Adhesive-concrete Interface Research Articles

Shear performance and durability of adhesively bonded spruce wood-concrete composite joints: Effects of indoor and outdoor environmental conditions, mechanical load, and their coupled effect

A long-term study was conducted on double-lap spruce wood-concrete joints to investigate their shear strength and stiffness over a 12-month period. These joints were manufactured using both wet and dry processes, each incorporating two adhesive types for bonding the wood to the concrete: a brittle epoxy and a ductile polyurethane (PUR). The experimental design exposed the joints to three specific long-term environments: (1) outdoor exposure, (2) indoor conditions with applied load, and (3) outdoor conditions with applied load. The wood-concrete joints exposed to outdoor conditions were subjected to destructive shear testing at intervals of 0 (serving as the reference sample), 2, 4, 6, and 12 months, respectively. For joints subjected to both indoor and outdoor conditions with shear loading, the shear deformation of joints was monitored continuously over the 12 months before performing the destructive tests. A gradual reduction in the shear stiffness and strength of dry joints (produced using the dry bond method) exposed to outdoor conditions was observed over a 12-month period, primarily due to bond failure at the concrete-adhesive interface. The wet joints exhibited no degradation in shear stiffness and strength across long-term conditions over the same period. The bond failure observed in dry joints was predominantly associated with stresses arising from dimensional changes in the wood. No degradation was found in the cross-linking density of the adhesive or in the concrete's compressive stiffness and strength.

IMPACT OF THE GLUE LAYER PROPERTIES ON THE STRESS-STRAIN STATE OF THE GLUE ANCHOR FOR THE STEEL ROD IN CONCRETE

The article deals with the distribution of stresses and displacements along a steel anchor fixed in concrete with a polymer binder - an acrylic compound. It was established that the maximum values of tangential, radial, and circular stresses, which more fully characterize the operation of the connection, change depending on the strength characteristics of the adhesive layer and its thickness according to the exponential law. The obtained results of stress at any point of the adhesive joint allow us to propose a methodology for the design of steel rods in concrete fixed with polymers. As a result of solving the problem of the stressed-strained state of the anchor connection on acrylic adhesives, equations were obtained for determining stresses and strains at any point. As a result of the analysis of the obtained dependencies, the following conclusions can be drawn. When calculating the strength of anchor joins on acrylic adhesives, it is necessary to take into account the maximum values of tangential, radial, and circular stresses. In order to calculate the strength of the join, it is necessary to know the strength limit at uniform separation of the glue from the metal surface, as well as at shear for the glue-metal contact. Tangential and normal stresses in the adhesive cylinder and at the adhesive-concrete interface decrease with an increase in the modulus of elasticity of the acrylic adhesive. But this leads to an increase in normal axial stresses in the part of the anchor embedded in concrete and radial stresses at the glue-anchor and glue-concrete contacts. The elasticity modulus of the glue layer is smaller than the elasticity modulus of concrete and metal. Therefore, the adhesive distributes the stresses that arise from the application of the pull-out force between the anchor and the concrete massif. This is explained by the fact that the pull-out stresses from the anchor are completely transferred to the adhesive layer and then to the concrete. The main vector of tangential stresses does not depend on the ratios of the elasticity modulus of the materials which form the anchor join. The thickness of the adhesive layer has a slight effect on the stress in the glue-anchor contact, but significantly on the stress in the glue-concrete contact.

Repair of ordinary Portland cement concrete using alkali activated slag/fly ash: Freeze-thaw resistance and pore size evolution of adhesive interface

Adhesive interface is the weak part of old concrete after repair, which is an important factor affecting the functionality and durability of new-to-old concrete. In order to make full use of industrial solid waste, the old concrete was repaired with the mixture of slag and fly ash (SFA) as cementitious materials in this paper considering its strong cementitious effect under the condition of alkali activator. The modification of new-to-old concrete adhesive interface was studied using different mass ratio of slag to fly ash. The cohesiveness and durability of new-to-old concrete interface were investigated systematically. Pore surface fractal dimension (PSFD) was used to further explore the mechanism of improving durability adhesive interface durability. The results indicated that the splitting tensile strength and durability of adhesive interface can be improved by adjusting the mass ratio of slag to fly ash. With 50% slag addition, the defects and harmful pores in adhesive interface were the least. The contents of C-S-H, C-A-S-H, and N-A-S-H gels in adhesive interface repaired with AASFA were increased significantly, among which the OPC-G50 was most improved. The adhesive interface was the weakest part of the repaired structure, the utilization of AASFA promoted the formation of amorphous gels, which improved the microstructure density, interfacial pore volume content, mechanical behaviors and F-T resistance significantly.

