Look down on Illinois from the air and you might think the state has lots of asphalt roads. What you can’t see is that underlying the asphalt is a concrete base. The state has a historical belief in concrete pavement. Nearly all of the state’s highways were originally built with concrete.
Over the past three decades, as the concrete pavement has aged and cracked at the surface, the state has fixed the concrete with patches and asphalt overlays to extend the pavement’s life. Finally, about a 20-mile segment of I-70 in eastern Illinois had too much deep, age-related damage to be repaired; it had to be reconstructed.
The Illinois Department of Transportation (IDOT) started the pavement selection process about the same time the Illinois General Assembly passed a bill in 1999 to require the state to start building long-lasting pavements as demonstration projects. The goals were to try to build pavements that would last 30 years and need less repair and less traffic disruption and to offer warranties on the pavements for their first five years.
IDOT was skeptical when the Illinois Asphalt Pavement Association (IAPA) proposed reconstructing I-70 as an asphalt pavement from the bottom up. The agency also was skeptical about rubblizing the concrete pavement to serve as a base for the asphalt.
The stretch of I-70 that needed rebuilding is in Clark County, Ill., on the border with Indiana. The highway runs through a rural area, but it is a major route from Indianapolis through St. Louis to Kansas City, so it sees lots of truck traffic. Almost half of its 24,000-25,000 vehicles per day are trucks.
The thicker the better?
IDOT used a pavement model that said the heavier the truck traffic the thicker the pavement has to be. IDOT had two primary objections to the asphalt proposal. First, in their model, to withstand very heavy truck traffic, the asphalt would have to be so thick it would no longer be cost-competitive with concrete. IDOT’s second objection was that asphalt would rut and have to be repaired.
“We take exception to both of those,” Marvin Traylor, Ph.D., director of engineering for IAPA, told ROADS & BRIDGES. “One, the perpetual pavement says that once you get your pavement thick enough, around 14 in. or something like that, you don’t need to get any thicker than that, because it won’t wear out from loading.”
Second, Traylor said, the rutting problem in asphalt can be solved with Superpave polymers.
The asphalt contractors in Illinois were eager for a chance to persuade IDOT to try asphalt on I-70 and ensure asphalt would continue to get a slice of Illinois’ interstate paving pie in the future.
Traylor and others told IDOT that perpetual pavement would fail at the surface and be easily resurfaced, unlike concrete which eventually fails at the joints through the full depth of the pavement and must be reconstructed.
What finally enticed IDOT to try perpetual pavement was the willingness of the asphalt backers to offer a 20-year warranty on their pavement.
“We were confident that, given an opportunity to compete head to head against a concrete solution with a long-term warranty,” Traylor said, “because our failure modes were different than theirs were, we could have a much higher reliability of understanding our future risk and we would win that bidding contest.”
Traylor added, “In order for us to get our point across that we truly weren’t long-term expensive and that we could handle the truck traffic, the only way we could get IDOT to change their thinking was to do this radical offer.”
Ultimately, IDOT decided to split the paving of I-70 in half: 9 miles would be paved in concrete, and almost 11 miles in asphalt. Both types of pavement would provide a five-year warranty.
IDOT also was skeptical about rubblizing the existing 8-in. depth of reinforced concrete and constructing the asphalt pavement over the top of it. The state had very little experience placing asphalt over rubblized concrete in a high-traffic area. What’s more, IDOT said the soil was bad under that section of I-70.
IAPA and the University of Illinois reviewed the soil analysis and told IDOT they were confident the soil would hold up under the rubblized material and asphalt.
IDOT agreed but still wanted to be conservative. Their model would have required over 20 in. of asphalt pavement above the rubblized concrete. They compromised and agreed to 17.5 in.
“Our opinion is that’s way more than they need,” said Traylor. “We think 11 [in.] would have done it over a rubblized section.” There is disagreement in the industry about exactly how thick a pavement has to be to carry certain traffic for a certain number of years before it fails, according to Traylor, but the consensus is between 12 in. and 15 in.
Hot mix meets road
According to IDOT’s final specifications, the first lift over the rubblized based was 6 in. of asphalt with an N90 binder. Then there was a 4-in. lift using the same binder. Then came a 3-in. lift of a harder N105 binder and another 2.5-in. lift of N105 asphalt. Then to top it off was 2 in. of stone-matrix asphalt (SMA) with N80 binder as a surface layer.
“We basically did not have any problems with density on the entire job,” Charles Adams, president of Howell Asphalt, Mattoon, Ill., told ROADS & BRIDGES. “We used material transfer devices on every lift, so segregation was not a problem either.”
