Fiber Reinforced Polymer Systems Research Articles

Strength, Durability and Finite Element Analysis of Hybrid Jute/Basalt Fiber Reinforced Polymer Confined Concrete Column under Axial Compression

Implementing retrofitting measures for a civil structure may guarantee its ongoing safety and operation, while also extending its lifespan. The present investigation focused on the examination of compressive axial loads on concrete columns that were confined by natural fiber reinforced polymer (FRP). In particular, concrete cylinders confined with jute and basalt fiber epoxy composites were evaluated for their strength and durability. Various strength tests were conducted on unconfined and, jute, basalt, and hybrid jute-basalt FRP confined concrete cylinders with varying thicknesses of the FRP layers. Effectiveness of these natural FRP systems in providing external confinement to concrete columns in various environmental conditions were investigated, including exposure to acidic, alkaline, seawater, and potable water environments. Test results demonstrated that external confinement with hybrid FRP wraps, i.e. with both jute and basalt fibers, enhanced the load-bearing and energy absorption capacities by 63.64 % and 287 %, respectively. The confinement effectiveness of FRP wrapped specimens were 213 %, 164 %, 166 % and 163 % respectively compared to the unconfined specimens after exposure to acidic, alkaline, seawater and potable water environments. These impressive outcomes may be ascribed to the intrinsic rigidity of hybrid fibers. Furthermore, a finite element analysis (FEA) model of FRP confined concrete columns was performed using ABAQUS software calibrated with the experimental data. A close agreement between the experimental results and the adopted numerical model was observed. The outcome of the study suggests that the confinement with natural FRP can be used as a prominent retrofitting technique for columns in a variety of environments which can thus enhance the durability and sustainability of civil constructions.

FIRE RESPONSE OF CIRCULAR RC COLUMNS STRENGTHENED WITH PBO FRCM

The use of externally bonded fiber-reinforced system, specifically fiber-reinforced polymer (FRP) system, has increased over the past decades due to their demonstrated efficacy in enhancing the structural integrity of various RC members. However, the vulnerability of FRP systems to elevated temperatures has raised a major concern and led researchers to explore different strengthening systems. This paper investigates the fire performance of circular RC columns strengthened with poly-paraphenylene-ben-zobisoxazole (PBO) fabric-reinforced cementitious matrix (FRCM) system. Four identical columns were cast, three of which were strengthened with varying number of layers of PBO-FRCM. The fire exposure followed ASTM E119 standards. The temperature response curves were analyzed, and post-fire conditions were assessed. Initially, columns with a greater number of PBO-FRCM layers exhibited significantly lower temperatures. As the fire exposure time increased, FRCM strengthened columns experienced more significant spalling than the control column, where the reinforcement was visible from all sides. This excessive concrete spalling resulted in matching temperature readings in both the strengthened and non-strengthened columns.

Evaluating the impact of different anchor configurations and patch arrangements on the performance of fiber-reinforced polymer (FRP) anchors

The use of fiber-reinforced polymer (FRP) anchors to enhance the efficiency of externally bonded (EB) FRP systems has received considerable attention in recent years. However, their widespread application has been constrained by the challenges associated with their installation due to complexity in anchor detailing. To date, there has been limited research aimed at simplifying anchor detailing while maintaining its efficiency. This paper presents an extensive experimental study involving 88 tests on concrete beams with anchored FRP material, with variations in the number of FRP strips, anchor material ratio (AMR), fan length, and rounding radius of the anchor hole. The study focuses primarily on different aspects of the anchor configuration. The first part of the study compares the performance of two anchor details, while the second part assesses the impact of different FRP patch arrangements on enhancing the performance of the anchors. The efficiency of the newly suggested end anchor detail was found to be equivalent to the previously used end anchor detail. The use of FRP patches over anchors proved very effective in certain cases but ineffective in others.

