Composite Rebars Research Articles

Strength and deformability of concrete beams reinforced by non-metallic fiber and composite rebar

Production of durable and high-strength concrete structures with unique properties has always been crucial. Therefore special attention has been paid to non-metallic composite and fiber reinforcement. This article describes the experimental research of strength and deformability of concrete beams with dispersed and core fiber-based reinforcement. As composite reinforcement fiberglass reinforced plastic rods with diameters 6 mm and 10 mm are used. Carbon and basalt fibers are used as dispersed reinforcement. The developed experimental program includes designing and production of flexural structures with different parameters of dispersed fiber and composite rebar reinforcement. The preliminary testing of mechanical properties of these materials has shown their effectiveness. Structures underwent bending testing on a special bench by applying flexural static load up to complete destruction. During the tests vertical displacements were recorded, as well as value of actual load, slippage of rebars in concrete, crack formation. As a result of research were obtained structural failure and crack formation graphs, value of fracture load and maximum displacements of the beams at midspan. Analysis of experimental data showed the effectiveness of using dispersed reinforcement of concrete and the need for prestressing of fiberglass composite rebar.

Utilization of finite element analysis for rapid curing of fiber-reinforced polymers in a novel two-phase curing technique for braided rebars

This study focused on determining the capability of a proposed two-step curing process for composite rebars production. A finite element analysis is carried out on rapid curing of fiber-reinforced polymer rebars during a continuous braid trusion manufacturing process. This process combines pultrusion and braiding techniques to produce fiber-reinforced polymer rebars. The system uses a novel two-step curing technique to obtain a uniform cure profile. This is achieved by embedding small diameter steel wires within the core of the rebar. In the first step, as the rebar passes through an induction coil, a curing radially in the outward direction is initiated due to the induction coil. In the second step, the induction-initiated curing rebar enters a series of ovens, initiating radially inward curing. The resulting fiber-reinforced polymer rebars can be used as alternative to steel reinforcement in applications where steel cannot be utilized due to its corrosive or metallic nature. The result of this study showcased the importance of induction unit in obtaining a uniform cure profile.

RESEARCH OF EFFICIENCY OF USING CARBON FIBER IN ARNORED CONCRETE SPANS OF RAILWAY BRIDGES

Purpose. This work presents using carbon fiber as composite rebar by way of rods of fittings for reinforcement armored concrete span 13,5 meter length compared to same-length span with usual fixture. Methodology. The calculation is carried out as described in the methodological guidelines for the design and calculation of concrete span with frame-welded fittings. Findings. On the basis of the above study was to determine how the use of composite reinforcement as working for the reinforcement of its span. Originality. The possibility of using composite rebar as an element that works in tension in the span was proved. Practical value. Install valves of this type will reduce the cost of the span and increase its operating period.

Experimental Study on Flexural Bearing Capacity of Concrete Beams Strengthened with NSM CFRP-PCPs Composite Bars

The flexural behavior of concrete beams strengthened with near surface mounted (NSM) CFRP-PCPs composite rebars was studied. Experimental results showed that embedded CFRP-PCPs reinforcement method can effectively improve strength, stiffness and cracks of the reinforced concrete member, and PCPs increased with concrete bonding area, thus avoiding the strip damage of the traditional embedded reinforcement.

Long term durability of pultruded polymer composite rebar in concrete environment

Pultruded glass fibre reinforced polymer (GFRP) composite rebar was immersed in alkaline concrete environment for 0, 1, 2, 3, 4, 6, 14 and 24 months at 60 °C to evaluate its durability in concrete structure. Moisture absorption of the rebar was found to be only 0.76%. It was also found that both the glass transition temperature (Tg) and the short beam shear strength were retained by about 91.5%; and the above properties were remained almost unchanged during the ageing period from 1 month to 24 months. Design tensile strength and tensile elastic modulus of the rebar were retained by 100% after 24 months exposure in concrete environment. Degradation of GFRP rebar was not evident in the FT-IR results as supported by scanning electron micrographs and energy dispersive X-ray analysis. Moisture absorption was found to be a critical factor that controlled thermal and mechanical properties of GFRP rebar.

