Thursday, April 16, 2009

Porous Pavement – Part II – Dr. John Kevern

Pervious Concrete/Porous Pavement in Winter Applications

Please also refer to the interview with Dr. Kevern in Show #5.

In the winter traditional, impervious pavement surfaces such as concrete and asphalt can pose slip fall hazards due to ice formation. Typically salt and sand are applied to pavement surfaces in the winter. The salt dissolves creating a brine on the surface in attempt to prevent "black ice" formation. Sand is often included with the salt to provide traction if and when the temperature drops below a level salt is effective (about 20°F). Due to the high permeability of pervious concrete, ponding of melt water is reduced or eliminated. Lack of standing water reduces the potential for ice formation on the surface. Also the surface of pervious concrete contains many peaks and valleys which improve traction over traditional pavements by allowing space for water, snow, and ice to accumulate below the surface. Another recent and interesting finding has shown that pervious concrete surface is warmer than surrounding adjacent pavement, but is cooler underneath. This phenomenon is much like sand at the beach in the summer. Even though the sand is light colored the surface is very hot, but much cooler just below the surface. Due to the porous nature of the sand heat accumulates at the top and the air below provides insulation. It has been observed that in the winter pervious concrete surfaces can still melt snow and ice even when the air temperature is lower than that for melting ice using salt. In the summer the insulating capacity of the air in the pavement keeps the pavement cooler and helps to reduce the urban heat island effect.

Wet spot made on pervious pavement from a running hose.
The snow seems to disappear into the surface even before plowing.
A traditional pavement the morning following a snow, notice the standing water.
Pervious concrete pavement the morning after the same snow, notice no standing water.

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