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Research Development and Applications of FRP Reinforcements, Part 1 of 4

Tuesday, October 19, 2021  4:00 PM - 6:00 PM

Fiber-reinforced polymers (FRP) reinforcements have become one of the most used construction materials during the last decade. ACI Committee 440 is leading the writing of design standards and guidelines and is sponsoring these full sessions. Four 2-hour sessions will highlight and collect the most recent research, development, and application of FRP reinforcement in the concrete industry. Numerous important topics related to external and internal FRP reinforcement will be presented.
Learning Objectives:
(1) Discuss the bond properties of GFRP bars embedded in eco-friendly concrete;
(2) Describe FE modeling of mechanical splices of FRP bars;
(3) Experimentally evaluate the development bond length using 3-point bend beam test for FRP and steel bars;
(4) Describe modelling of thermal spalling of GFRP-reinforced concrete Slabs;
(5) To learn how to use the non-destructive ultrasonic technique to monitor the degradation of mechanical properties of GFRP bars in aggressive environments.

This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.

Bond Study of Corrosion-Free Reinforcement Embedded in Eco-Friendly Concrete

Presented By: John Myers
Affiliation: Missouri S&T
Description: This paper presents an investigation of the bond performance of corrosion-free sand-coated glass fiber reinforced polymer bars (GFRP) implanted in two types of fly ash-based eco-friendly concrete. Steel reinforcement is prone to corrosion and is expensive to fix, therefore finding an effective alternative has become a must. One of these alternatives is GFRP bar. On the other hand, conventional concrete (CC) is not issueless, as it significantly affects the environment through its high-intensity CO2 emissions. Thus, other alternatives have been looked into to mitigate the CO2 problems. One of these alternatives is partially substituting Portland cement with another CO2 emission-free material such as fly ash. In this study, two levels (50% and 70%) of high-volume fly ash concrete (HVFAC) were used to investigate their bond performance with GFRP bars. Cylindrical specimens were tested under the effect of pullout load. Furthermore, the bars were investigated chemically and microstructurally to see if the fly ash had some influence of the GFRP bar. For concrete, performance rank analysis was carried out to identify the best HVFA concrete. In addition, to verify the experimental work, two-dimensional finite element models were built using translator elements to present the bond action between the concrete and its reinforcement. The results of investigation showed that the bond strength of GFRP bars were less than that of mild steel owing to its deformation. In addition, CC resulted a higher bond strength than HVFAC. The bar analyses did not yield any obvious signs of microstructural deteriorations or chemical attack.

Mechanical Splices for GFRP Reinforcing Bars

Presented By: Nafiseh Kiani
Affiliation: University of Miami
Description: A common challenge in reinforced concrete (RC) construction is the need to connect rebars of finite length in order to provide reinforcement continuity. Lap and mechanical splices are the common methods that have been used to create reinforcement continuity. Lap splicing may cause additional congestion making the concrete consolidation difficult. Therefore, when the lap splicing is not practical, mechanical splices are used. Mechanical couplers are cost-effective, provide reinforcement continuity, and speed up construction time. Different types of mechanical couplers are commercially available for steel rebars. For the case of GFRP reinforcement, mechanical couplers are a must in staged construction because the reinforcement cannot either be bent at the site or there is insufficient space for lap splicing in congested urban corridors. Mechanical couplers for GFRP bars, however, must account for the bars low transverse stiffness and strength. For these reason, only selected couplers can be used with GFRP bars and careful consideration must be given to their installation and effectiveness. In this study, a commercially available swaged coupler is selected to investigate splicing GFRP bars. Expected performance was numerically evaluated using Finite Element modeling in order to develop a framework for test validation. The coupler strength, bar tensile strength, and slip between the coupler and bar were investigated through a parametric study. The outcome of this work allows for the definition of an efficient test campaign.

