Concrete Failure Research Articles

Bond durability between geopolymer-based CFRP composite and OPC concrete substrate in seawater environments

Geopolymer binders are regarded as promising environmentally-friendly approaches for repairing damaged structures because of their excellent bonding and durability. The interfacial bonding properties between the geopolymer and the damaged structures are critical to the effectiveness of the repair, however, the durability of this interfacial bonding in complex environments remains poorly understood, impeding the application of the aforementioned repair methods. Therefore, this study investigates the durability of the interfacial bond between geopolymer and ordinary Portland cement (OPC) concrete in seawater environments, providing valuable insights for engineering applications of geopolymer-based repair techniques. The adoption of OPC concrete as the substrate was based on its widespread use as a cementitious material in existing structures. Additionally, geopolymer repair mortars and epoxy resin were utilized as the bonding matrix adhered to the OPC concrete substrates, while small-diameter carbon fiber-reinforced polymer (CFRP) bars served as reinforcement for the bonding matrix. Single-shear tests were conducted to investigate the bond strength and failure modes between the geopolymer mortar/epoxy resin and OPC concrete substrates after 90, 180, and 360 days of exposure to a seawater environment. The interfacial degradation mechanisms were captured using scanning electron microscopy (SEM) techniques. The results showed that the interface between the geopolymer repair mortar and the OPC concrete was identified as the most vulnerable component, which dominated the failure of the geopolymer-bonded OPC concrete. SEM analysis revealed an increase in the microcrack width at this interface, resulting in a 2.86-times increase in slip between the geopolymer repair mortar and the OPC concrete after 360 days. Due to the degradation of epoxy caused by seawater exposure, the failure modes of the epoxy-bonded OPC concrete transformed from OPC concrete cracking to epoxy rapture with increasing exposure time. The bond strength of post-exposure epoxy-bonded OPC concrete was higher than that of the geopolymer–bonded OPC concrete, but the former exhibited a more brittle failure behavior.

Bond behavior of deformed rebar in concrete containing recycled brick aggregate and waste rubber

The reuse of aggregates and crumb rubber (CR) in concrete is gaining interest globally for reducing the adverse effects on the environment and maintaining construction sustainability. The bond strength of reinforcing rebars in such concrete is one of the key issues to be addressed before their practical application, particularly in structural elements. Pull-out tests were performed on 80 specimens to assess the bond performance of deformed rebars in rubberized recycled brick aggregate concrete (RRBAC). After investigating the strength properties of RRBAC, pull-out tests were performed on two sizes of cylindrical specimens. RBA%, CR%, rebar diameter (d), embedment length (le), and concrete cover-to-rebar diameter ratio (c/d) were among the test variables in this bond behavior investigation. Bond stress-slip relationships were obtained, examined, and average bond strengths were compared with the available codes. Concrete split failure was observed in 79% of the tested specimens, whereas rebar fracture was not seen in any of the tests. The bond strength was found to be decreased with the inclusion of RBAs and CRs though relative improvement was observed for higher percentage RBAs. Additionally, regression analysis was performed on the experimental data to produce a closed-form equation for forecasting the bond strength for RRBAC. With a strong coefficient of determination (R2 = 0.97) and low values of error terms, the predicted bond strengths were seen to be a good agreement with the test results.

Infrared temperature evolution law and thermal effect mechanism of concrete impact failure

