Two big cold mills were used in tandem to prep busy I-10 for a hot-mix asphalt overlay late last year west of Houston.
The project involved a mill-and-fill surface overlay for the Yoakum District of the Texas Department of Transportation. “At the moment we are doing profile milling to eliminate wheel rutting and to provide a level surface for the overlay,” said Matt Downing, project manager and safety officer, Durwood Greene Construction Co., Stafford, Texas.
The 16-mile-long project was undertaken in September 2011 and was located in the vicinity of Sealy, Texas, some 50 miles due west from downtown Houston. It encompassed both eastbound and westbound main lanes, including shoulders. Approximately 120,000 tons of asphalt were placed on the project.
The existing pavement structure was an approximately 17-year-old asphalt overlay over jointed concrete pavement. The asphalt overlay had developed rutting in the wheel paths, and the underlying concrete pavement’s transverse joints also had reflected through the existing asphalt surface.
Extensive use of cold mills was not planned at first, but was later implemented to improve ride quality on the westbound main lanes.
“Originally we were just to mill the end points of the pavement at transverse joints to provide smooth tie-ins at the bridges and end points,” Downing said. “We also were to mill underneath overpasses so we would not raise the elevation of the driving surface below bridges. But the state noted that preconstruction high-speed profile ride data showed that the left westbound main lane had a high number of bumps and dips, in excess of 700, and wanted to see how profile milling could improve the ride, and that’s what we are doing.”
The pavement was being milled from 0.75 to 1.5 in. in depth, and Durwood Greene was coming back with an under seal and two separate 1.5-in. courses of HMA.
“The first lift is an inch-and-a-half compacted of what we call a ‘level up’ course, and the second lift is a final surface mix, also an inch-and-a-half compacted,” Downing said. “We are placing a standard Type D TxDOT hot mix, a performance-graded mix.” The same mix was used in each lift and was provided by American Materials Inc., Jersey Village, Texas.
Both lifts were placed with Durwood Greene’s Vögele Vision 5203-2 10-ft. wheeled asphalt paver utilizing dual “big skis” for grade control. The Vögele Niveltronic control system was giving the contractor the smoothness it needed to satisfy TxDOT specs.
“A lot of what we like about the paver is its noncontact skis,” Downing said. “They eliminate contact with the freshly laid surface and eliminate imperfections that can give you trouble with other systems.”
Durwood Greene had already earned smoothness bonuses on this project using the control system.
Mills in echelon
To expedite milling, Durwood Greene used two of the largest cold planers available, W 210 and W 2200-12 mills from Wirtgen America Inc.
“The W 210 has a 7-ft, 2-in. drum and the W 2200 has a 12.5-ft, full-lane drum,” Downing said in September. “Both machines have the Level Pro system that allows the ground men to establish grade and slope,” he said. “The W 2200-12 is doing full width at the moment, starting on the inside lane with the first pass, and working to the outside.”
The milling and paving took place at night and the two cold mills operated in echelon, one in front of the other. Between 40 and 50 trucks were in rotation each night for the milling operations.
Reclaimed asphalt pavement (RAP) was being stockpiled for use on the same project along the edge of the shoulders.
“We call it ‘shouldering-up,’” Downing said. “After we pave the shoulder, we will put the RAP along the edge to stabilize it. It’s typically placed with a road widener, and then a single pass is made with a roller.” This provides an enhancement for the safety of the traveling public by addressing the issue of shoulder drop-off.
“After we put the RAP down on the edge of the shoulder, we will shoot oil on it to help bind it together and hold it in place,” he said.
A gentle roll
Besides the mills on this project, Durwood Greene also has a Wirtgen W 2100. In addition to the Vision 5203-2 10-ft wheeled asphalt paver that was used on this project, a Hamm HD O130V tandem roller with oscillation compaction in one drum, and conventional vibration compaction in the other, was used as a breakdown roller.
The firm was using oscillation in breakdown mode. Oscillation compaction is nonaggressive because it compacts with a gentle rocking motion, not a vertical pounding. Horizontal forces are transmitted from the drum into the pavement, and the result is better compaction in fewer passes, with less vibration-related wear and tear on operators and surroundings. While conventional compaction works by “bouncing” the drum on the ground, the oscillation technology used on the I-10 job ensures that the roller drums maintain constant contact with the surface for faster, more effective compaction.
On I-10, the company also used a Hamm HD 140 VV HF roller with high-frequency vibration for intermediate rolling and a pneumatic roller to achieve final compaction.
Durwood Greene was doing its milling and paving on I-10 at night, as required by TxDOT. “We get the highway from 7 p.m. to 5 a.m.,” Downing said, with lane closure fees assessed for failure to vacate a lane. Unlike some other states, Texas does allow driving on the milled surface. R&B