Those flying the "friendly" skies since 9/11 have more than likely experienced the hassles associated with security measures designed to keep us safe. If you think it's difficult flying, try being a paving contractor working on the runways, taxiways and aprons at the airports. Security clearance, background checks and escorts are just the tip of the iceberg. Paving contractors working at airports have stricter mix design standards, smoothness and elevation specs, and scheduling nightmares to deal with.
North Liberty, IA-based paving contractor, L. L. Pelling Company, recently completed its portion of a $6.7-million project at the Eastern Iowa Airport in Cedar Rapids. As a paving subcontractor to Streb Construction Company Inc., the general contractor, Pelling had to juggle its asphalt schedule between the dirt contractor, Streb's concrete paving itinerary and the contract's October 2007 deadline. "It was a little difficult getting our paving crews on the job, since the unusually wet conditions this summer delayed the dirt work," says Chuck Finnegan, president of the L. L. Pelling Company.
The project called for the complete reconstruction of a major portion of Taxiway B and tying it into the crosswinds runway 13/31 and Taxiway A. Previously running diagonal to main runway 9/27, the new Taxiway B now runs parallel to it.
While the surface to Taxiway B is portland cement concrete (PCC), the base of the concrete pavement will consist of a four-inch asphalt open drainage layer, requiring 5,800 tons of a P-401C "popcorn" asphalt mix that includes little to no fine material. "We were competing with a cement stabilized base at the airport, but the asphalt drainage layer was cheaper and more flexible," Finnegan explains. The specs for the drainage layer required Pelling to lay a mat that allows four gallons of water to flow through a two-inch tube in 60 seconds.
The popcorn mix was placed over six inches of a dense-graded P-403 asphalt. Additionally, the P-403 mix was used to pave 25-foot wide asphalt shoulders along the left- and right-hand sides of Taxiway B, laid in two, three-inch lifts.
An additional 5,000 tons of a P-401 mix serve as a surface lift for the crosswinds 13/31 and Taxiway A.
Pelling's paving train for the project was led by a Cedarapids (now Terex) CR561R rubber track paver equipped with a Stretch 20 diesel screed, capable of paving widths reaching 30 feet. Although paving widths varied, Pelling laid an 18-foot wide mat for much of Taxiway B. When it came time to pave the surface lift, a 25-foot Topcon non-contact ski was attached to the paver to help achieve final smoothness.
A breakdown IR DD130 tandem vibratory roller, intermediate Dynapac pneumatic tire roller and a DD110 tandem vibratory roller (operating in static mode) served as the rest of the paving train. Through the use of this paver/roller combination, Pelling was able to beat spec densities and smoothness numbers of seven inches per 1/10th of a mile segment with a zero blanking band.
When paving the mainline or any other roadway for that matter, it's standard practice for concrete pavers to get their grade off of a stringline. It's a labor-intensive and costly practice that nine times out of ten the asphalt paving contractor does not have to worry about.
That tenth time comes into play when working for the Federal Aviation Administration. Making it more difficult to pave at an airport, the FAA typically requires asphalt contractors to use a stringline. "The specs call for us to lay a stringline or use other approved methods for making grade," Finnegan says. Standard grade control systems used in mainline paving are not on the FAA's approved list. So asphalt contractors will typically go through the time, expense and hassle of running the stringline.