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Mill to Grade: A New Way to Pave
Article from The Asphalt Contractor, April 22, 2000, story by Tracy D. DeStanzio

Over the years, Warren Paving has met the challenge of numerous and varied projects for its community and beyond.

Innovative ideas such as paving at night has been the benchmark of standard-setting ideas typical of Warren Paving.

In a marketplace that is advancing technologically faster every day, Warren Paving is on the cutting edge of progress with fresh ideas.

Using the Paveset grade control system from Dunn Equipment Co. Inc., Stone Mountain, Ga., crews were able to design and construct a smooth road by milling to grade prior to placing a 2-inch (50-mm) asphalt overlay.

Contractors, for the most part, are eager to try new paving techniques that promise to make their paving work easier and more accurate. Giving the owner agency what it wants in terms of pavement smoothness and grade and slope perfection is enough to drive a contractor to the most innovative of approaches, such as the use of profilographs, computerized grade control systems and design software.

These components were all used on a mill and overlay project for a 2.5-mile (4-km) long segment of Pass Road in Gulfport, Miss., a four-lane urban street carrying an average daily traffic (ADT) load of approximately 25,000 vehicles, according to Bill Powell, Gulfport's city engineer. The contractor, Warren Paving, Hattiesburg, Miss., used the Paveset grade control system distributed by Dunn Equipment Co. Inc., Stone Mountain, Ga. Using the Paveset Model E52000 profilograph as a survey profiler to collect data on the existing pavement, Warren Paving was able to design and construct a smooth road by milling to grade and then paving an overlay.

Road design provides grade and cross slope Project engineer Gamer Russell, of A. Garner Russell and Associates, consulting engineers in Gulfport, provided the design for Pass Road and supervised its construction. "Pass Road was an old road in need of rehabilitation," says Russell. "We had to maintain very good grade control on it and vary the cross slopes each way to drain (water) to the curb and gutter sections."

B.J. Sellers, manager of Warren Paving's Gulf Coast division, says that the existing pavement was in poor condition. "It had been quite some time since any work had been done on the road," says Sellers. "It was pretty severely cracked and oxidized, and parts of it exhibited signs of linear deformation. In other words, you had some up-and-down bumps and dips."

Russell says that while he designed the road for specific final grade and slope elevations, he let Warren Paving decide how they went about achieving those final results. "We were shooting for a specific end result, but we let Warren Paving handle the type of control to use to achieve it," says Russell. "We set the final grades up and told them what they had to finish with." How Warren's crews accomplished the task wasn't as important to Russell as the fact that they accomplished what he needed them to do.

"The main goal of the finished grade was a smooth riding surface and good, proper drainage off the roadway," says Sellers. To do that, Sellers and his crews used the Paveset system to mill off those bumps and dips, creating a smooth flat surface on which to pave.

Crews work to establish a level base surface

Warren Paving crews used Paveset's 25-foot (7.6-m) long Model F52000 Profilograph, a California-type profilograph that gathers two-wheel paths of data simultaneously, to measure the existing road's surface deviations. "We ran the profilograph on each lane (of Pass Road), which gave us a computer image of the surface, including the dips, bumps and rolling hills," explains Sellers. "The system takes that information and you can then create what you want the new surface to look like." Steve Dunn, of Dunn Equipment, explains that the Paveset software collects surface deviation data and establishes parameters - nominal, minimum and maximum thicknesses - for designing a smooth surface. The software allows the user to divide the section of roadway to be milled and paved into stations, making a table of thicknesses for each station. This data is then used to produce a surface plot showing the position and size of the bumps and dips, as well as the average crossfall. Once the data is transferred to the computerized grade control system, it can be used for milling the surface to meet those established parameters. The grade control system was mounted on Warren Paving's Wirtgen 1900-DC milling machine to control the variable depths of fills and cuts required to meet the project's elevation and smoothness requirements. Sellers says they set limits on the milling at 3 inches (75 mm) for a maximum cut and 1 inch (25 mm) for a minimum cut. "The system will use that tolerance and make the smoothest profile it can make," says Sellers. "Once you have the existing profilograph image and the proposed profile, you can start milling at certain intervals along the profile," continues Sellers. His crews used 25-foot (7.6-m) intervals. At station zero, for example, the cut between the existing profile and the proposed profile was 0.1 foot (0.03 m). At 25 feet (7.6 m), the cut may have been 0.15 foot (0.05 m). And at 50 feet (15 m), it may have been 0.22 foot (0.07 m). "Using that technique, you are cutting the existing surface down to the new profile you want, removing the humps, bumps, low spots and high spots," says Sellers.

