As fuel costs and environmental concerns rise in conjunction with shrinking road budgets, cold in-place recycling paving, or CIRP, methods continue to gain interest nationwide. Cold in-place recycling has been used on low-volume roads for some time, but the technique may gain acceptance on higher-volume roads as well.
"Recycling has been around for a long time in Europe and Asia," says Mike Marshall, directing of recycling products for Wirtgen America. "In North America, it's been slower to take off generally because energy costs had been low." But now, instead of two- to four-mile-long projects, "we're going 30 miles and more."
Rather than buying and transporting new aggregate to patch up a section, two to five inches of the current road layers are pulverized, mixed with a new asphalt emulsion and paved back in place. The mix specifications are developed using core samples from the existing pavement.
The Federal Highway Administration notes that New York, Kansas and Nevada have used CIRP for two decades. The Nevada Dept. of Transportation has saved $600 million over that time, says NDOT's senior materials engineer, Gayle Maurer. "Hauling materials is expensive, as is liquid asphalt. Cold in-place recycling acts as a good stabilized foundation for an asphalt overlay—it can bring a road back into shape for certain structural defects."
CIRP has gained swift ground in northern California, becoming a key growth piece for Fonseca McElroy Grinding Co. Inc. "Six years ago, we saw a machine on a calendar. I picked up the phone and asked Wirtgen, 'What is that?'" recalls Mike McElroy, a co-founder. The asphalt company bought a milling machine and has since done several projects. While some CIRP projects use emulsion—watered-down liquid asphalt with chemicals added—others use foam consisting of bulk cement and liquid asphalt to save extra days of recompaction, he says. "You inject cement, liquid asphalt and water and [then] put the pavement right back down again. Within three hours, you have 98% compaction."
Using CIRP with foam on 700,000 sq ft of a six-lane arterial saved $400,000 on the $3-million job, says Mike Witkovski, San Jose city engineer. "We have 11 [planned] roads, and seven include a CIRP performance spec. [CIRP] really shines when you have a road where the thickness is OK—it's just old," he notes.
The city kept an eye on the Virginia Dept. of Transportation's 2011 milestone test project on Interstate 81, where a 3.7-mile section of one lane received full-depth reclamation—a method that goes further than CIRP, 10 in. down into the base layers. The asphalt layer under the driving surface received cold central-plant recycling, using stockpiled milled asphalt processed at an on-site mobile plant. The other lane received CIRP. "I really think these methods will change the way we pave at VDOT," says Brian Diefenderfer, an agency pavement researcher. "On a national level, there are better indications for allowing us to use these on the Interstate."