Concrete impact failure can occur quickly and cause severe failure, which is of great significance for effective monitoring of concrete impact failure. Infrared thermal imaging technology possesses the merits of high sensitivity, noncontact, and nondestructive monitoring, rendering it extensively employed in monitoring the stability of concrete structures. However, the infrared radiation temperature (IRT) evolution law and thermal effect mechanism of concrete impact failure are not clear at present. In this study, infrared monitoring experiments were conducted on concrete impact failure and static load failure using drop hammer (DH) testing machines, pressure testing machines, and infrared thermal imagers. The infrared thermal images and the IRT change law of concrete subjected to DH impact failure were analysed. The infrared thermal effect difference and mechanism between DH impact and static load failure were compared. The results indicate that there is an infrared high-temperature point at the impact location of concrete DH impact failure, and both average infrared radiation temperature (AIRT) and maximum infrared radiation temperature (MIRT) increase suddenly. The increase in the MIRT is tens of times that of the AIRT. Compared with that of static load failure, the infrared high-temperature area of concrete DH impact failure is concentrated, while the IRT of static load failure increases overall, and the heating area is large. Moreover, the change in the IRT under DH impact failure is much greater than that under static load failure. The infrared thermal effect of concrete under DH impact failure was mainly composed of the thermoelastic effect, frictional thermal effect and tensile failure endothermic effect. The infrared data obtained for concrete impact failure should focus on the highest and lowest IRT change indicators. The highest IRT corresponds to the impact failure point, and the lowest IRT corresponds to the tensile failure position. The research results provide a new infrared thermal effect approach for monitoring the stability of concrete under impact failure.

Experimental investigation of bond behavior with lap splice for CFRP-steel composite bars in coral sea-sand aggregate seawater concrete

The pull-out tests on a total of 81 lap-spliced specimens in 27 groups were conducted to investigate the lap-spliced behavior and the appropriate splice length for CFRP-steel composite bars (C-FSCB) in coral sea-sand aggregate seawater concrete (CSSC). The test variables included the C-FSCB diameter (dc), splice length, concrete cover thickness, concrete strength, lap spacing, stirrup ratio, and materials type. Then, the influence of various test variables on the lap-spliced behavior of C-FSCB in CSSC was analyzed. The results showed that when the splice length was less than 17dc, the specimens exhibited pull-out and concrete splitting failure, while C-FSCB fracture failure occurred when the splice length exceeded 17dc. Severe shear damage was observed on the C-FSCB surface in the case of pull-out and concrete splitting failure. When the splice length was less than 14dc, the bond strength of the specimens was approximately 7.2 MPa. As the splice length increased beyond 14dc, the bond strength gradually decreased. After the cover thickness was greater than 4dc or the compressive strength of CSSC was greater than 30 MPa, the variation in bond strength of the specimens can be negligible. Increasing the stirrup ratio led to an increase in bond strength and a significant reduction in crack width. Compared to specimens with steel bars, the bond strength reduction for specimens with C-FSCB exceeded 25%. Based on the test results, calculation formulas for the bond strength and splice length of C-FSCB in CSSC were established. Furthermore, referring to the approach in the Chinese code GB 50010–2010, a simplified calculation formula for splice length was proposed.

Study on the dynamic response characteristics of lining structures in large-section tunnel blasting using JH-2 model analysis

The lining structures of tunnels are typically constructed using sprayed or cast concrete materials, and their performance and quality during tunnel excavation and blasting are crucial for the stability and safety of tunnels. Therefore, the safe distance between the lining structure and blasting source should be determined to avoid concrete damage caused by blasting vibrations. In this study, taking the subway tunnel of Danshan Station in Qingdao as an example, the JH-2 model is introduced as the constitutive model of the tunnel blasting simulation, and the JH-2 model parameters of the local surrounding rock are obtained by experiments, and finally the numerical simulation and theoretical verification are carried out to study the safety distance of shotcrete under various safety judgment standards. The results indicate that the JH-2 model can effectively simulate the propagation of stress waves under different media conditions, and the closer the strength parameters and pressure constant of the lining structure are to those of the surrounding rock, the safer the concrete–rock bonding interface. During tunnel blasting construction using the ring blasting method, the peak particle velocity (PPV) of the lining structure increases with an increase in the arch angle. Based on the numerical simulation results, we recommend that concrete lining be constructed at a distance of at least 62 m from the blasting source to avoid damage caused by vibrations. The effect of concrete tensile failure caused by longitudinal stress is much smaller than the damage to the bonding interface caused by the PPV and can be neglected.

