Recently I saw dramatic film footage from the 1960s showing an asphalt plant belching black smoke. It reminded me of how far our modern facilities, where emissions are very low and well-controlled, have come since that time. The industry has made huge strides in environmental stewardship while increasing production. From 1960 to 1999, hot-mix asphalt (HMA) tonnage increased by 250%, but total emissions decreased by 97%.
Not content to do just what’s prescribed by regulation, the HMA industry continues to take action and encourage innovations that improve working conditions, protect the environment and make our facilities an even better neighbor. We create incremental changes where we can, and we keep looking for true breakthroughs.
In my estimation, warm-mix asphalt technology has the potential for being one of the most important breakthroughs for the asphalt industry in over 50 years. It could rank with recycling, milling machines, the floating screed, stone-matrix asphalt (SMA) and perpetual pavements.
In the 1990s we saw that mix temperatures were edging upward as a result of the implementation of Superpave, SMA and the wider use of polymer modifiers. NAPA and the State Asphalt Pavement Associations funded research at the National Center for Asphalt Technology on the effect of temperature on emissions. That research showed that temperature is one of the most significant drivers affecting the quantity and chemistry of fumes.
Warm-mix activities in the U.S. have really taken off since 2002. Information sessions at NAPA meetings, numerous technology demonstrations beginning with one at World of Asphalt in 2004 and the new website at www.warmmix asphalt.com are a few of the indicators of the high level of interest.
The various technology vendors have been very responsive. They have invested in research and have worked with contractors and DOTs to conduct numerous field trials. Several new technologies have evolved, and some hot-mix producers have even developed their own in-house technologies.
As interest in warm mix grew, NAPA and the Federal Highway Administration formed a Technical Working Group (TWG) in 2005 to foster proper implementation through the evaluation and validation of warm-mix technologies and to guide development of a generic performance specification. At the TWG’s most recent meeting, held in Baltimore in December 2007, representatives of no fewer than seven warm-mix technologies presented information on their products, processes, research and field trials.
The environmental benefits seem clear, and the opportunity to reduce fuel consumption by 10 to 20% is compelling. But what does warm mix mean for performance? The consensus is that in adopting warm mix, we must not sacrifice the high performance of today’s asphalt pavements, including Superpave, SMA and open-graded friction courses. We need to continue to evaluate warm mix and be able to demonstrate through field observation and research that it has the same coating, the same workability, the same air voids and the same performance as hot mix.
Encouragingly, early indications from both laboratory and field trials are that warm mix may actually offer benefits for performance. For example, warm mix may allow us to use a higher percentage of reclaimed asphalt pavement (RAP) without excessive emissions or poor workability. Less aging of the virgin binder in warm-mix production also may allow higher RAP percentages without changing the virgin binder grade. Several potential operational benefits from field projects are yet to be fully evaluated or understood. These include more time for compaction, the ability to store and haul the mix for a longer time and the opportunity to extend the paving season.
In the short term, it is likely that contractors will start using this technology in their private-sector or commercial work. Acceptance by state DOTs, cities and counties may take a little longer, but public agencies are showing great interest in technologies that are “green” or use sustainable construction practices and materials.
The current market environment includes high energy prices, pressures on highway funding, the likelihood of more restrictive environmental regulations, continued pressure on plant zoning and permitting and a surge in mainstream environmentalism. Controlling emissions at the source is the gold standard for environmental excellence. The industry now has an opportunity to meet that gold standard and to keep several steps ahead in an ever-changing and difficult operating environment. We have made tremendous strides. Let’s continue to lead and put our best foot forward.
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