By now almost everyone in the concrete industry has heard about pervious concrete. It is one of the most marketed concrete products in the industry today. And although there are installations more than 20 years old, there have been many changes in the technology that installs it, plus concrete mixes designed to improve constructability and durability. Asphalt paving equipment even is being used to install projects with very large areas.
Decorative concrete contractors have been working on ways to make pervious pavement more decorative as well as functional. Learning how install durable work remains the first most important step. Owners are willing to forgive some problems with plain concrete work, but they can be very unforgiving when problems arise with decorative work. For pervious concrete the number one problem is “raveling,” a condition that occurs when aggregate is dislodged from the surface. It can result from improper mix designs, poor compaction of the surface, or inadequate curing—a particular problem for pervious concrete.
Examples of decorative work
When Sergio Ilic, owner of Heritage Bomanite, Fresno, Calif., decided to pave the 5000-square-foot parking area in front of his office, he thought the project should be cutting-edge decorative work that would showcase what the company can do. The design he chose included colored bands utilizing color hardeners, an infield of colored and stamped concrete, and infield areas of pervious concrete. Around the perimeters of the pervious concrete, he and his crew stamped concrete the old way by placing thin-mil plastic on the fresh concrete and stamping a 12x12 quarry tile pattern using open-topped stamps (no texture). Brad Bowman invented this type of stamp in 1950 to pattern concrete. Ilic is proud of the finished product, saying that it exceeded his expectations. He completed the work a year and a half ago and reports that there is no raveling of the surface. The parking area fits with the rest of the company's landscaped, decorative concrete showcase that demonstrates to customers the possibilities available.
Byron Klemenske, vice president for TB Penick, San Diego, says that his company has completed more than 100,000 square feet of pervious concrete to date. This includes both commercial and residential projects. They also are installing an increasing amount of decorative pervious work, primarily integrally colored and ground surfaces. One project involved tree planter areas that provide an architectural surface, which allows water to reach the tree roots.
Grinding the surface of pervious pavement shows the color of the aggregate in contrast to integrally colored cement paste. Klemenske says they used carborundum grind stones similar to those used for terrazzo grinding. The rounded edges of the stones don't catch on the aggregates like diamond pads do.
David Mitchell, owner of Bunyan Industries, Salt Lake City—which manufactures roller screeds commonly used for pervious concrete work—says he recently visited sites in China that installed pervious concrete. He says they often place a base course of pervious first, adding inch-thick toppings of colored pervious concrete. “The color loadings are heavy, providing more intense colorations but because they are only one inch thick the costs are reasonable. This approach also makes it possible to use bulkheads to install different colors next to each other,” he says. They also are using decorative aggregates in their mixes, spraying them with special surface retarding admixtures to reveal the colored aggregates afterward.