Flexural Strength Of Concrete Beams Research Articles

Effect of Rice Husk Ash (RHA) and slake-lime as partial replacement of cement in the production of concrete

This study examines the utilization of rice husk ash (RHA) and slaked lime as substitutes for a portion of the cement in manufacturing concrete. The RHA was acquired from a nearby source, subjected to calcination at temperatures ranging from 500 to 700 °C, and then passed through a sieve to obtain particles with a size of 150 microns. Concrete mixes were made using Ordinary Portland cement (OPC), fine and coarse aggregates, and water, with different amounts of RHA and slaked lime. The concrete mix design adhered to established standards, with a mix ratio of 1:1.5:3 (cement: fine aggregate: coarse aggregate). The experiment was designed using response surface methods, with RHA, slaked lime, and cement as factors, each having five levels. Concrete cubes were formed using 100 mm steel moulds and then submerged in water to assess their workability. The compressive strength was measured using universal testing equipment after 7, 28, and 90 days of cure. The flexural strength of concrete beams was assessed after 7 and 28 days. Samples were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examination after 28 days. The compressive and flexural strengths increased as the curing period progressed, with the 10% RHA substitution showing the maximum strength. The SEM analysis showed that RHA10 exhibited the maximum concentration of silicon, which corresponds to the recommended 10% replacement level of OPC and meets the concrete specifications specified by ASTM M20 grade. Utilising RHA decreases expenses and minimises the amount of concrete that is discarded. The most effective replacement for OPC was 10% RHA, which produced long-lasting and strong concrete.

Exploring Damage Patterns in CFRP Reinforcements: Insights from Simulation and Experimentation.

Carbon Fiber Reinforced Polymers (CFRP) have become increasingly significant in real-world applications due to their superior strength-to-weight ratio, corrosion resistance, and high stiffness. These properties make CFRP an ideal material for reinforcing concrete structures, particularly in scenarios where weight reduction is crucial, such as in bridges and high-rise buildings. The transformative potential of CFRP lies in its ability to enhance the durability and load-bearing capacity of concrete structures while minimizing maintenance costs and extending the lifespan of the infrastructure. This research explores the impact of reinforcing structural elements with advanced composite materials on the strength and durability of concrete and reinforced concrete structures. By integrating Carbon Fiber Reinforced Polymer (CFRP) reinforcements, we subjected both rectangular and T-section concrete beams to comprehensive three-point bending tests, revealing a substantial increase in flexural strength by 45% and crack resistance due to CFRP reinforcement. The study revealed that CFRP reinforcement increased the flexural strength of concrete beams by 45% and improved crack resistance significantly. Additionally, the load-bearing capacity of the beams was enhanced by 40% compared to unreinforced specimens. These improvements were validated through finite element simulations, which showed a close alignment with the experimental data. Furthermore, an innovative simulation study was conducted using a finely tuned finite element numerical model within the Abaqus calculation code. This model accurately replicated the laboratory specimens in terms of shape, dimensions, and loading conditions. The simulation results not only validated the experimental observations but also provided deeper insights into the stress distribution and failure mechanisms of the reinforced beams. Novel aspects of this study include the identification of specific failure patterns unique to CFRP-reinforced beams and the introduction of an enhanced interaction model that more accurately reflects the composite behavior under load. In CFRP-reinforced beams, specific failure patterns were identified, including flexural cracks in the tension zone and debonding of the CFRP sheets. These patterns indicate the points of maximum stress concentration and potential weaknesses in the reinforcement strategy. The study revealed that while CFRP significantly improves the overall strength and stiffness, careful attention must be given to the bonding process and the quality of the adhesive used to ensure optimal performance. These findings contribute significantly to the understanding of material interactions and structural performance, offering new pathways for the design and optimization of composite-reinforced concrete structures. This research underscores the transformative potential of composite materials in elevating the structural integrity and longevity of concrete infrastructures.

