Structural Carbon Nanotube-Based Composites: Developing Composite Technology to Rehabilitate Aging Bridges

As steel bridges age, accumulating stress from traffic can cause structural fatigue, weakening of solid components such as girders, and degrading of connections that hold bridge elements together. In 2016, 16 percent of the 178,923 steel bridges in the United States were considered in poor condition, according to the Federal Highway Administration (FHWA) National Bridge Inventory. (FHWA 2018) That same year, 18,706 of the Nation’s steel bridges, regardless of condition, were described as “fracture critical”—i.e., they contain tension members whose failure could cause a portion of or the entire bridge to collapse. For these bridges, FHWA requires a hands-on inspection, at intervals not to exceed 24 months, to detect damage such as fatigue cracking. (GPO 2016) When inspectors find damage, bridge engineers use rehabilitation methods such as bolting steel plates to reinforce cracks or restore corroded sections. Engineers also may use strain gauges, accelerometers, and displacement sensors to monitor crack growth as well as the integrity of repairs.

Supported by FHWA’s Exploratory Advanced Research (EAR) Program, researchers at the University of Delaware have developed strong glass fiber reinforced plastic (GFRP) composites for the rehabilitation of damaged areas. The GFRP patches developed through this project, “Development of Structural Carbon Nanotube-Based Sensing Composites,” also incorporate electrically conductive carbon nanotube (CNT) networks for monitoring postrepair crack growth and, thus, provide an integrated strengthening and monitoring system.