United States Department of Transportation
i
Durability of GFRP Bar Reinforcement Extracted from In-service Concrete Structures
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2020-01-01
[PDF-26.19 MB]
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Edition:Final Report, Period: 1/1/2017 – 12/31/19
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Abstract:Glass fiber reinforced polymer (GFRP) rebars have been used in concrete structures as a substitute for steel rebars due to their non-corrosive behavior. To validate their performance in concrete structures, it is important to understand their long-term durability. A collaborative study between the Missouri University of Science and Technology (Missouri S&T), University of Miami, Penn State University, and Owens Corning Composites investigated the durability of GFRP rebars extracted from eleven bridges in service for 15 to 20 years. The bridges investigated are located in the U.S. and are exposed to wet and dry cycles, freezing-and-thawing cycles, and deicing salts, therefore making them prone to corrosion of steel reinforcement. To investigate the durability of in-service GFRP rebars, 4 in. (102 mm)-diameter concrete cores were extracted from each bridge subjected to this investigation. A variety of tests were performed to evaluate the physico-chemical and mechanical properties of the GFRP bars and the condition of the surrounding concrete. Carbonation depth, chloride penetration and control pH tests were performed on the concrete. The extracted bars were tested for horizontal shear strength and tensile strength using cut-off strips. The cross sections of GFRP specimens were analyzed by scanning electron microscopy (SEM) imaging and energy dispersive Xray spectroscopy (EDS) to observe any changes in their microstructure. Bars were also tested for fiber content, water absorption, moisture content and glass transition temperature (Tg). The results of these tests were compared to collected data from pristine bars at the time of installation or to current standards when pristine data was not available. During the extraction of cores, the bridge structures were visually inspected and no signs of deterioration were detected. The SEM and EDS results showed minimal physical damage (0.05 to 0.12%) and minimal elemental distribution changes in some bridges. Most of the results from fiber content and Tg were in accordance with ASTM D7957 for quality control and certification, while the results of the horizontal shear test were inconclusive. The tensile strength test indicated a reduction in tensile stress of 2.13% over a period of 17 years in service. This study provides positive indication on the long-term durability of GFRP bars as an internal reinforcement for concrete structures.
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