As an environmentally friendly product that provides far more than just a paved surface to drive or park on, pervious concrete offers a new frontier for concrete contractors. Now contractors can offer a "stormwater solution" that allows water to pass through unimpeded, reducing runoff and stormwater treatment requirements and acting as a biological filter.
But pervious concrete, also known as "no-fines" concrete, differs from standard concrete in significant ways. It has an open structure that includes 15% to 25% voids. When hardened, it requires both strength and openness to perform properly, so close attention must be given to mix design and placement techniques.
Even more than with standard concrete projects, success with pervious concrete requires contractors to collaborate with their concrete producer. They also need to learn some placing and finishing techniques. For detailed information, see Learning To Do Pervious (a how-to article) and A Lesson in Pervious (a what with article) and visit Ozinga Green Building.
A snapshot of typical pervious concrete
|Aggregate type||gap-graded crushed stone or gravel|
|Aggregate top size||1/4- to 1/2-inch size|
|Voids||15% - 25%|
|Water/cement||0.26 - 0.35|
|Unit weight||128 to 138 pounds per cubic foot|
|Thickness||5 to 8 inches|
|Joints||optional, for appearance|
- Hydration stabilizer
- Polypropylene fibers
- Some fine aggregate in freeze/thaw areas
- Parking lots
- Residential streets
- Bike paths
- Vacuum sweep as needed to open surface
- Patch as needed where raveling occurs