Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/85927
HighwayContractor cross-falls at two locations, but FNF changed that to eight locations using change orders. "So we had a chal- lenge of doing some survey work and a little bit of engineering to fi gure 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 uni- form thickness over the milled sur- face. 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 fi nal depths of as- phalt 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 signifi cantly boosted trucking effi ciency. If milling and paving had been done with separate trucks, the project would have required a total of about 35 trucks. FNF fi gured the more effi cient op- eration into its bid. "It worked out real well, and cut down tremendously on the number of trucks we needed and, therefore, the trucking hours," says Amator. Most of the truck tractors were made by Kenworth or Navistar (International). And by using double trucks, FNF could haul up to 26 tons of pay- load per hauling unit. By contrast, a street belly dump can only haul 24 tons. FNF used a few single-trailer belly dumps for locations, such as bridges, that required the trucks to back up. Double trucks don't back up very well. As is common in the Western United States, the trucks laid down the asphalt cooled down to about 180 degrees, we put a fi nish roller on it and ran that one in static mode," Amator says. "We would make two static passes to fi nish off the compac- tion effort." With the placement of a 1 ⁄2 -inch open graded wearing course, the paving was complete. Bonuses Galore ADOT allows up to a $4.00 per ton bonus for mix quality. Half of that comes from meeting asphalt content and gradations, and the other $2.00 can result from achieving compac- tion. "We averaged about $2.30 of the $4.00 per ton possible bonus on that," Amator says. For ride quality, ADOT awards bo- nuses for an International Roughness Index of anything below a 39. FNF averaged a 28 on the IRI – and won smoothness bonuses of $250,000. How was that smoothness The contractor won $250,000 in smoothness bonuses on the $10.3 million project. a windrow of asphalt, in this case in front of a Cedarapids pickup machine. For paving, FNF used a Caterpillar AP 1055 paver. Compaction was accomplished by three Caterpillar Model 634 rollers, all steel-wheeled machines. The breakdown roller ran close be- hind the paver and made six passes. Behind that came the intermediate roller, which typically made four passes in vibratory mode. "And once achieved? "We ran leveling skis on the milling machine itself," says Amator. "And we had leveling skis on the paver also. We try to maintain a constant speed with our paver, and had good communications between the hot plant and the paving crew. If the hot plant had to slow down for any reason, the paver would do the same, to match the plant's produc- tion rate. That way we seldom have to stop the paver. "Plus we had a very experienced paving crew out there. Rick Allen was our paving superintendent, and he has more than 35 years of experience at this. The project went very well. We were very pleased. And again, that success doesn't come from FNF alone – ADOT was a very good partner for us." Better Roads August 2012 11