At its recent fall seminar, the Ontario Hot Mix Producers Association was challenged to raise the bar on some key procedures by two industry experts from south of the border.
Speaking to an audience of more than 400, the former State Bituminous Materials Engineer for the Florida Department of Transport laid out the case for increasing the amount of reclaimed asphalt pavement (RAP) in new pavement.
But increasing RAP contents has to be done in a quality-focused manner or there will be failures that will lead to restrictions on its use, said Jim Musselman, who assumed the position of asphalt performance manager with Oldcastle Materials this past May.
Of the approximately 350 million tonnes of asphalt mix produced and used to pave roads annually in the United States, 20 per cent, or 70 million tonnes, was old recycled asphalt.
"That saves a lot of space in landfills," said Musselman, emphasizing the environmental and financial benefits of those recycling efforts.
These measures include an estimated US$2.3 billion in savings annually compared to the cost of purchasing raw materials, the conservation of 22 billion tonnes of asphalt binder and 68 million tonnes of aggregate, plus the reduced associated costs of producing, processing and trucking of those materials. Using RAP can also speed up construction, he said.
The Federal Highway Administration (FHWA) has been encouraging the use of recycled materials for a number of years and the use of RAP has increased from 15 per cent in 2009 to 21 per cent currently. For various reasons, the percentage varies from state to state, he said.
"We have a competitive market here," said Musselman, referring to his home state of Florida where the average RAP content of all the asphalt mixes produced and placed statewide is roughly 30 per cent, according to a National Asphalt Pavement Association survey.
Another economic driver is the fact that aggregate and asphalt binder are fairly expensive in the state. In central and north Florida, aggregate has to be obtained from other states and Canada, he said.
Although Musselman encouraged increased RAP contents, his presentation was equally devoted to the measures and precautions required in producing high quality asphalt mixes with those higher contents — both at asphalt plants and on the construction road site.
Some basic steps include proper aggregate stockpiling and handling, establishing the goals and expectations for the mixture, understanding the specifications, properly evaluating the materials through frequent sampling, developing a high quality mix design and "properly constructing the pavement," he explained.
Achieving those standards requires good and constant communications with the entire project team, including producers, contractors and transportation agencies. Clearly understanding the specifications is particularly important, "because they can change quite frequently and are not written in a vacuum. Understand the specifications as well as the person who wrote them," Musselman added.
Higher quality mixes with RAP will create greater confidence in allowing and using increased contents and that in turn will eliminate, "some of the barriers" associated with RAP and make its use more commonplace and acceptable. That acceptance will help lower construction costs, he said.
In response to an emailed question after the seminar, Musselman predicted that, "in the next 50 years RAP contents will average well over 50 per cent."
There is a wealth of information available on producing high quality asphalt with high RAP, said Musselman, citing studies by the National Cooperative Highway Research Program and the National Asphalt Paving Association.
During the fall seminar the audience also learned about efforts now underway in the United States to increase in-place (or on the job site) density of asphalt pavement to enhance durability.
"Higher air void levels mean lower density," said Mark Buncher, director of engineering for the Asphalt Institute, an international trade association of petroleum asphalt producers, manufacturers and affiliated businesses.
"Improved compaction has typically not been considered," said Buncher on industry and state initiatives to improve durability.
But, as he noted, "if you don’t compact properly, you won’t get good performance."
A top priority of the FHWA is attaining better performance at minimal cost, "by using existing technologies and best practices to achieve better compaction."
To meet that objective, the FHWA and the Asphalt Institute have developed an enhanced durability through an Increased In-Place Pavement Density Workshop. Some of the topics covered include air voids, density, compaction and getting good density at longitudinal joints. The workshop has been conducted in several states and is now coming to Ontario, said Buncher.
To be held at the Mississauga Convention Centre Feb. 6, the workshop will be conducted by the Asphalt Institute’s Canadian engineer Sandy Brown and its northeastern regional engineer Greg Harder.