High-altitude roadbuilding requires number of adjustments for prep and paving.
The Nevada Colque Cruz in the Peruvian Andes is breathtaking. The views of the glacier-clad summit are sublime, but more than 16,000 feet above the sea the scant oxygen in the frigid air means even small movements leave a person gasping. It is a brutal place to build a road.
The work zone crosses about 35 miles of one of the highest reaches of the $1.3-billion InterOceanic Highway project now being built across Brazil and southern Peru. When completed in 2010, the highway will create a 3,100-mile paved connection between the Atlantic and Pacific oceans.
Conirsa, a consortium of several Peruvian firms led by the Brazilian construction firm Odebrecht, has developed a number of unusual strategies to handle the high-altitude job, with its thin air and pervasive cold.
Paving for the 2008 construction season began in early June and will include sections of the Tramo II project, as this phase is called, that are above 13,000 ft. To cope with the high altitude and cold, Conirsa engineers have concocted two innovations: a series of heating tents to keep trucks loaded with prepared asphalt up to working temperature in the early morning cold, and a machine called the Dragon, with gas jets to heat the roadbed in advance of the crews.
Crews spent last season preparing to pave.
A 1,640-ft-long tent shelters worksite from weather.
When first used late last season the measures doubled the paving capacity to 40 trucks per day at a cost of less than $50,000. Project managers say last September alone the innovations saved the venture $400,000 and $1 million over the paving season.
Sergio Panicali, director of the Tramo II project, says finding ways to work in extreme conditions have become the norm. “Every new situation requires a unique approach,” says Panicali. “In each of these critical sectors, we must see what is happening, understand it and study the engineering solution best suited to address it.”
Conirsa’s Tramo II contract is a 186-mile stretch across the Andean highlands. It is one of two contracts, with a combined value of $562 million, out of five contracts to build the $1.3-billion highway that Conirsa won in 2005.
Although Conirsa paved approximately 62 miles in last year’s push, the primary focus on the high-altitude section at that time was on bridge building, grading and roadway preparation to allow for continuous paving at high elevations this year. Panicali says laying down asphalt now is the focus. Some of the job’s biggest challenges lie within this segment.
The highway will have two 10-ft-wide lanes with 2-ft shoulders and a 2.5% crown. The surface will be finished with a micropolymer in the last year of the contract.
Although daytime temperatures at high elevations during the construction season regularly top 90ºF, nighttime temperatures fall below freezing, and even below 0ºF, which means it can take hours for the sun to bring the roadway to the minimum 50ºF necessary for paving. Paving is only possible from June through September and even then the daily window is typically five hours or less. In addition, wild temperature and weather swings are common. Mix batches are aggressively adjusted with poly-mer additives to maintain workability. Although additives are expensive, Panicali says they are necessary for roadbuilding and should significantly prolong the roadway’s service life. Without extraordinary measures, work cannot start until about10:00 a.m. and has to stop a little after 3 p.m.
Enter “the Dragon”
When they began, crews were only able to lay down 20 truckloads of asphalt a day—not nearly enough to stay on schedule. During the 2007 season engineers began searching for ways to speed production. They started by modifying a tractor and rigging it with 54 natural-gas burners to project heat downward to warm the surface in the early morning for paving. The goal is to get a jump on the sun’s midday warmup by removing ice and moisture from the roadbed, which delays the natural warming. On the best days the machine can help extend the paving window by as much as five hours.
To further boost production in foul weather, the company also shifts a 1,640-ft-long tent along to shelter the paving site. “The weather can vary significantly by wind or rain,” says engineer Guisselle Montoya. “The tent generates an optimal indoor microclimate for paving.”
The new highway will pass through the sparsely populated high Andes to link both coasts of the continent with a paved road.
Conirsa first introduced paving tents on a lower-altitude stretch, Tramo III, the venture’s other section of the InterOceanic project. That segment runs through the Peruvian jungle where long, torrential rains were bedeviling paving crews. Engineers there hit upon moving large, plastic-covered tents along with the pavers to protect the jobsite and maintain productivity during the region’s long rainy season.
Through use of the tents and the Dragon on the high-altitude site last summer, the paving rate was increased by eight trucks per day, with promise for even more. At the same time, another problem that limited the amount of asphalt that could be batched, maintained and delivered warm to the worksite in frigid conditions was being overcome.
“If the plant is started before 7 a.m. it produces too much asphalt to be taken immediately to the work front,” Panicali says. “The morning cold makes it impossible to produce additional asphalt and have it waiting to be transported.”
Crews work in harsh conditions and among locals.
The solution, once again, was shelter. Several tarp-covered tents were built at the Ocongate camp near the asphalt plant. They are 328 ft long and have a thermal layer to reduce heat loss, while 16 1,000-watt lights and 16 heaters fight the chill. Each tent costs less than $3,000.
As the loads of asphalt are produced, trucks are driven into heated tents in which a 55ºF temperature can be maintained. It is just warm enough to keep the asphalt ready for paving. Then, when the Dragon and sun have warmed the road surface sufficiently for the day’s work, trucks roll to the job from up to about 40 miles away.
The arrangement lets the asphalt plant get a head start on the day, cranking up at 5 a.m. Eight truckloads can be on hand as soon as the surface is ready for paving, making it possible on an ideal day to put down 40 truckloads of asphalt.
In the next three months, Conirsa plans to pave more than 25 miles of road, allowing them to complete 40% of the project by the end of the year.