Rehabilitation work is at full throttle at the Miami International Airport. One of the world's busiest hubs for international travel, MIA sees nearly 34 million passengers annually. Its four active runways withstand the abuse doled out by a bevy of traffic consisting of up to Group V Status aircraft, those with wingspans reaching 214 feet, like the Boeing 747-400 and Airbus A340-600.
The nearly $30 million, 454-day facelift includes $10 million dollars of new lighting and reconstruction and resurfacing projects. The airport's second longest runway - 8R 26L - and adjoining M and N taxiways and connectors will see the vast majority of the attention.
The pavement of choice for the Miami Dade Aviation Department (MDAD): asphalt. The reasons: economy and service flexibility. While other airports rely on concrete runways, nearly everything at MIA is blanketed in asphalt.
Ernie Beltre, chief of aviation civil engineering at MDAD, sees no reason to try concrete runways. "Asphalt has performed well at the airport, is very serviceable and lends itself to the climate," he says. "Asphalt lasts long, holds up well to traffic and any surface distress is easily addressed at night."
The asphalt base for the runways can be considered perpetual pavements, withstanding the abuse of heavy cargo and passenger aircraft for decades. Only the surface layer has required servicing to remove oxidation damage, surface deficiencies and rutting.
The early 1990s was the last time resurfacing was required on Runway 8R 26L. Phases 3 and 4 of the current 7-phase rehabilitation contract at MIA includes milling portions of the 10,000-foot-long by 200-foot-wide runway. Depth of milling varies throughout the runway.
"Thicknesses ranged from 0.25-inch texturing to get a better bond between the new and the old asphalt up to 5 inches to allow for minimum new asphalt thickness," explains Robert Lopez, president of General Asphalt Co. Inc., Miami. The goal after milling was to give the runway's center keel section at least 3 inches of fresh asphalt. "This will help to optimize the life of the surface and preserve the strength of the pavement's structure," adds Beltre.
Completion of Phase 3 and 4 work must be accomplished in 42 days to minimize the length of runway closure and air traffic disruption. It is critical that General Asphalt hits this mark, as any delay in these phases could jeopardize total contract completion and result in a penalty. "Disincentive for missing the target is $30,000 per day," says Omar DelRio, project manager for General Asphalt.
In addition, MDAD and General Asphalt are addressing a trouble spot leading up to the runway. This 5,000 square yard ABC Pad is where Taxiways M, N, P and Q all converge for runways 8R 26L and 12/30. "This was a recurring problem area that we had to patch about every three years, so we decided to fix it while the runway was closed to give it time to cure," mentions Beltre.
Subcontractor Marks Brothers, Inc., Medley, FL excavated the area to within 12 inches of the water table. The subbase was replaced by 18 inches of stabilized base, 12 inches of lime rock and 24 inches of a P401 black base. Five in of polymer-modified P401 PG 76-22 asphalt capped the pad, so this section could withstand the constant pounding of aircraft traffic.
MDAD selected a Federal Aviation Administration P401 mix design for all of the rehab work. For the leveling courses, General Asphalt paved with both the PG 76-22 polymer-modified and PG 67-22 binder mixes featuring, a 0.5-inch top aggregate size. The final surface course called for identical binders with a 0.75-inch maximum aggregate.
"The FAA likes the polymer mix for rut resistance," mentions DelRio. "We paved the west- and east-end sections of the runway and taxiways with the polymer mix and the center with the standard."