Comparison between ASTM D7205 and CSA S806 tensile-testing methods for glass-fiber-reinforced-polymer bars

The American Society of the International Association for Testing and Materials (ASTM) D7205 / D7205M-06 and the Canadian Standards Association (CSA) S806 contain the commonly used test methods for characterizing the tensile properties of glass-fiber-reinforced-polymer (GFRP) bars for use as reinforcement in concrete structures. These two standards, however, use different anchor dimensions and loading rates, thereby possibly yielding different properties for the same type of FRP bars. This paper assessed the results of a four-laboratory testing program comparing the sample preparation methods and test results according to ASTM D7205 and CSA S806. Each laboratory tested at least 10 samples prepared according to the recommendations in Annex A of the ASTM standard, and Annex B of CSA S806. Each type of sample was prepared by a single laboratory in order to minimize variation among the test specimens. The results show a statistically significant difference between the tensile strength measured using the CSA and ASTM provisions. Regardless of specimen preparation, the modulus of elasticity of the GFRP bars was the same with both test standards, but the ASTM standard returned a wider variation than the CSA

Evaluation of physical and durability characteristics of new headed glass fiber–reinforced polymer bars for concrete structures

This paper presents the results of a collaborative research project with Quebec’s Ministry of Transportation and the Ontario’s Ministry of Transportation, which aimed at characterizing a new type of headed glass-fiber-reinforced-polymer (GFRP) reinforcing bar and evaluating its suitability as internal reinforcement for concrete structures. To achieve these objectives, the project was implemented in three stages: (1) evaluation of the physical and mechanical properties; (2) determination of the pullout behavior in concrete; and (3) characterization of the long-term durability of the headed GFRP bars. A total of 57 specimens embedded in a 200 mm concrete cube were tested with the direct pullout test to investigate the effect of confinement, bar size, concrete compressive strength, and exposure conditions on the pullout behavior of the headed GFRP bars. Simultaneously, microstructural analyses and measurements of the physicochemical and mechanical properties were carried out on conditioned and unconditioned headed GFRP bars. The results show that the materials, geometry, and interface configuration of the head provided very good mechanical interlocking to the GFRP bars. Up to 63% and 53% of the guaranteed tensile strength of the straight GFRP bars were achieved for 15.9 mm and 19 mm diameter bars with headed ends, respectively. Scanning electron microscopy and differential scanning calorimetry showed no material changes in the head and bars after exposure to alkaline solution and freeze–thaw cycling. Exposure to the alkaline solution under sustained loading had the most detrimental effect, with the bar retaining 79.4% of its pullout strength. The results indicate that the tested headed GFRP bar has suitable mechanical and durability properties for use as reinforcement in concrete bridge components

Flexural response of GFRP-reinforced geopolymer concrete beams

This study investigated the flexural response of glass fibre reinforced polymer-reinforced geopolymer concrete (GFRP-RGC) beams using a four-point static bending test. Three full-scale beams were cast and reinforced with nearly same amount of longitudinal GFRP reinforcements but of varying diameters at the bottom (4-12.7 mm, 3-15.9 mm, and 2-19.0 mm), two 12.7 mm GFRP bars at the top, and 9.5 mm GFRP stirrups spaced at 100 mm on-centre. The average compressive strength of the geopolymer concrete was 38.2 MPa. Based on the experimental results, all the tested beams showed nearly similar crack pattern, load-deflection response, bending-moment and deflection capacities, and strain readings, suggesting that the flexural response of a GFRP-RGC beam was not significantly influenced by the bar diameter; instead, by the properties of the geopolymer concrete. The 0.3Mu criterion suggested by Bischoff must be adapted in the serviceability design of a GFRP-RGC beam. The flexural capacities of the tested beams were generally higher than the predicted values from ACI 440.1R-06 and CSA S806-12 standards. Furthermore, the GFRP-RGC beams have higher strength compared with their GFRP-reinforced concrete counterparts. Thus, it can be concluded that the GFRP-RGC beams have structural properties that are suitable for civil infrastructure applications

Effect of spiral spacing and concrete strength on behavior of GFRP-reinforced hollow concrete columns

Hollow concrete columns (HCCs) are one of the preferred construction systems for bridge piers, piles, and poles because they require less material and have a high strength-to-weight ratio. While spiral spacing and concrete compressive strength are two critical design parameters that control HCC behavior, the deterioration of steel reinforcement is becoming an issue for HCCs. This study explored the use of glass fiber-reinforced polymer (GFRP) bars as longitudinal and lateral reinforcement for hollow concrete columns and investigated the effect of various spiral spacing and different concrete compressive strengths (f′c). Seven HCCs with inner and outer diameters of 90 and 250 mm, respectively, and reinforced with six longitudinal GFRP bars, were prepared and tested. The spiral spacing was no spirals, 50, 100, and 150 mm; the f′c varied from 21 to 44 MPa. Test results show that reducing the spiral spacing resulted in increased HCC uniaxial compression capacity, ductility, and confined strength due to the high lateral confining efficiency. Increasing f′c, on the other hand, increased the axial-load capacity but reduced the ductility and confinement efficiency due to the brittle behavior of high compressive-strength concrete. The analytical models considering the axial load contribution of the GFRP bars and the confined concrete core accurately predicted the behavior of the HCCs after the spalling of the concrete cover or at the post-loading behavior

