Asphalt Field School

All American Asphalt used this Material Transfer Vehicle to transfer asphalt concrete from hauling trucks to the paving machine. Nicknamed the shuttle buggy, it receives the asphalt concrete, mixes it thoroughly while maintaining the same temperature throughout the mix, and introduces it to the paving machine. (All - JWA)

Carroll McCormick reports on how the John Wayne Airport and its general contractor learned how to use polymer-modified asphalt.

All American Asphalt used this Material Transfer Vehicle to transfer asphalt concrete from hauling trucks to the paving machine. Nicknamed the shuttle buggy, it receives the asphalt concrete, mixes it thoroughly while maintaining the same temperature throughout the mix, and introduces it to the paving machine. (All - JWA)

With just a single, heavily used commercial runway, engineers at the John Wayne Airport, Orange County in California opted to use an extra-strong, polymer-modified asphalt for its resurfacing project last winter.  The challenge to both airport and contractor however, was learning how to work with the polymer modified binder and the special-purpose Performance Grade 76-22 Polymer Modified asphalt itself. 
“We picked PG 76-22PM because our runway is used heavily.  We need a stiffer pavement,” explains Ambi Thurai, project engineer with the John Wayne Airport.  The conventional choice for the project would have been PG 70-10 asphalt, which is not polymer-modified, but a report from the University of California Berkely Technology Transfer Program (Tech Topic #7) suggests PG 76-22PM for applications including: “highly stressed, heavily loaded sections such as highway off-ramps, intersections, port loading facilities, and major airfields.”  A Federal Aviation Administration (FAA) Airport Pavement Workshop in October 2007 had also suggested using polymer modified asphalt binders for heavily loaded airfields.
“The higher the PG grade , the stiffer the binder, and the higher the rut resistance.  One of the major factors in selecting a binder is rate of loading, which is very high for our airfield,” explains Rick Cathey, project manager with the airport.  “The challenge though, is that the polymer modified asphalt is a new concept for many contractors.  Not many have used this type of asphalt and the handling is different from the regular FAA mix, which utilizes PG 64-28 or PG 70-10 asphalt binder.”
Of four pre-qualified contractors, only one had used PG 76-22PM, but he did not bid on the project.  The airport selected Corona, California-based All American Asphalt Inc as the general contractor, which had no prior experience with PG 76-22PM.  “They were a great contractor but it was a learning curve for everybody,” says Cathey.
Kimley Horn & Associates Inc was responsible for project administration, engineering and design; Butier Engineering, Inc provided construction management; All American Asphalt supplied construction supervision, materials, labour and the equipment for the job.
The entire project cost an estimated US$3.7 million.  The FAA Airport Improvement Program will pay 80.59% of the cost, with the remainder being funded by the John Wayne Airport’s operating budget.
Once paving crews finished their work each night, painters re-striped the runway for the day’s flights. As the airport’s only commercial runway, it was never closed to scheduled flights.

The airport’s 5,700ft (1,727.4 m) runway 1L/19R opened in 1965; a 2,800ft (853.4 m) runway is for private general aviation.  It was last resurfaced in 1994.  This most recent resurfacing consisted of milling 3.5 – 4 in (8.9-10.2 cm) off the centre 54 ft (16.4m) of the runway for its entire length.  The last 200 ft of each runway end was milled for their full, 150-foot (45.7m) width, as was a 550 ft x 50 ft (167.6m x 15.2m) area of runway at Taxiway E.  The milled surface was replaced with 3.5 – 4 inches of PG 76-22PM.
Work on the runway was divided into four wide lanes: two measuring 12 ft (3.7m) and two at 15-foot (4.6m), which ran the length of the runway. The airport closed the runway each night at 23:00 and as many as 65 workers began bringing in equipment at 23:30.  Crews milled and paved according to how much asphalt they could mix, as the runway had to be reopened every morning for regular operations.  All American Asphalt mixed from 550-1,200 tons (498.85-1,088.4 tonnes) per night, and averaged 850 tons (771t) of asphalt each night.  The contractors were able to mill and repave as many as 3,000 linear feet (914.4m), of one 12’ or 15’ foot lane, in a night.  They laid down a total of 9,200 tons (8,344.4t) of asphalt – approximately 373,700 sq ft (34,700m2).
“We had redundancy for everything, including our mix plant.  We occasionally had to use our backup equipment,” Cathey says.
The paving crew left the runway at 03:00 each morning, and then the painting team re-marked any missing lines.  Operations took over at 06:00 to inspect the runway and reopen it for regular flights at 07:00.  The milling and paving took eleven nights between October 8 and November 5, 2008.
All American Asphalt encountered several challenges working with the PG 76-22PM: It had to be mixed at 320°F, but trucks were hauling the binder from Benicia, California, 423 miles (677 km) and a seven-hour drive up the coast.  By the time the trucks rolled into the asphalt plant it had cooled too much.  When All American did the FAA-mandated test strips, the binder would start to separate out, and compression tests were inconsistent.
“With normal asphalt, whatever temperature the binder comes in, we use it.  With the PG 76-22PM, because it varied in temperature, the polymers were separating out from the asphalt,” explains Robert Schwartz, quality control manager, All American Asphalt.  “The properties of the binder were changing so dramatically.  This is why we decided to use a booster heater, which brought the polymer-modified oil up to a constant temperature of 320°F.  Every day we started with fresh binder, because the longer we kept it, the more inconsistent it became.”
1L/19R John Wayne Airport
Runway 1L/19R sees 90,000 commercial operations a year, mainly the B737 and B757 and Airbus 319/320.

