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International Concrete Abstracts Portal

Showing 1-5 of 1384 Abstracts search results

Document: 

SP-356

Date: 

October 1, 2022

Author(s):

ACI Committee 440

Publication:

Symposium Papers

Volume:

356

Abstract:

Fiber-reinforced polymer (FRP) reinforcements for concrete structures and civil engineering applications have become one of the innovative and fast-growing technologies to stop the rapid degradation of conventional steel-reinforced concrete infrastructure. FRP reinforcements for construction can be divided into three main types: 1. External sheets or plates to rehabilitate and repair existing concrete and masonry structures, and in some cases steel and wood structures; 2. Internal FRP bars or tendons for new and existing reinforced concrete structures, and 3. FRP stay-in-place forms to be filled with unreinforced or reinforced concrete. A considerable and valuable development and application’s work has been accomplished during the last three decades, leading to the development of numerous design guidelines and codes around the world, making the FRP-reinforcement technology one of the fast-growing markets in the construction industry. During the ACI Concrete Convention, Fall 2021, four full sessions were sponsored and organized by ACI Committee 440. Session S1 was focused on the bond and durability of internal FRP bars; Session S2 on codes, design examples, and applications of FRP internal reinforcements; Session S3 on external FRP reinforcements; and Session S4 on new systems and applications of FRP reinforcements, such as CFFT post-tensioned beams, GFRP-reinforced concrete sandwich panels, FRP-reinforced masonry walls, CFFT under impact lateral loading, near-surface mounted FRP-bars, and GFRP-reinforced-UHPC bridge deck joints.


Document: 

SP-356_07

Date: 

October 1, 2022

Author(s):

Mahmut Ekenel, Hossein Roghani, Francisco De Caso y Basalo, and Antonio Nanni

Publication:

Symposium Papers

Volume:

356

Abstract:

Advances in technology have opened doors for building construction with new materials that are lightweight, efficient, noncorrosive, and reliable in terms of durability without a sacrifice in strength and performance. One of these technologies is the use of FRP bars and meshes in concrete members as internal reinforcement. Although FRP bars as structural reinforcement in concrete members have been successfully utilized in building and bridge projects (i.e., slabs, beams, etc.) for the past three decades; recently, there has been an interest in using FRP bars and meshes as secondary reinforcement for non-structural concrete members such as plain concrete footings, concrete slabs-on-ground, and plain concrete walls in lieu of code-compliant conventional temperature and shrinkage steel reinforcement. Because the use of FRP bars and meshes as secondary reinforcement is not within the provisions of the International Building Code (IBC), the predominant building code in the United States, an acceptance criterion (AC521) has been developed under IBC Section 104.11. This paper explains the requirements of AC521, and how FRP bars and meshes as secondary reinforcement of nonstructural concrete members are evaluated to show compliance with the provisions of the IBC.


Document: 

SP-356_06

Date: 

October 1, 2022

Author(s):

Piotr Wiciak, Maria Anna Polak, and Giovanni Cascante

Publication:

Symposium Papers

Volume:

356

Abstract:

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 aging 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 a maximum error of 7%). The amplitude-based ultrasonic technique is also capable of bond loss between concrete and GFRP bars.


Document: 

SP-356_14

Date: 

October 1, 2022

Author(s):

Wael Zatar, Hai Nguyen, and Hien Nghiem

Publication:

Symposium Papers

Volume:

356

Abstract:

Fiber-reinforced polymer (FRP) materials provide an excellent alternative for shear, flexure, and confinement retrofitting of deteriorated infrastructure. Despite the advanced technology employed in fabricating FRP materials, the monitoring and quality control of the FRP installation still present a challenge. For externally bonded FRP-rehabilitated structures, the existence of undesirable defects, including surface voids and debonding, on the concrete surface should be evaluated, as these defects would adversely affect the durability and capacity of the FRP-rehabilitated structures. Nondestructive testing has the potential to provide a fast and precise means to assess these FRP rehabilitated structures. This paper presents an experimental and theoretical investigation of the use of ground-penetrating radar (GPR) and infrared tomography (IRT) methods to evaluate reinforced-concrete (RC) slabs externally bonded with glass fiber-reinforced polymer (GFRP). Four externally bonded GFRP RC slab specimens were fabricated. Surface voids, interfacial debonding, and vertical cracks were artificially created on the concrete surface of the RC slabs. Test variables include the location and size of surface voids, interfacial debonding, and diameter of steel reinforcement. Improved two-dimensional and three-dimensional image reconstruction method, using the synthetic aperture focusing technique (SAFT), was established to effectively interpret the GPR test data. The results showed that an in-house developed software, that employed the enhanced image reconstruction technique, provided sharp and high-resolution images of the GFRP-retrofitted RC slabs in comparison to those images obtained from the device’s original software. The data suggests that the GPR testing could effectively be employed to accurately determine the size and location of the artificial voids as well as the spacing of the steel reinforcement. The GPR, however, could not well predict the debonding and concrete cracking, as the GPR signals were corrupted because of the direct wave and coupling effect of the antennae and background noise. Results obtained from the IRT testing showed that this technique can detect and locate near-surface defects including surface voids, interfacial debonding, and cracking with acceptable accuracy. The study suggests the combined use of the GPR and IRT imaging to accurately detect possible internal defects of FRP-rehabilitated concrete structures.


Document: 

SP-356_03

Date: 

October 1, 2022

Author(s):

Mohammod Minhajur Rahman, Xudong Zhao, Tommaso D’Antino, Zahra Ameli, Francesco Focacci, and Christian Carloni

Publication:

Symposium Papers

Volume:

356

Abstract:

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 in RC structures due to the absence of corrosion and the low weight-to-strength ratio of the FRP bars when compared to steel bars make FRP bars a cost-effective solution 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 and the bond mechanism.

In this paper, experimental results are presented that aim at identifying a suitable setup to study the bond behavior and determining the effect of different bonded lengths on the stress transfer mechanism. Pull-out tests present some advantages to studying the bond mechanism without the complication of flexural stresses. Once the mechanism of the bond is studied at the small scale, and the interfacial cohesive material law is obtained, it is possible to simulate the behavior of full-scale members. The majority of the pull-out tests are performed with a short bonded length, which does not allow to fully establish the stress transfer between the bar and the surrounding concrete. In this paper, bars are embedded in concrete cylinders and pull-out tests are performed in displacement control with four bonded lengths. The first bonded length is equal to 5 times the bar diameter in order to consider the case of ASTM D7913. The other three bonded lengths are equal to 10, 20, and 40 times the diameter of the bar, respectively. Loaded-end displacement is obtained from the measurements of three linear variable displacement transformers (LVDTs). For some specimens, the free-end displacement was measured by two additional LVDTs. The load responses in terms of applied load versus machine stroke, loaded-end slip, and free-end slip are plotted and compared for the different bonded lengths. The results show that the average shear stress calculated according to ASTM D7913 is not constant for the different bonded lengths. In addition, the slip at the free end is activated at a different percentage of the peak load as the bonded length increases, which indicates that the bond phenomenon requires a certain bonded length to be fully established. The experimental peak stress versus bonded length and the stress level in the bar as a function of the embedded (bonded) length, according to ACI 440.1R-15, are compared. The results indicate that for the bar type studied in this paper, the provisions of ACI 440.1R do not match the results of the pull-out tests.


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