Frequently Asked Questions
Won’t it clog?
Proper design is pivotal to preventing clogging. Runoff from adjacent areas laden with sediment should not be directed onto pervious concrete. Short of that, normal debris from traffic, trees and people have little effect on the ability of pervious concrete to drain water.
The only substances that can truly clog up pervious concrete installations are chewing gum and asphalt fines (the small debris that sheds from asphalt pavement). When the asphalt surface warms up from the sun, the asphalt fines melt and get into the air pockets of the pervious concrete, which then seals the air pocket and becomes permanently clogged.
How do I know my installer is qualified?
It is important that you verify your installer is certified by the National Ready Mix Concrete Association (NRMCA). Although it is technically concrete, pervious concrete has unique properties that cause it to behave very differently. As such, it requires a completely different set of skills and knowledge that can only be acquired through completion of both the certification program and hands-on experience with the product, so be sure and ask your installer for their certificate.
What about maintenance?
Most high quality pervious concrete installations will need minimal maintenance. If the surface should ever clog, cleaning with a power washer and/or a vacuum truck will restore the pervious concrete to its original state.
Is it really concrete?
Yes, it is.
Pervious concrete is made with aggregate (rocks), portland cement and water, just like regular concrete. By leaving out the fine aggregate/sand and making very specific changes in the mix proportions, we are able to create a large quantity (approx. 20%) of interconnected voids. Compressive strengths are generally in the 3,000psi range.
How fast does it infiltrate?
A high quality installation will allow for 1200-3800 centimeters of water to pass through per hour; even if it was 95% clogged, it would still allow 60 to 190 centimeters of water to pass through per hour.
What is the expected lifespan of pervious concrete?
The same as traditional concrete, approximately 30-50 years.
My site has silty clay soil; will pervious concrete work?
Yes! Using site-specific soil infiltration rates, the pervious concrete system can be designed to compensate for slow draining soils. We have modeled and installed systems on everything from sandy-based soils to the silty clay soils found commonly in Christchurch. From the first flush to capturing all the impervious cover runoff, we can plan, model, and install a system that captures and infiltrates all your stormwater without the need for a conventional stormwater infrastructure.
