Asphalt roadbuilding costs are under pressure and pretty much everyone – from owners to contractors – agrees on the need to get them under control. Foamed asphalt, first developed in the U.S. about 50 years ago, holds potential to keep a wide array of costs down on both new road construction and road rehabilitation. Use of the technology has been growing quickly, starting in Europe a couple of decades ago and spreading around the world. Today, foamed asphalt is in use from Northern Europe to Saudi Arabia.
There are a number of technological alternatives in producing warm-mix asphalt, notes Bob Forfylow, president of the Canadian Technical Asphalt Association and director of Quality for Lafarge Canada Inc.’s Asphalt Paving Group in Calgary. Some are based on waxy additives while others involve the use of chemicals. The third alternative is mechanical foaming.
“There was a sort of a proliferation of all these different technologies,” says Forfylow. The original work focused on additives, since they were relatively easy to produce and test in the lab. Mechanical foaming was of less interest to researchers at first, since the technology that made it productive was slow to develop.
However, there was a problem with additives: the additional cost. “It can cost $4 to $6 a ton to make this [kind of] warm mix, so the savings that were being generated were being offset by the costs of these proprietary products,” notes Forfylow.
That drove renewed interest in mechanical foaming, which has burgeoned in the past decade. “That has kind of taken over, today,” he says.
The concept is pretty straightforward. Water, equal in volume to about two per cent of the binder, is injected into the binder as steam. The steam bubbles result in foaming that causes the binder to expand to approximately 18 times its original volume. “Because of that tremendous increase in volume of the binder, you get better coating of the aggregate,” says Forfylow.
Demand drove the solution to the production puzzle and a small number of manufacturers supply this market now. “The first foam job done in Canada was in Calgary back in the mid-2000s,” says Forfylow.
The beauty of foamed asphalt lies as much in what it does not do as in what it does. It does not usually require special mixes or testing. It might help the contractor bypass heavy expenses in materials or logistics. It can be used with high percentages of recycled asphalt (up to 100 per cent) and aggregate, reducing energy, transportation and material costs. In addition, as with any recycled product, the impact on the environment is much less severe.
The foaming can also help with compaction. “It seems like there’s more lubricity in the mix because there’s better dispersion of the asphalt binder,” says Forfylow. That can give a contractor more time to work and compact the mix.
What ultimately determines whether foamed asphalt will be used in a given application? Oddly enough, it often is not the application itself. “It has been tried in all kinds of applications, and to date has performed quite well,” says Forfylow. “It’s more a question of the experience and knowledge of the specifiers. It’s a question of how comfortable they feel with it.”
Is there a downside? Foamed asphalt pavement will often take a little longer to cool and cure. “Once you have density, you have to be careful you don’t open the road to traffic too quickly,” says Forfylow.
“On average, it’s about three to five days before you can pave the surface,” says Jason Herring, technical supervisor, BA Blacktop Ltd., North Vancouver, BC. “They recommend you wait until the moisture content in the new structure is about two per cent below the optimum… Obviously, the hotter the ambient temperature, the quicker it is going to cure. Ideally, you want to do this process in the summer, when you can get away with maybe two to three days of curing.”
Users need not be concerned about excessive moisture in the mix as a consequence of the foaming technology, emphasizes Forfylow. “One of the biggest fallacies about mechanical foam technology is that you’re putting water in the mix. We do not put moisture in the mix. We put moisture, two per cent by weight of the binder, into the binder itself. You spray this water as a fine mist and it instantly changes from water to steam. That’s what you get in the foam, the steam bubbles… and then, it’s dissipated.”
BA Blacktop Inc. has been involved in a number of foamed asphalt projects in B.C. since 2010, including fairly large projects for the cities of Coquitalm, Delta and Burnaby. “These projects have mainly been major arterial roads,” notes Herring.
The firm has been around since 1956. In 2009, Eurovia, a subsidiary of French conglomerate VINCI, acquired BA Blacktop. That gave BA Blacktop access to, and support for, new roadbuilding technology. Among those assets was Recyvia, an in-place full-depth recycling process for pavements that incorporated foamed asphalt technology.