Prediction of flexural strength in FRP bar reinforced concrete beams through a machine learning approach

PurposeThe purpose of this study is to assess the incorporation of fiber reinforced polymer (FRP) bars in concrete as a reinforcement enhances the corrosion resistance in a concrete structure. However, FRP bars are not practically used due to a lack of standard codes. Various codes, including ACI-440-17 and CSA S806-12, have been established to provide guidelines for the incorporation of FRP bars in concrete as reinforcement. The application of these codes may result in over-reinforcement. Therefore, this research presents the use of a machine learning approach to predict the accurate flexural strength of the FRP beams with the use of 408 experimental results.Design/methodology/approachIn this research, the input parameters are the width of the beam, effective depth of the beam, concrete compressive strength, FRP bar elastic modulus and FRP bar tensile strength. Three machine learning algorithms, namely, gene expression programming, multi-expression programming and artificial neural networks, are developed. The accuracy of the developed models was judged by R2, root means squared and mean absolute error. Finally, the study conducts prismatic analysis by considering different parameters. including depth and percentage of bottom reinforcement.FindingsThe artificial neural networks model result is the most accurate prediction (99%), with the lowest root mean squared error (2.66) and lowest mean absolute error (1.38). In addition, the result of SHapley Additive exPlanation analysis depicts that the effective depth and percentage of bottom reinforcement are the most influential parameters of FRP bars reinforced concrete beam. Therefore, the findings recommend that special attention should be given to the effective depth and percentage of bottom reinforcement.Originality/valuePrevious studies revealed that the flexural strength of concrete beams reinforced with FRP bars is significantly influenced by factors such as beam width, effective depth, concrete compressive strength, FRP bars’ elastic modulus and FRP bar tensile strength. Therefore, a substantial database comprising 408 experimental results considered for these parameters was compiled, and a simple and reliable model was proposed. The model developed in this research was compared with traditional codes, and it can be noted that the model developed in this study is much more accurate than the traditional codes.

Design methods and recommendations for flexural concrete beams reinforced with steel-fiber composite bars

This study aims to establish a complete theoretical model for the nominal flexural strength of concrete beams reinforced with steel-fiber composite bars (SFCB-RC), and determine an optimized range for the ratio of the diameter of the steel core to the diameter of SFCBs (η). Firstly, flexural failure modes for SFCB-RC beams were determined through theoretical analysis, and two failure modes including concrete crushing (compression failure) and FRP in SFCBs rupturing (tension failure) were recommended. It was confirmed that there exists a transition region between the failure modes of tension and compression, where both modes are possible. By conducting a statistical analysis of a database including 57 SFCB-RC beams, an upper-limit reinforcement ratio was recommended for SFCB-RC beams in the transition region. Simplified equations to predict the nominal flexural strength for compression-controlled SFCB-RC beams were proposed by directly using the constitutive model of SFCBs. The flexural strength equations for tension-controlled concrete beams reinforced with fiber reinforced polymer bars (FRP-RC) were confirmed to be also suitable for SFCB-RC beams. Validation of these equations was conducted using the assembled database. Furthermore, the parametric analysis revealed an optimal range of the ratio η (0.77–0.87). This suggested range can serve as a basis for standardizing the production specifications of SFCBs.

Experimental Investigation on Beam with Composite Reinforcement Using Mild Steel Tube In-Filled with Crumb Rubber

In today developing consequence, innovative alternates are being familiarized from recycled wastages used in concrete construction. This study concentrates on alternate reinforcement in the structural elements. The conventional reinforcement is replaced by the rubber composite reinforcement using in-filled tubes. The bond relation among the mild steel tube and concrete is simply good. The performance of the composite reinforcement using rubber in-filled tubes are comparing to the conventional reinforcement. The composite reinforcement is made by in-filling the mild steel tubes with cement slurry and crumb rubber. And the crumb rubber gained from the cracker mill. This crumb rubber institutes to the solid waste management. The scrap tires are prepared into crumb rubber and mixed with water – cement in a mortar ratio of 1:1:2 (water: cement: sand) to attain the colloidal consistency. 40% of 177-micron size crumb rubber sieves replaced instead of sand. This crumb rubber constitutes to the solid waste management and light weight. Hence these composite reinforcements will reduce weight of steel in reinforced concrete along with the decrease in cost of construction. This idea inspects the flexural strength of concrete beam with composite reinforcement, Mild steel pipe reinforcement and ordinary reinforcement by third point loading.