Novel adhesive anchoring system through engineered adhesive-concrete interface

This study was to verify an idea that improves the robustness of adhesive anchors, which usually consists of a threaded rod inserted into a drilled hole in concrete with adhesives acting as bonding agent. Bond on adhesive-concrete interfaces can be affected by many factors, including installation conditions, service conditions, and adhesive materials. The innovation is about creating threads/grooves in drilled holes in concrete before adhesive are injected and anchors installed. The hardened adhesive in the grooves creates reliable mechanical interlock to the load carrying mechanism. The new adhesive anchoring system was verified in this study using both unconfined and confined tension tests in uncracked concrete. The comparison tests considered two anchor sizes and three hole-cleaning conditions that represent actual practices. The tests, though limited in considered variables, showed that the new adhesive anchors greatly improved consistence of adhesive anchors and the new anchors achieved higher tensile capacities compared with the traditional adhesive anchors.

Bond durability of epoxy and cement- bonded CFRP reinforcement to concrete interfaces subject to water immersion

Durability is a critical concern for concrete structures externally bonded with fiber-reinforced polymer reinforcement. This paper presents the results from an experimental study which compared the bond durability of epoxy-bonded CFRP sheets and cement-bonded CFRP grids to concrete interfaces subjected to water immersion. Totally twelve groups of CFRP sheet or grid-strengthened concrete beams with a notch at their midspan were carefully fabricated through epoxy- and cement-based bonding systems and tested under monotonic loading before and after water immersion exposure, respectively. The cement binder included polymer cement mortar (PCM) and ductile engineered cementitious composite (ECC). The CFRP grids and sheets were designed with the similar tensile stiffness. The duration of water immersion ranged from 0 to 6 months. The test results indicated that debonding in concrete adjacent to the concrete-adhesive interface in accompany with a diagonal concrete crack near the notch was the main failure mode of the beams strengthened with epoxy-bonded CFRP sheet and ECC-bonded CFRP grid, while the tearing off of CFRP grids from the PCM matrix was the main failure mode of the beams strengthened with PCM-bonded CFRP grids. After water immersion exposure, the ultimate loads of the beams with cement-based CFRP grids were at least 50% higher than their epoxy-bonded counterparts, confirming the superior moisture durability of cement based bond to epoxy-bonded ones. The interfacial fracture energy was found to exhibit an exponential decline trend with water immersion duration.

Experimental study of bond behavior of laminated bamboo plate to concrete interfaces

This research experimentally studied the bond behavior of laminated bamboo (LB) plate to concrete interface. Totally forty-five single shear pull-out specimens, which were categorized in nine groups, were prepared and tested to determine the bond characteristics. Plate thicknesses, plate widths and bond lengths were the three major parameters considered in the specimen preparations. It was found that debonding in concrete near the concrete-adhesive interface often occurred in the specimens with bond length less than 150 mm, and a mixed failure mode of debonding at the bamboo plate-adhesive interface and debonding in concrete was observed in most specimens with bond length equal to and over 150 mm. The coefficient of variation of the LB-concrete bond specimens was lower than such value of similar FRP-concrete bond specimens. This confirmed that the interfaces of LB plate to concrete can exhibit sufficient reliability for engineering applications. The models for predicting peak load, effective bond length and bond stress–slip curve, originally used for FRP bonded concrete specimens, were calibrated for LB bonded concrete specimens based on the test results. Compared with other models, the models proposed by Teng et al. and Zhou were more accurate for the prediction of the peak load and effective bond length of the LB bonded concrete specimens. Classical power function model with a linear descending branch was able to effectively describe the nonlinear bond stress–slip curves and achieved good agreement with test results.