After boosting the temperature of the binder, All American Asphalt put it in a tank equipped with an auger to keep it stirred up.  “Once we accomplished that, it was stabilised.  Until that stage the properties were very inconsistent, but once we got consistent temperatures and homogeneity, we got consistent properties,” Schwartz recalls. “We were able to get the compaction we needed.”
The asphalt had to be placed at 300°F (148.9°C) or hotter, and compacted at 290 – 300°F (143.3 – 148.9°C); placing the asphalt at too low a temperature resulted in unacceptably high numbers of air voids.
After the paving was completed it was left to cure for 30 days until it was hard enough for grooving, which took place from December 2 – 12.
Next, crews sealed 12,000 linear feet (3,657.6m) of cracks before applying a protective coating on 612,000 sq ft (56,843m2) of runway surface that had not been resurfaced.  The airport settled on Carbon Plex H-25 by Delta Trading, Inc of Bakersfield, California.  It is waterborne, skid-neutral or better and insoluble to rain within one hour of curing.
“Normally we use a fog seal: a regular asphalt emulsion with a bit of sand – sort of a paint job.  We wanted a better product than fog seals.  We know that Carbon Plex breaks at 7.2°C (45°F).  We needed to cure the product within a few hours, at night and at about 10°C (50°F).  Carbon Plex met these criteria,” Cathey explains.
Subcontractor Ramsey Oil Inc, of Kansas applied the Carbon Plex.  First, crews sprayed three test sections with application rates of 0.05, 0.10 and 0.2 gallons (0.23, 0.45 and 0.91 litres) per sq ft.  “We chose the 0.10 gal/sq ft application rate, which required about two hours of cure time,” Cathey says. Having applied the preventative coating, which is a standard preventative maintenance technique, John Wayne should not need to resurface the remainder of its runway for several more years.
 
 
What is PG 76-22 PM?
The California Department of Transportation (Caltrans) adopted the Performance Grade system of asphalt cements in 2006, replacing the Aged Residue system.  Caltrans selected four primary asphalt grades to cover four classes of climate regions in the state.  It also adopted three Polymer Modified (PM) grades for extreme climate regions, or for areas with high traffic or heavy loading conditions.  Polymers can include plastics, elastomers, natural rubber or reclaimed tyre rubber.
In roughly 3% or more concentration, polymers improve the rut resistance and fatigue characteristics of asphalt mix at high temperatures.  At low temperatures polymers improve low-temperature cracking resistance.
Even though Imperial measures are the norm United States, the 76-22 refers to Celsius temperatures: PG 76-22 stands for an average seven-day maximum pavement surface temperature of 76ºC (168.8°F) and a minimum pavement surface temperature of -22ºC (-7.6°F).
As general contractor, All American Asphalt learned with the John Wayne Airport runway resurfacing project, this mix requires quite different handling from regular asphalt in order to control its properties.  “This polymer-modified binder took awhile to understand,” says Robert Schwartz, quality control manager, All American Asphalt.  “But now we know how to use it.”
Airport spokesperson Jenny Wedge adds, “Our project will be an example for using 76-22 elsewhere.  All American Asphalt worked really hard to make sure this all worked out.  The FAA was really pleased with it.”