Evaluation of Kinetic and Viscosity Based Parameters for Fiber Reinforced Composite Rebars at Elevated Temperatures: A Parametric Study

Fiber reinforced polymer (FRP) composites are high performing materials and offer a wide range of applications. This has led to an increased use of FRP rebars in new construction with concrete as an alternative to steel in buildings. In building applications, FRP rebars need to conform to fire endurance ratings. Unfortunately, there has been very limited effort for understanding the fire endurance of FRP rebars in concrete structures. This limited effort is only available for glass conversion (kinetic parameter) in the glassy state. There is none available for decomposed state (kinetic parameter) and viscosity based parameters influencing the fire endurance of FRP rebars. Moreover, understanding the fire endurance of FRP composite rebars through the standard fire tests is expensive and time consuming. Therefore, this research makes an attempt to develop models that incorporate various transition states of FRP rebars at elevated temperatures to study kinetic and viscosity based parameters. The kinetic parameter in the glassy state is compared with a limitedly available approach in literature. In addition, a parametric study involving decomposed state, and viscosity based parameters in rubbery and leathery states is also carried out to provide some understanding of rebars endurance in fire. A basic understanding is obtained. In order to highlight basic implications on design approaches, a design model is also developed that incorporates the useful transition states in predicting the creep behavior of FRP reinforced concrete structures. This model can serve as a first step in the future design approaches for the construction industry in an economical way.

Experimental Research on Bending Performance of Concrete Beams Reinforced with CFRP-PCPs Composite Rebars

The flexural behavior of concrete beams reinforced with CFRP-PCPs composite rebars was studied. Experimental results showed that the deflection of beams reinforced with highly prestressed prisms is at service loads coMParable to deflection of steel reinforced beam. Flexural cracks of CFRP-PCPs composite rebars reinforced beams are hairline before prism cracking, and widened after the prism cracking. When the concrete beam was reinforced with the prestressed concrete prisms, the crack width decreased as the prestress in the prism increased.

Experimental Investigation on Flexural Bearing Capacity of Concrete Beams Reinforced with CFRP-PCPs Composite Rebars

The flexural behavior of concrete beams reinforced with CFRP-PCPs composite rebars was studied. Experimental results showed that the performance of CFRP-PCPs composite rebars beams is superior to that of CFRP beams at service and ultimate and comparable and even better than RC beams at service condition. Flexural cracks of concrete beams reinforced with CFRP-PCPs composite rebars are hairline before prism cracking, and they widen after the prism cracking Keywords: CFRP-PCPs, composite rebars, beam, flexural

Nonlinear Finite Element Analysis for the Flexural Behavior of Concrete Beams Reinforced with CFRP-PCPs Composite Rebars

The nonlinear finite element analysis for the flexural behavior of the concrete beams reinforced with CFRP-PCPs Composite Rebars,which was a new structural form, has been studied in ANSYS. The effects of material nonlinearities of concrete £¬steel rebar £¬CFRP rebar were considered in the analytic model. Load-displacement curves were received through calculation in this paper. Compared the present result with the experimental results has proved that the model provided is correct and convenient for the analysis of the beams.

Experimental Research on the Cracking Behavior of GFRP/Steel Wire Composite Rebar Reinforced Concrete Beam Based on Cracking Mechanics

The different mechanical property determines the difference on cracking behavior between GFRP/steel wire composite rebar reinforced concrete beams and steel rebar reinforced concrete beams according to cracking mechanics. In order to study the cracking behavior of concrete beams reinforced with GFRP/ steel wire composite rebar, five simply-supported beams were tested under three-point static load. The test variables were beam section size and concrete cover depth. Based on analysis on the test results, the calculation methods of cracking capacity and maximum crack width were proposed, and the limit value of crack width was suggested.

