Fibre Reinforced Polymer (FRP’s) composites are engineered materials with their strength dependant on several factors such as fiber type and volume, fiber orientation, resin type, manufacturing method, and the bonding materials used in the final assembly.
Bakelite was the first fiber-reinforced plastic invented in 1909. FRP composites were later used in World War II in the construction of British Spitfires and have since been developed extensively for use in the automotive, marine and aviation industries. However, in the last few decades their potential has begun to be recognised in the construction industry too and advances are now rapidly being made in this field.
Initially, the use of FRP’s in bridges was restricted mainly as non-structural elements. Then, during the 1970’s and 1980’s, the Swiss Federal Laboratories for Materials Research undertook a lot of research and development work in the area of the strengthening of reinforced concrete bridges using both glass, carbon and aramid fibre reinforced polymers. However, it wasn’t until 1992, when the Aberfeldy footbridge was completed, that the world’s first major advanced composite footbridge was constructed (it still remains the longest span advanced composite bridge in the world), and was rapidly followed by the Bonds Mill Lifting bridge in Surrey in 1995, which was the first entirely FRP road bridge.
Since then, bridges manufactured with FRP composites are increasingly being considered as an alternative to concrete and steel. FRP is also being seen as a substitute for steel in reinforced concrete applications with the first steel-free concrete bridge deck slab in the world cast in 1995 on the Salmon River Bridge, part of the Trans Canada 104 Highway near Kemptown, Nova Scotia, Canada. The industry is gradually moving from the demonstration phase to acceptance of composites for these applications. A recent database of global FRP use indicated that approximately 100 vehicular bridges consist of entirely FRP decks and at least 34 all FRP pedestrian bridges. Hundreds more vehicular and pedestrian bridges containing FRP components such as decks, beams, trusses, rebar, grid, tendons, cables, or panels have been built in the last 15 years.
The benefits of FRP composite bridge decks include; durability – corrosion and fatigue resistance; lightweight – FRP decks typically weigh 80 percent less than cast-in-place concrete decks; high strength – mechanical properties can be designed by varying the volume and orientation of the fiber reinforcement; rapid installation; competitive life cycle cost – due to significantly lower maintenance requirements and a longer overall service life and; long service life.
However, there are several issues that are still being debated and researched, including; deflection/design criteria; uncertainty in relation to the long term performance; extreme temperature behaviour; difficulty in achieving adequate connection details; higher initial costs and; lack of nationally accepted standards. These issues are being addressed and the current pace of development means that solutions are rapidly being found and there is no doubt that this will continue to be an area of rapid growth in the future. One of the latest research advances in the use of FRP composites, applicable to bridges, is the use of nano-materials which often have properties dramatically different from their bulk-scale counterparts. For example, nanocrystalline copper is five times harder than ordinary copper with micrometer-sized crystalline structure. The development of such materials could have dramatic effects on the constructability of both long span and the ability to cross environmentally sensitive sites.