It’s easy to see why Koss Construction won a Quality in Construction Award this year from the National Asphalt Pavement Association for 10.3 miles of asphalt paving on Interstate 40 near Hazen, AR. Talk about smoothness! The company’s average deviation from a two-tenths-inch blanking band was a miniscule 0.08 inches per mile.
Koss not only won the award from NAPA, but it also won $140,000 in smoothness incentive bonuses from the Arkansas State Highway and Transportation Department. And the company won $500,000 in incentive payments for a combination of achievements on density and air voids in the asphalt.
The specification on density was 93% to 96% of maximum density, and Koss averaged 93.7% on the surface course, 94.0% on the binder course and 94.4% on the base course.
We asked Mark Haines, P.E., a senior engineer with Koss, how the company managed to achieve such a smooth pavement. “We used a long traveling stringline on the paver, and we take care with our finish rolling,” says Haines. “We used a Roadtec Shuttle Buggy, which definitely helps, because it maintains a surge of material out in front of the paver. That’s how our guys pave. They pride themselves on creating a very smooth pavement. The paver never stops.”
The $54 million project took just 215 working days to complete. Koss’s contract included totally reconstructing four bridges, breaking the existing faulted concrete pavement, and paving 416,000 tons of asphalt in three courses.
The project was designed with median cross-overs, and traffic was moved to one side of the Interstate while Koss worked on the other side. Traffic ran head-to-head with a concrete barrier wall to separate the two lanes. When one side of the four-lane divided highway was completed, Koss would switch traffic onto that side.
Once traffic control was set up, subcontractor RMI (Resonant Machines) began rubblizing the 10-inch-thick concrete pavement. “They did a great job,” says Haines. “They’re one of the few contractors that have the machines capable of meeting the resonant requirement of the Arkansas Highway Department.”
RMI says its “resonating beam” technology breaks concrete into uniform particle sizes down to 6 inches and de-bonds the rebar from the concrete. Based on more than 28 years of experience, RMI says contractors have found that rubblizing the concrete and using it for sub-base is 60% less expensive than removing and replacing the concrete. One machine can rubblize one lane mile per day. Following the rubblization process, Koss seated the concrete by rolling it with a steel-drum roller.
Koss began paving by placing the base course with a Roadtec asphalt paver. The base averaged 7 inches in thickness. “The job consisted of correcting the cross-slope to their new standards,” Haines says. “So there are some areas where the base course was only 2 inches thick and in some areas it took three or even four lifts.
“The binder course was 3 inches thick,” he says. “And the surface course was placed in two, 2-inch lifts. We paved 16 feet wide on the inside lane, and that includes the inside shoulder. We paved the driving lane at 12 feet wide by itself, and the outside shoulder was a 10-foot pull.”
Asphalt came from a portable Astec plant set up near the job site. The plant could produce more than 300 tons per hour—and Koss averaged more than 2,500 tons per 12-hour shift.
We asked Haines if completing the job in 215 working days was a challenge. “It definitely was,” came the answer. “We had a large quantity of asphalt to pave, and traffic conditions made it difficult to get trucks into and out of the work zone. A typical paving day would start at 1 a.m. and last through 1 p.m. or 2 p.m. the next day. That way the crew avoided the heaviest traffic in the afternoon through the evening.”
Koss used a combination of Hamm and Ingersoll Rand steel-drum rollers to compact the asphalt. Both the breakdown and intermediate rollers ran in vibratory mode, as did the finish roller on occasion. “We had a quality-control technician out there all of the time, verifying density with each pass, to make sure that we were getting adequate density but not going too far,” Haines says.
The base asphalt mixture had an optimum asphalt content of just 3.3%. “That’s common in Arkansas on a base mix,” Haines says. “Base mix in Arkansas is 1.25 inches nominal maximum aggregate size and with the compaction level required on this Interstate, that asphalt content is common. The aggregates that we used there allow very little absorption. It’s a very hard, durable granite aggregate.”
The binder used on the base course was a polymer-modified PG 76-22, and the air voids spec was 4%. The binder course used the same asphalt cement, and asphalt content for it was 3.8%. The nominal maximum aggregate size (NMAS) was 1 inch on the binder course. Asphalt content rose to 4.8% for the surface course, and the NMAS was one half-inch.
Koss not only won smoothness and density bonuses, but also a bonus for finishing the project early—30 days early.
Author’s Bio: Daniel C. Brown writes on technology, safety, and the construction industry.