In the beginning, they brought in the technical director of Eurovia. “We also brought in the main project superintendent from our subsidiary in Quebec, DGL Construction. We brought them out for several days during the first project for the city of Coquitlam,” explains Herring.
For that first job, all the materials went to DGL for the mix design. “Prior to the foaming, they came out and did a full training program with all the different equipment. Then our technical director and our project superintendent came out and helped us monitor things,” says Herring.
“With this process, everything is left in place,” explains Herring. “You’re doing what’s called a foamed-asphalt-base stabilization. You’re using the existing materials to create a much stronger foundation for the road structure.”
The existing material is pulverized and blended. “Ideally, you get a 50/50 blend of recycled, pulverized asphalt with your existing granular material,” says Herring.
As an example, he cites Marine Way in Burnaby. “That particular road needed to be re-profiled… We ended up having to put in a layer of virgin road base (a crushed, 100-per cent quarried aggregate) and we put in a layer on top of the blended, pulverized material. Then, we re-blended that into the existing materials to build up the profile.” A new asphalt pavement was laid on top of that.
“This process allows you to dramatically reduce the cost of shipping materials off-site,” notes Herring. “At the tail end of this process, we are coming back with our reclaimer and we are hooking up an asphalt cement truck. Then, we are spreading a certain amount of Portland cement in front
of the area we are going to do.” Typically, BA Blacktop was putting in about 2.5 per cent asphalt cement and one per cent Portland cement. They re-pulverized this material and foamed the asphalt.
“You are creating a much more stabilized structure. It’s a structure that is a lot stronger than conventional asphalt but also has the flexibility capacities.”
Herring foresees a strong future for the technology in road rehabilitation.
“You are basically reclaiming your existing road structure. We are pulverizing the existing asphalt and blending it in to the granular materials underneath. We are not removing and trucking off any materials. There is a huge savings in trucking and in purchasing new materials. If the road is deemed to need a complete rehabilitation, this is the ideal process,” he says.
As municipalities attempt to renew their infrastructure, foamed asphalt offers many advantages. Herring notes that many older roads in B.C. have inferior granular material underneath. “Back then, they used a lot of what we call pit-run fill – whatever material happens to be available in the general area.” Such roads may not have the structural capacity for today’s heavier trucks and higher traffic volumes and need to be strengthened.
Decades of service
The process probably has a longer, deeper history in Eastern Canada than in the rest of the country. “Ontario has sort of taken the lead,” says Forfylow.
The Ministry of Transportation – Ontario constructed its first full-depth reclamation project with foamed asphalt on the Trans-Canada Highway (Highway 17) north of Sault Ste. Marie in 2001.
This 22.5 km stretch of highway was originally constructed in 1959 and was resurfaced in 1981, noted Tom Kazmierowski, manager of MTO’s Materials Engineering and Research Office, in a 2012 paper entitled 10-Year Performance of FDR with Foamed Asphalt Stabilization.
ARAN (Automatic Road Analyzer) surveys carried out in the following years found that the pavement remained smooth (International Roughness Index of <1) and in good condition (Pavement Condition Index of >85) after 10 years in service, according to the report.
Foamed asphalt is ready for prime time. By some estimates, as much as 85 per cent of all the warm mix asphalt in North America is performed with mechanical foaming technology.
It is well on its way to becoming the norm in many North American jurisdictions. “There is no such thing as hot-mix asphalt or warm-mix asphalt anymore. It’s just asphalt concrete,” says Forfylow. “The state of Texas doesn’t even specify. They do not differentiate because there is no difference. Warm mix has the same properties or better properties than conventional hot mix.”
What about the technology’s future in this country? “Canadians are a bit of a cautious bunch. Our American cousins have really adopted the technology, and most of the work being done there now in most of the states is warm mix,” explains Forfylow. “Most of the work in Canada has been done on a trial basis – trial, by trial, by trial.”
Jim Barnes is On-Site’s contributing editor.