Tiptoeing around a broom closet. At times that is how it must have felt as Des Moines Asphalt & Paving Co. maneuvered massive asphalt paving equipment in an 18-ft-wide working area surrounded by traffic on Iowa’s I-235 in Des Moines.
“The crew was challenged every single day,” Liz Baloun, project manager of the job for Des Moines Asphalt & Paving Co., told Roads & Bridges. “There was so much traffic out there [90,000 ADT]. There were about five different stages on the project and we were constantly moving traffic around to keep paving.”
All those careful steps allowed Des Moines Asphalt & Paving Co. to run with a successful strategy from start to finish, and the industry was just as quick to recognize it as the best asphalt paving project in the U.S.
On March 20, the crew accepted the Sheldon G. Hayes Award at the National Asphalt Pavement Association’s annual meeting in San Francisco. To qualify, a contractor must win a Quality in Construction (QIC) Award, which is determined by numerical scores given by pavement engineers at the National Center for Asphalt Technology on the basis of how well the contractor met the specifications and achieved density on the finished pavement. All the pavements that meet a benchmark figure are given the QIC award.
This is the second time Des Moines Asphalt & Paving Co. has struck black gold. The only similarity between the two projects, however, was the fact that asphalt was used. In 1998, the Iowa contractor claimed the Hayes on work done on State Highway 141 in Dallas County. Located 20 miles northwest of Des Moines, the project was out on a rural setting and involved building two new lanes.
“It was pretty much a ‘go down the road’ type of paving job,” Jim Gauger, president of Des Moines Asphalt & Paving Co., told Roads & Bridges.
The challenges were wrapped a little tighter around the I-235 job, which consisted of adding one new lane and a shoulder in each direction and resurfacing the existing lanes. “This job had a lot of staging, a lot of night work. It was a very demanding schedule under a lot of traffic,” said Gauger.
Finding the time, and the room
The crowning three-mile stretch of I-235 is just one part of a king-size project going on in Iowa today. In all, 14 miles are being worked on along the interstate, which links Des Moines with I-35/I-80 to the west and east. When it is all said and done, more than 100 different projects will make up the total reconstruction of I-235, which is set to officially end in October.
With so many sections dependent on one another, scheduling was crucial.
“When we looked at this schedule of all these projects, it was really clear to us that we had to have a very tight schedule because one followed another, followed another, followed another, and so on,” Bob Younie, District 1 engineer for the Iowa DOT, told Roads & Bridges. Younie was the state engineer on the Hayes job. “So if you delayed one, pretty soon you had a whole string of projects being delayed.”
Keeping the paver moving became critical on I-235. The section Des Moines Asphalt paved, however, redefined the comfort zone. Dealing in sections that were often just 18 ft wide, the contractor had to find a way to fit asphalt pavers, a material transfer vehicle (MTV) and compaction equipment on the road. The ultimate solution was to have trucks and the MTV positioned on one side of the project’s barrier wall, with the paver and rollers on the other. The MTV ultimately fed the paver by reaching over the wall.
“The MTV was one of the most important pieces of equipment we had there because of the tight space,” said Gauger. “That is why we had the Shuttle Buggy to keep them on the closed lanes at night and deliver the mix over the top of the wall so we could keep our trucks moving.”
Staging was another critical function of the project. The contractor was required to keep a certain number of lanes open at certain times of the day. To accomplish this, Des Moines Asphalt & Paving Co. divided the job up into stages. According to Younie, the contractor was set up to pave one lane at a time.
“The goal was to close a portion of the roadway on off-peak hours, resurface it, paint it and open it back up for traffic before the next day’s rush hour,” he said.
To do this, Des Moines Asphalt & Paving Co. broke it down into longitudinal sections, laying down both the base and intermediate course of the 14-in.-thick pavement, shifting traffic over and repeating the process when it came to laying the surface course.
