Fiber-reinforced polymer (FRP), stainless steel, stainless-clad steel, and MMFX steel bars comprise the new generation of concrete reinforcing materials being used for durable construction. Their service life impressively surpasses traditional materials.
Advanced fiber-reinforced polymer composite is made of fiber reinforcement, resin, fillers, and additives. Fibers provide increased stiffness and tensile capacity. The resin offers high compressive strength and binds the fibers into a firm matrix. Fillers serve to reduce cost and shrinkage. The additives help to improve not only the mechanical and physical properties of the composites but also workability.
Stainless steel, stainless-clad steel, and MMFX steel provide corrosion protection for the reinforcement in concrete structures. If maintenance and repair of carbon steel reinforced structures are factored into the economic evaluation, stainless steel emerges as an outstanding choice for designers concerned with concrete durability in harsh environments.
A stainless steel clad reinforcement, Nuovinox, has the same resistance to corrosion as solid stainless at about a quarter the price, according to the manufacturer.
MMFX, a new microstructure steel has demonstrated superior properties in strength and corrosion resistance, and at lower cost than stainless bars.
The federal government has boosted the use of these new reinforcing materials. Funding from FHWA through the TEA-21 Innovative Bridge Research and Construction Program (IBRC) has provided new construction materials the opportunity to meet both federal and state DOT goals of reducing infrastructure maintenance and life-cycle costs of bridges.
While the corrosion resistance of new materials is highly desirable for infrastructure durability, there are unknowns.
Sami H. Rizkalla, chairman of ACI Committee 440, believes "the challenge for FRP reinforcing is to change the mindset of an industry that shies away from risk. The future will be exciting as young engineers design with these new materials in ways we cannot yet imagine."