The pavement was placed in four lifts, with the three 3-inch base/binder courses consisting of a PG 64-28 AC, ½-in. aggregate dense mix with lime additive to prevent stripping. The top 2-inch wearing course was produced with a PG 70-28 AC binder, ½-inch aggregate and lime additive.
"The contract called for a rich mix design (6.5 percent) and an anti-stripping agent (lime)," Seehawer says. "We were also allowed to use up to 30 percent RAP (reclaimed asphalt pavement) in the mixes we produced and placed; but since we were constructing a new road, we didn't have a RAP resource and had to go with all virgin materials."
Since the U.S. 97 project was a new road, the contractor's crews had the luxury of working without the traffic challenges normally associated with a typical mill and fill project.
"We had as many as four different pavers (Blaw-Knox) on the project at any given time, allowing us to pave in echelon," Seehawer says. "Paving in echelon not only allowed us to increase production, but also allowed us to achieve better longitudinal joints, especially between the two mainline travel lanes and do so using only three or four (IR) double-drum vibratory rollers."
Without traffic concerns, paving crews were also able to extend screeds to hot-lap turning lanes and other expanded areas, which eliminated longitudinal joints in the process. Along with the two 12-foot-wide travel lanes in each direction, the paving crews also constructed a 10-foot-wide outside shoulder and a 7-foot-wide inside shoulder along the concrete barrier.
To feed the echelon paving process, the contractor used belly-dump trailer trucks to deposit windrows of HMA in front of pick-up machines that transferred the mix into the paver hoppers.
"We were using a portable CMI counterflow plant with a 100-ton storage silo to supply our paving crew," Seehawer says. "That plant can crank out as much as 450 to 500 tons per hour; and on days where we were placing our mainline (travel lanes) lifts, we were laying 4,500 to 4,800 tons in a 10- to 10.5-hour shift."
The resulting smooth ride
Paving in echelon not only allowed Oregon Mainline Paving to maximize production, but to do so in a way that also produced the smoothness requirements the project outlined.
Using a profilometer, ODOT established a smoothness price adjustments based on a Profile Index of acceptable smoothness deviations in specified sections (mm/km or inch/mile). The contract allowed a price adjustment based on the results of the Profile Index (PI) for each 200 m (1/10th mile) segment.
The price adjustment applied only to wearing course material placed in the travel lanes of the project.
The price adjustment was applied to the contract unit price for Level 3 12.5mm dense lime treated HMAC and PG 70-28 asphalt in lime-treated HMAC. If the paving contractor achieves fewer than 3 inches per 1/10th mile of smoothness deviations, the smoothness price would be adjusted by +5 percent.
"We achieved full bonus on the job for ride smoothness and density requirements," Seehawer says. "Our ride smoothness numbers came in below the allowed deviation spec to receive the additional 5 percent and we hit the required 92 to 93 percent density requirement."
For Oregon Mainline Paving, meeting the smoothness and mix quality requirements of the project represented approximately $250,000 in additional bonus pay.
"In a competitive market, bonus pay is crucial to the overall profitability of company," explains Seehawer. "You have to submit a tight bid to get the job, but then you have to deliver the job to the customer's expectations in order to make a profitable return on your investment. It's just the nature of bidding and building government agency projects and we're proud to be one of ODOT's leading contractors."