Composite Rebars Research Articles

Development of sustainable and high-performance polymer composite rebar using vegetable waste biochar and areca fiber as reinforcement materials for green construction

Development of sustainable and high-performance polymer composite rebar using vegetable waste biochar and areca fiber as reinforcement materials for green construction

Research on fatigue life of lightweight concrete bridge decks reinforced with GFRP composite rebars

Betonowe płyty pomostowe wykonane z betonu lekkiego (LWC) i zbrojone prętami kompozytowymi (FRP) stanowią korzystną alternatywę dla konwencjonalnych płyt żelbetowych, w szczególności przy modernizacji istniejących mostów. Jednym z krytycznych stanów granicznych warunkujących możliwość zastosowania płyt LWC/FRP w pomostach mostów drogowych jest nośność zmęczeniowa. Niniejsza praca przedstawia wyniki badań w zakresie nośności zmęczeniowej takich płyt. Badaniom poddano łącznie dziewięć pełnowymiarowych płyt betonowych o wymiarach 3,0 m × 1,0 m × 0,18 m. Głównymi parametrami płyt porównywanymi w badaniach były: rodzaj betonu (lekki vs. zwykły), stopień zbrojenia płyt oraz poziom obciążenia zmęczeniowego. Wyniki badań zmęczeniowych przeanalizowano w oparciu o analizę stanu zarysowania i ugięcia płyt oraz ocenę liczby cykli zmęczeniowych i postaci zniszczenia. Zweryfikowano także procedury projektowe przyjęte w wybranych normach.

Bond properties of GFRP rebars in UHPC under different types of test

Bond properties of Glass Fiber-Reinforced Composite (GFRP) rebars in Ultra-High-Performance Concrete (UHPC) are the key to designing the FRP-reinforced UHPC structures. In this paper, bond properties between sand-coated/deformed GFRP rebars and UHPC within various embedment lengths and covers were estimated using three types of tests, namely the pullout test, modified pullout test and beam test. It was revealed that the dominant failure mode was the pulling-out of GFRP bars, evidenced by interlaminar shearing devastation, showing the shearing of the ribs and a significant reduction of the rebar diameter. Two classes of bond stress-slip relationships were summarized depending on the embedment length. The micro-slip, slip, decline and oscillation parts were captured, with the oscillation characteristic being more related to the ribs of GFRP rebars. Bond strengths of GFRP rebars under the beam test increased by 4.2 %− 10.0 % to the pullout test, and those obtained from the modified pullout test and pullout test remained little difference within 3.3 %. Both increasing the embedment length and lowering the cover could cause a linear decrease in the bond strength. Specifically, regarding beam tests, the bond strength demonstrated reductions of 11.4 % and 29.5 %, respectively, when the embedment length increased from 2.5d to 5d and 5d to 10d. Moreover, the bond strengths under three types of tests were compared with the ones predicted by existing methods, and the design recommendation was presented.

Experimental investigation of the behavior of concrete beams containing recycled materials reinforced with composite rebars

The application of various Fiber Reinforced Polymer (FRP) composite materials is very widespread in the world. The use of recycled materials in concrete, can improve some of the mechanical properties of concrete. In this laboratory research, the behavior of reinforced concrete beams with composite rebars with glass fibers made of concrete containing recycled materials such as glass, rubber and micro-silica with different mixing plans has been investigated. These mixing plans are such that recycled glass and rubber aggregates have replaced a percentage of fine and coarse concrete aggregates, and glass powder and micro-silica have also replaced a percentage of concrete cement. The results showed that the replacement of coarse rubber, glass powder, and micro-silica in concrete materials increases the bending strength and ductility of concrete beam. In examining the microstructure of concrete by Scanning Electron Microscope (SEM) the adhesiveness of the rubber Interfacial Transition Zone (ITZ) in concrete was suitable.

