Source: The San Jose Mercury News (August 14, 2001–Page 1F)
Headline: NEW ASPHALT COULD SUPPORT A BETTER COMMUTE
Subhead: Materials Improve Safety, Expected to Last Longer
By GARY RICHARDS, Mercury News
There’s something new under your tires on many Bay Area roads, and it promises to make the commute much smoother. Rubberized and porous asphalt are gaining favor with road designers, and the materials are being used to varying degrees on Highway 17 over the Santa Cruz Mountains, on the major repaving effort now under way on Interstate 880 from Oakland to Fremont, and on expressways in Santa Clara County. And some motorists are noticing. “The road is so much different and better,” said Jeanne Catherine O’Kelly, a Highway 17 commuter, about the new open-graded asphalt designed to drain away water and provide better traction on mountain curves. “It’s amazing,” she added.
The technological advancements come at a time when road expansion throughout California is almost at an end due to a lack of land, environmental concerns and a push toward more public transit. Faced with having to move thousands of additional vehicles on existing lanes over the next several decades, traffic planners have been looking for ways to keep those routes safer and lasting longer before potholes and cracks zigzag through the pavement. They are turning to smaller bits of gravel and the 33 million recycled tires clogging state landfills. “There’s a lot of new stuff going on in respect to recycled materials and asphalt,” said Michael Murdter, head of Santa Clara County’s roads department. “There are fliers going out all the time on the new technology. It’s exciting, especially the idea that this can stretch our maintenance dollars.”
Highway 17 offers an early glimpse of the promise. A year ago, Caltrans repaved the mountain road from Scotts Valley to Los Gatos, installing a top layer consisting of open-graded asphalt. It uses gravel similar in size, about three-eighths of an inch thick, instead of the variety of sizes used in other paving procedures. The uniform rocks do not bind as tightly as gravel of different sizes that are combined with tar, which allows water to seep through the first couple inches of pavement and spread out to the side of the highway. “Think of it as popcorn,” said Saeed Shahmizai, the lead engineer on the I-880 repaving effort, where the open-graded asphalt will also be used. “There are openings, and water drains right through.” All that adds up to less water on the road, better traction and fewer cars skidding out of control.
In the first three months of this year on Highway 17, the number of injury accidents decreased by 64 percent and the number of crashes fell 41 percent, compared to the same period two years ago. While beefed-up enforcement by the California Highway Patrol is credited with slowing drivers, many say the new pavement has been a significant factor in lowering the number of crashes. When it rained in the winter, not only were there fewer large puddles, but there often was no spray of water being kicked up by cars ahead and blinding drivers. “It’s like riding on fairly dry pavement, even though it’s been raining like heck,” said Mike Giuliano, Caltrans head of maintenance design in San Luis Obispo. Added Nevin Sams, a state traffic planner: “From a traffic-safety view, we love this stuff.”
First used in 1970s
The porous asphalt first was placed on California highways in the 1970s, but engineers stopped using it. The theory at the time was that repaving over open-graded material would trap water underneath the pavement, creating sinkholes and eating away at the stability of the road. But that hasn’t happened. “This is a case where theory did not match reality,” Giuliano said. “We’ve found that not only are the roads holding up well, but it’s cost-effective and preventing accidents.”
The same material will serve as a one-inch top layer on Interstate 880, where a $1.8 million, two-year paving job is now in its fourth month. Underneath will be two inches of rubberized asphalt, material that engineers say is more flexible and may withstand the wear and tear of heavy big rigs twice as long as conventional asphalt. More than 400,000 discarded tires, or 270,000 tons of rubberized asphalt, will be used in the process, compared with 140,000 tons of traditional pavement.
The main worry is getting the rubber pavement installed properly. Nighttime temperatures must be above 50 degrees, and the mix itself has to be heated to between 285 and 325 degrees. Mess up those marks and “you’ll have a disaster,” said Caltrans’ Shahmizai. “If it’s too cold, the elastic won’t hold and will peel off the next day. If it’s too hot, it gets sticky and unravels.” That means dozens of trucks must be ready to roll, sending costs soaring. But one inch of rubberized asphalt is equivalent to a two-inch layer of regular asphalt. In the long run, costs may be 20 to 30 percent lower.
Recycled tires will also serve as the underground support for an elevated ramp, a test project at Dixon Landing Road and I-880. Here, tire shreds will be part of the fill under the roadbed. Nearly 8,600 tons of used tires will be shredded into two- to 12-inch chips, encased in soil and wrapped in a special fabric to anchor the ramp. “It’s perfect for the Bay Area,” said University of Maine Professor Dana Humphrey. “You have soft, mushy soil, and this is lightweight. That’s what is driving its use here.” Rubber is 60 percent lighter than the usual mix of soil and rock, so there is less weight on the soft soil, and the road is less likely to sink. Using recycled rubber will save the state nearly $230,000 — for one 700-foot ramp. Multiply that by dozens of ramps, and you have quite a savings.
Rubber pavement is now being installed on San Tomas Expressway in Santa Clara County, and it has been used on Oregon and Foothill expressways. Open-graded asphalt, however, is not used on the expressway because curbs along urban streets can trap running water. One problem is that dust and debris can clog the porous material, stopping water from flowing through. Officials say this is a trade-off they are willing to accept for safety reasons.
Caltrans is also involved in a test project on Interstate 710 in Southern California, using a more flexible pavement to rehabilitate a 2.5-mile stretch of the freeway between the Pacific Coast Highway and Interstate 405. “This is a pretty big deal,” said Stuart Mager, a sales representative for Granite Rock. “Most pavement can last 20 years. They think this can go for 35 years.”
Reprinted with permission from the San Jose Mercury News.