Experimental study to evaluate the flexural behavior of concrete beams reinforced with CFRP grid

Fiber reinforced polymer (FRP) is evaluated as an excellent material to replace rebar in reinforced concrete due to its advantages such as high tensile strength-to-weight ratio and high corrosion resistance. Many studies have been conducted to use FRP as substitutes for steel rebar. However, most of these studies were conducted using FRP bars, and research on using FRP grids in the construction field is focused on the field of repair and strengthening. Therefore, this study reports the results of an experimental study to evaluate the flexural behavior of concrete beam with Carbon FRP (CFRP) grid tensile reinforcements as a basic study to evaluate the feasibility of using FRP grid as a as substitutes for steel reinforcement. Thirteen test specimens were prepared for the experiments. The CFRP grids were applied to the specimens as tensile reinforcement. The concrete cover thickness, layers of the CFRP grid and the spacing between the CFRP grids were considered as test variables. The experiment results showed that the specimens without spacing between the CFRP grids were destroyed by side CFRP grid fracture. Also, as the CFRP grid layer increased, the ultimate load increased by 53% to 94%, and when the cover thickness decreased by 10 mm, the ultimate load decreased about 10%. The ratios of the nominal flexural strengths calculated according to the CSA S806–12 and ACI 440.1R-15 standards were 1.004 and 1.09, respectively. Thus, the use of the CSA S806–12 standard enables a relatively accurate prediction of the nominal flexural strength of concrete beams reinforced with CFRP grids.

Flexural strength of concrete beams strengthened with BFRP and GFRP using cement and epoxy adhesives subjected to elevated temperatures

Flexural strength of concrete beams strengthened with BFRP and GFRP using cement and epoxy adhesives subjected to elevated temperatures

EXPERIMENTAL FLEXURAL STRENGTH OF GLASS FIBER REINFORCED POLYMER (GFRP) HYBRID REINFORCED CONCRETE BEAMS

Materials technology is an excellent opportunity to be developed industrially and on a needs scale according to the demands of society, namely supporting the environment, low maintenance, and long-term use. Using composite materials with reinforced polymers is a hot topic of discussion in civil engineering as new materials, strength/stiffness enhancers, or applications in building rehabilitation or renovation. Fiber Reinforced Polymer (FRP) is excellent as a new material because, in addition to being lightweight, corrosion resistant, and easy to work with, it also has high flexural strength, so it is a consideration to replace and or strengthen steel materials that are high in cost value. However, until now there has not been found the correct pattern or variant and volume of fibre so that it can be an alternative to the use of steel. The purpose of the study was to experimentally determine the flexural strength of Glass Fiber Reinforced Polymer (GFRP) hybrid beams either with steel reinforcement, with GFRP reinforcement, or with steel and GFRP combination reinforcement and different GFRP ratios (variants) through two-point load bending tests.The designed model is a development of a previous study that used one layer of 4 mm and produced a flexural strength smaller than the targeted flexural strength, so in this study, two layers of 8 mm were used. In addition, other experimental data that has been carried out from the literature is also used where the results of parametric studies provide evidence of the positive effect of hybrid steel and GFRP reinforcement ratios when obtaining GFRP models and volumes.The materials used to manufacture concrete beam test specimens 53x15x15 cm3 with quality of fc'35MPa have been tested according to SNI standards and meet both the minimum and maximum requirements specified. Based on the results of the material test, it is planned that the characteristic concrete quality fcr'=40.31 MPa, and based on the compressive strength test, the quality fcr'=41.68MPa is produced.The hybrid designed material with concrete or concrete and steel has been tensile tested with a maximum arcing load for the two layers = 8 mm variant; the tensile strength of the GFRP woven roving type with two layers 2 x 4 mm is 92.66 MPa. While plain steel reinforcement Diameter 8mm quality 280 MPa has a minimum tensile strength of 350 MPa (3.8 times the tensile strength of GFRP 8 mm).The results of testing and calculating the effect of GFRP as a substitute for steel reinforcement contributed to the flexural strength of concrete beams on average by 47.52%. In comparison, the contribution of flexural strength produced by concrete with steel reinforcement was 107.09%. The concrete variant of hybrid steel reinforcement and GFRP contributes to an increase in the average flexural strength of 117.02% > 4.8% compared to steel-reinforced concrete beams alone.