FRP-concrete bond performance under accelerated hygrothermal conditions

Drawing on information obtained via double lap shear tests, this paper discusses FRP-concrete bond behavior following five weeks of exposure to several accelerated hygrothermal conditions. Material tests were also carried out for both dry carbon fibers and the epoxy used in the bond study under similar hygrothermal conditions. The bond-slip relationship for the hygrothermal conditions were developed, and fracture energy calculated for the FRP-concrete bond. The use of degraded material properties obtained from material test coupons under the same exposure conditions prevented overestimation of the FRP-concrete bond fracture energy. Testing revealed that the FRP-concrete bond strength increased as temperature increased at low humidity (dry heat) — a potential consequence of alteration in the epoxy glass transition temperature. The bond strength of concrete with steel slag incorporated was superior at all temperatures and low humidity. In response to continuous or periodic submergence in water, specimen failure mode transitioned from substrate failure to adhesive-concrete interface failure. Alternating two-day wet/dry cycles resulted in a 12% drop of FRP-concrete bond strength. Under low humidity, the FRP dry fiber tensile stress increased as temperature increased (dry heat), while the opposite dynamic was observed in the epoxy coupons.

Effect of Different Bond Parameters on the Mechanical Properties of FRP and Concrete Interface.

This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC (digital image correlation) technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types.

The combined effects of wet–dry cycles and sustained load on the bond behavior of FRP–concrete interface

Effective bonding between the adherents plays a key point when dealing with the retrofit of concrete structures by using fiber‐reinforced polymers (FRPs). However, lack of adequate studies on the long‐term performance of the bond behavior of FRP–concrete interface under harsh environments will inhibit their application in the repair of aged structures. Therefore in this study, 60 double‐lap shear‐bonded FRP‐concrete composite specimens were designed and tested under wet–dry cycles and sustained loading. The effect of FRP type (GFRP and CFRP), wet–dry cycling times (0–360 days) and sustained loading level (0–60% of the ultimate load of the control specimen) on the failure modes, stress transfer, and local bond‐slip curves of the composite specimens were investigated. The experimental results showed that wet–dry cycling exposure changed the failure mode of the composite specimens from the concrete substrate to the adhesive–concrete interface, further extended the local debonding area and decreased the ultimate strains of composite specimens from 12,000 to 8,000 μɛ. The degree of the degradation will be further increased under the combined effect of sustained loading and wet–dry exposure. The effects of FRP type, wet–dry cycling times and sustained loading level on the fracture energy of the specimens were quantitatively analyzed. A regression model was then proposed that was able to predict the fracture energy after environment exposure with reasonable accuracy, which can provide a reference for the design of bond durability factors in relevant specifications, such as ACI 440R‐08 POLYM. COMPOS., 40:1006–1017, 2019. © 2018 Society of Plastics Engineers

Behaviour of Adhesive Bonded and Mechanically Connected Steel-concrete Composite under Impact Loading

The aim of the study was to observe and provide a qualitative comparison of the behaviour of mechanically connected and adhesively bonded steel-concrete composite connections under impact load. For this, steel-concrete composites connections were subjected to drop-weight impact test. The number of blows required for crack initiation and final failure (serviceability failure in case of the stud connection) were noticed. It was found that the adhesively bonded connection can resist comparatively higher number (twice) of blows for crack initiation but, the number of blows required for final failure were relatively less. The adhesively bonded connection showed a brittle failure in concrete near the adhesive concrete interface whereas the mechanically connected specimen showed ductile failure due to concrete crushing in composite specimen nearby the studs.

An Experimental Study on the Debonding of Steel and CFRP Strips Externally Bonded to Concrete in the Presence of Embedded Shear Connectors

