Granite Construction
Builds Porous Parking Lot
for Kaiser

Reprinted from HMAT magazine by permission of NationalAsphalt Pavement Association.

Reprinted from HMAT magazine by permission of NationalAsphalt Pavement Association. (Top) Granite Construction's Stockton California crew took on the project. (Above) The completed nine acre porous parking lot at Kaiser Permanente, Modesto, CA.

When Kaiser Permanente officials planned to construct a new 225-bed hospital facility in Modesto, Calif., they wanted it to be environmentally friendly. That included the parking lot.

The site for the medical facilities covered 49 acres and called for a nine acre porous parking lot. Cahill Associates, the environmental consultants
on the project, was part of a design team that included Lionakis Beaumont Design Group and Mark Thomas Co. Granite Construction Co. produced the mix and did the paving.

The porous asphalt system was topped with a 2.5-inch layer of asphalt in which fines were kept to a minimum, creating a pavement surface that looks and wears like standard asphalt but allows water to drain through the pavement. The asphalt was set on a base of uniformly-sized, open-graded clean stone, underlain by a non-woven geotextile and uncompacted subgrade. The stone had approximately 40 percent void space and served as the storm water storage area.

Andrew Potts, project manager for Cahill, was pleased with the outcome of the project as well as with its design. “The environmental benefits of such a system are significant,” he said. “Rainwater drains through the pavement into the stone bed and then slowly infiltrates into the underlying soil and groundwater. Runoff from roof areas is also conveyed directly into the stone beds beneath the pavement.”

Porous pavements have been constructed since the mid-1970s in the East and Midwest, but are still somewhat new in the West. Granite Construction's Stockton, Calif., operation took on the project, knowing there would be a learning curve for all involved. Granite laid 850 tons of asphalt per day for five days. “This type of pavement is certainly better for the environment,” said Tom Samuel, Granite's project manager. “When we had finished paving, we sprayed the pavement with water from one of our water trucks. I admit I was a little nervous, because this was the first time we had done one of these pavements. But the water filtered through the pavement immediately, just like it was supposed to.”

The paving crew did encounter some problems, beginning with the inevitable traffic jam that kept the trucks from arriving on site on time. Several of the trucks had trouble with the mix sticking to the bed. The truckers solved the problem in subsequent loads by using a different release agent. Workers also found the mix somewhat difficult for the handwork required with the numerous islands in the parking lot.

“We were able to solve our problems the first day and the final five days of paving went smoothly,” said Samuel. “Because of the unusual mix design, it also required that we clean out the plants thoroughly before running the mix for the porous pavements through the plants.” Cc