Final surface lift thicknesses averaged 2 to 2.5 inches, and crews set the screed to just over 16.5 feet wide to complete the runway in 12 passes.
General Asphalt produced the polymer-modified and standard P401 mixes at two plants, including this Terex E500R plant located at the White Rock Quarry.
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."
General Asphalt pulled mix from its two nearby plants. The bulk of the material came from a five-ton batch plant, located just minutes from the airport. A Terex Cedarapids E500R counterflow drum mix plant located at the White Rock Quarry site also supplied mix, especially when the crews were paving the 24-inch (610 mm) of black base on the ABC pad.
Intense 42 days
While the overall contract lasts from September 14, 2009 to December 11, 2010, the most critical work took place over a 42-day period from April to May when Runway 8R 26L was closed. "We spent months preparing for Phases 3 and 4 of this project," comments Lopez.
On April 16, General Asphalt, Mill-It Inc. of Altamonte Springs, FL and Hy Power Inc. of Fort Lauderdale put all the planning into action when paving, milling and electrical lighting operations commenced. The fast and furious pace was non-stop with both milling and paving taking place simultaneously. In just over a week, Mill-It completed nearly 400,000 square yards of milling on the runway and taxiway connectors.
Concurrent with this activity, Marks Brothers excavated the pad area, only to be delayed by torrential rains. "We lost two days of work within the first week," says DelRio. No sooner had crews finished pumping water from the excavated 5,000-square-yard pad that it had to be pumped a second time.
These delays meant that an already tight paving schedule was nearly impossible. To meet the challenging time timetable, General Asphalt used two paving crews. They relied on two Terex CR452 10-foot pavers, one purchased specifically for the MIA job, to pave the bulk of the 80,000 tons of asphalt. At times, a Terex Cedarapids CR352L 8-foot paver was brought in to pave the connectors and runway shoulders.
The rest of the paving train included Dynapac breakdown and finish vibratory rollers and BOMAG and HYPAC rubber wheel traffic rollers. "We only work with the best equipment that will give our crews the best chance for success," says Lopez.
Paving began with a leveling course using the 0.5-inch PG 76-22 and PG 67-22 mixes. A 25' by 25' surveying grid of the runway helped General Asphalt's crews to meet a tight 0.5-in grade specification.
The CR452 and CR352 pavers feature a unique Three-Point Suspension system, which aids in maintaining grade control. Three-Point Suspension isolates any drive system movements from the rest of the paver. Any irregularities in the mat encountered by the bogies or drive tires are absorbed by the drive system, allowing the screed to remain at established grade and deliver a smooth mat.
After crews paved the first leveling course, another topographical survey was conducted, and the grid sections were inputted into a PaveSmart grade control system for the second leveling course. This allowed the crews to meet a 0.14 inch elevation target and move into surface paving.
Final lift thicknesses averaged 2 to 2.5 inches. The crews set paving width on the Terex Stretch 20 electric screed to just over 16.5 feet wide for the runway, making 12 passes in total.
General Asphalt was required to meet spec densities of 96.3% across the mat and 93.3% at the joint or face pay reductions. Additionally, the Aviation Department required a narrow 0.25-inch smoothness specification.
"We had no problem achieving density and smoothness specifications with our paving equipment," says DelRio.
In the early stages of leveling course paving, crews averaged 2,000 tons per day production. During the final lift, crew boosted production with the two CR452 pavers to 2,800 tons per day, while still maintaining the tight smoothness and density specs. "General Asphalt is truly a professional organization that believes quality is paramount," adds Beltre.
Lopez is quick to mention it was a true team effort, and they are only as strong as their weakest link. "From the Aviation Department, Hy Power and Mill-It to Marks Brothers and Hi-Lite (used for pavement striping), we really had a good team that worked well together," he says. "Additionally, we could not have pulled this off without Ike Wetherill and Jim Murphy's (supervisors of security and airside operations at MDAD) teams putting together a security program that helped to meet everyone's needs."
In the end, additional work and unforeseen events prompted MDAD to extend the deadline for completing Phases 3 and 4 by 11 days. "While we extended this deadline, we are still on target to meet the overall 454-day contract deadline," says Beltre.
On Tuesday, June 8 at 6:45 p.m., Runway 8R 26L was turned over to MDAD and aircraft, once again, were taking off and landing on the runway. This time with a fresh, smooth asphalt surface designed to give the Aviation Department two decades of trouble-free service.