Nondestructive Testing (NDT) for Damage Detection in Concrete Elements with Externally Bonded Fiber-Reinforced Polymer

Fiber-reinforced polymer (FRP) composites offer a corrosion-resistant, lightweight, and durable alternative to traditional steel material in concrete structures. However, the lack of established inspection methods for assessing reinforced concrete elements with externally bonded FRP (EB-FRP) composites hinders industry-wide confidence in their adoption. This study addresses this gap by investigating non-destructive testing (NDT) techniques for detecting damage and defects in EB-FRP concrete elements. As such, this study first identified and categorized potential damage in EB-FRP concrete elements considering where and why they occur. The most promising NDT methods for detecting this damage were then analyzed. And lastly, experiments were carried out to assess the feasibility of the selected NDT methods for detecting these defects. The result of this study introduces infrared thermography (IR) as a proper method for identifying defects underneath the FRP system (wet lay-up). The IR was capable of highlighting defects as small as 625 mm2 (1 in.2) whether between layers (debonding) or between the substrate and FRP (delamination). It also indicates the inability of GPR to detect damage below the FRP laminates, while indicating the capability of PAU to detect concrete delamination and qualitatively identify bond damage in the FRP system. The outcome of this research can be used to provide guidance for choosing effective on-site NDT techniques, saving considerable time and cost for inspection. Importantly, this study also paves the way for further innovation in damage detection techniques addressing the current limitations.

Cognizant Fiber-Reinforced Polymer Composites Incorporating Seamlessly Integrated Sensing and Computing Circuitry.

Structural fiber-reinforced polymer (FRP) composite materials consisting of a polymer matrix reinforced with layers of high-strength fibers are used in numerous applications, including but not limited to spacecraft, vehicles, buildings, and bridges. Researchers in the past few decades have suggested the necessary integration of sensors (e.g., fiber optic sensors) in polymer composites to enable health monitoring of composites' performance over their service lives. This work introduces an innovative cognizant composite that can self-sense, compute, and implement decisions based on sensed values. It is a critical step towards smart, resilient infrastructure. We describe a method to fabricate textile sensors with flexible circuitry and a microcontroller within the polymer composite, enabling computational operations to take place in the composite without impacting its integrity. A microstructural investigation of the sensors showed that the amount of oxidative agent and soaking time of the fabric play a major role in the adsorption of polypyrrole (PPy) on fiberglass (FG). XPS results showed that the 10 g ferric chloride solution with 6 h of soaking time had the highest degree of protonation (28%) and, therefore, higher adsorption of PPy on FG. A strain range of 30% was achieved by examining different circuitry and sensor designs for their resistance and strain resolution under mechanical loading. A microcontroller was added to the circuit and then embedded within a composite material. This composite system was tested under flexural loading to demonstrate its self-sensing, computing, and actuation capabilities. The resulting cognizant composite demonstrated the ability to read resistance values and measure strain using the embedded microcontroller and autonomously actuate an LED light when the strain exceeds a predefined limit of 2000 µε. The application of the proposed FRP system would provide in situ monitoring of structural composite components with autonomous response capabilities, as well as reduce manufacturing, production, and maintenance costs.

Prediction of compressive strength of brick columns confined with FRP, FRCM, and SRG system using GEP and ANN methods

This study assesses the strength capacity of brick columns under various confinement materials, including fiber-reinforced polymer (FRP), fiber-reinforced cementitious matrix (FRCM), and steel-reinforced grout (SRG) using gene expression programming (GEP) and artificial neural networks (ANN) models. To achieve this, a comprehensive database of masonry column test results from existing scientific literature is compiled. The models' performance is evaluated using statistical errors like the coefficient of linear correlation (R2), mean absolute error (MAE), mean square error (MSE), and root mean square error (RMSE). Additionally, sensitivity analysis is carried out to assess the significance of individual parameters in the models. The findings reveal that ANN predictions closely match empirical data, demonstrating a strong correlation coefficient of 0.95. The accuracy of the ANN approach is reasonably high, with only 26% of the predicted values deviating by more than 20% from the actual data. Based on the statistical analyses, the correlation coefficient between the actual and estimated data was 0.88, for GEP method. Also, the GEP model yields outcomes, with roughly 43% of the predicted values differing by 20–50% from the actual data. In a comparison of the two models, the ANN model outperforms the GEP model, displaying a 40% reduction in error when estimating the compressive strength of masonry columns. The data estimated by the GEP were sparser than those estimated by the ANN. Nevertheless, the GEP model still maintains an acceptable correlation coefficient and error rate, making it a viable choice for precise predictions. It offers a user-friendly formula and meets the needs of both customers and builders.