The problem of debonding failure is a fundamental issue in concrete structures that are externally strengthened with adhesively glued plates. Many standards and studies recommend using single-lap pull-out tests to measure the ultimate force that causes debonding failure. The pull-out test also allows defining and calibrating interface bond-slip relationships between concrete and the bonded plates to obtain the maximum interfacial bond strength. The aim of this research was to enhance bond strength in the presence of embedded shear connectors, which were fabricated at concrete–adhesive interface level to delay debonding of the externally bonded strips from the concrete surface. A new rational model was also proposed to predict the bond strength of adhesively glued plates-to-concrete joints in the presence of connectors. In the experimental programme, 60 concrete prisms with adhesive and steel bar connectors were fabricated. The specimens were divided into two main series of concrete prisms bonded with steel plates and CFRP strips using the new connectors. Different diameters of connectors were used with and without adhesive on the surfaces of concrete prisms to bond the strips for investigating the capacity of the new embedded connectors. The experimental results showed that the interfacial bond strength increased remarkably when these connectors were used. Moreover, it was found that increasing the connector’s diameter has a great effect on increasing the bond strength and uniformly distributes the interfacial shear stresses, leading to the minimisation of premature debonding failure of bonded plates. The results exhibited that the steel connectors are more effective at increasing the shear bond strength for all specimens adhesively glued with both CFRP strips and steel plates. Finally, the proposed bond strength model was satisfactorily verified through the experimental investigations.

Residual performance of concrete–adhesive interface at elevated temperatures

This paper presents a two-phase experimental program to evaluate the performance of concrete–adhesive interface subjected to thermally-induced distress, including material- and interface-level investigations. Elevated temperatures ranging from 25°C to 200°C are applied to three adhesive types (i.e., low viscosity, high viscosity, and high temperature epoxies). The residual thermal behavior of these epoxies and corresponding concrete–adhesive interface is characterized by various test methods such as dynamic mechanical analysis (ASTM D7028), dynamic elastic modulus test (ASTM C215), and bending test (ASTM C78). With an increasing temperature, the resonant frequency and dynamic modulus of the concrete–adhesive interface decrease due to the physical softening of the adhesive layer. Strength recovery is observed with a change in adhesive-morphology when the applied thermal load disappears, while such an effect is not pronounced for the high temperature adhesive. Thermomechanical observations indicate that the deformability and stiffness-softening of the concrete–adhesive interface tend to augment at elevated temperatures, and the failure of the interface is controlled by material cohesion rather than adhesion. Technical recommendations are proposed towards the performance-based design of concrete–adhesive interface subjected to temperature load.

An extended high order cohesive interface approach to the debonding analysis of FRP strengthened beams

Abstract The paper studies the debonding mechanisms in concrete beams strengthened with externally bonded fiber reinforced polymer (FRP) composite strips. The paper develops a nonlinear analytical model that combines an extended high order multi-layer consideration of the strengthened beam with a cohesive interface modeling of its physical interfaces. The handling of the adhesive layer uses 2D elasticity and considers the layer as an isotropic medium with shear, vertical-normal, and longitudinal-normal stiffness. This allows for capturing the variation of all stress components through the thickness of the adhesive layer and for implementing two distinct cohesive interfaces, one at the adhesive–concrete interface and one at the adhesive–FRP interface. By means of this combination, the model responds automatically with the nucleation and evolution of debonding mechanisms in each physical interface. The study looks into the debonding mechanisms triggered by the localized effects near the edge of the bonded layer and near a flexural crack in the concrete beam. The numerical results, the quantitative comparison with reference results, and the qualitative comparison with experimental observations reported in the literature gain insight into the nucleation and evolution of the failure mechanism. This effort takes another step towards the understanding of the debonding phenomenon and towards the development of a high-resolution analytical platform for its handling.

A State-of-the-Art Review on Debonding Failures of FRP Laminates Externally Adhered to Concrete

There is significant concern in the engineering community regarding the safety and effectiveness of fiber-reinforced polymer (FRP) strengthening of RC structures because of the potential for brittle debonding failures. In this paper, previous research programs conducted by other researchers were reviewed in terms of the debonding failure of FRP laminates externally attached to concrete. This review article also discusses the influences on bond strength and failure modes as well as the existing experimental research and developed equations. Based on the review, several important conclusions were re-emphasized, including the finding that the bond transfer strength is proportional to the concrete compressive strength; that there is a certain bond development length that has to be exceeded; and that thinner adhesive layers in fact lower the chances of a concrete-adhesive interface failure. It is also found that there exist uncertainty and inaccuracy in the available models when compared with the experimental data and inconsistency among the models. This demonstrates the need for continuing research and compilation of data on the topic of FRP’s bond strength.