Quasi-static and dynamic mechanical elastic moduli of alkaline aged pultruded fibre reinforced polymer composite rebar

Due to the increased use of glass fibre reinforced polymer composite (GFRP) rebar in concrete structures, the durability performance of GFRP rebar has been an important research topic in recent years. This paper presents elastic modulus of alkaline environment (pH≈13) aged pultruded GFRP rebar as evaluated by three different methods, namely, quasi-static tensile, quasi-static flexural and dynamic mechanical thermal tests. It was found that elastic modulus of the GFRP rebar samples did not change significantly due to exposure in alkaline environment at 60°C for 1, 2, 3, 4, 6 and 14months when compared with that of control sample. Elastic modulus was found to be in the range of 52.5–56.5GPa irrespective to testing methods and ageing time. In addition, it was estimated from the long time projected results that quasi-static tensile, quasi-static flexural and dynamic mechanical moduli will be retained by about 93%, 95% and 85%, respectively, after 100years in alkaline environment at 60°C. Microscopic analysis indicated that quasi-static tensile and flexural failure was mainly due to matrix cracking and shear failure of fibre/matrix interface.

Experimental Investigation on Tensile Mechanical Properties of CFRP-PCPs Composite Rebars

The behavior of CFRP-PCPs composite rebars on tensile test was studied. Experimental results showed that using CFRP-PCP composite rebars as reinforcement utilizes high strength of FRP effectively, reducing the reinforcement ratio and consequently the cost while simultaneously satisfying structural requirements. Tension stiffening in CFRP-PCPs composite rebars is significant when higher concrete strength and higher prestressing level are applied.

Experimental Study on Mechanics Properties of CFRP-PCPs Composite Rebars under Uniaxial Load

The mechanics properties of CFRP-PCPs composite rebars under uniaxial load was studied by experiment. The results showed that the application of a reasonable amount of prestress to the prisms can limit service load deflections and crack width to acceptable levels, using CFRP-PCP composite rebars as reinforcement utilizes high strength of FRP effectively, reducing the reinforcement ratio and consequently the cost while simultaneously satisfying structural requirements.

Tensile fracture mechanism of claviform hybrid composite rebar

Based on the shear-lag theory, a hexagonal model of fiber bundles was established to study the tensile fracture mechanism of a claviform hybrid composite rebar. Firstly, the stress redistributions are investigated on two conditions: one condition is that interfacial damage is taken into account and the other is not. Then, a micro-statistical analysis of the multiple tensile failures of the rebar was performed by using the random critical-core theory. The results indicate that the predictions of the tensile failure strains of the rebar, in which the interfacial damage is taken into account, are in better agreement with the existing experimental results than those when only elastic case is considered. Through the comparison between the theoretical and experimental results, the shear-lag theory and the model are verified feasibly in studying the claviform hybrid composite rebar.

Near-Surface-Mounted Composite System for Repair and Strengthening of Reinforced Concrete Columns Subjected to Axial Load and Biaxial Bending

This paper aims to examine the effectiveness of near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) composite rebars in combination with external confinement with carbon fiber-reinforced polymer (CFRP) composite sheets to repair and strengthen reinforced concrete (RC) columns exposed to axial load and biaxial bending. Nine columns with a square cross section of 150×150 mm were constructed and tested under biaxial eccentric loading with equal eccentricity along each principal axis. Test parameters included load eccentricity, concrete grade, and level of the CFRP confinement used in combination with the NSM-GFRP reinforcement. The effectiveness of the NSM-GFRP reinforcement was greatly affected by the CFRP-confinement level and the load eccentricity. For columns with a high level of CFRP confinement, the gain in the load capacity attributable to the NSM-GFRP reinforcement was higher at a lower eccentricity. For columns with a low level of CFRP confinement, the gain in the load capacity attributable to the NSM-GFRP reinforcement was higher at a higher eccentricity. The enhancement in the load capacity was more pronounced in the columns with a lower concrete grade. An analytical model for predicting the load capacity of RC columns strengthened with NSM-GFRP rebars in combination with CFRP confinement under axial load and biaxial bending is introduced. The model accounts for the nonlinear behavior of materials and the change in geometry under biaxial eccentric loading. The model accuracy is demonstrated by comparing the model predictions with the experimental results.

