy resin with an interfacial shear strength and pullout energy of 6.728 MPa and 40.237 N·mm, respectively. The principal analysis shows that the method can form both mechanical interlocking and chemical bonds at the interface to enhance the interfacial bonding ability. This study provides a more suitable method for improving the interfacial properties of coir-fiber-reinforced epoxy resin composites and has implications for the study of natural fiber composites.

Replacement with larger diameter screws is always used in pedicle screw loosening but carries a risk of pedicle wall violation. A pedicle screw with more preserved bone stock is the preferred primary fixation choice. The purpose of this study was to evaluate whether a newly designed proximal-conical dual-thread screw with less bone occupancy provides fixation strength comparable to that of a traditional screw. Six types of pedicle screws based on three different shapes (cylindrical, conical, and proximal-conical) and two thread profiles (single-thread and dual-thread) were grouped. Conical and proximal-conical screws differed mainly in the slope of the outer diameter from the hub to the tip. Conical screws had an outer diameter (6.5 mm) that differed from the hub and tapered by 30% to an outer diameter (4.5 mm) at the tip and proximal-conical screws had the same outer diameter from the hub and tapered by 30% (4.5 mm) at 20 mm from the hub and then maintained the outer diameter (45 mm) to the tip. A total of 36 L4 Sawbones® vertebrae were used in the study and six trials for each screw group. The results of the imaging, screw volume in bone, insertion torque, and pullout force were analyzed. For screws with the same shape, insertion torque and pullout force were significantly higher for those in the dual-thread groups than for those in the single-thread groups (p < 0.05). For screws with the same thread profile, there was no significant difference in either biomechanical test between the different screw shapes (p > 0.05). Our results demonstrated that these proximal-conical dual-thread screws, with the property of relative bone stock preservation, display a comparable biomechanical performance to traditional dual-thread screws and a better performance than single-thread screws. This screw design could serve as the primary pedicle screw choice to reduce revision difficulty.

Significant issue in reinforced concrete (RC) structures is corrosion of steel. High alkalization of cement matrix, low permeability, and sufficient cover plays an important role to shield from corrosion of steel. There is a replacement material for steel is fiber‐reinforced polymer (FRP) bars as reinforcement. The FRP bars are nonconductive and durable material and they are composited from fibers and polymers matrix. In this study, new technology geopolymer concrete (GC) was used along with glass fiber‐reinforced polymer (GFRP) and basalt fiber‐reinforced polymer (BFRP) bars. GC is produced from industrial by‐product materials such as fly ash and ground granulated blast furnace slag (rich in silica and alumina) and treated as sustainable material. The long term durability of many RC structures affects drastically by the reinforcement corrosion. Main aspect of bond behavior is tension stiffening as it has capability to control the reinforcement to shift the tensile stresses to concrete. This paper evaluates the bond strength between the GC reinforced with GFRP/BFRP and the results were evaluated with conventional concrete (CC) reinforced with steel. The pullout test method was used to determine the bond between FRP and steel bars with the surrounding concrete based on IS: 2770 (part I)‐1967. The comparison of bond strength GC with FRP almost same as CC with steel. The tension test and double shear test were also carried out in FRP and steel bars based on IS 432–1982 and 5242–1979, respectively. [ABSTRACT FROM AUTHOR]

The effect of nano-kaolinite clay (NKC) on the bond behavior between rebar and concrete was studied in a series of experiments. An electrical corrosion method was used to corrode the rebar embedded in concrete specimens. Chloride diffusion and chloride content tests were performed to evaluate the effect of nanoclay on the chloride diffusion depth and chloride ion content in concrete. Pullout tests were performed to assess the bond properties, including the bond-slip curve and ultimate bond strength, between concrete and rebar before and after corrosion. The results revealed that NKC improved the chloride resistivity and bonding in the concrete specimens. The specimens with a 5% nanoclay addition showed the lowest percentage of the rebar corrosion level and bond strength degradation due to corrosion. After 48 h of corrosion, the rebar corrosion ratio decreased by 52%, and the ultimate bond strength increased by 35% compared to the control specimen. [ABSTRACT FROM AUTHOR]

This research evaluated the bond behavior of reinforcement and the mechanical characteristics in a reactive powder concrete (RPC) replacing 35% cement with blast-furnace slag. Pullout tests were performed at the ages of 3, 7, 28, 56, 63, and 91 days on cylindrical samples. The embedded length used was double the diameter of the bar. At 3 days it presented compressive strength of 41% of the maximum obtained, which was 123.06 MPa at 91 days. There was an increase in strength until the age of 56 days and after stabilization of the curves. In pullout tests, it was noticed the considerable influence of the rib, because in tests with plain bars, the bond force was below 20% of the results with ribbed bar, which reached 54.38 MPa of strength. The compression curve was similar to the bond curve. Underestimated values were observed when the researchers' equations were applied to calculate the maximum bond strength. [ABSTRACT FROM AUTHOR]

