Corrosion of reinforcing steel that occurs in concrete structures subject to the harsh environment is one of the pressing durability concerns. The problem of corrosion can be eliminated if steel reinforcement is permanently replaced by chemically inert FRPs. Glass fiber reinforced polymer (GFRP) is probably the most economical choice among the available composite construction solutions. In situations where deicing salts are frequently used to keep roads free of ice, the highway and bridge components vulnerable to rust can be made corrosion-free by replacing steel bars with fiberglass bars.
Research and development
The development efforts and extensive research carried out at the University of Sherbrooke in Canada have led to the GFRP bars’ current success and their increased use as internal reinforcement in concrete infrastructure. The purpose of the on-going research and experimental studies is to transfer the FRP technology from research centers to the marketplace. The major subject of the research and studies is to understand the behavior of concrete structures reinforced with GFRP rebar.
A study conducted by ISIS Canada in 2004 to determine the durability of GFRP reinforcement in concrete analyzed the performance of GFRP reinforced structures that have been in service for 5 to 8 years. Following are the three of all selected concrete structures:
1. Chatham bridge
A more than 8 years old concrete structure located in Chatham, ON, Canada, Chatham Bridge was built with steel-free deck slabs. The bridge deck is subject to deicing salt and continuously changing environmental conditions from wetting-and-drying to freezing-and-thawing.
2. Joffre bridge
Constructed over the St-Francois River, Joffre bridge was built with GFRP rebar. Joffre bridge experiences harsh environmental conditions similar to those of Chatham bridge.
3. Hall’s Harbour Wharf
Hall’s Harbor Wharf was the first marine structure in Canada constructed using GFRP reinforcement. The structure is subject to extreme weather, salt water, and chloride-laden moisture.
All the selected structures are exposed to harsh environmental conditions. GFRP reinforcement was analyzed for its physical and chemical composition at the microscopic level. The study concluded that there was no sign of corrosion or deterioration of the GFRP in the concrete structures for up to 8 years and that FRP bars are effective reinforcement to column, beams, and slabs. The bond between concrete and reinforcement was in good shape concluding that phenomena such as deicing salt, freeze-thaw cycles, and wet-dry cycles had no adverse effect on the fiberglass rebar.
The study instills a sense of confidence in the construction industry to permit the use of GFRP as primary reinforcement in concrete structures. As a result of this research, the use of advanced composites as internal reinforcement in concrete structures where steel corrosion is one of the concerns has gained considerable acceptance. However, the structural engineers are not fully aware of the unique benefits of this technology.
The successful field applications in North America and internationally demonstrate the feasibility of FRP rebar as an ideal alternative internal reinforcement to environment-sensitive structures such as bridges, retaining walls, transportation infrastructure, water tanks, sewer plants, military and research facilities. More durability tests and experimental evidence will further improve the quality of FRP construction product, increased utilization of this innovative material, and new market opportunities.