Torsional behavior of FRP-strengthened reinforced concrete members considering various wrapping configurations: Theoretical analysis and modeling

Reinforced concrete (RC) structural members such as spandrel, flanged and curved beams, slab beams, and bridge girders may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, very little is known about the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, very limited guidelines apply to the design of externally bonded FRP systems for torsional strengthening, and no design provisions exist for the U-wrapped and 2-sided strengthening systems in torsion. This study aims to contribute to this growing area of research by developing a new analytical model to predict the full torsional response of strengthened RC members with many conventional configurations such as spiral, transverse and longitudinal FRP, continuous and intermittent strips along the beam length, side bonded, and full-wrapped systems. Moreover, this study provided an analytical model accurately predicting the contribution, efficiency, and failure mode of side-bonded strengthening systems. Additionally, the influence of various parameters such as FRP stiffness and transverse steel reinforcement ratio is taken into account in the constitutive law of concrete and internal reinforcement for the first time. The good agreement between the test results of 32 collected FRP-strengthened RC beams from the literature and the theoretical ones, which were predicted through programming proves the validity and accuracy of the presented theory.

Damage and Defects in Fiber-Reinforced Polymer Reinforced and Strengthened Concrete Elements

Fiber-reinforced polymer (FRP) composites are becoming increasingly popular as an alternative to conventional civil engineering materials in existing structures as externally applied systems for strengthening purposes, and in new structures as internal reinforcements in the form of bars, meshes, and strands. The next phase of development in the application of FRPs in concrete structures could culminate in elements possessing both internal and external FRP systems simultaneously. With these advancements in the application of FRP in civil engineering, it is conceivable that traditional steel reinforcements could become obsolete in certain aggressive and hostile environments, such as coastal areas. Although higher durability and performance are associated with FRP materials in some respects when compared to steel, concerns remain regarding the damage and defects in this material, many of them related to their unique features. Regardless, similarly to other structural materials, it is necessary to understand the damage and defects associated with the use of FRP composites, as well as to identify their sources. This knowledge will support the positive prospects for FRP technology, promoting its application in civil infrastructure. Accordingly, this study investigated the types, characteristics, and identification of the observed or expected damage and defects associated with using FRP in reinforced and strengthened concrete elements. The damage was classified according to location and time of initiation. In addition, the sources of these defects and damage were determined, and a damage etiology was established for preventing the occurrence of such damage in future use. The results of this study are intended to provide the background for the development of a guide and training material for the inspection of structures that use FRP materials. The ability to inspect and properly maintain structures containing FRP will result in the enhanced durability and service life of concrete structures reinforced or strengthened with FRP materials.

Improvement of structural performance of RC Beams with external reinforcement method: an experimental investigation

The old existing RC structures around the world need to be examined and reinforced to increase their capacity for different reasons. Fiber-Reinforced-Polymer (FRP) is believed to be the most efficient system to retrofit and improve the strength of the RC members. However, in certain cases, engineers need to utilize the combination of flexural and shear FRP systems, which was not mandated in the standard code. Therefore, this research was focused on the structural behavior of RC beams strengthened with a flexural and shear FRP combination. The beam specimens were tested for failure under a two-point load configuration and the confining effect of the FRP was also investigated. The finding of the experimental test revealed the enhancement of the load capacity and ductility performed in RC beams. The specimen failure was indicated by the concrete crushing at the top part of the beam and the yield condition at the bottom longitudinal reinforcement. It was also discovered that the externally bonded FRP system could confine the concrete and result in the enhancement of ductility and compressive strength. The evidence presents the understanding of the structural behavior of the RC beam strengthened with the combination of flexural and shear FRP systems.