As lightweight materials, granulated rubber–weathered rock material (WRM) mixtures could be utilized as backfills in geosynthetics reinforcement structures to reduce deformations. However, the deformation behaviour of geosynthetics in granulated rubber–WRM mixtures is not clear. In this paper, pullout tests considering different normal pressures (30 kPa, 50 kPa and 100 kPa) and different granulated rubber contents (10%, 15% and 30%) are performed. Sensor-enable geobelts (SEGB) are employed, which can realize distributed measurements on the strains of SEGB inside soil. Two constitutive models—bilinear model and hyperbolic model are established based on tensile tests and direct shear tests to capture the full stress–strain curves and the interfacial shear responses, respectively, and are employed in the derivation of load transfer equation for pullout process. Numerical results of load transfer equation give distributions of tensile forces, strains, displacements and shear stresses. Test results validate the established constitutive models. Rubber content has an optimal value for the best geobelt–soil interaction. The deformations of geobelts in pullout process start from the front end, but decrease rapidly in soil. Under high normal pressures, the front part of geobelts exhibit quasi-plasticity. The shear stress distributes more uniformly under low normal pressure. [ABSTRACT FROM AUTHOR]

The new PCI "Recommended Practice to Assess and Control Strand/Concrete Bonding Properties of ASTM A416 Prestressing Strand" specifies two new threshold limits for pullout tests conforming to ASTM A416 and new equations for the transfer and development length of prestressing strand. This article provides a summary of more than 30 years of research and knowledge advancement on the bond between concrete and prestressing strand related to the development of the new recommended practice. Discussions regarding the adoption and incorporation of the new recommended practice into structural design, strand production, and precast concrete fabrication and quality control practices are ongoing. [ABSTRACT FROM AUTHOR]

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This study aims at investigating the influence of moisture conditions on interface shear behavior of element-grouted anchor specimens embedded in clayey soils. The tests involved comparatively short embedment lengths and a device that was specially designed to facilitate moisture conditioning. Rapidly loaded pullout tests as well as pullout tests under sustained (creep) loading were conducted to characterize both the short-term and long-term ultimate shear strength of anchor–soil interfaces. Both values of the interface shear strength were found to decrease exponentially with increasing moisture content values, although their ratio was found to show a linearly decreasing trend with increasing moisture content. The interface shear creep response under pullout conditions was characterized by a rheological hybrid model that could be calibrated using experimental measurements obtained under increasing stress levels. The accuracy of the hybrid model was examined by evaluating the stress-dependent prediction model as well as its governing parameters. This investigation uncovers the coupled impact of soil moisture condition and external stress state on the time-dependent performance of grouted anchors embedded in clayey soils by correlating the interface shear strength with soil moisture content and associating the creep model with stress levels applied to the grout–soil interface. [ABSTRACT FROM AUTHOR]

This paper investigates the bond behavior between epoxy-coated reinforcing bars (ECR) and seawater sea-sand concrete (SSC) to study the detrimental effect of coating on bonding performance. A total of 80 pullout specimens were fabricated and tested under uniaxial tensile load. The main test parameters include the reinforcing bar diameter, concrete cover, bond length, concrete strength, and stirrup ratio. Test results show that the ratio of bond strength of epoxy-coated reinforcing bars to similar specimens with uncoated bars embedded in SSC ranges from 0.85 to 0.95. Moreover, it can be speculated that the bond strength is increased with the concrete strength, concrete cover, and stirrup ratio and decreased with an increase of the reinforcing bar diameter and bond length. Finally, a new bond-slip model was proposed both for coated and uncoated reinforcing bars embedded in SSC and good agreement can be achieved between the test observations in this study and theoretical predictions based on the proposed model. [ABSTRACT FROM AUTHOR]

