BY MYRON LOVE - With short summers limiting road reconstruction in the province, Manitoba Infrastructure and Transportation is constantly on the lookout for any technological innovation that can extend road work for a few more weeks into the fall.
One of those innovations that the department has been experimenting with is using a warm mix asphalt (WMA) in place of the more common hot mix asphalt (HMA).
Tara Liske, the surfacing materials engineer, reported that her department has been experimenting with warm asphalt since 2009.
“We began investigating the benefits of using warm mix asphalt in 2008,” she said.
“The product has been successfully applied in Alberta, Ontario and the Maritimes.”
Liske describes the warm mix asphalt process as a greener technology.
She pointed out that as a result of mixing asphalt at a lower temperature, you use less fuel at the plant and reduce the amount of greenhouse gases the process produces.
“What we hear from the construction crews is that when laying asphalt mix on really hot days, less heat and fumes are given off with warm mix asphalt,” she said.
“It is more comfortable for the workers.”
She reports that there are about 30 different products that can be used to create warm asphalt.
They can be added at the time of mixing or prior to mixing with the aggregate.
“We have tried three different products since 2010,” Liske said.
“We have found that Evotherm is the one we have been using most often.”
She noted that Evotherm is readily available and that it can be added to the asphalt cement prior to mixing in the aggregate.
A bonus, she added, is that the temperature of the mix can be dialed down and it requires the same or less compaction effort.
“We have seen temperature reductions over the last couple of years of 28 degrees C. in the mixing temperature and 25 degrees C. in compaction temperatures,” she said.
Another benefit is that construction crews can haul warm mix asphalt from greater distances as compared to hot mix asphalt.
It can be brought in from up to two hours away from the construction site – she pointed out.
“The warm mix retains heat and workability longer,” she said.
“And we have found Evotherm enhances the durability of our mixes.”
Most importantly, warm asphalt can be applied at temperatures as low as zero degrees Celsius.
It extends the road reconstruction season.
“We had crews working into November in past years,” Liske said.
Another process that the department has been experimenting with has been adding water to create warm mix asphalts.
“The water creates foaming and allows the asphalt cement to expand and coat the aggregate,” she explained.
“One of our contractors is doing that on a regular basis. It is good to see our contractors adopting new technology. We are using more and more warm asphalt technology, especially in the fall when temperatures are cooler.”
The department has also been experimenting with cold-in-place recycling.
Liske said that the department has been trying the technique on one project a year in different parts of the province.
This technique involves the contractor rotomilling the existing surface, sizing it and adding an emulsifier or foamed asphalt cement to the aggregates as it is being laid and compacted.
“This is another green technology,” Liske explained.
“We save on aggregate because we reuse the existing aggregates and asphalt cement and cap it with a layer of fresh asphalt. We have had some good success with this method.”
She cautioned that one needs to select the right situations for this add-in-place process.
The road needs to be structurally sound, if it is just a matter of replacing surfaces cracked by age, she said.
It doesn’t work if there are sub-grade issues. For all of these new techniques, Liske noted, the department has done its due diligence and compared notes with departments of transportation and infrastructure in other jurisdictions.
“We have to be careful not to sacrifice performance in the field,” she said.