Ten Strategies for Ensuring a Successful Pervious Concrete Installation

Use of a powered roller screed to
compact the pervious allows the
curing blankets to go on sooner.

Joints must be cut with
a "pizza cutter" roller.

Hand rollers must be quickly
followed with curing blankets.

Pervious concrete has many wonderful properties, but without an experienced contractor and ready-mix supplier, a failed installation is possible. Pervious concrete is difficult to place and finish properly. The right mix and proper compaction and curing are critical to success. Attention to the following steps will help improve the performance and durability of your pervious pavement installation.

Design the pavement system to prevent saturation of the pavement during freeze-thaw cycles.
In freezing climates, prevent water runoff from buildings or adjacent impervious pavements from draining onto frozen pervious concrete.
Pervious concrete pavement systems should only be used where the underlying soil percolates well or when there is a subbase drainage system.
To get the proper mix, work with an experienced ready-mix supplier and insist on 600 pounds per cubic yard of cementitious material (no more than 50 pounds per cubic yard of fly ash), a water-cement ratio of 0.26 to 0.30, aggregate at ½-inch maximum size (3/8 inch is best), and no fine aggregate smaller than #4. This should result in a concrete with a unit weight of 120 pcf with voids at 20% after compaction.
Adding 5 ounces per hundredweight of cement of hydration stabilizer (not retarder) is essential to prevent hydration before placement; some contractors also like to use a viscosity modifier and a mid-range water reducer.
Contractors must have experience working with pervious concrete, since it is different than conventional concrete. The National Ready Mixed Concrete Association (NRMCA) offers a training program, but installers should also have some hands-on experience.
Proper compaction—to a void ratio of 12% to 20%—is essential. This can be achieved with a roller screed followed by cross rolling with hand rollers that weigh 40 pounds per foot.
Don't overwork edges or joints. Joints should be cut with a "pizza cutter" roller, not with a saw.
Curing must begin within 10 minutes after concrete placement and continue for at least 7 days. During the interval between screeding and placing plastic sheeting, spray evaporation retarder onto the surface.
If a pattern is to be stamped into pervious concrete, stamp through the plastic curing film using open-faced stamps.