Pull-out behavior of cluster stud-post pouring UHPC connectors in prefabricated steel-concrete composite beam

The use of ultra-high performance concrete (UHPC) as a connection material for cluster studs of prefabricated steel-concrete composite beams can achieve higher connection strength and less space for reserved holes. However, in addition to bearing the shear force, the studs need to bear the pull-out force to counteract the vertical relative separation between the steel and concrete. The pull-out behavior for cluster stud-post pouring UHPC connectors is complex and has not been clarified completely. Thus, a total of 30 cluster stud pull-out tests in 10 groups were carried out in this study, and the interface type, length-to-diameter ratio of the stud, transverse spacing of stud group, dimensions of the reserved holes, and type of post pouring concrete were considered. The results showed that the pull-out behavior of the cluster studs was different from that of studs embedded in cast-in-place intact UHPC slabs due to the UHPC conical integrity having been reduced significantly by the old-to-new concrete interface. The rough groove interface and UHPC as a post pouring material significantly improved the pull-out capacity and stiffness of the cluster studs. The stud fracture belongs to ductile failure, whereas UHPC and normal concrete (NC) cone failures are brittle. The bearing capacity of the UHPC cone is observed to increase with the effective embedment depth of the stud, the transverse spacing, and the dimensions of the reserved holes. The angle of the UHPC conical failure surface is 70° based on 3D laser scanning. Finally, the theoretical equations for predicting the pull-out capacity of stud-post pouring UHPC connectors with a rough groove interface were proposed, and the critical length-to-diameter ratio of the stud was calculated for different combinations of stud and UHPC strength.

Experimental investigation on bond behaviour of the GFRP bars with normal and high strength geopolymer concrete

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.

The influences of type, length, and volumetric fraction of fibers on the direct shear strength of the fiber-reinforced concretes

Besides the common modes of failure including compressive, tensile, and bending in concrete structures, cracking and failure due to the shear is also considered as a significant and hazardous mode of failure. The shear failure mode can be observed in structural elements such as deep beams, locations having high point loads, connection cores of beams and concrete columns, short columns, punching shear in slabs and foundations, etc. However, the direct shear strength of the fiber-reinforced concretes has seen limited studied. Hereupon, this study aims to experimentally investigate the influences of the type, length, and various volumetric fractions of the steel fiber (SF) and polypropylene (PP) fiber on the compressive strength, the tensile strength, and specifically on the direct shear strength of the fiber-reinforced concretes. To this end, four different mixture design schemes of the plain concrete were examined by adding PP and SF with lengths of 3 cm, 5 cm, and their half-half combination with volumetric fractions of 0.5 %, 1 %, and 1.5 % to measure the compressive strength (the cubic sample), the tensile strength (the cylindrical sample), and the direct shear strength (the prismatic sample) of the concrete specimens. In addition, the plain concrete specimens as the witness specimens were built to compare with fiber-reinforced ones. The experiments were not only performed for 20–25 MPa concrete strength category, but were also executed for 25–30 MPa. The constructed concrete specimens were exhaustively surveyed in terms of the contribution of the fibers, the failure patterns in various specimens, the force-displacement diagrams in shear, the maximum displacement in specimens, the aspect ratio of the fibers, and the shear ductility index in various specimens. The obtained results indicated that, with increasing the length and volumetric fraction of the fibers (i.e., the aspect ratios), the compressive, tensile, and direct shear strengths have been subsequently augmented in the concrete specimens. Moreover, the strain and ductility of the concrete specimens have also been enhanced. Remarkably, in most tests, the SF-reinforced specimens have excellent performance compared with other specimens. However, the specimens containing the PP fibers have not considerably improved the compressive and direct shear strengths of the concrete specimens.