Integrating near‐surface mounted SMA and externally bonded CFRP for concrete beams strengthened in flexure

AbstractThis study aims to develop a new hybrid strengthening approach for reinforced concrete beams by integrating near‐surface mounted shape memory alloys (SMAs) and externally bonded carbon fiber reinforced polymers (CFRPs). Due to the superelasticity and shape memory effect of SMAs, the proposed strengthening can enhance the flexural strength of concrete beams without compromising ductility. The recovery behavior of deformed SMA wires was studied to determine the optimal prestrain level that can achieve the highest recovery stress. Afterward, the flexural performance of concrete beams strengthened with SMA, CFRP and both was investigated by performing three‐point tests. The results show that integrating SMA and CFRP has more influence on increasing the ultimate moment than the cracking moment and leads to a more significant improvement in the ultimate moment than individually utilizing SMA and CFRP. Besides, the effect of the integrated approach on enhancing the ductility is more notable than increasing the ultimate moment. The ultimate moment was analytically calculated, and the calculations show reasonable agreement with experimental results. The effects of the SMA and CFRP amount on the ultimate moment were also clarified through a parametric study.

Study on flexural behavior of concrete beams reinforced with hybrid high-strength and high-toughness (HSHT) and ordinary steel bars

To study the flexural behavior of high-strength and high-toughness (HSHT) reinforced concrete beams with negative Poisson’s ratio and special spiral grooves on the surface, fifteen beams of 250 mm × 450 mm × 3200 mm were designed and manufactured to conduct bending tests. The effects of different parameters, including the reinforcement ratio, compressive strength of concrete, loading mode, the number of HSHT steel bars in hybrid reinforcement, and longitudinal steel bars type, were studied on failure modes, crack patterns, flexural stiffness, flexural strength, ductility, and energy absorption capacity. The load versus mid-span deflection curves for concrete beams reinforced with HSHT steel bars can be divided into five stages. The concrete beams reinforced with HSHT steel bars can also bear higher residual strength (approximately 0.9 Fp) and exhibit superior crack width control ability. The peak load increases by a maximum of 22.9 % with the reinforcement ratio of HSHT steel bars increasing from 0.86 % to 1.08 %. Hybrid reinforcement can improve the service performance of concrete beams, take full advantage of HSHT steel bars, and increase the energy absorption capacity of beams. Based on strain analysis of cross-section, the flexural strength model of concrete beams reinforced with hybrid reinforcement was proposed by considering the ultimate compression strain. The calculation results show that the proposed model can accurately calculate the flexural strength of concrete beams reinforced with HSHT steel bars.

Flexural Strength of Concrete Beam Reinforced with Basalt Fiber Reinforced Polymer and Steel Bars

Flexural Strength of Concrete Beam Reinforced with Basalt Fiber Reinforced Polymer and Steel Bars

Finite element analysis of the effect of type, number, and installation angle of FRP sheets on improving the flexural strength of concrete beams

Using FRP material to strengthen concrete beams is one of the best methods to prevent cracks propagation in the tensile zone. In this article, a concrete beam is modeled using the finite element software Abaqus. In order to investigate the effects of type, number, and installation angle of FRPs, a total number of 25 numerical models are considered. In these models, 3 types of covers made of GFRP, CFRP, and AFRP materials, including 6 and 12 sheets, are used at the installation angles of 30, 45, 60, and 90 degrees. Also, at the bottom of the beam in all the models, FRP layers are used to prevent the growth of cracks. After applying a constant load of 60 kN on all models, the stresses produced in the beam together with displacement at the middle of the beam, are investigated. The results showed that with an equal number of sheets and equal distance of installed sheets, the effect of FRP sheets on reducing displacement is greater at an installation angle of 45 degrees compared to that of a 60-degree angle. Also, this effect is greater at an installation angle of 60-degree angle compared to that of a 90-degree angle. Furthermore, by the addition of plates, the maximum lateral strain at the middle of the beam span is reduced up to 12.5 %. Also, CFRP material had a better performance compared to the two other types of fibers. The addition of prestressed FRP sheets to the specimens increases their strength. The load increase continues to the point wherein the beam fails due to the crushing of the compressive concrete. Adding the prestressed FRP sheets to the specimens increases the strength against the ultimate load from 5.4 % to 26.4 %, compared to the beam, which has internal confinement by the inner rebars.

