When Every Minute Counts

The project

The ramp work was a key element to the project at Rafael Nuñez International Airport. It also created challenges. The ramp had to be built higher than the rest of the existing runway. In addition, it required an extremely dense hot mix better able to handle the impact of the landing aircraft.

"The planes are bringing a lot of weight and force to that specific area, and the airport engineers wanted it reinforced," said Oscar Polo, civil engineer with Pavimentos Universale SA, the firm handling the work. "The mix also has more fines to help prevent damage to the plane tires as they land. That material is expensive, so the planner didn't want to use it on the entire runway."

Plans called for milling the landing/takeoff ramp, then building it up with base material, and finally placing new asphalt. The rest of the runway also was paved, but not milled. "We were asked to put only a new surface course on the remainder of the runway," Polo said.

The ramp

The entire runway is 3200 m long, of which 250 m is considered part of the ramp. Pavimentos Universal milled at a depth of 140 mm for the 250 m. Recycled materials helped to build the ramp.

Ramp paving was accomplished with a Cat® AP1000D Asphalt Paver. The ramp work required a trucking pattern similar to what was used for the longer, flatter stretch of runway. "We used 25 trucks no matter what mix we worked with," Polo said.

Because of the warm, humid weather in Cartagena, Polo was able to have the mix delivered hours in advance of its placement. "It takes the mix a long time to cool," he said. "We usually have most of the trucks lined up before we start paving."

Many trucks arrived at the jobsite before midnight, when Polo's crew was first allowed to pave. Pavimentos Universal had to be off the runway by 5 a.m., so Polos had the luxury of knowing there would be no transport problems before starting with that night's paving.

"If there were problems getting the mix there, we could choose to not work," he said. "That's better than starting and not being able to finish the work, especially on a job like this. If we started here, and had problems, it could create many complications."

That approach also meant his calculations for the amount of mix must be precise. "The Cat Paver is very exact in the amount of mix it uses," he said. "The paver's consistency helped us calculate the proper amount."

The average of fines in the mix was 2-4 mm. The placement of the mix on the ramp portion also was unique: The paver worked across the width of the runway, instead of the length of the runway. The ramp portion is 250 m long, and 40 m wide. That meant the paver worked in 40 m increments.

"That is what the specifications called for," Polo said. "Because of the fine materials, the consensus was that it made more sense to pave in shorter increments, and then reach compaction goals. With that level of fines, there can only be a few passes with the roller before the danger of damaging the mix becomes very real."

Paving over the width, and not length, of the ramp also meant less chance for wasting material during the compaction process. Less of the costly material is lost when rollers work across the runway than if they had rolled (and pushed) material toward the top and perhaps over the end.

The material also had to cool to at least 130° C before rolling. There were joints to consider too. This led Pavimentos Universal to place a mat at a width of about 8 m; then leave the adjacent 8 m unpaved; then place another 8 m; then skip the next 8 m, and so on. Each night it placed five lifts of 40 m each. After completing the first three lifts, and leaving two of five stretches unpaved, the paver returned and filled in the missing lifts.

"This allows the asphalt to cool enough so that we can work on it, and compact the joints, while also making sure we don't damage the fine material by working it too early and too extensively," Polo said.

Compaction

Handling breakdown compaction was a Cat® CB534D Asphalt Compactor. It made two passes without vibration, and one pass with vibration. A Cat® CB434D Asphalt Compactor followed, making several static passes. "The number of passes depends on a particular day," Polo said. "We'll adjust based on how things are going."

A Cat® PS150C Pneumatic Compactor was inserted between the CB534D and CB434D if more compaction was needed.

The Main Runway

The mix on the main runway included larger aggregate, and therefore cooled faster. As it had done during the ramp paving, Pavimentos Universale worked every 8-9 m when handling the main portion of the runway.

"We do the work in eight passes," Polo said. "We start at the low end, then skip a lane, then do another, then skip. We do this all the way across, for a length of 70 m—the maximum length the airport officials allow us to pave in a single night. Then we go back and fill in the gaps. When we do that we pave 1 cm higher on each side to help make the joints even."

The compaction train is similar to that used on the ramp portion of the project.

Finishing the Job

Pavimentos Universale was able to finish the job on time and on budget. "The nightly timeframe was tight," Polo said. "With only five hours to work, you have to make every minute count. Our crew was able to make the most of our time. The Cat Paver helped, too. With time that tight, we really needed a reliable, productive machine."

Polo also praised his Cat Dealer, GECOLSA, for their timely support during the project.

The machine delivered, as did the Pavimentos Universale crew. "The job went well, and we hit our specs," Polo said. "It's a much improved runway."

Visitors to the beautiful city will now receive a smooth reception.Ω