Effect of chloride binding and sulfate ion attack on the chloride diffusion in calcium sulfoaluminate-based material under seawater environment

The diffusion of chloride ions in reinforced concrete under the seawater environment will affect the physical or mechanical properties and durability. Sulfate ions also influence the diffusion of chloride ions by generating expansion products through physical and chemical reactions. Further research on the effects of chloride binding and sulfate ion attack on chloride ion diffusion will deepen the understanding of concrete failure mechanism. In this paper, a quaternary blend based on calcium sulfoaluminate (CSA) cement was prepared and laboratory immersion tests were conducted in artificial seawater with varying salt concentrations. Initially, chloride ion concentration measurements and XRD tests were conducted at different corrosion ages and salt concentrations. Subsequently, the chloride binding properties of CSA-based materials was quantified through the analysis of chloride ion concentration and the phases of hydration products. Meanwhile, the corrosive effect of sulfate ions on chloride ion diffusion was determined corresponds to the content of expansive hydration products. Furthermore, numerical simulations were employed to evaluate the impact of sulfate ion corrosion, chloride binding, and their combined effects on chloride ion diffusion, and the results were compared with free chloride ion concentration (Cf). The results indicate that the total chloride ion concentration (Ct) exhibits a linear relationship with increasing salt concentrations of seawater in CSA-based materials. Meanwhile, the bound chloride ion concentration (Cb) follows a logarithmic growth pattern. The chloride binding rate experiences a linear decline with the increase of chloride ion concentration in the artificial seawater. Additionally, the relationship between Cf and Cb or Ct can be described using different isothermal adsorption models for the CSA-based materials. Among these models, the Langmuir model is suitable for characterizing the relationship between Cf and Cb, while the Freundlich model is suitable for describing the relationship between Cf and Ct. Furthermore, it is noteworthy that sulfate ion attack and chloride binding exert nearly equivalent effects on the diffusion of chloride ions in CSA-based materials at short corrosion age and low chloride ion concentration. However, the corrosive impact of sulfate ions gradually evolves into the dominant factor in the progression of corrosion over time and the increase in seawater salt concentration.

Finite element analyses of failure of fiber reinforced polymer-concrete interface considering the concrete tension–compression softening effect

The concrete near the shear failure surface of the FRP (fiber reinforced polymer)-concrete interface is subjected to both tensile and compressive biaxial stress. However, existing finite element methods of the interfacial failure behavior of FRP-concrete interface to describe the tension–compression softening effect of concrete failure are not sufficiently accurate, and some detailed results may not be reflected. To address these issues, a finite element analysis method is proposed that accurately considers the tension–compression softening effect on concrete failure. The effectiveness of the method is demonstrated through analysis of literature data from experiments on plain concrete failure, FRP-concrete interface shear, and three-point bending. The method accurately reflects the generation of interfacial discontinuous micro-cracks, the oscillation singularity of stress field near the interfacial crack tip, the phenomenon of interface mismatch, the dispersion observed in the bond-slip curves, and the phenomenon of interfacial shear stress reversal. Moreover, this finite element analysis method is applied to the double shear experiments of the fully-bonded FRP-concrete interface under different boundary conditions, and the reasons for the different failure modes observed in the specimens are explained. The results indicate that considering the biaxial effect on concrete failure strength in numerical analysis can more accurately and comprehensively describe the shear failure behavior of the FRP-concrete interface.

Experimental investigations of dry-dry timber-concrete composite notched connections designed for disassembly

Timber-Concrete Composite (TCC) decks offer an efficient, and environmentally friendly alternative to conventional concrete slabs. Traditionally the concrete is cast directly onto the timber with a permanent connection arrangement that does not allow non-destructive disassembly at end-of-service-life. This will prevent the reuse of the materials and ultimately decrease the extent of the environmental benefit. This paper presents a deconstructable dry-dry notched connection made from fully prefabricated timber and concrete elements. The concept was investigated through 30 experimental pure-shear push-off tests, where various design parameters, such as prestressing degree, fastener placement, and notch length, were varied. The experimental results indicate that the new connection exhibits the same stiffness characteristics as a traditional wet-dry notched connection. Five different failure modes were observed in the series, and experimental measurements such as Digital Image Correlation and fastener force measurement provided insight into the connection behavior during failure. Two rigid-plastic upper bound solutions were established to estimate the load-carrying capacity for two of the observed concrete failures, and a satisfactory agreement with the test results was obtained. In conclusion, the experimental results indicated that dry-dry notched connections are feasible for achieving a more environmentally friendly TCC structure.