Review on Flexural Behavior of Slabs Reinforced with FRP Bars Subjected to Static and Cyclic Loads

One of the main issues that reduces the lifetime serviceability of concrete buildings is the corrosion of steel reinforcing. The degradation of concrete buildings caused by the corrosion of steel reinforcing can be prevented, delayed, or repaired using a variety of currently available techniques. Fiber reinforced polymer bars are an effective and affordable solution to the corrosion issues that steel rebars in severe settings are prone to. Steel alternatives that are robust and extremely corrosion resistant include fiber reinforced polymers. The fiber reinforced polymer bars have a high strength, a low center of gravity, are simple to handle, and require little maintenance. Glass fiber reinforced polymer bars are among the most widely used composite rebars, mostly because of their reasonable price and high performance. The Glass Fiber Reinforced Plastic's mechanical characteristics Steel bars were inferior to polymer bars in a number of respects. This study examines how glass fiber reinforced polymer slabs behave under flexure under static and cyclic loads. Keywords: GFRP bars, Steel.

Investigation of flexural behaviour of composite rebars for concrete reinforcement with experimental, numerical and machine learning approaches.

Three different types (with glass, basalt and hybrid fibres) of composite rebars manufactured using the pultrusion process were loaded in four-point bending tests. All tests were carried out with acoustic emission sensors to better understand the mechanisms of damage. The data obtained were investigated using standard parameter analysis and also using unsupervised machine learning techniques called K-means. It was found that the best number of clusters is four or five. The numerical model using the finite-element method was calibrated on the basis of the experimental data. Further research will focus on numerical modelling of flexural behaviour of concrete beams reinforced with the presented composite rebars. The presented paper focuses on the characterization of the mechanical properties of composite rebars using a micromechanical approach, as well as analysis of progression damage processes appearing under flexural loading, using different perspectives provided by techniques such as acoustic emission analysis with machine learning-based clustering and numerical simulations. The presented research confirms that the proposed experimental-numerical approach can be applied in order to describe the flexural behaviour of Fibre Reinforcement Polymer (FRP) rods, which is relevant for investigating more complex cases of FRP concrete structures. This article is part of the theme issue 'Physics-informed machine learning and its structural integrity applications (Part 1)'.

Optimization of reinforcement characteristics on eco-friendly polymer composite rebar building material developed using domestically discarded vegetable waste biochar and areca chopped fiber

Optimization of reinforcement characteristics on eco-friendly polymer composite rebar building material developed using domestically discarded vegetable waste biochar and areca chopped fiber

The effect of the bent of FRP rebar on its short-term mechanical properties

In the construction industry, FRP (fibre-reinfoced-polymer) reinforcement is used mainly because of its high resistance to aggressive environments. The production and design of straight FRP rebars are now very well understood and described. However, when designing concrete elements, it is usually necessary to adapt the reinforcement to the structure shape and to use bent rebars. However, during the production process, unfavourable changes in the fibre distribution across the cross-section may occur at the bent section. It has a significant effect on the short and long-term properties of the rebar. The paper addresses the highly topical issue of the composition, manufacturing and testing of shaped composite rebar. Consequently, the article presents experimentally determined values of mechanical characteristics obtained from the performed tests.

Prediction of the FRP reinforced concrete beam shear capacity by using ELM-CRFOA

In reinforced concrete structures, the utilization of composite rebar has been increased by considering their high corrosion resistance, anti-magnetic properties, and significant tensile strength. According to the lower elasticity modulus of composite rebar in comparison with steel rebar, concrete beams reinforced including composite rebar possess a relatively lower shear strength by comparing with steel rebar. In addition, in concrete beam, reinforced shear failure by composite rebar is commonly brittle and requires precise performance prediction of the members. Thus, the reinforced concrete beams' shear strength by composite rebar is predicted utilizing an Extreme Learning Machine network based on Chaos Red Fox Optimization Algorithm (ELM-CRFOA) according to a wide range of data. The most important parameters, which are considered in this investigation, are the web width, beam effective depth, the strength of concrete compressive, the ratio of the shear span to depth, FRP longitudinal bars elasticity modulus, and ratio of the longitudinal reinforcement. This method's precision has been proved by having a comparison among the model predictions and the accumulated data and available shear design equations. According to the study outcomes, the presented model has precise outcomes in computing the concrete beams' shear strength in comparison with other existing relations. For assessing input parameters' impact on the FRP-reinforced concrete beams' shear strength, a sensitivity analysis is executed.