Howell Asphalt shared the paving duties in a joint venture with Champaign Asphalt Co., Champaign, Ill. Howell paved the east end of the section, and Champaign did the west end.
Both companies bought new asphalt plants to accommodate the quantity and specifications of the perpetual pavement mix. Adams said on an average paving day on I-70, they needed to produce 6,000 tons of hot mix.
“We have—as does Champaign—several older asphalt plants that do a great job on regular mixes that you’re running in June, July and August,” said Adams, “but when you’re running these newer mixes, particularly the SMA that requires fibers to be used . . . you really have to have equipment that is designed to run those. The newer equipment is, but some of our older equipment is not.”
Howell and Champaign both chose to buy Astec Turbo 400 asphalt plants.
The two companies shared equipment and at times even combined crews on the job.
The mix called for polymers throughout the entire 17.5 in. of asphalt and lime as an antistripping agent in all mainline mixes. It is unusual to have polymers in all layers of a perpetual pavement, but IDOT was worried about rutting in the pavement and wanted to be conservative.
Howell started construction on the two eastbound lanes. They used crossovers to put eastbound traffic on the westbound lanes while they reconstructed the eastbound lanes. Likewise for reconstructing the two westbound lanes.
They had the eastbound lanes finished and open to traffic by July 4, 2003. The whole job had to be finished by the end of October 2003.
“The thing that I really like about the whole process is that it is extremely logical,” said Adams. “You can go in very quickly and mill off the pavement and begin the rubblization process and then begin laying asphalt. From a contractor’s standpoint, you don’t like disjointed operations; you like things that you can set in motion and then it’s smooth and it flows. This type of reconstruction process in my opinion is wonderful.”
At 5 a.m. Howell started the milling machines going down the road. At 7 a.m. they started the rubblization machine down the road.
The rubblization was done by a subcontractor, Antigo Construction Inc., Antigo, Wis. Antigo has a patented piece of equipment called a multiple-head breaker that looks like a collection of small pile drivers, according to Adams. As the drivers go up and down, they break the concrete into chunks in a 12-ft-wide swath, leaving the reinforcing steel in place. The speed of the machine and various other parameters can be adjusted to get the desired rubble characteristics. Antigo had a minimum of three multiple-head breakers at a time on the job, sometimes four.
By 8 or 8:30 a.m. they started laying asphalt. The pavers were followed by a typical Illinois paving train: two vibratory rollers, a rubber-tire roller and a static finish roller.
Howell and Champaign each had a quality control person at their HMA plant, plus a quality control manager for the entire project.
As part of the quality program, Howell and Champaign tested smoothness with a California profilograph before and after placing the final lift of asphalt.
Howell and Champaign received $174,200 in incentive money for the smoothness of their finished pavement and another $950,000 for completing the midpoint of the job before the Fourth of July and finishing the entire project early. The joint venture also received $10,000 for bridge-section smoothness.
Some materials were naturally consistent across Howell’s and Champaign’s halves of the asphalt pavement because they came from the same supplier. That was true for the liquid asphalt and the steel slag for the SMA. The aggregate for everything but the SMA came from different suppliers. And there was a lot of aggregate.
In fact there was so much aggregate needed for the job in such a short period of time that the paving companies told their suppliers to start producing early and stockpile it.
“The thing that we were most concerned with from the very beginning was how we were going to get enough aggregate for a project this size,” said Adams. IDOT let the contract in June 2002, so a lot of the preparation work could be done the summer before the serious paving had to start.
“The real advantage was we were able to then give the stone quarries basically an opportunity to start producing aggregate in July 2002, the majority of which we would not need until the spring of 2003. By the time we started production in the spring of 2003, both of the stone quarries, a Vulcan quarry in Casey and Quality Lime in Marshall, Ill., had huge quantities of aggregate on the ground.”
Vulcan is a very large company. Quality Lime is a small, privately owned company, but they have a big enough yard to hold some of the aggregate stockpiles and they trucked some of it to the site of Champaign’s asphalt plant, where they made a second storage area. Vulcan’s quarry had recently opened a new section, which was put to work with an asphalt plant and aggregate storage.
If the Howell-Champaign joint venture had not had as much lead time before starting mainline paving, the quarries could not have kept up with the demand for aggregate.
Good planning and efficient operation paid off for the joint venture of Howell Asphalt and Champaign Asphalt. Fast construction and long-lasting pavement should pay off for IDOT and the travelers of Illinois.