Analytical model to predict axial stress-strain behavior of heat-damaged unreinforced concrete columns wrapped by FRP jacket

Although there are several confinement models to obtain analytically the axial stress-strain response (fc-εc) of concrete columns wrapped with fiber-reinforced-polymer (FRP) jacket at ambient conditions, a reliable design-oriented model to determine the fc-εc of heat-damaged concrete columns post-confined with FRP is still lacking in the literature. This study aims to address this research gap, by proposing a formulation that predicts the favourable effects of FRP confinement on concrete elements previously exposed to high temperatures. This model proposes a closed-form formulation to derive a fc-εc expression, including a set of strength and strain sub-models to calculate the stress/strain information at transition and ultimate points defining the stress-strain response. To develop the model and calibrate its key components by data analysis of statistical treatment techniques, a large test database of FRP confined unheated/heat-damaged concrete of circular/square cross-section consisting of 1914 specimens was collected. The proposed design-oriented model is able to demonstrate the influence of pre-existing thermal damage on the axial fc-εc relationship, whose reliability is revealed comprehensively through predicting data from several experimental heat-damaged concrete specimens confined with FRP systems.

Repair of corroded steel bridge girder end regions using steel, concrete, UHPC and GFRP repair systems

Practical means of affecting in situ repair of corrosion-induced section loss of steel bridge girders at their supports are compared. Potential repair strategies are reviewed leading to large-scale experimental evaluation of four methods of repair: conventional bolted steel repair, encasement in conventional reinforced concrete (RC), encasement in ultra-high performance concrete (UHPC), and reinforcement with externally bonded fiber-reinforced polymer (FRP) plates and sections. Modified W24x55 girders representing half-scale 1400 mm deep plate girders were used. Section loss mimicking typically-observed severe corrosion was machined into the girder ends. Monotonic load tests to failure were conducted on the repaired girders and companion tests were conducted of identical specimens subject first to one million cycles of fatigue loading before being loaded to failure. Results indicate the efficacy of conventional bolted steel repair methods. UHPC and RC encasement was also shown to perform well and may be suited to certain scenarios. Despite extensive surface preparation and chemical enhancement, the bond of the FRP system to the damaged substrate steel was poor; this system is not an appropriate repair method for this damage scenario.

The Reinforcing Effect of Nano-Modified Epoxy Resin on the Failure Behavior of FRP-Plated RC Structures

The ability to manipulate concrete-based and composite materials at the nanoscale represents an innovative approach to improving their mechanical properties and designing high-performance building structures. In this context, a numerical investigation of the reinforcing effect of nano-modified epoxy resin on the structural response of fiber-reinforced polymer (FRP)-plated reinforced concrete (RC) components has been proposed. In detail, an integrated model, based on a cohesive crack approach, is employed in combination with a bond–slip model to perform a failure analysis of strengthened structures. In particular, the proposed model consists of cohesive elements located on the physical interface between concrete and FRP systems equipped with an appropriate bond–slip law able to describe the reinforcing effect induced by the incorporation of nanomaterials in the bonding epoxy resin. Preliminary analyses, performed on reinforced concrete prisms, highlight an increment of 28% in the bond strength between concrete and the FRP system, offered by the nanomaterials embedded in the adhesive layer with respect to the standard one. Moreover, the numerically predicted structural response of a nano-modified FRP-plated beam shows an increment of around 5.5% in the failure load and a reduction in the slip between concrete and the FRP plate of around 76%, with respect to the reinforced beam without nanomaterial incorporation. Finally, the good agreement with experimental results, taken from the literature, highlights the excellent capability of the proposed model to simulate the mechanical behavior of such types of reinforced structures, emphasizing the beneficial effects of the nano-enhanced epoxy resin on the bond strength between concrete and FRP systems.

