![]() GFRP failure occurred within the length of the rebar, not at anchors. Laboratory testing delivered results consistent with previous studies. While initial cracks grew in the first year of service, no significant cracks formed in the second and third years of monitoring. Early investigations found cracking near abutments that was related to the concrete placement, not the deck reinforcement. Inspection identified no unusual cracking behaviors. We learned a lot about the design process, ironed out some ambiguities in the design code and are trying GFRP in another new bridge to compare its performance to epoxy-coated rebar,” said Paul Rowekamp, bridge standards and research engineer, MnDOT Bridge Office. Strain and temperature relationships became and remained consistent over subsequent years. In the first 150 days of service, standard concrete shrinkage had more impact on strain levels than did temperature variation. Under live loading, the Dry Creek bridge deck and girders performed as expected, resisting loads consistently over the three-year period. GFRP reinforcement resisted corrosion very well and offered sufficient structural capacity and performance. Researchers also conducted a life cycle cost analysis, comparing initial expenses and expected maintenance needs over the expected service life of GFRP compared with epoxy-coated rebar. Laboratory tests examined the loading capacity and failure characteristics of GFRP rebar used in the bridge. Load tests were conducted again in November 2017 and in late October 2018.īridge inspections documented the surface cracks and overall deck condition during the three-year course of the research project. Researchers used this loaded dump truck to conduct load testing on the Dry Creek bridge.īefore the deck was opened to regular traffic, the research team conducted live load tests in November 2016 with a three-axle dump truck loaded with sand and driven slowly over the structure. Temperature and stress response data were collected every hour for the three-year period of this study. What Did We Do?Īfter reviewing research on GFRP performance in the lab and field, investigators placed an array of strain and temperature gauges on the GFRP rebar at the Dry Creek bridge before the concrete deck was placed and connected the gauges to the monitoring equipment mounted beneath the deck. In the current study, researchers examined this pilot implementation, evaluating the performance of the bridge deck over its first three years of service. In 2016, MnDOT built a GFRP-reinforced concrete bridge deck on State Highway 42 over Dry Creek, north of Elgin. GFRP, which does not corrode, has been used in Canada but not to the same level in the United States. Over the last decade, GFRP reinforcement has gained interest among Minnesota bridge owners. The long-term saving advantages in repair, maintenance and labor compared with conventional steel can be significant,” said Behrouz Shafei, assistant professor, Department of Civil, Construction and Environmental Engineering, Iowa State University. “GFRP is a promising reinforcement alternative. Epoxy coating of reinforcement, for example, is frequently used in Minnesota to help rebar resist corrosion. Crack sealing and drainage systems help manage moisture and chloride impact, but bridge owners often consider alternatives to enhance the longevity of the reinforcement. Multiple cycles of freezing and thawing can also cause concrete to crack, further exposing reinforcement.ĭamage to bridge decks increases over time, requiring costly maintenance and repair, and potentially shortening the bridge deck’s service life. What Was the Need?Ĭorrosion of reinforcing steel is the primary cause of bridge deck degradation and cracking. They found that GFRP performed well, proving sufficiently strong for use as an alternative to corrosion-susceptible steel rebar. ![]() In a recently completed research project, funded by MnDOT and the Local Road Research Board, researchers studied a rural bridge built in 2017 near Elgin, MN, that used glass fiber–reinforced polymer (GFRP) rebar in the bridge deck. But bridges in climates like Minnesota’s are exposed to moisture and chlorides from road salts that may penetrate these structures and corrode the steel. Reinforced concrete bridges are built to handle heavy loads and routine traffic for 75 years or more.
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