By reducing land use, cutting development costs, and increasing the sustainable aspects of any development onsite infiltration is shown to be a huge win for all stakeholders. Aside from private parking areas, public works departments and municipalities have used it extensively for sidewalks, trails, park-and-rides, and residential streets.
For public works, the most important aspect seems to be proper design of other features abutting or adjacent to the pervious surfaces. Designs that sheetflow water from other surfaces and/or landscaping can be quite problematic. After experiencing too much clogging from asphalt fines, many designers in the Northwest don't advise using asphalt areas that drain to pervious concrete. If possible, using de-icing salts must be strictly managed and avoided, and melt water from snow containing salt must not be infiltrated into the pervious concrete.
Advise owners that pervious concrete is a filter which must be maintained. Last year, NRMCA developed the “Pervious Concrete Pavement Maintenance and Operations Guide, which can be downloaded here.
Many are amazed at the new developments. Some believe that any specification more than two years old is obsolete. While some of the admixtures have not proven to be effective, others warrant further investigation. Currently under evaluation are various super-absorbent polymers, mix water conditioners, surface densifiers, and fibers.
The RMC Research and Education Foundation is funding research to identify the process and better-understand the process of chemical attack on pervious mixes from de-icing salts. Although pervious concrete is holding up well in freeze/thaw environments, there have been issues with chemical attack. In addition to this research, industry professionals are developing admixtures that can prevent the breakdown of the cement paste from chemical attack. On cleaning and maintenance, several manufacturers are developing equipment to remove material from the void structure, allowing the pervious concrete to perform at close to the original infiltration rate.
There are also ongoing developments with decorative pervious. Contractors are doing stamping, inlays, and colors.
We've also developed a technique to produce a “two-layer” pervious, where a mix of #57 stone and cement is placed a few inches deep, followed by a thinner topcoat of traditional small rock pervious. This makes the application of a surface color much more economical.
Several repair techniques have been developed. Spalling joints can be repaired and returned to service in hours. Brian Lutey at Ozinga Brothers has had success with complete overlays of early parking lots that had spalling or damage from de-icing salts.
Dave Frentress is chairman of the NRMCA Pervious Concrete Subcommittee. He thanks the committee members for their time in reviewing this article.