You’ve probably heard of recycled paper, recycled glass or recycled plastic, but we’re wiling to bet that you’ve never heard (or thought) about recycled asphalt.
Recycling “old” asphalt is a relatively new and environmentally friendly way for WSDOT to repave its highways. We first tried this “hot-in-place paving” out in 1996 on SR 97, southwest of Yakima, and we’re now using it to repave a 16-mile stretch of SR 542 (Mount Baker Highway) in Whatcom County.
Hot-in-place paving involves a long train of equipment that heats and softens the existing asphalt, mechanically removes the top 2 inches of pavement surface, mixes it with a recycling agent and approximately 20 percent new gravel and oil, and replaces it on the road without ever removing the material from the work site.
If you’re watching it from the roadside, it’s pretty impressive. As the train of machinery slowly chugs by, you can watch the process unfold. The old asphalt disappears, gets rejuvenated with new gravel and oil, and reappears behind the train, smooth, flat and (almost) ready for traffic. Crews typically give the new asphalt a couple hours to cool before traffic is allowed on it.
Crews began hot-in-place paving Tuesday, Aug. 18, near milepost 15 on Mount Baker Highway, just east of the SR 9 (Valley Highway) intersection in Deming. Project Engineer Mark Hammer said the hot-in-place method moves at an average speed of approximately 16 feet per minute, and crews are paving about one and a half lane miles per day.
Though it’s about half as fast as conventional paving, also called “mill and fill” paving, the hot-in-place paving is more cost-effective. Conventional mill and fill costs about $150,000 to $175,000 per lane mile, while hot-in-place paving costs between $100,000 and $112,000 per lane mile. And although the life cycle of hot-in-place paving hasn’t been fully established yet, it is anticipated to last between 75 percent and 100 percent as long as conventional mill and fill paving.
And if you’re a driver, the hot-in-place method will also make your commute more convenient. During conventional paving, drivers typically have to navigate rutted and ground-down lanes in the interim between grinding and paving – which usually takes a couple days. If you’ve driven northbound I-5 between Lynnwood and Everett in the past month, you’ve more than likely driven in those ground-down lanes. Hot-in-place paving makes that rutted drive a thing of the past.
If you’re headed up to Whatcom County in the next couple of weeks, you can check out the process in person. Or you can check out our photos and videos on Flickr.