Adding texture could potentially raise the bar on bridge longevity

University of Illinois researchers and Illinois Department of Transportation (IDOT) staff are leading a series of research studies to improve the overall longevity of bridges.

A bridge generally consists of three parts: the foundation (pile caps and piles); the substructure (abutments and piers); and the superstructure (decks, slabs, and girders). Like most structures, bridges need periodic maintenance. One area of concern facing many agencies is the costly maintenance of bridge decks, especially in regions with severe winter seasons. The damage is a result of the combination of freeze-thaw cycles and the heavy use of de-icing salts. This causes cracks in the concrete, which can lead to severe spalling, reinforcement corrosion, and damage to the substructure.

The use of epoxy-coated steel reinforcement bars is common among many departments of transportation. Although the epoxy coating protects the steel from corrosion, it compromises bond strength. Consequently, the increased cracking exacerbates durability issues in bridge decks. With the goal of improving bond and reducing the formation of cracks, IDOT proposed texturizing the surface of epoxy-coated bars.

IDOT developed a prototype of the textured epoxy coating and partnered with researchers at the Illinois Center for Transportation (ICT) to examine its effectiveness. Project R27-SP35, “Behavior of Epoxy-Coated Textured Reinforcing Bars,” was a preliminary study on the bond strength of reinforcing bars with this new style of coating. The research team explored the bond strength of the new textured epoxy-coated (TEC) rebar by conducting two types of tests: pull-out and flexure. The results of the new rebars were compared to those of conventional epoxy-coated and uncoated (black) rebars.  

The project was guided by a Technical Review Panel (TRP) chaired by Jayme Schiff, Engineer of Design at IDOT’s Bureau of Bridges and Structures.

“The added texture on the epoxy coated bar has the potential to provide a higher bond strength and reduce deck cracking, thereby extending the service life of bridge decks. This preliminary research project gave us a good foundation of data that we can build upon,” Schiff said.

Dr. Bassem Andrawes served as principal investigator on this project. Andrawes is an associate professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign.

“This was an exploratory study. However, the initial results indicate that the new textured rebars have the potential to prevent the sudden slip of the rebars once concrete cracks. More detailed investigations are needed to optimize the texture (roughness) of the rebars and determine their development length,” Andrawes said.

IDOT and ICT are working together on a second textured epoxy coated TEC rebar study that will start in the summer of 2018. Phase 2 will evaluate TEC’s level of sensitivity to the manufacturing process, investigate TEC’s effect on the bond behavior of rebars, and examine the impact of using TEC rebars on the crack patterns during curing (due to shrinkage) and ultimate stages.

The final report detailing the results of the research project is available here.