Shear Capacity on Corroded Fly Ash Reinforced Concrete Beam Using Galvanostatic Method

Corrosion can be triggered by a chemical reaction to the materials, establishing reinforced concrete's failure. For a long time, researchers have tried to find out how to prevent corrosion, a main structural construction issue. As a technology of waste material, fly ash has predominance, i.e., it is safer and greener than Portland cement. The finer size of fly ash can be an advantage in filling the concrete materials well. This research is about using fly ash as supplementary material on reinforced concrete beams and the galvanostatic method to accelerate corrosion. This research will compare the shear strength after corrosion of each normal beam and fly ash as a supplementary beam. A shear test of fly ash and a normal reinforced beam has been applied. Results showed that fly ash beams have 14% higher compressive strength and 3% higher shear strength with 14% smaller crack width than normal beams after corrosion. It also has a 3,5 times lower rate and 62% level of corrosion than normal beam

Strain rate and size effects on dynamic tensile behaviour of standard and high-strength concrete: An experimental study

The strain rate and specimen size are the main dominant factors affecting the splitting tensile behaviour of concrete. The static size effect is well-known for concrete behaviour, but it needs more knowledge about the dynamic size effect. The present study investigated the strain rate sensitivity and size effect dependency of dynamic tensile behaviour of two different grades of concretes (M35 and M60) using the Split Hopkinson Pressure Bar (SHPB) setup. From the outcomes of the experimental analysis, it was noted that the quasi-static tensile strength underwent a reduction of 8.96% and 11.39% in standard and high-strength concrete, respectively. This decrease occurred as the diameter increased from 29.5 mm to 45 mm, aligning notably with the principles outlined in the "Bazant Size Effect Law," as proposed by Bazant et al. [52]. Whereas, the dynamic tensile strength and DIF increased with increased specimen diameter, which is opposite to the quasi-static size effect. The maximum split tensile strength observed was 18.56 and 19.86 MPa, corresponding to 13.30 and 12.13 s−1 strain rates with 3.69 and 3.51 dynamic increase factor (DIF) for standard (M35) and high-strength concrete (M60), respectively. The dynamic results also demonstrated a size-effect dependency, where larger diameter specimens exhibited higher strain rate sensitivity, leading to increased strength and DIF due to lateral inertial and crack propagation effects. The modified DIF model of CEB-FIP proposed by the Malvar et al. [17] considering the strain rate and size effect simultaneously strongly supported the experimentally obtained DIF values with an ± 13% deviations. In addition, the strain rate significantly influenced the concrete failure pattern, but no size effect was observed. At a low strain rate, the initiated crack propagated towards the loading ends and split the specimen into two semi-cylindrical halves with penetration cracks. While at higher strain rates, additional wedge-shaped crushed regions formed at the loading end due to tensile and shear damage generated due to stress concentration and local crushing. The crack width becomes wider, and the triangular-shaped local crushing zone continuously moves toward the centre of the specimen from both loading ends and generates the crushed strap.

Compressive performance of eccentrically double-cell concrete-filled circular steel tubular columns

This paper presents a series of tests conducted on axial compression of concrete-filled steel tubes with double inner circular steel tubes (DIC-CFST) stub columns. The DIC-CFST stub columns are composed of four elements: an outer circular steel tube, two inner hollow circular steel tubes arranged symmetrically along the diameter of the outer tube, and concrete filling the space between the three steel tubes. A total of 27 specimens with varying eccentricity ratio (e), hollow ratio (ψ), and concrete strength (C) were subjected to the tests. The results indicate that under axial compression, noticeable local buckling failures occur in both the inner and outer steel tubes. Concrete failure manifests as vertical through cracks and circumferential crushing zones. The load-deformation curve of the specimens remains essentially the same as that of a full-section concrete-filled steel tube. A general positive correlation exists between the ultimate bearing capacity and the strength of concrete, and the range of eccentricity ratio and hollow ratio significantly influences the relationship between these two parameters and the ultimate bearing capacity of the specimens. As the concrete strength increases, the initial stiffness exhibits a noticeable increase. Conversely, the initial stiffness experiences a significant reduction with an increase in the hollow ratio. The ductility decreases with increasing concrete strength and eccentricity ratio. Furthermore, in comparison to the AISC 360–10 Specification, Eurocode 4, and Han's method, the calculation formula proposed in this paper for determining the ultimate bearing capacity of DIC-CFST stub columns has exhibited superior accuracy.