Process Mining IPTV Customer Eye Gaze Movement Using Discrete-time Markov Chains

Human-Computer Interaction (HCI) research has extensively employed eye-tracking technologies in a variety of fields. Meanwhile, the ongoing development of Internet Protocol TV (IPTV) has significantly enriched the TV customer experience, which is of great interest to researchers across academia and industry. A previous study was carried out at the BT Ireland Innovation Centre (BTIIC), where an eye tracker was employed to record user interactions with a Video-on-Demand (VoD) application, the BT Player. This paper is a complementary and subsequent study of the analysis of eye-tracking data in our previously published introductory paper. Here, we propose a method for integrating layout information from the BT Player with mining the process of customer eye movement on the screen, thereby generating HCI and Industry-relevant insights regarding user experience. We incorporate a popular Machine Learning model, a discrete-time Markov Chain (DTMC), into our methodology, as the eye tracker records each gaze movement at a particular frequency, which is a good example of discrete-time sequences. The Markov Model is found suitable for our study, and it helps to reveal characteristics of the gaze movement as well as the user interface (UI) design on the VoD application by interpreting transition matrices, first passage time, proposed ‘most likely trajectory’ and other Markov properties of the model. Additionally, the study has revealed numerous promising areas for future research. And the code involved in this study is open access on GitHub

Flexural behaviour of concrete slabs reinforced with GFRP bars and hollow composite reinforcing systems

Glass Fibre Reinforced Polymer (GFRP) bars are now attracting attention as an alternative reinforcement in concrete slabs because of their high resistance to corrosion that is a major problem for steel bars. Recentlyhollow concrete slab systems are being used to reduce the amount of concrete in the slab and to minimise the self-weight, but the internal holes makes them prone to shear failure and collapse. A hollow composite reinforcing system (CRS) with four flanges to improve the bond with concrete has recently been developed to stabilise the holes in concrete members. This study investigated the flexural behaviour of concrete slabs reinforced with GFRP bars and CRS. Four full-scale concrete slabs (solid slab reinforced with GFRP bars; hollow slab reinforced with GFRP bars; slab reinforced with GFRP bars and CRS; and slab reinforced with steel bars and CRS) were prepared and tested under four-point static bending to understand how this new construction system would perform. CRS is found to enhance the structural performance of hollow concrete slabs because it is more compatible with GFRP bars than steel bars due to their similar modulus of elasticity. A simplified Fibre Model Analysis (FMA) reliably predicted the capacity of hollow concrete slabs

Effects of diameter on the durability of glass-fiber-reinforced-polymer (GFRP) bars conditioned in alkaline solution

Current standards do not consider the diameter of glass-fiber-reinforced-polymer (GFRP) bars used as internal reinforcement in concrete structures to be a factor influencing bar durability. This paper investigates the effects of bar diameter on the physical and mechanical properties as well as the durability of GFRP reinforcing bars conditioned for three months at 60°C in an alkaline solution simulating a concrete environment. Five diameters (nominal diameters of 9.5 mm, 12.7 mm, 15.9 mm, 19.1 mm, and 25.4 mm) were considered; bar properties were assessed before and after conditioning. Microstructural analyses and measurement of physicochemical properties were also carried out. The results show that bar size had no significant effect on bar physical properties, except for water absorption. The smaller diameter bars had higher water absorption than the larger ones due to their higher surface-area-to-volume ratios. In the case of the unconditioned bars, the tensile strength and modulus were not significantly affected by bar diameter, but there was a size effect for interlaminar shear strength and flexural strength. On the other hand, the conditioning in the alkaline solution had a greater negative effect on the tensile strength of the larger bars than on the smaller ones. Scanning-electron-microscope (SEM) observations and Fourier-transform-infrared-spectroscopy (FTIR) analysis revealed that the degradation remained at the surface of all the conditioned specimens. Nevertheless, there were only small variations between the physical and mechanical properties of the GFRB bars of different diameters. This indicates that the current provisions in standards that do not relate strength-retention limit to bar size are acceptable

Laboratory assessment and durability performance of vinyl-ester, polyester, and epoxy glass-FRP bars for concrete structures

In the last decade, noncorrosive glass fiber-reinforced-polymer (GFRP) bars have become more widely accepted as cost-effective alternatives to steel bars in many applications for concrete structures (bridges, parking garages, and water tanks). Also, these reinforcing bars are valuable for temporary concrete structures such as soft-eyes in tunneling works. The cost of the GFRP bars can be optimized considering the type of resin according the application. Yet limited research seems to have investigated the durability of GFRP bars manufactured with different types of resin. In this study, the physical and mechanical properties of GFRP bars made with vinyl-ester, isophthalic polyester, or epoxy resins were evaluated first. The long-term performance of these bars under alkaline exposure simulating a concrete environment was then assessed in accordance with ASTM D7705. The alkaline exposure consisted in immersing the bars in an alkaline solution for 1000, 3000 and 5,000 h at elevated temperature (60oC) to accelerate the effects. Subsequently, the bar properties were assessed and compared with the values obtained on unconditioned reference specimens. The test results reveal that the vinyl-ester and epoxy GFRP bars had the best physical and mechanical properties and lowest degradation rate after conditioning in alkaline solution, while the polyester GFRP bars evidenced the lowest physical and mechanical properties and exhibited significant degradation of physical and mechanical properties after conditioning