Preliminary Experimental Results of the Bond Between GFRP Bars and Concrete

Presented By: Mohammod Minhajur Rahman
Affiliation: Case Western Reserve University
Description: Fiber-reinforced polymer (FRP) bars are an alternative solution to traditional steel bars for internal reinforcement of reinforced concrete (RC) structures. The potential reduction of damage of RC structures due to the absence of corrosion and the low weight-to-strength ratio of the FRP bars when compared to steel bars outweighs the increase of cost and make FRP bars valuable when durability is a concern. While a recent ASTM standard (ASTM D7913) has been issued to test the bond of FRP bars, limited work is available in the literature that deals with the determination of the interfacial properties between the FRP bars and concrete. In this paper, some preliminary experimental results are presented that aim at identifying a suitable setup to study the bond behavior and determine the effective bond length. Bars are embedded in concrete cylinders and pull-out tests are performed in stroke control. Different embedded lengths are considered. The first bonded length is equal to 5 times the bar diameter in order to consider the case of ASTM D7913. The second and third bonded lengths are equal to 10 and 20 times the diameter of the bar, respectively. Loaded-end displacements are measured by means of three linear variable displacement transformers (LVDTs). The load response in terms of applied load versus load-end slip and applied load versus the machine stroke are plotted and compared for the different bonded lengths.

Development Length of GFRP Rebars in Reinforced Concrete Members under Flexure

Presented By: Alvaro Emparanza
Affiliation: University of Miami
Description: In reinforced concrete (RC) structures, a proper bond between the reinforcement and the concrete is key for an appropriate composite action. To-date limited studies exist that evaluate the bond of fiber reinforced polymer (FRP) bars in concrete members under flexure and its effect on the development length required to ensure a full stress transfer. In this paper, the bond strength developed by glass FRP (GFRP) and steel rebars is evaluated and compared by testing 16 RC beams under three-point-bending. The beams were 6 ft long and had a section of 150 x 360 mm. Three different development lengths were evaluated as a function of the bar diameter, db. (i.e., 20 db., 30 db., and 40 db.). Two different GFRP rebar types (six beams for each) and conventional steel (four beams) were used as reinforcement. Based on the results presented herein, GFRP rebars have a lower bond capacity than steel rebars; however, their embedded lengths as suggested by actual code provisions for GFRP rebars appear to be over-conservative.

Modeling of Thermal Spalling for a GFRP-Reinforced Concrete Slab

Presented By: Jun Wang
Affiliation: University of Colorado Denver
Description: This paper presents an analytical approach to simulate the heat transfer and thermal spalling of a glass fiber reinforced polymer (GFRP)-reinforced concrete slab. Employing an agent-based model, differential equations are solved with the thermal properties of concrete and insulation layers. The model provides pore pressure and temperature-dependent stress to predict concrete spalling, which is assumed to occur when the pressure exceeds the tensile strength of the concrete. With an increase in external temperature, the thermal conductivity and thermal diffusivity of the slab system alter. The degree of heat transfer to the reinforcement level is retarded with the presence of the insulation that can better preserve the bond between the concrete substrate and GFRP. A comparative study on the insulation and extra concrete cover shows that their initial performance is similar, whereas bifurcations are noticed due to the different thermal characteristics. Notwithstanding the marginal implications of tensile strength in the concrete, the likelihood of spalling rises as the concrete strength increases.

Evaluation of Progressive Damage in GFRP Bars – Low and Large Strain Experimental Program and Numerical Simulations

Presented By: Piotr Wiciak
Affiliation: Univeristy of Waterloo
Description: The long-term durability of glass fiber reinforced polymer (GFRP) in concrete remains an unresolved issue. The necessity of reliable NDT techniques for GFRP bars is critical for in-situ testing of concrete members with GFRP reinforcement. Such bars embedded in concrete show no visual deterioration and cannot be cut out of a structure to test in a traditional way. This paper presents a study of progressive damage of GFRP bars subjected to accelerated ageing in alkaline solution and elevated temperature. The study offers four sections: (i) ultrasonic evaluation based on wave velocity and amplitude attenuation approaches, including characterization of ultrasonic transducers using the laser vibrometer, (ii) numerical simulations adding a more comprehensive understanding of wave propagation and investigating other testing methods, (iii) a destructive shear test carried on the bars, which investigates the level of damage in the bars and verifies the ultrasonic evaluation, and (iv) ultrasonic evaluation of bond loss for GFRP bar embedded in concrete beams. The comparison of ultrasonic evaluation, destructive shear test, and numerical simulations shows that ultrasonic techniques can successfully predict the degradation of shear strength (and ultimately tensile strength) of GFRP bars (with the maximum error of 7%). The amplitude-based ultrasonic technique is also capable of bond loss between concrete and GFRP bars.

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