For the past few years, the Utah Department of Transportation (UDOT) was regularly forced to patch and repair a highly traveled 9-mile section of I-80 that begins at the top of the Wasatch Mountain summit and extends to Salt Lake City, UT.
Previously, the state used an open graded surface course (OGSC) that was made up of a thin layer of hot-mix asphalt, comprised of 1/2-inch aggregate. An OGSC surface treatment is designed to have very small voids so precipitation seeps through it and drains off the side of the road. This process often works well, but not in this part of Utah. Extremely cold temperatures prevented the treatment from bonding correctly to the existing asphalt overlay.
"The OGSC lasted only two years and it was failing," said Deryl Mayhew, UDOT Resident Engineer and overseer of the project. "We were patching potholes constantly because the surface was cracking severely. We have many freeze and thaw cycles here because it might be in the 20s in the morning, and then up into the 50s by the afternoon. The OGSC really takes a beating during these cycles, so we decided to see if micro surfacing could do better because of its history of being a good product."
Micro surfacing to the rescue
Utah-based Intermountain Slurry Seal (www.intermountainslurry.com) won the Parley's Canyon I-80 micro surfacing bid. The company is a wholly owned subsidiary of Granite Construction Company, one of the nation's largest heavy civil contractors and construction materials producers. With a specialty in various pavement preservation methods, Intermountain Slurry Seal's three branches in Utah, Nevada and California work together and cover most of the western United States.
This particular project consisted of six total lanes -- three going east and three going west -- over a stretch of nine miles. Intermountain Slurry Seal milled the previous surface, and then used Bergkamp Inc.'s M1 full-size continuous micro surfacing paver to apply two layers, or a total of 1,211,553 square yards, of Type III micro surfacing treatment.
Intermountain Slurry Seal took on many challenges when they executed this high-profile job:
Challenge 1: The Existing Surface. Micro surfacing is well suited for protecting roads in the early stage of deterioration and serves as a surface treatment that extends the life of the existing asphalt. It doesn't provide structural stability to the road.
With the previous surface in such bad shape, Intermountain Slurry Seal performed a 1 1/2-inch mill to remove the unstable OGSC layers before applying the micro surface. A fine head mandrel with milling tools, or teeth, only a 1/4-inch apart was used to create a smooth milling surface that appeased ongoing traffic and provided a better bond between the existing asphalt and the new micro surfacing treatment.
Challenge 2: UDOT Restrictions. With an average traffic volume of 51,000 vehicles going in each direction per day, the UDOT and Intermountain Slurry Seal set up general guidelines to keep traffic moving as efficiently as possible. During rush hours, the contractor was allowed only a single-lane closure, while off hours allowed for a double-lane closure to do the necessary milling and surfacing. Failure to comply with any of these lane closure limitations would result in a penalty of $1,500.00 for every 15-minute violation.
"We did all of the milling work at night due to traffic restrictions," said Rusty Price, General Manager for the Utah-based Intermountain Slurry Seal branch. "We cut the road the full width every night so it would be ready for motorists the next day. That meant backing up the mills and doing smaller stretches than normal. On an average night, we would cut between 4,500 to 5,000 feet."
Challenge 3: Proper Bonding. Due to temperature fluctuations and the considerable amount of snow the Parley's Canyon area receives, proper bonding of the new micro surface to the existing asphalt was crucial. Intermountain Slurry Seal thoroughly cleaned the surface so the pavement would adhere directly to the new treatment. Nearly all of the micro surfacing was done during the day because it adheres better in warmer temperatures, so the contractor was forced to keep a concise schedule.