Composites for metal sign repair
Just like roadways and bridges, those omnipresent large aluminum highway signs — termed OSS (overhead sign structures) — can suffer from structural deterioration and corrosion. The New York State Department of Transportation (NYSDOT) inspected all of its OSS about five years ago and found that 10 percent of the structures, many dating from the 1960s, were structurally deficient. The American Association of State Highway and Transportation Officials (AASHTO) recently authorized a Technology Implementation Group (TIG) to identify and champion the development of easy-to-use products or methods for cost-effective and speedy OSS repairs.
NYSDOT, together with the Utah DOT, is spearheading a national campaign to encourage departments of transportation throughout the U.S. to adopt the AASHTO-supported composite repair kit concept for signs. Thus far, kits are being produced by Air Logistics Corp. (Azusa, Calif.) and Fyfe Co. LLC (San Diego, Calif.). The Air Logistics kit consists of three different types of E-glass/polyurethane prepreg: thin biaxial tape, knitted tubular sleeves and stitched unidirectional fabric. Since the material is water-activated, the company formulates its own resin and produces the prepreg in a humidity-controlled dry room. Airtight foil bags prevent premature cure during shipping. Once at the job site, the crews rip the bags open, take out the pieces they need, dip them in a bucket of water and apply them to the sign joints, which have been cleaned and abraded beforehand to remove dirt and corrosion. Cure is complete in 30 to 40 minutes.
Air Logistics' Franz Worth says that typical OSS truss structures have elements joined at acute angles, which can be difficult to wrap, but the kit's varied selection of precut pieces facilitates the repair process. A manual with step-by-step instructions comes with the kit. A short training session is enough to accustom workers to the process, Worth maintains.
"We are urging states that have large aluminum signs needing repair to contact us as soon as possible for a free demonstration, before our funding runs out," says Harry White, structural design engineer for NYSDOT and the technical contact for the AASHTO effort. "The repairs can be done in three hours, with three workers, for less than $3,000 total cost, which includes traffic protection," states White. (For more information about the kits, e-mail Harry White: email@example.com, or contact Jeremy Fissel at AASHTO: firstname.lastname@example.org.)