Reliability-based analysis of the flexural strength of concrete beams reinforced with hybrid BFRP and steel rebars

Reliability-based analysis of the flexural strength of concrete beams reinforced with hybrid BFRP and steel rebars

Flexural Strength of Concrete Beam Produced with Scrap Rubber Tyres as Partial Replacement for Coarse Aggregates

The quantities of waste generation in Nigeria have increased significantly; posing greater risk to public health owing to indecent manner of disposal. Some solid wastes had been recycled; however, studies on scrap rubber tyre have not been fully exhausted. This research therefore investigated the flexural behaviour of concrete produced using scrap rubber tyre as partial replacement of coarse aggregate. Scrap Rubber Tyres (SRT) were chopped into smaller sizes; with 19 mm maximum size and used to partially replace coarse aggregate within 0 to 12% at 3% interval. The constituents were batched by weight. 45 concrete beams of grade 20 were cast and cured for 7, 28 and 90 days. Flexural strength behaviour of the specimens was tested; and the 0% SRT concrete serves as control. Data were analysed using Analysis of Variance at 5% Significance level. The slump and compacting factor of the fresh concrete ranged from 29-100 mm and 89-99%, respectively. The flexural strength of the rubberized concrete at 28 days were 21.3, 14.0, 13.2, 12.2, and 13.3 N/mm2. Rubberized concrete at 3% partial replacement can be useful for light weight structural members. The scrap rubber tyres possess significant potentials which could advance its utilization under improve technology.

Structural Performance of Reinforced Cement Concrete Beam with Sawdust

Sawdust materials are important for several reasons. They are cheap, lightweight, and have high insulation properties. Some of this material is incorporated into the concrete as part of the cement binder phase and as gravel. Micro-cracks and defects in concrete are responsible for the low tensile strength of concrete. This study proposes the use of sawdust as a partial replacement for fine aggregate. By volume, the sawdust gradually replaced the sand with a replacement percentage that varied from 0% to 100%. Nine reinforced concrete beams with a cross-section of 90 mm × 150 mm × 1000 mm (width × depth × length) and different replacement percentages were cast and tested after 28 days. All concrete beams are supported, with two simple supports at the ends of the beam and a loading point at the center of the beam to apply load gradually using 100 kN load cells and transverse frames. The addition of sawdust results in a reduction in the flexural strength of concrete beams. The flexural reinforced concrete beam test results were compared to the design strength calculated using British Standards. According to the results of the study, both the compressive and tensile strength of concrete decreased as sawdust content increased. The weight of the sawdust concrete mixture decreased with increased sawdust content. When the replacement percentage of sand was between 5% and 20%, the sawdust concrete mixture showed good results for the structural performance of the reinforced concrete beam.

Flexural Strength of Concrete Beam Reinforced with CFRP Bars: A Review.

Conventional reinforced concrete (RC) structures are commonly associated with the corrosion of steel reinforcement. The application of carbon fiber reinforced polymer (CFRP) bars as flexural reinforcement has become a new promising option. This paper presents a state-of-the art flexural strength on concrete beams reinforced with CFRP bars. Concrete compressive and CFRP bar tensile strain, reinforcement ratio, types of surface treatment on CFRP bar and concrete compressive strength were identified as aspects of behavior. Significant findings in the literature had manifested all aspects of behavior that were affecting the flexural strength, deflections and crack characteristics of CFRP RC beams. In addition, the experimental result on 98 specimens of CFRP RC beams from the literature show that ACI 440.1R-15 and CSA S806-12 standards underestimate the ultimate flexural moment capacity of CFRP RC beams. On the other hand, Kara and Ashour predictions are more accurate with the experimental values. Moreover, hotspot research topics were also highlighted for further considerations in future studies.

Flexural Performance of Small-Scale Textile-Reinforced Concrete Beams

Textile-reinforced concrete (TRC) as a novel high-performance composite material can be used as a strengthening material and component bearing load alone. The flexural performance of TRC beams strengthened with textile reinforcement such as carbon tows was experimentally examined and associated with those of steel-reinforced concrete (SRC) beams. Through four-point bending tests, this research explores the effects of textile layers and dosages of short textile fibre on the flexural strength of concrete beams. A total of 64 prism samples of size 100 mm × 100 mm × 500 mm were made, flexure-strengthened, and tested to evaluate various characteristics and the efficiency of TRC versus SRC beams. TRC beams performed exceptionally well as supporting material in enhancing concrete’s flexural capacity; in addition, TRC’s average ultimate load effectiveness was up to 56% than that of SRC specimens. Furthermore, the maximum deflection was about 37% lesser than SRC beams. The results showed that by increasing the number of layers, the TRC’s effectiveness was significantly increased, and the failure mode became more ductile.

