Hot Mix Asphalt Technology - March/April 2008 - (Page 48)

San Diego Uses Porous Asphalt continued the porous pavement and underlying stone bed is cleaner than water washing off a traditional parking lot. Impurities such as drippings from cars, pesticides, and other materials can be trapped in the body of the pavement and in the stone bed. Proper care of the porous lot is important, however. The surface should not be sealcoated, but rather vacuumed to keep sand, dirt, and other materials from clogging up the pores at the asphalt surface and preventing water from ﬁltering through the pavement structure. “Water quality is becoming very important to states and counties,” said Tom Cahill, president of Cahill Associates, who designed the lots for San Diego County. “Stormwater pollutants tend to get into the groundwater and streams. Porous asphalt pavements are proving to be an effective means of keeping pollutants from entering the water table.” Although the porous pavements do not require specialized training or equipment, they do require attention to best practices. ABC Construction did the laydown on all three lots. Vulcan Materials produced the asphalt and provided the aggregate. Construction at the Flinn Springs County Park parking lot began with a geotextile fabric over the subgrade to prevent ﬁnes from working upward into the stone recharge bed. Perforated pipes were installed to further assist water in draining into the water table. Construction crews then loaded a foot of rock on top of the subgrade (1.5 to 3.0-inch rock), followed by a 1-inch layer of small, single-sized stone. Paving crews laid 3 inches of asphalt with in 20 percent air voids on top of the rock. The to project required 570 pr tons of asphalt. “We to took the extra precaution of installing drains at the top of the pavement, so that if we get more than eight inches of rain, we have means to handle the overﬂow and not have it run directly into the creek,” said Dane Clingan, project manager for San Diego County. Paving practices Paving crews found the mix to be stickier than a traditional mix. “We had to make sure the truck drivers used a release agent on their tires to keep them from tracking the mix into the streets,” said Clingan. “During the construction, we also tried to keep the heavy equipment off the subgrade and to do limited compaction on the rock.” Clingan supervised the construction of all three lots, and sees a bright future for porous asphalt. “The projects look great and are holding up well,” he said. “I can see that in the future more lots will need to be porous pavements; they are an excellent means of managing stormwater.” HMAT The porous asphalt lot (right) absorbs water during a rainstorm while the traditional lot creates runoff. 48 • Hot Mix Asphalt Technology – MARCH/APRIL 2008

Table of Contents Feed for the Digital Edition of Hot Mix Asphalt Technology - March/April 2008

Hot Mix Asphalt Technology - March/April 2008 Contents Chairman’s Commentary Industry News Top-notch Teams Overcome Obstacles to Build the Nation’s Finest Roads Ecological Award Winners: Environmentally Sound, Neighbor Friendly Safety Award Winners: Rewards, Reminders and Technology Roadway Safety Program Trains Workers Preventing Back-overs Is Serious Business Driving Through Work Zones: Be Careful! San Diego Uses Porous Asphalt Lots for Stormwater Management Legislative Messages Tools for the Trade Calendar of Events Index of Advertisers Advertiser.com NAPA Roadmap to CONEXPO-CON/AGG

Hot Mix Asphalt Technology - March/April 2008

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