Acoustic Testing of Composite Rebars Taking into Account Reinforcement Ratio

Acoustic Testing of Composite Rebars Taking into Account Reinforcement Ratio

Manufacturing of prestressed glass fiber reinforced polymer rebars and effect of fiber pretension on durability of rebars after conditioning in alkaline solution

Applying specific amount of fiber pretension during the manufacturing process of the composite rebars would potentially enhance their performance and durability. In this study, five sets of lab-scale prestressed glass fiber/vinyl-ester composite rebars were fabricated. Each set was manufactured using unique amount of fiber pretension. A set of unprestressed composite rebar was prepared as well. The effect of fiber pretension on the microstructure, tensile properties and long-term durability of rebars was investigated. In addition, the performance of the prestressed composite rebars was compared to composite rebars currently available in the market. An improvement in fiber alignment and a reduction in void content were observed within the pretensioned rebars. The composite rebars fabricated with pretension of 30 MPa showed the maximum increase in tensile properties. The guaranteed tensile strength and average tensile modulus were improved by 7.5% and 2.6%, respectively, compared to the unprestressed counterpart. The prestressed rebars showed relatively less surface degradation and lower moisture absorption after conditioning in alkaline solution at 60°C for 90 days. After conditioning, the tensile properties of the prestressed composite rebars showed superiority over the unprestressed rebar. Comparing to composite rebars available in the market, the prestressed composite rebars prepared in this study showed high performance in both short-term and long-term use.

Experimental and Numerical Comparison of the Concrete Slabs Reinforced with Composite Rebars

The evaluation of non-metallic reinforcing in slender concrete slabs is discussed in this article. The experimental campaign investigated the flexural behavior and the bending capacity of concrete slabs reinforced with Glass fiber reinforced polymer bars. A total of 6 slabs with a length of 1.36 m and cross-sectional dimensions of 0.50 x 0.04 m were tested until failure. The effective depth and reinforcement ratio are the same for all slabs. With an effective span of 1.3 m, the slabs were simply supported and tested in a four-point bending experimental setup. ATENA 3D, a finite element nonlinear solver, was used to simulate the experimental approach. The meshing was done using brick elements, and the calculation was performed with the Newton-Raphson method. The article compares the experimental program and nonlinear analysis performed in ATENA 3D program. The theoretical analysis outcomes are also introduced by calculating the deflection of the slab in the midspan. The correlation and a good agreement between numerical results and experimental outcomes are presented in the paper.

Experimental studies of the stress-strain state of reinforced concrete structures strengthened by prestressed basalt-composite rebar

Relevance. In recent years, composite materials have become widespread in the construction of reinforced concrete structures for industrial, civil and transport structures. It is proposed to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite rebar. It took an experimental and theoretical substantiation of technical solutions to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite reinforcement. The aim of the work was to carry out a set of experimental and theoretical studies of the stress-strain state and internal forces in low-reinforced concrete structures of hydraulic structures reinforced with prestressed basalt composite rebar. Methods. Experimental studies of the stress-strain state and internal forces were carried out on the basis of low-reinforced concrete beam-type models with interblock construction joints, harden with prestressed basalt composite reinforcement in the stretched (compressed) zones of the models. Theoretical studies of the stress-strain state and internal forces were carried out on the basis of the theory of reinforced concrete and structural mechanics. Results. As a result of the research carried out on typical low-reinforced concrete structures of hydraulic structures with interblock construction joints, the main stages of the stress-strain state of hydraulic reinforced concrete structures were formulated. Based on the data of experimental and theoretical studies, taking into account the reinforcement with prestressed basalt composite rebar, as well as with prestressed clamps in the shear zone, a method was developed for calculating the strength of low-reinforced hydrotechnical reinforced concrete structures with interblock construction joints.

Load-Bearing Capacity of Beams Reinforced with Composite Rebar in Regard to Existing Guidelines.