Enhancing the Flexural Strength of Concrete using Recycled Iron and Steel Slag Aggregate

Concrete is strong in compression but weak in tension hence, considerable effort is required to improve concrete’s tensile strength by the use of pre-stressed concrete and addition of admixtures or additives. In this study, the use of recycled iron and steel slag (RISS) aggregate to improve the tensile strength of concrete was considered. The paper assessed the mineralogical composition of RISS and granite aggregates, and gradation. It also determines the effects of RISS aggregate on the flexural strength of concrete beams of 150 × 150 × 600 mm containing 0, 10, 20, 40 and 60% RISS aggregate replacement in mix ratios 1:1½:3, 1:2:4 and 1:3:6 with water cement ratios 0.65,0.60 and 0.55 respectively. Diffractograph of RISS and granite aggregate showed that RISS contains Magnetite, Ilmenite and Quartz, while granite contains Quartz, Annite, Microcline and Albite as the predominant minerals. The coefficient of uniformity and concavity of RISS and granite aggregate for maximum aggregate size of 37.5 mm are 4.35 and 1.33; and 4.64 and 1.76 respectively. Both aggregates contain quartz as the predominant mineral and are well graded. The result of the Flexural strength at 28 days curing is within 0.135 – 0.250 MPa specified byBS8500 – 2:2015. Flexural strength of concrete beams cast with RISS aggregate is relatively higher than concrete cast with granite aggregate. Flexural strength, a measure of tensile strength of concrete is improved as percentage RISS aggregate increased.

Experimental investigation on the flexural and post-cracking behaviour of geogrid-reinforced concrete overlays

Innovative materials are on the rise as alternatives to steel reinforcement in concrete structures. Recently, the use of polymeric geogrids as reinforcement elements has expanded into Portland cement concrete (PCC) overlays rehabilitation. Research conducted to date has indicated that the use of geogrids as reinforcement in concrete pavements shows both post cracking ductility and superior load capacity. Although this topic is not so explored in the literature, the use of geogrids in thin concrete overlays, pathway, pedestrian sidewalks and floating slabs is promising and gives a new employment area for the use of geogrid reinforcements. This paper presents an experimental investigation on the flexural behaviour, post-cracking and fracture energy performance of geogrid-reinforced concrete beams under four-point bending test. Different geogrids were embedded at one-third depth (from bottom) of concrete beam specimens (500 × 150 × 150 mm). The PCC mix was prepared using Ordinary Portland Cement (OPC grade 53) with compressive strength of 40 MPa. Results confirmed that the flexural performance and post-cracking resistance of the concrete beam specimens could be enhanced by the presence of geogrids, as evidenced by load-deflection response, crack mouth opening displacements and change in failure mode. Triaxial geogrids showed 11% increase in flexural strength of concrete beam, highlighting the potential benefits of geogrids reinforcements in PCC overlays.

Analysis of flexural strength of beam elements reinforced with GFRP bars

The durability of reinforced concrete structures is associated with the strength of both concrete and reinforcement against aggressive environmental factors. Once a crack or local damage to the cover occur in the structure, traditional methods of protecting the reinforcement are no longer functional and the sensitive steel reinforcement is exposed to corrosion and deterioration. Therefore, a composite reinforcement made with fibre-reinforced polymer (FRP) can be a suitable alternative to the traditional reinforcing steel due to its mechanical and physical properties - high corrosion resistance, high tensile strength, electrical and electromagnetic neutrality. The FRP reinforcement is made of continuous fibres immersed in a polymeric resin. The function of the fibres is to provide adequate strength and stiffness of the composite. Whereas the resin is responsible for bonding the fibres with an appropriate distance between them, protecting their surface against damage and transferring stresses to them. For the purposes of this paper, an analysis of the flexural strength of concrete elements reinforced with FRP bars with varying reinforcement ratios was conducted. The tests were performed on six beam elements reinforced with glass fibre-reinforced polymer (GFRP) bars. The beams with dimensions of 0.15x0.2x2.5 m were subjected to 4-point bending. This study aimed to assess the influence of the reinforcement ratio on the flexural strength of concrete beams reinforced with composite bars and to verify the failure mechanisms against the guidelines presented in the standard ACI 440.1R-06. The reinforcement ratio has a significant impact on the failure mechanism and the flexural strength of beam elements reinforced with GFRP bars. An increase in the reinforcement ratio results in an improvement in the flexural strength of the specimen and is likely to change the failure mechanism - from rebar rupture to concrete crushing. The guidelines of ACI 440.1R-06 correctly estimate the flexural strength of the beam elements reinforced with GFRP bars.