Are porous pavements a pollution solution?
Three types of permeable pavement systems hold promise for combating run-off: interlocking block, pervious concrete paving, and porous asphalt. Interlocking block roads use interlocking concrete blocks with small openings between permeable joints. These roads can be laid in interesting, stylish patterns in urban areas. Pervious concrete is a special concrete mix that uses fewer fine materials, such as sand, resulting in stable air pockets introduced into the mix, the same process as used when creating porous asphalt, according to BMPClean.org.
Asphalt is the most popular substance for U.S. roads, so the question is: Can porous asphalt prevent toxic run-off? The Georgia Asphalt Pavement Association (GAPA) says "yes." Porous asphalt roads also conserve water, facilitate natural cleansing, are economical and last for decades, it adds. And, with proper instruction, existing manufacturing plants can easily incorporate air pockets to mix porous asphalt. Construction methods vary; GAPA describes a stone bed of 18 to 36 inches (45 to 91 centimeters) at the bottom and porous asphalt on top. When it rains, porous asphalt roads more closely emulate nature; water drains downward into the stone bed, then slowly makes its way into the soil, where nature's processes take over.
The University of New Hampshire had great success with a porous asphalt parking lot built in 2004. In three years of measuring, it found no surface runoff. What's especially interesting is that runoff from adjacent structures can be directed into the porous asphalt stone bed, cleansing those waters as well.