Non-metallic reinforcement such as fiber-reinforced polymer (FRP) is now being increasingly used in construction. Despite numerous similarities, elements reinforced with non-metallic bars work differently from the ones reinforced with steel bars, including cracking and failure mode. The examination of the stress state in these elements, so important for their proper design, raises many difficulties. The article presents the results of tests of bended beams reinforced with GFRP bars. The results of the experimental tests were compared with calculations based on selected design instructions. The results have shown that beams reinforced with GFRP exhibit increased cracking, higher deflection, and often mode of failure through crushing of concrete. The results have shown that in bended elements reinforced with the GFRP bars, the rebar often does not achieve the strength declared by the manufacturer. The study has shown that theoretical values of load-bearing capacity of beams reinforced with composite rebar differ greatly between different guidelines and instruction. The analysis showed that the use of GFRP bars as a replacement for steel bars is possible in demanding environmental conditions. However, excessive deflections and cracks may result in limited application due to overall serviceability requirements of the element.

Flexural Pseudo-Ductility Effect in Hybrid GFRP/CFRP Bars under Static Loading Conditions.

The problem with composite rebars in the civil engineering industry is often described as the material’s brittleness while overloaded. To overcome this drawback, researchers pay attention to the pseudo-ductility effect. The paper presents four-point bending tests of pure unidirectional (UD) rods with additional composite layers obtained by filament winding and hand braiding techniques. Two types of core materials, glass FRP (fibre reinforced polymer) and carbon FRP, were used. Regarding the overwrapping material, the filament winding technique utilized carbon and glass roving reinforcement in the epoxy matrix, while in the case of hand braiding, the carbon fibre sleeve was applied with the epoxy matrix. Microstructural analysis using scanning electron microscopy (SEM) and computed tomography (CT) was performed to reveal the structural differences between the two proposed methods. Mechanical test results showed good material behaviour exhibiting the pseudo-ductility effect after the point of maximum force. The two applied overwrapping techniques had different influences on the pseudo-ductility effect. Microstructural investigation revealed differences between the groups of specimens that partially explain their different characters during mechanical testing.

Shear Capacity Prediction of FRP Reinforced Concrete Beams Using Hybrid GMDH–GA

In recent years, the use of composite rebars in reinforced concrete structures has received much attention due to its high corrosion resistance, significant tensile strength, and appropriate non-magnetization characteristics. Due to the lower modulus of elasticity of composite rebars than steel rebars, concrete beams reinforced with composite rebars have relatively lower shear strength compared to beams reinforced with steel rebars. On the other hand, shear failure in concrete beams reinforced with composite rebars is generally brittle and requires accurate prediction of the behavior of these members. Therefore, in this study, the shear strength of concrete beams reinforced with composite rebars is predicted using a combination of GMDH type neural networks and genetic algorithms based on a wide range of experimental results. The key effective parameters that consider in this study are the width of the web, effective depth of the beam, shear span to depth ratio, concrete compressive strength, modulus of elasticity of FRP longitudinal bars, and longitudinal reinforcement ratio. The accuracy of the proposed method has been verified by comparing the model predictions with the collected experimental results and existing shear design equations. The results show that the proposed model has more accurate results in calculating the shear strength of concrete beams than other existing relationships. A sensitivity analysis is also performed to assess the effect of the input parameters on the shear strength of FRP-reinforced concrete beams.

Multifunctional Triboelectric Nanogenerator-enabled Structural Elements for Next Generation Civil Infrastructure Monitoring Systems.

There is a critical shortage in research needed to explore a new class of multifunctional structural components that respond to their environment, empower themselves and self-monitor their condition. Here, we propose the novel concept of triboelectric nanogenerator-enabled structural elements (TENG-SEs) to build the foundation for the next generation civil infrastructure systems with intrinsic sensing and energy harvesting functionalities. In order to validate the proposed concept, we develop proof-of-concept multifunctional composite rebars with built-in triboelectric nanogenerator mechanisms. The developed prototypes function as structural reinforcements, nanogenerators and distributed sensing mediums under external mechanical vibrations. Experiential and theoretical studies are performed to verify the electrical and mechanical performance of the developed self-powering and self-sensing composite structural components. We demonstrate the capability of the embedded structural elements to detect damage patterns in concrete beams at multiscale. Finally, we discuss how this new class of TENG-SEs could revolutionize the large-scale distributed monitoring practices in civil infrastructure and construction fields.