Modeling in-plane and out-of-plane displacement fields in pull-off tests on FRP strips

The present paper deals with modeling FRP strips bonded to concrete blocks and tested in pull-off. The investigation starts from the experimental observations obtained by means of an optical image-correlation measurement system which is able to monitor the 3D displacement components of a fine mesh of points on the surface of both the FRP strip and concrete block. Thus, refined measurements of both in-plane and out-of-plane displacements of the FRP strips are available. A brief overview of the key contributions available in the scientific literature on modeling the bond behavior of FRP strips glued to a concrete substrate is firstly proposed. Then, a novel model based on simulating the behavior of the FRP strip as a Bernoulli beam on a layer of springs is formulated. It is aimed at determining the 2D displacement field of the FRP strip during a pull-off test up to debonding which actually occurs in a mixed fracture mode. The model is firstly formulated within the linear range by assuming elastic behavior for the above mentioned springs. The nonlinear behavior due to the cracking of concrete beneath the adhesive interface is then introduced for simulating the above mentioned experimental results. In particular, a bilinear relationship is assumed between interface slips and shear stresses, as is generally accepted within the scientific literature. Furthermore, a damage model is considered for reducing the stiffness of the transverse springs and simulating the crack propagation at the adhesive–concrete interface. Although this is a simplified way of modeling the nonlinear behavior of concrete in shear/tension, it results in rather accurate simulations of the available experimental results. In fact, it can simulate accurately the overall behavior observed in three experimental tests on specimens characterized by significantly different mechanical properties of the strip. Since the model assumes a small set of mechanical parameters for describing the mechanical behavior of the adhesive FRP–concrete interface and results in a reasonable small set of equations, it can be easily employed for identifying the above mentioned mechanical behavior indirectly. Other numerical models already available in the scientific literature (especially those based on the theory of finite elements) for simulating the 2D displacement field in the debonding stage are generally based on much more equations and require a much higher computational effort which makes impractical their use in an indirect identification procedure like the one presented in this paper. In fact, one of the main results of this study consists in determining the distribution of normal (peeling) stresses throughout the adhesive-to-concrete interface. This stress component (Mode I) can neither be directly measured during the tests nor determined by the theoretical models usually adopted for simulating the fracturing behavior of FRP-to-concrete joints in the so-called fracture process in “mode II”. Finally, it was found that the shear stresses are significantly higher than the peeling ones and control the crack propagation process.

Residual Behavior of Shear-Repaired Concrete Beams Using CFRP Sheets Subjected to Elevated High Temperatures

This paper presents the residual behavior of unreinforced concrete beams repaired with carbon fiber-reinforced polymer (CFRP) sheets in shear subjected to elevated temperatures up to 200°C. An experimental program is conducted to examine the effects of high-temperature exposure on the response of constitutive materials, adhesive–concrete interface, and shear repaired beams. All test beams are notched to represent various levels of shear deficiency. A predictive modeling approach is proposed based on classical laminate theory. Elevated temperatures influence the capacity and interfacial characteristics of the repaired beams. Temperature effects, however, are not significantly correlated with the formation of diagonal tension cracks (shear crack) and their propagation rate. Shear resistance of the CFRP is found to be independent of high-temperature exposure because of the load-resisting mechanism associated with crack-plane strains and shear-failure angle.

Cohesive Interface Modeling of Debonding Failure in FRP Strengthened Beams

A theoretical model that incorporates the concept of the cohesive interface approach for the debonding analysis of reinforced concrete beams strengthened with externally bonded fiber reinforced polymer (FRP) strips is presented. The cohesive interface concept is adopted for modeling of the debonding process near the critical adhesive-concrete interface, whereas the adhesive layer itself is modeled as a two-dimensional elastic medium. Thus, the stress and deformation fields within the adhesive layer, the coupling between the shear and normal stresses and, especially, their influence on the tractions across the cohesive interface are taken into account. The nonlinear relations between the tractions and the displacement jumps across the cohesive interface are derived using a potential function and account for the peeling effects and for the coupling between the shear-slip and the peeling-separation laws. Numerical results that examine the capabilities of the model, provide insight into the stability characteristics of the debonding mechanism, and highlight some aspects of the debonding problem are presented. A summary and conclusions close the paper.