Evaluation of Hybrid Fiber Multiscale Polymer Composites for Structural Confinement under Cyclic Axial Compressive Loading

Fiber reinforced polymer (FRP) confinement is recognized as the most promising technique for the strengthening and retrofitting of concrete structures. In order to enhance the performance of conventional epoxy-based FRP composites, nano filler modification of the epoxy matrix was implemented in the current study. In particular, the cyclic loading response of standard concrete specimens externally confined by epoxy-based natural and hybrid fiber reinforced polymer systems was investigated. The confinements were realized with sisal fiber reinforced polymer (SFRP) and hybrid sisal basalt fiber reinforced polymer (HSBFRP). Moreover, the effects of multiwalled carbon nanotubes (MWCNT) were also investigated. Three different specimen sets were considered for study: (i) unconfined specimens, (ii) epoxy-based FRP confined specimens and (iii) MWCNT incorporated epoxy-based FRP confined specimens. The specimens were tested in repeated compressive mode in loading-unloading cycles at increasing displacement levels. The test results revealed that FRP wrapping could enhance the mechanical behavior of unconfined columns in terms of strength and ductility. Moreover, it was evident that the mechanical properties of the epoxy matrix were enhanced by MWCNT incorporation. The developed epoxy-based FRP confinement containing MWCNT ensures improvement in axial strength by 71% when compared with unconfined specimens. The epoxy-based FRP confinement, with and without MWCNT, exhibited a high strain redistribution behavior around the concrete core. In comparison to the unconfined specimens, the confinement could increase the sustained axial strain from 0.6 to 1.4% using epoxy-based FRP confinement and to 1.6% with MWCNT incorporated epoxy-based FRP confinement. Further, an empirical model was developed to predict the ultimate axial stress of concrete columns confined externally with FRP jackets. The ultimate compressive strength obtained from the experimental study was compared with the proposed model, and the observed deviation was lower than 1%.

Experimental and statistical investigation on synergistic effect of nano based epoxy hybrid FRP on strength and durability of circular concrete columns

Strengthening and retrofitting of concrete structures using fiber reinforced polymer (FRP) wrapping is a promising technique in construction sector. Epoxy is the commonly used matrix which possess a higher rate of degradation under exposure to harsh environment. The evaluation of strength and durability of concrete cylinders confined by multi walled carbon nanotube (MWCNT) incorporated epoxy with hybrid sisal and basalt fiber composite systems exposed to various environmental conditions forms focus of this paper. Specimens are subjected to various environmental exposure such as elevated temperature, acidic, alkaline and sea water conditions. Two varieties of epoxy viz. neat epoxy and MWCNT modified epoxy systems are considered. Mechanical and durability properties are analyzed based on axial compressive behavior, stress strain response, visual inspection and modes of failure. The MWCNT incorporated epoxy based hybrid FRP confined specimens exhibited a strength reduction less than 10% when compared with unexposed confined specimens under aggressive environmental conditions, while unconfined specimens showed strength reduction by 40% when compared to unexposed unconfined specimens. The MWCNT modified epoxy based hybrid confinement showed an energy absorption of 6.24 times that of unconfined specimens upon chemical exposure. Ultrasonic Pulse Velocity test revealed efficacy of confinement system in protecting concrete core from a sudden failure, which in turn increases the compressive strength of system. A statistical analysis using ANOVA was employed to find significance of these factors and confirmed with experimental results. The effect of MWCNT incorporation is significant in FRP confinement and shows the possibility of the FRP system to be adopted as a major retrofitting material in alkaline and sea water environments.

Nano filler incorporated epoxy based natural hybrid fiber confinement of concrete systems: Effect of fiber layers and nano filler addition