Experimental Investigation of Long Term Seawater Durability and Shear Properties of Pultruded GFRP Composite

The effect of long term immersion in seawater at different temperatures on the properties of pultruded glass fibre reinforced polymer (GFRP) composite rebar was investigated. Samples were conditioned in seawater and in dry at 23, 55 and 75 °C for 0, 8, 20, 30 and 36 months to analyse the changes in shear properties such as transverse shear strength (TSS) and short beam shear strength (SBSS). Both TSS and SBSS increased after conditioning in dry at 55 and 75 °C; on the other hand, TSS decreased gradually due to conditioning in seawater at 23, 55 and 75 °C, whereas SBSS decreased due to conditioning in seawater only at 75 °C. Microscopic analysis specified that the shear strength decreased due to fibre/matrix interfacial failure as a result of de-bonding and fibre pull-out. Compared to the short beam shear test, the transverse shear test was found to be a sensitive technique to measure the durability of pultruded GFRP rebar. FT-IR analysis indicated superficial hydrolysis reaction of polymer matrix occurred when the sample was conditioned at 75 °C. A reversible change in glass transition temperature (Tg) and in viscoelastic property of the polymer matrix was observed due to conditioning in seawater at 23 and 55 °C.

Static and Flexural Fatigue Behavior of GFRP Pultruded Rebars.

This paper presents the experimental results of composite rebars based on GFRP manufactured by a pultrusion system. The bending and radial compression strength of rods was determined. The elastic modulus of GFRP rebars is significantly lower than for steel rebars, while the static flexural properties are higher. The microstructure of the selected rebars was studied and discussed in light of the obtained results—failure processes such as the delamination and fibers fracture can be observed. The bending fatigue test was performed under a constant load amplitude sinusoidal waveform. All rebars were subjected to fatigue tests under the R = 0.1 condition. As a result, the S-N curve was obtained, and basic fatigue characteristics were determined. The fatigue mechanism of bar failure under bending was further analyzed using SEM microscopy. It is worth noting that the failure and fracture mechanism plays a crucial role as a material quality indicator in the manufacturing process. The main mechanism of failure under static and cyclic loading during the bending test is widely discussed in this paper. The results obtained from fatigue tests encourage further analysis. The diametral compression test reflects the weakest nature of the composite materials based on the interlaminar compressive strength. The proposed methodology allows us to invariantly describe the experimental transversal strength of the composite materials. Considering the expected durability of the structure, the failure mechanism is likely to significantly improve their fatigue behavior under the influence of cyclic bending. The reasonable direction of searching for reinforcements of composite structures should be the improvement of the bearing capacity of the outer layers. In comparison with steel rebars (fatigue tensile test), the obtained results for GFRP are comparable in the HCF regime. It is worth noting that in the near fatigue endurance regime (2–5 × 106 cycles) both rebars exhibit similar behavior.

Plasticized epoxy composites for manufacturing of composite reinforcement

Composite rebar is a promising building material due to its advantages over steel rebar. Polymer reinforcement consists of a hardened matrix reinforced with a continuous fiber. The main role of the matrix is to determine the performance properties of the composite and to distribute stresses in the reinforcing filler. Optimization of the polymer matrix composition in terms of strength and technical parameters makes it possible to obtain a composite with high performance properties. The aim of the research was to determine the effect of modifying additives on the properties of the matrix for the production of composites with high technical requirements. When performing research, we considered modifiers that interact differently with the components of the polymer matrix as plasticizers. The first type of additive is able to combine with reactive groups of epoxy resin to form a three-dimensional product. Urea resin was used as such a compound. The second group of samples contained a furfurolacetone monomer-a substance that does not contain reactive groups with the resin, but interacts with the hardener of the epoxy resin. And the third type of modifier is dioctyl phthalate, whose role is to change the intermolecular and intramolecular interaction of the spatial structure that it fills. Optimization of compositions to identify areas with high physical and mechanical values was carried out using mathematical methods of experiment planning. Based on the results of the research, it can be concluded that with the optimal content of plasticizers, in all cases, there is an increase in the compressive and tensile strength indicators compared to materials without additives. Further increase in the content of modifying additives (above the optimal amount) leads to a decrease in strength.