Bolt is an important connection in underground construction and monitoring its stress characteristics is essential to evaluate the effectiveness of bolt. The strain information collected along a rock bolt reveals the long‐term movement characteristics of rock mass, which greatly helps toward disaster prevention and risk warning. Grooving on the surface of a bolt and embedding an optical fiber is one of the main methods for monitoring the anchorage performance and stress distribution around the bolt in underground engineering. In this study, Pulse Pre‐Pumped Brillouin Optical Time Domain Analysis (PPP‐BOTDA) technology is used to evaluate the stress, axial force, and shear stress distribution of the bolt under tensile load for different types (grooved and nongrooved) of bolts embedded in concrete with resin as anchoring agent. The results show that the PPP‐BOTDA sensor can be used to monitor the stress state of the bolt embedded in concrete with resin as anchoring agent when the bolt is subjected to a tensile force. However, the apparent stress value measured in this way is not the actual stress value of the bolt, but is an increased value caused due to the groove. The closer to the exposed end of the bolt, the greater is the deviation between the apparent stress value and the actual stress value of the bolt. Based on the monitoring results from this experimental study, a stress reduction calculation method is proposed, which can change the measured value into the actual stress of the bolt. [ABSTRACT FROM AUTHOR]

Vegetation can enhance the stability of slopes by increasing the shear resistance of the soil. Shear stress applied to the soil matrix is resisted by the pullout strength of the roots via the friction at contact points between the soil and the roots. The effectiveness of root reinforcement depends on interface friction between soil and roots. In this study, tests were carried out on Indigofera amblyantha Craib roots, by measuring resistance as they are pulled out of the soil where the soil has varying dry densities. The results reveal three phases in the relationship between the pullout force and the slippage of the roots, i.e. (1) steep rise, (2) steep fall, and (3) gradual decline. In the first phase, the pullout force is increasing sharply and linearly up to a maximum when the slippage is about 10mm. With continued slippage, the required pullout force decreases significantly and nonlinearly in up and down fluctuations. Eventually, the pullout force reaches zero. For soil with a given dry density, the maximum pullout force increases linearly with increasing root diameter, and the correlation coefficient is greater than 0.9. Further, for a root with a given diameter, the maximum pullout force increases with increasing soil dry density. When the root breaks on pulling, it is called tensile failure; when the root is fully pulled out, it is called friction failure. The mode of failure for all roots is friction failure, for soil with dry densities of 1.35 g/cm³, 1.45 g/ cm³, and 1.55 g/cm³ . For soil with a dry density of 1.65 g/cm³, and root diameter under 0.716 mm, the observed failure mode is generally tensile; for diameters over 0.716 mm, the failure mode changes to friction; that is, thin roots break, thick roots get pulled out. [ABSTRACT FROM AUTHOR]

The support technology of temporary slope engineering such as building foundation pit, has the problems of small anchorage force, non-recyclable and excessive length of anchor. Focusing on these issues, this study puts forward a new support structure system named as inflatable controlled anchor. This new type of anchor was designed and manufactured for field test. To investigate the performance of the proposed anchor, a series of full-scale field model tests were carried out with the variables of inflation pressure, anchorage length, embedment depth, and steel strip thickness. The results show that the bearing capacity of inflatable controlled anchor mainly depends on the friction resistance between the steel strips and the hole wall. The rubber membrane as an independent part only provides the compressive pressing to steel strips, and the bearing capacity can be greatly improved by increasing the inflation pressure. The bearing capacity of the anchor is also improved by the increasing of anchorage length and embedment depth. If the thickness of the steel strips is too thin, the steel strip has obvious bending deformation under inflation pressure, which affects the anchoring effect, so the thickness of steel strip has a critical value of 5 mm. According to the experimental results, the working mechanism of inflatable controlled anchor is discussed, and the calculation method for the bearing capacity is proposed. The calculated values of the proposed formula are basically consistent with the experimental results, which verifies the correctness of the formula for forecasting the bearing capacity of inflatable controlled anchor. [ABSTRACT FROM AUTHOR]

Longwall face fall in the open face area is one of the most difficult ground control problems in mining thick coal seams in China especially under difficult geological conditions. This paper has proposed a new flexible bolting and grouting technology for face support. The flexible support method includes face support using flexible coir ropes and face grouting with cement and accelerator mixtures. Numerical and laboratory studies of pullout tests are performed to further improve the flexible support performance including optimization of boreholes and flexible bolts diameters, and selection of grouting materials. The results show that (a) The optimized rope‐borehole diameter ratio is around 0.5 to ensure the best face reinforcement; (b) The grouting material (a mixture of ultrafine cement, mineral powder and sodium silicate) shows advantages of low cost, effective waste disposal, reduced setting time, and good pullout limit force and is recommended for industrial application with sodium silicate at a proportion of 10% by weight and mineral powder at 30%. The application of the new flexible bolting and grouting method in Chenmanzhuang mine shows improved face stability and reduced capital cost. [ABSTRACT FROM AUTHOR]