The utilization of environment friendly materials in the construction industry is essential for sustainable development. For the purpose of strengthening and retrofitting concrete structures, fiber reinforced polymer (FRP) composites have been predominantly used. In the area of structural strengthening, as an alternative to synthetic fiber reinforced composites, the application of natural fiber reinforced composites is of immense interest. This study discusses the mechanical properties of externally strengthened concrete cylinders using a natural hybrid fiber system with two layers of sisal fiber sheets followed by 1 to 3 layers of basalt fiber sheets. In addition, the effect of multi walled carbon nanotubes (MWCNT) incorporation in the epoxy matrix from 0.5 to 1.5 wt%, on the various properties are analyzed. The inclusion of MWCNT in the epoxy matrix improved the overall performance of the FRP significantly. The results show that there is substantial improvement in mechanical properties up to 1 wt% MWCNT content in composites, beyond which it is reduced due to agglomeration of nanofiller. The MWCNT incorporated epoxy based five layered hybrid sisal basalt FRP confined specimens showed an improvement of 114% and 427% in peak strength and strain values under axial compressive strength tests. Moreover, the axial compressive behavior, stress–strain response, energy absorption and ductility characteristics of the confined column specimens were evaluated. The major focus of the study is to assess the influence of basalt FRP layers on the ultimate load carrying capacity and performance of hybrid sisal basalt FRP (HSBFRP) confined specimens. Statistical analysis of variance (ANOVA) was carried out and revealed that the number of FRP layers and addition of MWCNT in epoxy significantly affect the overall performance. The addition of basalt fiber layers in hybrid sisal basalt FRP systems is found to improve the load carrying capacity and energy absorption characteristics of confined specimens. Therefore, HSBFRP confinement can be used in areas where moderate strength and greater ductility is commanded.

Ultimate torsional resistance and failure modes of FRP-strengthened reinforced concrete members: A nonlinear design model

Reinforced concrete (RC) structural members, especially flanged and spandrel beams, bridge girders, curved beams, and eccentrically loaded beams may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, far too little attention has been paid to the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, a limited number of guidelines specified the design of externally bonded FRP systems in torsion. This study provides an important opportunity to advance the understanding of the torsional behavior of FRP-strengthened members by developing a nonlinear design model predicting the failure mode and ultimate torsional resistance of FRP-strengthened RC members subjected to torsion. Serious discussions and analyses of desired failure modes emerge by defining two balanced conditions between the components, and eight failure regions. The first balanced condition defined between FRP and concrete specifies the failure mode of the member, and the second balanced condition defined between steel and concrete is used for the analysis of steel reinforcement stresses. A clear design approach is proposed in this study to access the desired percentage of the externally applied FRP sheets based on the required torsional strength. Moreover, the ultimate stresses and strains of concrete struts, steel reinforcements, and FRP sheets are derived by incorporating the nonlinear behavior of concrete. To evaluate the validity of the design method, 70 FRP-strengthened specimens are collected from 11 previous studies; then, a comparative analysis is conducted among the experimental results, the estimations of the presented model, and the predictions of the commonly available guidelines for torsional strengthening. The excellent agreement between the test results and the presented model estimations confirms the validity and accuracy of the presented model.

Prediction of compressive strength and evaluation of different theoretical standards and proposed models of brick columns confined with FRP, FRCM, or SRG system

The strength capacity of confined masonry column is one of the topics that need to be studied. In this study, the efficiency of using different types of advanced composite (non-corrosive materials) such as fiber reinforced polymer (FRP), fiber reinforced cementitious matrix (FRCM), or steel reinforced grout (SRG) in confining masonry columns is investigated. A wide range of experimental database of masonry column specimens has been collected from the results that available in scientific literatures. Different theoretical standards and proposed models that used to predict the capacity of masonry columns confined with FRP and FRCM are evaluated based on collected experimental database. Since there is no standard code or specific proposed model for SRG system, the confined capacity of this system is predicted and evaluated using the FRCM proposed models. The justification of using these models is that both FRCM and SRG systems have the same concept of using inorganic material as a paste material. An index named “equivalent fiber reinforcement index (EFRI)” is proposed to capture the key factors that control the behavior of the confined masonry columns with different advanced composite. This index is used as reference parameter for the purpose of the comparison between different strengthening systems. As a result, all types of advanced composite presented a significant increase in ultimate capacity. Also, the behavior of the masonry columns was significantly dependent on the type of fabric used. Different modes of failure were reported, including crushing of masonry block, as well as a deboning of FRP from the masonry substrate and deboning or slippage of fabric within inorganic paste matrix. Compared with other models and standards, the American Concrete Institute Committee 440 (ACI 440) and American Concrete Institute Committee 549 (ACI 549) shows very good predictions for the confined capacity of masonry columns strengthened by FRP and FRCM or SRG respectively.