Tensile resistance and shear-tension interaction relationship of T-type perfobond rid shear connectors

This study aims to investigate the mechanical performance of T-type perfobond rib (T-type PBL) shear connectors under complex load cases. Initially, the experimental tests were conducted and finite element analyses (FEA) were performed. Subsequently, a parametric study was carried out to assess the impact of geometric parameters on tensile resistance and the effect of tension ratio on the shear-tension interaction resistance of T-type PBL connectors. Finally, based on the test and FEA results, prediction methods were developed for evaluating the tensile resistance and shear-tension interaction relationship of T-type PBL connectors. The test results showed that the pull-out of the concrete below the flange led to the failure of T-type PBL shear connectors under tension. The concrete failure angles were approximately 33°. The failure under shear was manifested as concrete collapse and connector yielding. The ultimate capacity decreased with the increase in tension ratio. The specimens with tension ratios of 25%, 45%, and 65% decreased 7.9%, 16.3%, and 24.2%, respectively, compared to the specimen under pure shear. The parametric study suggested that the rib height and perforated rebars were the main factors impacting the tensile resistance of T-type PBL shear connectors. When the tension ratio reached 55% of the ultimate, the failure mode of the shear connectors was dominated by the pull-out of the concrete. The tensile resistance evaluation formula was verified by the test and FEA results, demonstrating an average calculated-to-FE-results ratio of 0.99 with a standard deviation of 0.04. The suggested shear and tension interaction relationship for T-type PBL connectors had reliable predictive outcomes, with a coefficient of variation of 0.02. This study could provide guidance for the design of T-type PBL shear connectors and promote the application in long-span composite structures.

Characterising mechanical properties and failure criteria of steel slag aggregate concrete under multiaxial stress states

To advance the application of steel slag aggregate concrete (SAC) in civil engineering, this study introduces a comprehensive experimental program to explore the failure mode, strength, deformation, and failure criteria of SAC under multiaxial stress conditions. In this investigation, SAC specimens containing 50% stabilised steel slag as a coarse aggregate were examined for mechanical behaviour (e.g. stress–strain relationships) under diverse loading scenarios, including uniaxial tensile and compressive loadings, biaxial compression, and true triaxial compression loadings. Subsequently, three distinct failure criteria (i.e. the Ottosen criterion [1], William–Warnke criterion [2], and Guo criterion [3]) for SAC were formulated and authenticated based on the experimental outcomes. The results showed varied failure modes in the SAC, such as prism type, splitting tensile, sheet-like tensile, and oblique shear, which depended on the stress state of the specimen during failure. A significant elevation in the ultimate strength and deformation of SAC specimens was observed, with an increment in the first-to-third principal stress ratio (σ1/σ3). Furthermore, the failure criterion introduced by Guo was validated as adept at reproducing all geometric characteristics of the concrete failure surface and precisely forecasting SAC’s ultimate strength of the SAC. Overall, this investigation proposed a reliable failure criterion based on true triaxial test data that can not only describe the multiaxial strength characteristics of SAC but also provide design advice for the applications of SAC in engineering structures.

Investigation on shear behavior of the interface between engineered cementitious composites and normal-strength concrete

Engineering cementitious composites (ECC), possessing excellent mechanical properties for good durability, can be applied to repair and strengthen reinforced concrete structures. In the present study, the interface shear behavior between ECC and normal-strength concrete was studied. Thirty bonded joint specimens were fabricated and subjected to push-out direct-shear tests. The construction methods of ECC mixture (precast and cast-in-place), ECC strength, and interface bonding methods (i.e., Epoxy resin, UHPC, cast-in-place ECC, cast-in-place ECC with chiseling, and bolts) were investigated. The results indicated that interface bonding methods have a significant influence on the failure modes and interface shear strength between ECC and existing concrete. There were three failure modes: interface debonding, interface debonding converted to concrete fracture, and concrete matrix destruction failure. Epoxy resin bonded specimens exhibited the highest shear strength, and cast-in-place ECC bonded specimens showed the lowest shear strength. Moreover, the shear performance of the ECC and the normal-strength concrete interface was analyzed in terms of interfacial shear strength and shear stiffness, bond-slip curve, and shear transfer mechanism. Finally, an analytical model for estimating the interfacial shear strength considering the interfacial bonding methods was established, with its predictions having high accuracy.

