Concrete has stayed gray on the outside for years, but scientists now are seeing green on the inside.
Mixed into fresh concrete, new types of tiny synthetic fibers can eliminate reinforcing steel and reduce the amount of labor needed on a construction jobsite. When applied, the savings could add up to lower costs for owners and less stress on the environment, according to fiber producers.
Performax, for example, is a replacement for welded-wire fabric, light-gauge steel and steel fiber in concrete slab construction. Developed by Polymer Group Inc. (PGI) of Kingman, Kan., it's a proprietary blend of synthetic resins that provide reinforcement for crack control, flexural toughness, and increased shatter resistance.
Tudor Van Hampton/ENR
Bendable concrete hits the market this year.
The product is ideal in industrial floors, concrete pavement, and commercial slab construction, says PGI’s Paul Schmidt. The company also offers fibers for precast concrete as a welded-wire-fabric replacement.
Rising steel and asphalt prices are resulting in higher concrete "densities," or the amount of cement used per construction dollar, reports the Portland Cement Association. PGI, as a result, brought in $85 million in sales last year, and expects a 15% growth in 2007, says Schmidt. The 27-year-old firm is also pursuing accreditation from the U.S. Green Building Council.
Another patented fiber recently developed at the University of Michigan may soon yield bridges without rubber expansion joints and high-rise buildings designed with cheaper seismic devices. The finished product is commonly called "bendable concrete" and made its first major public appearance this week at the World of Concrete show in Las Vegas.
Bendable concrete is an engineered cement composite that is 500 times more resistant to cracking and 40% lighter than traditional concrete. Tiny polyvinyl-alcohol fibers chemically bond to the fresh mix as it cures.
Using existing equipment, methods and admixtures, the fiber can be blended into any type of concrete to replace glass fibers, rebar and wire mesh. But it also works along with steel to reduce concrete cover, says Michael D. Lepech, who helped develop the product at the University of Michigan. Pilot projects around the world have bendable concrete in various bridge decks and high-rise buildings, and engineers think it could be useful to line tunnels and support railroad tracks.
Currently, the PVA fibers are produced by Japan-based Kuraray Co. Ltd. and sold in North America through Westerly, R.I.-based Nycon Inc. The installed cost is about double that of typical concrete; however, Lepech says its long life and low maintenance makes it cheaper in the long run.
The scientist also sees sustainable benefits in PVA fibers, which are a byproduct of petroleum processing. "We can replace about 75% of the virgin materials with these industrial wastes," he says.