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When it rains. It drains.
Pervious concrete has a 15-25% void structure and allows 3-8 gallons of water per minute to pass through each square foot - accounting for far more than is generated during most rain events.
Pervious concrete puts rainwater back in the ground where it belongs.
The best application for pervious concrete is parking lots.
What is Pervious Concrete?
Pervious Concrete is an alternative to costly stormwater management practices. Pervious concrete acts as a drain and reduces the need for detention ponds in an environmentally safe way. Pervious concrete puts the rainwater back into the ground while the strength and durability remains strong. Pervious Concrete is made from cement, coarse aggregates, water, and other special components to produce sufficient paste and bonding ability to glue the aggregates together.
Pervious concrete is a mix of coarse aggregate, cement, water, and little to no sand. Also known as "no-fines" or porous concrete, this mixture creates an open-cell structure, allowing rainwater to filter through to underlying soil. By modeling natural ground cover, pervious concrete is an excellent choice for stormwater management.
Benefits of Pervious Concrete
- Reduces stormwater runoff
- Eliminates need for detention ponds and other costly stormwater management practices
- Replenishes water tables and aquifers
- Allows for more efficient land development
- Minimizes flash flooding and standing water
- Prevents warm and polluted water from entering our streams
- Mitigates surface pollutants
- Salmon Friendly
- Mimics Natural Infiltration
Why is Pervious Concrete a Sustainable Solution?
- Eliminates untreated storm water and creates zero runoff
- Directly recharges groundwater
- Mitigates first flush pollution
- Protects streams, watersheds, and ecosystems.
- Mimics the drainage and filtration of bioswales and natural soils
- Reduces surface temperatures & heat island effects
- Provides a higher albedo surface reflectivity index (0.35 or higher)
- Eliminates need for expensive collection and detention systems
Placement of Pervious Concrete (Simple Overview)
A. Finishing contractors should be trained and experienced in the placement of Pervious Concrete!
- Properly prepare subgrade to an uncompacted condition.
- Place & compact designed retention / recharge gravel layer.
- Some conditions may require installation of filter fabrics.
- Prepare paving lanes. Elevate final form grade 3 - 1 inch above forms.
- Bring pervious concrete to a "wet metallic sheen" condition.
- Place pervious concrete using concrete rakes or tines only.
- Screed pervious concrete to elevated form grade using minimal vibration.
- Remove elevated form shims.
- Insure edges of forms are uniformly filled with pervious concrete, lightly compact.
- Immediately cover pervious concrete with plastic sheeting.
- Using a heavy roller, compact pervious concrete to original form height.
- Install joints as per joint layout design (can be done following placement).
- Secure plastic sheeting to prevent wind removal.
- Cure pervious concrete with plastic sheeting in place for 7 days.
- Protect against landscaping materials and perimeter run on.
- Open to traffic!
What About Freeze / Thaw?
Pervious Concrete is not designed nor intended as a storage area. Water passes directly through the pavement and into the retention layer below. Freeze / Thaw is not a concern in western Washington as our temperatures and freeze / thaw conditions are nominal.
What About Clogging?
Clogging of any pervious surface can be a concern. It is highly unlikely a majority of any pervious surface will become 100% clogged. Water will always seek the next point of infiltration.
What About Maintenance?
Good common sense approaches to prevent placement of landscape materials and cleaning of any pervious surface are recommended practices. For parking areas, your regular parking lot sweeping / vacuuming should be sufficient.