From roofs to roads
Faced with high raw materials costs, Texas embraces recycled asphalt paving materials.
HWO: Texas DOT
PROGRAM: Paving with recycled asphalt
RESULTS: Doubled the amount of recycled materials used since 2008
INNOVATION: Asphalt shingles added to hot-mix
THE LATEST: On Jan. 1, 2009, the Texas DOT (TxDOT) updated its specifications, allowing reclaimed asphalt pavement (RAP) to be used in all of the state's paving projects. At the time, Dale Rand, director of the flexible pavements branch, estimated the department could save more than $50 million a year by replacing virgin materials with RAP.
Rand's estimate was based on the assumption that using RAP could save TxDOT at least $5/ton of hotmix asphalt, of which the department uses about 10 million tons/year. In 2010, the department placed 8.2 million tons of hot-mix that included up to 40% recycled content. However, TxDOT's total cost savings are harder to project today. “It's very difficult to pinpoint exactly how much money we've saved by using recycled asphalt,” Rand says. “A lot has changed, and there are so many factors involved.”
Asphalt costs less than it did in 2008, when crude oil prices peaked. RAP prices vary, depending on transportation costs. Changes in TxDOT specifications, such as requiring higher asphalt content, are also a factor.
Instead, Rand calculates the department's savings in terms of replacement. “Without RAP, we would have spent approximately $35 million more in raw materials last year,” he says. RAP replaced about $20 million worth of asphalt and $15 million of aggregates in the department's hot mixes. TxDOT used 827,000 tons of RAP in 2010 compared to 467,000 tons in 2008 — nearly an 80% increase.
Recycled asphalt offers a two-fold cost savings. According to Rand, a typical high-volume roadway project would normally require relatively stiff polymer-modified asphalt. When RAP is used in hot-mix, softer asphalt binders can often be used instead of polymer-modified asphalt, since the asphalt in RAP provides a stiffening effect. The contractor saves money by using RAP and by blending it with the softer, less expensive binder.
In 2010, TxDOT took another important step toward promoting recycled materials. The department's revised specifications allowed recycled asphalt shingles to replace up to 5% of fractionated RAP. This followed a 2009 ruling, in which the Texas Council on Environmental Quality legalized the use of recycled “tear-off” shingles in paving materials. Shingles are attractive to paving contractors because their asphalt content — up to 20% — is about four times the amount in RAP. By using shingles, TxDOT has roughly doubled the recycled content in its hot-mix over the past two years.
Other states are also adopting alternative paving materials. In February, Nevada DOT (NDOT) announced it will be using a rubber paving material on a major section of Interstate 15, near the Las Vegas Strip. The asphalt-rubber, or rubberized asphalt, is a hot-mix paving material that uses crumb rubber recycled from car and truck tires. NDOT estimates the I-15 project will keep more than 100,000 tires from landfills.
To read the original article that appeared in the April 2009 issue, “A second chance,” click here.