On-Site Magazine

MTO attempts first “hot-on-hot” project in North America

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February 1, 2012 by Andrew Snook

This past September, the Ministry of Transportation of Ontario (MTO) paved its way into North America’s history books, by testing out a new asphalt technology. The MTO’s hot-on-hot trial run on Highway 12 near Midland, Ont. was the first commercial construction project using the technology in North America.The drive to test this technology is the potential 35-per cent reductions in paving times, increased life spans for roadways, reduced closure times and less environmental impact.

The testing ground for this project was a 6.7-kilometre stretch of Highway 12 near Midland, which involved removing existing pavement and replacing it with two simultaneous layers of hot mix asphalt-a binder course then a wearing course.
The project began construction on September 8, 2011 and was completed on September 23, 2011.

Anil Virani, senior bituminous engineer for the MTO, explains the section of Highway 12 was chosen for the trial for a couple of reasons: it included thickness designs and mix types that the MTO uses in many applications; provided the opportunity to demonstrate two-lane-wide paving, as well as the conventional single-lane-wide paving; and there was enough tonnage of mix types for the process to be economically viable for a contractor.

The winning bid
The MTO specified that the trial project had to be hot-on-hot paving and the bid was awarded to King City, Ont.-based K.J. Beamish Construction Co. Ltd.

K.J. Beamish has been building and maintaining highways and roads since 1946, has operations located throughout central Ontario and employs more than 600 people.

The project’s overall cost is approximately $5.8 million.

There are two types of hot-on-hot paving technology currently available; Dynapac’s Compactasphalt and Wirtgen’s Vögele InLine Pave train. K.J. Beamish chose to go with Dynapac’s Compactasphalt, a single machine that paves both courses of asphalt, using two hoppers and two compaction screeds.

The InLine Pave uses two separate pavers and a conveyance system. Dynapac supplied its $1.8-million machine for the trial and K.J. Beamish rented the equipment on a monthly rate.

To ensure the project would run smoothly, K.J. Beamish sent its foreman and head mechanic to Dynapac in Germany to learn about the machine firsthand to prepare for the project.

“We weren’t going to take any chances that this thing was going to be a quick learn,” says Fernando Magisano, vice-president of technical services for K.J. Beamish. “Our schedule dictated that our guys had to be on it in a relatively short time here.”

Dynapac shipped over a team of three operators and one of its top technicians from Germany to assemble the machine and work side by side with K.J. Beamish’s crew, training them for almost two-and-a-half weeks. Dynapac also had two of its Canadian representatives on-site for the majority of the paving.

K.J. Beamish used an 11-man crew for the project, not a big difference from its standard paving crew of 8 to 10 people. It needed one extra person to operate an additional roller used on the project.

The Midland trial
The trial consisted of three different sections of Highway 12 being paved using the hot-on-hot process. The lift thickness varied from 90 mm (30 mm surface course and a 60 mm binder course) to 140 mm (30 mm surface course and a 110 mm binder course).

Magisano says there were challenges his crew had to overcome when getting used to the equipment, but in the end the team adapted quite well. “From day to day the German crew was doing less and less and our crew was doing more and more.” Magisano adds there wasn’t a lot of new technology; it was just put together in a new form.

“It’s complex in that it doubles up on what we traditionally have to control. Instead of one screed there’s two screeds, instead of one feed system, there’s two feed systems,” he explains. “Once they were used to the machine, they realized that even though there’s double the number of controls and some of the electronics were a little bit different from the particular paver that they’re used to operating, at the end of the day there wasn’t an awful lot of difference to what they were doing.”

In addition to learning how to use the technology efficiently, Magisano says another challenge was the logistics behind keeping the machine fed with binder mix and surface mix. It required two types of mixes at once, and they were arriving from two separate plants, one in Midland and another in Orillia more than 40 kilometres away.

The machine also takes more time to set up than conventional pavers, and is not proficient at paving short-radius ramps and intersections. Due to safety concerns stemming from creating 140-mm lifts that would be driven on by incoming traffic, conventional pavers were used for paving intersections, turning lanes and lane widenings.

Compaction satisfaction
Magisano says one of the biggest advantages he found using this technology was in the compaction. “With this mix, because the cooling time is so long, we had an awful lot of opportunity to do good compaction,” he says. “It just gives you so much more time behind the paver because you have such a thick mass that stays warmer longer.”

Chris Raymond, head of the bituminous section of the MTO, agrees. “Based on this project, compaction seems to be very good and we’re not seeing any crushing of the aggregates when you compact, which we sometimes see with conventional.”
Virani points out that one of the challenges this project posed was allowing enough time for the 140-mm thick lift to cool. “Some of the cooling curves that we presented showed up to 7 or 7.5 hours before we considered it appropriate to put traffic back on it.”

However, Raymond points out that one 110-mm interval of hot mix will take less time to cool than placing two thinner lifts of 70 mm and 40 mm in one night of operation.  

Potential advantages

There are several other potential benefits of using hot-on-hot paving. This includes reducing the surface course by 25 to 30 per cent, no longer requiring a tack coat between lifts and having the paver running a single rolling pattern.   
Raymond says the technology is not ideal for Highway 12 and is better suited for straight-line paving on higher-volume roads with extended closure times, such as green-field construction.