“Here you were doing something every day,” said Younie. “You were doing a little lick here, a little lick there, move in, move out. It’s a whole different kind of thing. You have to be very careful with your grade controls and cross slopes. It’s very, very complicated.”
From V-ditch to A+
Before paving factored into the picture, Reilly Construction, Ossian, Iowa, a subcontractor on the job, had to deal with a V-ditch that was to serve as part of the surface of the two new lanes. Crews brought in 1-in. limestone to form the 12-in. modified sub-base, which was placed on top of new storm sewer pipes ranging in size from 15 to 24 in. in diam. A 12-in.-thick concrete base also was poured over the section of pipe so crews could install the concrete barrier wall that the MTV used.
“Most of the storm sewer was about the level of the subgrade, so once you had the storm sewer in that was even more of a challenge because we were unable to cross that pipe without crushing it,” said Baloun. “We had to exit on one side or the other.”
Once the V-ditch was level, Des Moines Asphalt & Paving Co. took over the paving operations. Using two different asphalt plants—an Astec Double Barrel portable plant and a Cedarapids batch plant—located no farther than a couple of miles from the project, the contractor was able to crank out up to 400 tons of asphalt an hour. Mix was being produced at about 310°F. The base course mix consisted of 1 in., 75% crushed material with a PG 64-28 mild polymer asphalt binder. The intermediate course mix consisted of 1/2 in., 90% crushed material with a PG 70-28 asphalt binder, while the surface course mix also was made up of a 1/2 in., 90% crushed material with a PG 70-28 binder. The surface mix also had frictional requirements, meaning the contractor had to use quartzite to increase frictional characteristics. All mixes were designed to handle 30 million equivalent single-axle loads.
Once the mix arrived at the site, it was transported via a Roadtec Shuttle Buggy over the barrier wall and into a Caterpillar AP-1000 rubber-tired asphalt paver. Crews then laid the mat down at approximately 280-290°F. Following in the paving train was a pair of Caterpillar 634D double-drum vibratory rollers, a Caterpillar PS360 rubber-tired pneumatic roller and another Cat 634D double-drum vibratory roller. Des Moines Asphalt & Paving Co. formed a notched wedge joint to prevent future centerline cracking. Once crews reached the surface course section of the work, the asphalt pavers were working in tandem, according to Gauger. In all, a total of 55,000 tons of asphalt were laid for the base course, 57,000 tons were laid for the intermediate course and 25,000 tons were laid for the surface course.
Compaction was the most important function of the entire paving process. Iowa’s interstate asphalt mix carries a very short window relative to temperature. Here’s where the traffic situation again formed a thorn in the side of the operations. With the abbreviated temperature window, maintaining a proper flow of trucks was crucial. If a couple of them were held up in traffic, it could affect the quality of the mat.
“The contractor had to work very closely with the logistics of getting the mix in,” said Younie. “You can’t place it too fast or too slow. It’s a tight balancing act.”
In terms of testing, Des Moines Asphalt & Paving Co. ran hot-box samples to establish lab densities. Cores out in the field (in sets of seven) were taken every day. Cold-feed gradation also was monitored at the asphalt plant.
“The spec required that we run four mix samples daily and at least one [cold-feed] gradation, and we cut one set of cores for the roadway,” Mike Petermeier, QMA manager for Des Moines Asphalt & Paving Co., told Roads & Bridges.
According to Petermeier, crews were within one-tenth of the target of 4% air voids through the entire job. “We were very close to our gradation targets as well. We only had a deviation of perhaps 1 or 2%,” he said.
Field density readings were around 98%. For smoothness, a Laser Integrated Surface Analyzer was used for measurement. Des Moines Asphalt & Paving Co.’s work ranged between 0 and 1 in. per mile.
Iowa DOT also ran random state-acceptance tests.
“When we won this award the first time we were very shocked,” said Gauger. “Since we did that the guys have always had the goal to do it again. It really is unbelievable to do it twice.”