Strain gauges are the common means to measure local strains in structural elements. It is well known that the strain at a given coordinate on the boundary of a structural element depends on the geometry, boundary conditions, loading system, and material properties. The precise location of the strain gauge along a line is not considered critical to obtaining a quality strain measurement at a specific location, wherever a continuous variation of strain along this line is expected, and a slight deviation of the gauge location will yield similar measurements. In a recent study, precise measurement of the circumferential strains on the outer face of cylindrical concrete specimens was carried out during pullout of a central rebar. Analyzing the measured data indicated that a slight shift in the strain gauge location on the order of millimeters only may considerably affect the measured strain. These controlled pullout tests highlighted the pronounced effect of the relative distance between the rebar rib and the strain gauge location on the strain magnitude and its variation with the increasing slip. This effect has not been reported before. It means that a slight difference in the strain gauge location yields different strain–slip relationships. This new finding may affect the interpretation of the measured strains. Attention should be given to the exact strain gauges' locations and detailed rebar ribs locations to properly interpret the measured data. [ABSTRACT FROM AUTHOR]

Usually, in a fully grouted rock bolt pullout test the load-displacement curve of the rock bolt head is recorded. This paper presents an analytical method to use this curve for determining the bond (bolt-grout and grout-rock interface) shear strength parameters. For this purpose, the fully grouted rock bolt interaction with grout and surrounding rock in the pullout test is investigated and the loaddisplacement curve of the bolt head (beginning of the bonded section) is obtained analytically. For modeling the bolt-grout interface behavior a distribution of the shear stress along the fully grouted rock bolt by consideration of bolt shank failure is used. In this regard, different stages including complete bonding, partial decoupling, decoupling with the residual shear strength and complete decoupling are considered. With increasing the applied load, two possible cases involving the rock bolt complete pullout and bolt shank yielding are taken into account. Based on the presented analytical method, the obtained bolt head load-displacement curve can be compared with the one recorded in the pullout test. With this, the relevance of selected shear strength parameters compared to real parameters can be assessed. A flowchart for determining the bolt bond shear strength parameters is presented using the trial and error method (coded in Matlab). The proposed solution is used to determine two experimental pullout shear strength parameters. The results show good agreement between predicted and calculated load-displacement curves. [ABSTRACT FROM AUTHOR]

The interaction between soil and geosynthetic plays an important role in the design and analysis of reinforced soil structures. Pullout tests are commonly used to simulate the soil reinforcement interaction mechanism along the interface. Thus, different types of reinforcements are used in these structures and present different behaviours. In this paper, we propose a new kind of reinforcement based on horizontal corrugated strips in order to improve the parameters interfaces between the soil and the reinforcement. To simulate the pullout interaction process of horizontal corrugated strips, we carry out a numerical study using the software package FLAC3D. We have modelled the soil as an elastic-perfectly plastic Mohr Coulomb and the reinforcement as linear elastic geogrid elements. In fact, the most important aim is to explain the horizontal corrugated reinforcement's behaviour and to investigate the factors that affect the mechanical response (Confining pressure, friction angle, amplitude and number of the waves of the strip). A comparative study is also presented between the horizontal corrugated and planar strips. In our study, the numerical results showed that the confining pressure has significant influence on the interface properties of the horizontal strips corrugated. It also showed that the pullout shear stress on the head of horizontal corrugated strips is higher than the planar reinforcements. [ABSTRACT FROM AUTHOR]

Monitoring the stress change of bolt and knowing the anchoring condition in a reasonable and effective way, accurately, can effectively prevent tunnel accident from breaking out. The stress of rock mass around the roadway is usually transferred to the anchor rod in the form of axial load, so it is of great significance to study the axial load of the bolt. In this paper, a full size anchoring and drawing experiment system was designed and established, innovatively, which realized the pull-out test of 2.5 m prestressed end Anchorage and the full-length Anchorage by using the new resin anchorage agent under vertical and horizontal loads. Through the application of fiber Bragg grating (FBG) sensing technology to the test of full-scale anchor rod, the axial force distribution characteristics of the end Anchorage and the full-length Anchorage anchor rod were obtained under the action of pre-tightening torque and confining rock pressure. The comparison indicates that the proportion of high stress range accounts for only 17.5% and the main bearing range is near the thread end of anchor rod, the proportion of main bearing range of end Anchorage is 83.3%, and the feasibility of FBG force-measuring anchor rod is verified in the field. The research results have certain reference value. [ABSTRACT FROM AUTHOR]