Is it possible one day warm-mix asphalt (WMA) will replace hot-mix asphalt, and it will be called simply “asphalt”? (I’m reminded that there was no such thing as an “acoustic” guitar until the electric guitar came along and retroactively changed the name of its predecessor. Words are funny. But I digress.)
Anyway, the speakers at the 2nd International Warm-Mix Conference in St. Louis on Oct. 11-13 thought there was a good chance. More than 500 registrants attended the conference. Almost every state in the U.S. has now done test projects with warm-mix and is now monitoring the pavement to see how it stands up. U.S. contractors laid 47 million tons of WMA in 2010 (11% of all asphalt)—up from 17 million tons in 2009—and are set to surpass that this year.
So far the results are positive . . . in fact, more positive than is predicted by laboratory tests. The conference speakers spent a lot of their time reviewing lab measurements of moisture sensitivity, rutting resistance, tensile strength ratio, flow numbers, air void content, ease of compaction and so on.
For example, the lab tests predict greater moisture sensitivity in WMA than what is being seen in field trials. The lab tests also predict WMA might be more susceptible to fatigue cracking, but the cracks have not yet shown up.
The speakers seemed confident that the differences between field performance and lab-measured engineering properties will be reconciled and the industry will be able to move on. They indicated the Transportation Research Board was getting close to releasing its report on NCHRP 09-47A “Properties and Performance of Warm Mix Asphalt Technologies.” After that, conference speakers will probably focus more on interesting projects and less on numbers and graphs.
Not that there’s anything wrong with graphs.