The environmental benefits are promising too. According to Raymond, there are three “green thrusts” with this technology:
1. It allows operators to use less of the premium surface course aggregates, because the technology allows you to have a thinner surface course.
2. Reduced road closure times lessons the amount of emissions produced by traffic delays.
3.  The pavement lasts longer.

Virani points out that the paving process could also eliminate any deficiencies related to longitudinal joint construction.
Both the MTO and K.J. Beamish took a variety of full-depth core samples at the joints to test the level of compaction.
Magisano says K.J. Beamish will be doing some testing of the core samples during the off season to check the core densities, and may slice the cores into 50-mm cuts to see if there are any differences in compaction.

“We’re hoping we can answer it to the positive that the joints will work just fine,” Magisano says.
K.J. Beamish plans on sharing their findings with the MTO.

Bill Wilcox, Dynapac’s heavy equipment product manager, says using a dual paving system can make paving up to 35 per cent faster on the right project. “Upon the crews getting comfortable and fully trained, and logistics catching up to the truck deliveries, then those kinds of numbers can be realized,” he says. “It doesn’t happen on the first day out, intense training is required. It is a different c
oncept and different process, but those numbers are being realized in Europe where they have been doing this for four or five years.”

Wilcox says the very best opportunity for this type of technology would probably be in a big public-private partnership (P3) where parties are looking for a long-term guarantee on the asphalt they’re building.

Barriers to hot-on-hot technology
Magisano said a major barrier to this technology is the way some contracts are formed. “It comes down to the mindset of the owner, as to how you’re going to design a contract to allow this paving operation to work, and by that I mean you’ve got to realize that you have two different mixes coming to the paver,” he says. “The logistics of getting your trucks in the right order can’t happen in a single-lane closure. You just don’t physically have enough space to do that. You have to think of longer closure times, because this paver as compared to a conventional paver takes much longer to set up. You’ve got two sets of screeds, not one, because of the uniqueness of what it’s doing, the setup times and the shutdown times are roughly three times longer [than conventional machines].

“Most of our 400-series paving is done at night. We’re lucky to see 10 p.m. closures and we have to have the roads open at 6 a.m. That short time period is a real disadvantage to the equipment because it takes so much time to set up and shutdown the operation.”

The sheer size of the paver makes for additional challenges, particularly if it is double-lane paving. “We had it set up for an eight-metre paving lane section. Now, you cannot physically tear that paver down in under two or three hours and float it out of the roadway,” says Magisano. “It would have to have a place to park in between shifts. There are very few places where you could crawl that machine and have it park eight-metres wide until the next night. So it comes down to selecting the right contract in order to get the best productivity out of the machine.”

The MTO or owner of the highway would need to allow longer closure times, or extended lane closures instead of six-to-eight-hour closures.  

“They’re going to have to accept the fact they’re going to have to close down a section of road and have either a detour system or just a closure of a certain number of lanes for two to three days,” says Magisano. “Then you get good production and you can go two crews, 24 hours, get in and out, get a lot of tonnage done in an awful hurry. Unless we see those sort of changes in the way the contracts are designed, then there’s limited use for this sort of equipment.”

Lars Narsingh, manager of commercial support and development at Wirtgen America, offered a similar sentiment in regards to the need for more contracts that use this technology, stating that contractors will be hesitant to invest until there are more opportunities available.

“If the utilization of this equipment is increased, then contractors can afford to buy it,” Narsingh says.
Wirtgen’s InLine Pave costs approximately $1.2 million.

Pave-in time
The Ontario Hot Mix Producers Association (OHMPA) organized a “Pave-in” during the trial, and had more than 85 people from the road building and hot-mix paving industries in attendance to see the new process, as well as listen to presentations by the MTO, K.J. Beamish and Dynapac.

Michael O’Connor, CEO of the OHMPA, says he wasn’t sure that this technology would extend roads’ life expectancies 10 or 15 years, but he did think it would eliminate potholes. “You’re still going to have to go in after 22 years or 25 years and take the surface off by milling and grinding it and putting it back,” he says. “But, you’re going to have less maintenance and excellent surface to deal with. Just the fact that you’re putting both those pavements down at the same time, you get a complete bond between the two, so there’s no place for a pothole to go.

“They’re getting excellent compaction because of the very thick lifts, and it’s something we’ve been saying even in regular paving, especially when it gets late in the year. They should be finding ways to put down thicker lifts, because it holds the heat.”

According to O’Connor, the technology is ideal for green field construction such as the current project on Highway 407, or a 400-series highway, but making the technology affordable for a contractor to purchase all comes down to the MTO, since they are the prime candidate for using this equipment in Ontario.

“Unfortunately, that big hot-on-hot paver wouldn’t work well in most municipalities, unless you’re talking like the City of Toronto and the Don Valley Parkway,” he says. “So it really gets down to being mainline paving, and the absolute best mainline paving would be a new road or virgin territory. That would be amazing for that machine. You could really do, not only an excellent job, but do it very quickly and efficiently.”

As motorists make their way to-and-from Midland on Highway 12 over the next decade or two, only time will tell if this technology goes into North American history books as either a breakthrough or a bust.

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