Investigation of repair techniques for deteriorated end regions of prestressed concrete bridge girders

Deterioration of the end regions of prestressed concrete bridge girders is commonly observed in the field when girders are exposed to chloride-laden water that has leaked through failed expansion joints. Because the deterioration is often localized to the end regions of the girders, reliable repair techniques can provide a means to extend girder service life, avoiding the need for immediate superstructure replacement. To evaluate different repair methods and identify key design considerations for end region repair, shear tests to failure were conducted on prestressed concrete girders extracted from a decommissioned superstructure. Three repair systems were evaluated: an externally bonded fiber-reinforced-polymer (FRP) system, a near-surface-mounted FRP system, and a concrete end block. Only the externally bonded FRP system successfully restored both the strength and initial stiffness of the girder. Although the other two methods were not successful, the tests on the repaired girders highlight important factors that must be considered when designing repairs or conducting further research. The tests also demonstrate that end region deterioration can cause significant (> 40%) reductions in strength, underscoring the importance of addressing such deterioration observed in the field.

Performance of RC beams supported with hybrid FRP laminates: A review

The innovative world is perceiving the development of very exciting and tough civil Engineering Structures. To meet up the needs of enhance infrastructure, new innovative materials and technologies are created and used to defeat the earlier drawbacks. Efforts are taken in the field of concrete technology to formulate together and increase concrete with composites. Now days in the modern construction world the fibre reinforced compounds are extensively used for strengthening, rehabilitation and repair of RC structures. Most of the researches are carried out using different types of polymers with different thickness. The stress and strain features of fibre reinforced polymer Composites shows a negative influence on the total ductility of the strengthened beams. By the use of hybrid fibre reinforced polymer systems changes the performance of the material which comprises the combinations of fibres like carbon fibre and glass fibre, glass fibre and aramid fibre, carbon fibre and basalt fibres. This paper reviews the 10 research papers in external strengthening of reinforced concrete beams with hybrid FPR laminates.

High Temperature Performance of Concrete Confinement by MWCNT Modified Epoxy Based Fiber Reinforced Composites.

The conventional method of fiber reinforced polymer (FRP) wrapping around concrete columns uses epoxy as the binder along with synthetic or natural fibers such as carbon, glass, basalt, jute, sisal etc. as the reinforcement. However, the thermal stability of epoxy is a major issue in application areas prone to fire exposure. The current work addressed this major drawback of epoxy by modifying it with a nanofiller, such as multiwalled carbon nanotubes (MWCNT), and reinforcing it using basalt and sisal fibers. The effect of exposure to elevated temperature on the behavior of concrete cylinders externally confined with these FRP systems was analyzed. Three types of specimens were considered: unconfined; confined with sisal fiber reinforced polymer (SFRP); and confined with hybrid sisal basalt fiber reinforced polymer (HSBFRP) specimens. The test samples were exposed to elevated temperature regimes of 100 °C, 200 °C, 300 °C and 400 °C for a period of 2 h. The compressive strengths of unconfined specimens were compared with various confined specimens, and from the test results, it was evident that the mechanical and thermal durability of the FRP systems was substantially enhanced by MWCNT incorporation. The reduction in the compressive strength of the FRP-confined specimens varied depending on the type of the confinement. After two hours of exposure at 400 °C, the compressive strength corresponding to the epoxy-HSBFRP-confined specimens were improved by 15%, whereas a 50% increase in strength corresponding to MWCNT-incorporated epoxy-HSBFRP-confined specimens was observed with respect to unconfined unexposed specimens. The MWCNT-modified epoxy-incorporated FRP-confined systems demonstrated superior performance even at elevated temperatures in comparison to unconfined specimens at ambient temperatures.