Porous Pavement

What is Porous Pavement?

Porous pavement sidewalk and bike lane in OlympiaPorous pavement is concrete, asphalt, or pavers that allow rainwater to pass through and soak back into the ground naturally.

Because water freely passes through, porous pavement does not generate stormwater runoff. This helps protect our streams and Puget Sound since Stormwater carries pollutants from the surface to streams and erodes stream banks and bottoms.

In addition, Porous pavement helps to recharge our groundwater, which is where the majority of Olympia's drinking water comes from.

Porous Pavement Projects in Olympia

Frequently Asked Questions

We add a special admixture into the material and we withhold water so that the cement does not form a slurry, like regular concrete. We want the cement to form a paste and use that to stick the rocks together. The admixture allows the cement to bind to very fine aggregate (sand) in a paste form.

The concrete cost is about 3 times the cost of regular concrete. ($200/CY vs. $60/CY). The placing and finishing cost is about the same. There are additional costs for an under drain storage system. We are saving money by not having to buy land and build stormwater ponds to mitigate the additional runoff. On sidewalk projects and small projects, this can result in cost savings. On a large-scale project, costs can come out about the same depending on land costs.

Generally, porous concrete is weaker than regular concrete. While it can be strong enough for roadway traffic loadings, currently we are working on sidewalk and parking lots (lighter traffic load locations). It has the potential to be used for limited roadway applications.

Water expands when it freezes. This can cause some materials to break. Under natural and normal installations of porous concrete, it is not possible to fill all of the air voids in the material with water, or to freeze it solid. This means there is always air space in the porous concrete for ice crystals to expand, thus freezing temperatures have no effect on porous concrete.

Additional Information


Contact Eric Christensen at 360.570.3741 or echriste@ci.olympia.wa.us