Pervious concrete cannot replace standard ready-mixed concrete in every application, in part because permeability is inversely related to compressive strength.

However, pervious concrete has already proven itself as an environmentally sound and aesthetically pleasing alternative in a diverse array of applications, including parking lots, driveways, sidewalk and even low-volume streets.

The Land Conservancy for Southern Chester County (TLC) used pervious concrete in a formal parking area at its Nature Center. Pervious concrete was also a part of an expansion project at Parker Hill Church in Clarks Summit.

Designers should refer to ACI 522.1, "Specification for Pervious Concrete Pavement."

Given the porosity of this type of concrete, designers must astutely control stormwater runoff and debris accumulation:

• Consider local rainfall data when designing the aggregates detention base. In the colder PA climate, water must not get trapped in the pervious concrete during freeze-thaw cycles.
• Perform a subgrade percolation test to establish the depth of the aggregates detention base. Specify underdrain pipes when percolation rates require them.
• Avoid using pervious concrete in a catch basin. If this cannot be avoided, the maintenance plan becomes that much more important.
• To avoid debris buildup do not empty roof drains onto pervious concrete surfaces.
• Do not use mulch in adjacent areas unless the concrete layer is at a higher elevation or a curb is used to blocks the mulch.

The density standard for pervious concrete is stated in ACI 522.1-13. However, designers should not specify minimum cement content or water-to-cement ratio. Also, compressive strength should not be specified as an acceptance criterion.

The right concrete mix is crucial to long-term durability and permeability. Ready-mixed concrete producers should rely on ASTM C1688 to test the density and void content of fresh mixes. Give careful consideration to aggregate sizes to maintain proper void content, usually in the 17-23 percent range.

The first generation of pervious concrete was quite dry, so it was more challenging to work with. Today's next-gen mixes are easier to place.

When it comes to placement, prompt delivery is one key to success. Delays between trucks should be 20 minutes or less, and arriving trucks should not sit in a line.

Successful placement requires the use of a certified pervious concrete contractor. The National Ready Mixed Concrete Association (NRMCA) offers a Pervious Concrete Contractor Certification program through local sponsoring groups. Certifications must be renewed every five years, ensuring contractors will be up-to-date with the updated technology and placement practices.

Concrete professionals can pursue three different levels of pervious concrete certification: Technician, Installer and Craftsman.

Ensure the longevity of pervious concrete with these maintenance best practices.

• Clean pervious surfaces on a regular basis
• Periodically vacuum pervious concrete with power equipment set to 0.5-inch above the surface
• Replace deicing chemicals with sand
• Do not allow direct contact between pervious concrete and steel snow plow blades
• Do not seal or repave pervious concrete with non-pervious materials

Use testing procedure ASTM C1701 to ensure that filtration rates are restored through proper cleaning. It is relatively easy to deal with the snowplow issue by using a rubber surface boot or setting the blade to remain one inch above the surface.