Better Roads Staff
Achieving the high production/quality double on Interstate 10
FNF Construction and the Arizona Department of Transportation (ADOT) set the bar very high these days in hot mix asphalt paving on Interstate highways. Consider, for example, an 18-mile-long project on Interstate 10 in Cochise County. Not only did FNF achieve high rates of production on the $10.3 million project, but the company also won bonuses for both smoothness and mix quality. And, the project won a Quality in Construction Award from the National Asphalt Pavement Association and a Build Arizona Award from the Associated General Contractors.
“We moved down the road pretty good,” says Clint Amator, FNF project manager. “On some days we laid around 3,000 tons, and we had a few days where we actually placed more than 5,000 tons. Over the course of the project, we averaged right at 3,500 tons of asphalt per day.”
FNF ran a 24-hour traffic control operation for the project. “We were working about an 18-hour milling shift to keep up with our paving operations, so we really had to resource the project 24 hours a day to keep the traffic control running,” Amator says. The contractor kept traffic running in one lane at all times. ADOT limited the length of the one-lane closure to 4 miles.
Using one Roadtec RX 900 milling machine, subcontractor Valentine Surfacing of Vancouver, Wash., milled the pavement at 12.5 feet wide. Depths of milling ranged up to 5 inches. “When we did the 5-inch milling we were getting roughly 2 miles per day,” Amator says. “But when we were actually milling 3.5 inches, then putting back 3 inches of dense-graded mix, we achieved close to 3.5 to 4 miles per day on that.”
Amator says the major challenge of the project was the differential milling required to correct the cross-fall on super-elevations where the pavement curved. As designed, ADOT called for the cross-fall to be corrected in the paving phase. But because ADOT and FNF practiced partnering on the project, ADOT accepted FNF’s proposal to correct the cross-fall in the milling phase.
“If we saw a problem, we brought it up right away before it manifested itself into a real issue,” says Amator. “ADOT worked very well with us to listen to our concerns. For any potential problem, we put it out in the open and proposed a solution for them prior to having delays. Our handling of the super-elevations is an example of that.”
The original plans called for increases in cross-falls at two locations, but FNF changed that to eight locations using change orders. “So we had a challenge of doing some survey work and a little bit of engineering to figure out what kind of existing grades we had out there,” Amator says. “We went in there and used differential milling to increase the super-elevations to meet the requirement of a percent and a half cross-fall.”
That meant sometimes milling 5 inches deep on one end of the mill and a 1/2 inch deep on the other end. That way FNF could pave a uniform thickness over the milled surface. If the contractor had to correct cross-fall in the paving phase, the lift could become too thick in places and compaction would not be uniform.
In addition, the final depths of asphalt could be unknown if the grade correction is done with paving. That’s bad news, because everyone has to know how much the asphalt will cost to pave the project. “If you start over-running the asphalt too much, with oil prices these days, that would really have an adverse effect on the overall cost of the contract,” says Amator.
Average hot mix production from FNF’s Dillman asphalt plant – located 21 miles from the project – ran about 425 tons per hour. As designed, the asphalt mix called for 4.7 percent of PG 64-16 liquid asphalt. The top size aggregate was 3/4 inch.
For most of the project, FNF ran 23 belly dump trucks, most of them doubles, to haul asphalt out to the project. By using the same trucks to back-haul reclaimed-asphalt pavement (RAP) from the mill to the stockpile, FNF significantly boosted trucking efficiency. If milling and paving had been done with separate trucks, the project would have required a total of about 35 trucks.
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