A novel hyperboloid cone model for predicting tensile performance of studs in concrete of various properties

Concrete breakout (CB) failure is the most common failure mode for studs in tension. Based on the Griffith's strength theory, Mohr's circle method, and mechanics of materials, the breakout cone failure model and failure mechanism of the CB mode are analyzed; the shape of the breakout cone is hyperboloid cone, and the failure of CB mode is due to the concrete tensile failure. The classic concrete capacity design (CCD) method only applies to normal concrete (NC) substrate. To predict ultimate tensile strength (Nb) of the CB mode for a wider range of concrete properties, including high-strength concrete (HSC), ultra-high performance concrete (UHPC), engineered cementitious composite (ECC), etc., a new "Hyperboloid Cone Model" is proposed, which is based on the original form of CCD method and the Griffith's strength theory. The comparison between the experimental and predicted Nb for the studs in various substrates (NC, HSC, UHPC, and ECC) from past studies shows that the prediction of the proposed model on Nb is more accurate with significantly smaller variances compared to CCD method; the average ratio of the experimental to calculated value of the proposed model and the CCD model is 0.974 and 1.138, respectively, while the coefficient of variance of them is 11.27% and 40.44%, respectively.

Aggregate Type and Concrete Age Effects on Anchor Breakout Performance: Large Database and Insights

This contribution summarizes the largest available literature data collection on tensile and shear loaded anchor tests, obtained in two independent studies and performed by two different research groups. It was the objective of the two studies to investigate a possible effect that petrographically different coarse aggregate types may have on the tensile and shear load capacity for concrete breakout failure modes. In total, seven normal-strength and four high-strength concretes were tested at two different ages. Structural tests were performed on cast-in (tensile and shear tests) and post-installed adhesive anchors (shear tests). Parallel to the structural tests, each concrete was characterized in terms of compressive and tensile strength. Finally, the combined experimental data offer novel insights into the predictive quality of available design models for concrete cone capacity in tension and edge breakout in shear with respect to a potential aggregate effect. Systematic analyses indicate only minor aggregate effects after normalization by compressive strength (less than 7% difference between normalized values). However, the study reveals potential curing and concrete age effects where a 9% increase in predicted values is shown when concrete cures longer. The predictive equations remain conservative in comparison to all the investigated properties and their validity is shown in this study.

A REVIEW OF HYBRIDISED USE OF FIBRES IN SHEAR BEHAVIOUR OF FIBRE-REINFORCED CONCRETE BEAMS

Shear failure of the concrete beam is always disastrous due to unnoticed occurrences and is avoided in construction. Introducing fibres into concrete elements has provided significant shear support to reinforced concrete beam structures through stress redistribution after initial cracking and bridging mechanisms. Given their advantages over single fibre strengthening in past years, using hybrid fibres in an optimal combination as strengthening in cementitious materials has drawn much interest. However, research on this area remains inexhaustible based on the emerging various fibre combinations and the challenge of unnoticed concrete shear failure. Therefore, reviewed research articles on shear performances of Fibre Reinforced Concrete (FRC) beams considering the effect of fibre volume, lengths and orientation on the synergy. The findings reveal the possibility of synergising fibre to enhance reinforced concrete beam(RCB) shear performance for metallic-metallic, metallic-synthetic, synthetic-synthetic, and metallic-biofibre combinations, with varying performance. Using low-strength/modulus fibre with high strength has been effective for shear resistance. Also, beam type (deep/shallow), fibre type and volume fractions, length, aspect ratio, orientation and distribution remarkably affect the shear performance of RC beams.