Behaviour of Concrete Beams Reinforced with Hybrid FRP Composite Rebar

Extensive research has led to a better understanding of the application of various corrosion protection methods in reinforced concrete (RC) structures and the use of fiber reinforced polymer (FRP) rebars is a typical example. However different fibres come along with different deficiencies, such as low elastic moduli and poor alkaline resistance in glass fibre (Saikia et al. 2007); brittle fracture and high cost in carbon fibre. Taking advantages of the strength of different fibres and the cost effectiveness of steel fibre, a hybrid composite rebar was recently developed. Steel fibers and glass fibers are distributed within the core, while aramid and carbon fibers created a shell for strength and corrosion protection. A series of concrete beams reinforced with the proposed hybrid rebars were tested and it was demonstrated that the beams have the ability to undergo large inelastic deformations, and the ductility indexes were found to be similar conventional steel-reinforced beams. Besides, accelerated alkaline ageing tests were performed using concrete pore solutions at different temperatures, and the service life and alkaline resistance of the proposed rebar were proven to be very good.

Design recommendations for bond between GFRP/steel wire composite rebars and concrete

Due to significant advantages over GFRP rebars, namely high tensile strength, high elastic modulus, and good ductile properties, GFRP/steel wire composite rebars offer a superior alternative to ordinary steel rebars. However, experimental researches on this new type of rebar have been limited, especially those on the bond performance. This research is designed to investigate the bond behavior between GFRP/steel wire composite rebars and concrete. According to American Concrete Institute (ACI) code, a total of 180 pull-out specimens were tested under monotonic static loading conditions. The test parameters were the rebar rib spacing, rebar diameter, embedded length, concrete compressive strength, concrete cover thickness, and concrete cast depth. Based on the numerical analysis of the test results, new criteria for acceptable bond performance of GFRP/steel wire composite rebars to concrete were developed. Designed recommendations for the modification factor of concrete cover thickness, the modification factor of concrete cast depth, and the critical value of bond slip at both free and loaded ends were derived. The calculation formula of bond strength and the basic development length were proposed, and the calculation principle of development length of concrete structures reinforced with GFRP/steel wire composite rebars was suggested.

The effect of exposure to alkaline solution and water on the strength–porosity relationship of GFRP rebar

This study examined the accelerated degradation of E-glass fiber/vinylester resin composite rebar in alkaline solution and water and analyzed the relationship between the reduction in mechanical performance and the test conditions using microstructural degradation analysis. In this study, a pH of 12.6 was chosen for the alkaline test group, while water was used for the control group. After immersion for up to 300 days, the tensile strength of the glass fiber-reinforced plastic (GFRP) rebar was tested. In addition, the deformation of the GFRP rebar surface was evaluated under scanning electron microscopy (SEM) and the change in the internal pore distribution was measured using mercury intrusion porosimetry (MIP). The mechanical performance decreased as the exposure time and temperature increased. The SEM analysis showed that the internal pore distribution in the GFRP rebar increased as degradation progressed, reducing the mechanical performance. Moreover, the pore distribution increased with temperature, also reducing the mechanical performance.

Moisture Effects on Elastic and Viscoelastic Properties of CFRP Rebars and Vinylester Binder

The objective of the research was the evaluation of moisture effect on deformability of vinylester binder carbon-fiber- reinforced plastic (CFRP) rebars. Moisture sorption was investigated at different humid conditions. Maximal moisture content of the binder was about 1.86% by weight and for rebars 0.5%. For the CFRP rebars it was estimated that the degree of anisotropy of diffusion coefficient tensor is approximately 40. The elastic moduli of the materials were determined in stress–strain tests and compared with dynamic elastic and shear moduli. The moduli dropped about 10% for maximally moistened materials. The long-term deformability of the composite rebars and binder were examined in tensile creep tests. The principle of moisture–time equivalence was used for creep description of moistened specimen. Creep strain for the wet resin is approximately 5 times larger then for the dry one. Creep forecast was made for a period about 40 years .

Free vibration of composite re-bars in reinforced structures

The effect of composite rebar's shape in reinforced concrete beam-type structures on the natural frequencies and modes shapes is investigated through finite element analysis in this paper. Steel rebars are being replaced with composite rebars due to their better ability to resist corrosion in reinforced concrete structures for many infrastructure applications. A variety of composite rebar shapes can be obtained through the pultrusion process. It will be interesting to investigate their shape on free vibration characteristics. The results of natural frequencies and mode shapes are presented and compared for the different composite rebar shapes. The effects of various boundary conditions for different rebar shapes are also investigated.