Adds Russell, "We had to control the grade at every station, which is why we had to change the depth of cut, at certain intervals, to maintain the grade at that point and to meet the grade at the next point." A plate, with a sensor connected to the grade control system, was attached to the end gate on the back of the milling machine and run along the existing pavement, measuring each point as the milling machine progressed down the roadway. The sensor tells the system where the milling machine is along that surface plot. The system then automatically tells the milling machine how much it is supposed to be cutting at every point, and how much to vary the cuts between the points. "If you have one station cut at 0.1 foot (0.03 m), and at the next station you have to cut down to 0.2 foot (0.06 m), then between those two points the machine has to gradually cut lower," explains Sellers. "That way, there is not an abrupt drop between Point A and Point B, but rather a gradual, smooth transition."

The whole idea, says Sellers, was to get the surface corrected in the milling, which removed an average of 2.25 inches (55 mm) from the existing pavement. That way, when crews came in to pave the overlay, they could just do a constant lift and be assured that their pavement surface was smooth.

Paving made easier by mill-to-grade process

Once the base surface was established and leveled, crews were ready to place the overlay. Russell wanted a chip seal applied before paving the 2-inch (50-mm) asphalt overlay, though. Since the existing pavement was very cracked, some cracks going deep into the asphalt, the engineer wanted to place a single bituminous surface treatment on the pavement as a crack relief layer. This chip seal would separate the old pavement from the new, hopefully stopping any future
reflective cracking.

"The chip seal was used to isolate the cracking in the asphalt," says Russell. "We wanted to assure that the cracks from below didn't migrate up toward the new pavement."

The 0.375- to 0.5-inch (9.5- to 12.7- mm) layer of chip seal was placed directly on the milled surface. Because they could only shut down one lane at a time, in each direction, Warren Paving crews did much of the milling work at night. The chip seal operation followed right behind the milling operation. That way, the surface crews had milled the night before could be chip sealed the following morning and opened up to traffic. By the time crews got to the paving portion of the project, all they had to concentrate on was putting down a consistent thickness of asphalt; the grade had already been established with the milling. "The hard part was in establishing the grade we wanted in the milling process and getting the chip seal down," says Russell. "Once that was done, the rest was pretty easy."

Using a Roadtec 180-10 paver, Warren Paving crews placed the 2- inch (50-mm) asphalt overlay with approximately 8,500 tons (7,710 Mg) of Mississippi Department of Transportation surface-spec SC-i asphalt mix, which was produced by their Astec plant. Crews paved with single lane closures, starting from one side of Pass Road and working their way across. "It worked so easily that the public never got upset," says Russell. "A 20,000-plus ADT road can be disastrous if you are trying to lay asphalt in crowded conditions during the day, but there was very little inconvenience."

Technique saves time, pleases engineer and owner

Instead of running a measuring device along the pavement after it was paved and compacted, Warren used the Paveset system to run the smoothness long before paving ever took place. "This technique made it easier for us because we would typically have to go out and mark the pavement at each of those 25- or 50-foot (7.6- to 15-m) intervals," says Sellers.

"We would have to physically go out and paint our cuts on the pavement to get to the proper grades the engineer wanted," continues Sellers. "The system cut out a lot of time and effort on our part." In fact, Warren Paving finished the job in about 30 days. The milling, chip sealing and paving was completed in 26 days from start to finish.

In addition, explains Sellers, crews would normally have to run the milling machine manually, reading the cuts on the pavement and adjusting it up or down to meet those cuts. "This technique eliminated a lot of that effort, as well as the guess work and eye- balling we typically do." "Warren Paving did an excellent job," says Russell. "We were very pleased with their construction technique. And I think there was a benefit with the way they did the job - milling it down to grade and then bringing it back up with asphalt. It worked quite easily, versus doing it the traditional way - milling it down and paving it up to grade. It was Warren's innovative work that got the results we required."

Gulfport's Powell agrees: "We got very good results from this project. The city was pleased with the final product."


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