Concrete is all around us and it can be molded into many different shapes. It is used in many structures such as buildings, roads, and bridges to name a few.
Prestressing is the process of using steel reinforcement to permanently compress a concrete element. This method, which has been used in the State of Illinois for many years, is designed to make the concrete element stronger and last longer. In fact, prestressed concrete (PC) beams are used in many of the state’s bridges. However, like many northern states, Illinois experiences accelerated deterioration in concrete structures due to the harsh cold
weather seasons. While the body of the beams have been proven to last for a long time, the beam ends tend to suffer the most damage. This damage is caused by the failure of expansion joints, which allows water containing deicing salts to flow onto the girder ends.
In order to find a sustainable solution to this problem, the Illinois Department of Transportation (IDOT) initiated a project in collaboration with researchers at the Illinois Center for Transportation (ICT). Project R27-156, “Repair of Damaged End Regions of Prestressed Concrete Girders using Fiber Reinforced Polymer Composite Materials,” studied the use of fiber reinforced polymer (FRP) materials as a way to repair and retrofit the damaged ends of prestressed concrete beams. FRP is a lightweight and efficient material used for restoring and improving concrete infrastructures. FRP can be applied to concrete either as externally bonded laminates or as near-surface mounted (NSM) bars or plates.
The project was guided by a Technical Review Panel (TRP) chaired by Victor Veliz, Bridge Repairs Unit Chief at IDOT’s Bureau of Bridges and Structures. According to Veliz, IDOT maintains hundreds of precast prestressed concrete (PPC) I-beam bridge structures built over the years. When joint failure occurs, concrete spalling and beam end reinforcement deterioration commonly follow, which compromises the load carrying capacity of the beams.
“The use of FRP as recommended in this research provided us with a mechanism that will restore the integrity of these beams. By doing so, we can extend the life of the structures and eliminate the premature need for very costly replacements,” Veliz added.
Dr. Bassem Andrawes served as principal investigator (PI) on this project. Andrawes is an associate professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign (UIUC).
According to Andrawes, the research team conducted three-point bending tests on ½-scale beams fabricated in the lab to explore the concept of using FRP as a repair scheme for such damage. Next, they conducted tests on full-scale girders that were in service for over 40 years to confirm the validity of the repair method using FRP. Finally, with the application of finite element models, the researchers developed a new design method for FRP laminates to repair and strengthen damaged end regions in bridge girders.
“As a result of this research, our team was able to develop a new guideline for repairing distressed end regions in prestressed concrete (PC) girders using FRP laminates. A new design method was developed for each of these laminates that can be applied to the damaged areas depending on the level of existing damage,” Andrawes said.
The final report detailing the results of the research project is available here.