Cohesive fracture simulation and failure modes of FRP–concrete bonded interfaces

A work-of-fracture method using three-point bend beam (3PBB) specimen, commonly employed to determine the fracture energy of concrete, is adapted to evaluate the mode-I cohesive fracture of fiber reinforced plastic (FRP) composite–concrete adhesively bonded interfaces. In this study, a bilinear damage cohesive zone model (CZM) is used to simulate cohesive fracture of FRP–concrete bonded interfaces. The interface cohesive process damage model is proposed to simulate the adhesive–concrete interface debonding; while a tensile plastic damage model is used to account for the cohesive cracking of concrete near the bond line. The influences of the important interface parameters, such as the interface cohesive strength, concrete tensile strength, critical interface energy, and concrete fracture energy, on the interface failure modes and load-carrying capacity are discussed in detail through a numerical finite element parametric study. The results of numerical simulations indicate that there is a transition of the failure modes controlling the interface fracture process. Three failure modes in the mode-I fracture of FRP–concrete interface bond are identified: (1) complete adhesive–concrete interface debonding (a weak bond), (2) complete concrete cohesive cracking near the bond line (a strong bond), and (3) a combined failure of interface debonding and concrete cohesive cracking. With the change of interface parameters, the transition of failure modes from interface debonding to concrete cohesive cracking is captured, and such a transition cannot be revealed by using a conventional fracture mechanics-based approach, in which only an energy criterion for fracture is employed. The proposed cohesive damage models for the interface and concrete combined with the numerical finite element simulation can be used to analyze the interface fracture process, predict the load-carrying capacity and ductility, and optimize the interface design, and they can further shed new light on the interface failure modes and transition mechanism which emulate the practical application.

Experimental and analytical studies on peeling and spalling resistance of unidirectional FRP sheets bonded to concrete

In this paper, the peeling and spalling resistance of unidirectional fiber reinforced polymer (FRP) sheets externally bonded to concrete surface are investigated experimentally through a series of peeling tests. A peeling load is applied on the FRP sheet by a circular rod placed into the central notch of the beam. The effects of different FRP composites, adhesives, surface treatments and strength of concrete on peeling behavior are investigated. Three different modes of debonding failure are identified: debonding within concrete surface, debonding in concrete–adhesive interface, and debonding in FRP composites–adhesive interface. It is observed that the failure pattern debonding within concrete layer yields a higher peeling load carrying capacity. Moreover, a typical failure due to the FRP rupture is also observed experimentally. Based on the experimental results, a theoretical analysis is conducted on specimens representing the peeling behavior and spalling resistance. Load carrying capacity is expressed as the function of peel angle based on geometrical analysis and equilibrium of forces between FRP sheets and the circular rod. Interfacial fracture energy is calculated analytically using membrane-peeling method. Finally, a close agreement between the predicted and the experimental results is demonstrated by means of some numerical examples.

Effectiveness of CFRP Strengthening on Curved Soffit RC Beams

The objective of this research program was to study carbon fiber reinforced polymer (CFRP) strengthening of reinforced concrete (RC) members which have concavely-curved soffits. In the presence of such curvature, the FRP laminates attempt to straighten under tension, leading to direct transverse tensile stress at the adhesive-concrete interface, which may cause premature peeling. This tensile stress could also lead to concrete cover delamination. Ten beams, each 6 m in length and having the same soffit curvature (i.e., 4 × 10−5 mm−1 or in−1), extending over 1, 3 and 5 meters, were tested under three-point static flexure. Two different types of CFRP strengthening techniques, namely wet layup laminates and pultruded precured laminates, were used for external strengthening. One of the beams strengthened with CFRP wet layup laminates (with a curved soffit over an extent of 5 m), used glass FRP spike anchors to prevent peeling. Beams with soffit curvature limited to an extent of 1 m, failed at similar loads when compared with control specimens containing flat soffits. For beams having a soffit curvature extending over 3 and 5 m, reduction in strength was observed because of premature peeling. Inclusion of the GFRP spike anchors with the wet layup system led to a performance superior to the control specimen (flat soffit) confirming that application of GFRP spike anchors delays premature peeling.