By Sean O’Keefe
Innovation is the lifeblood of construction and as the industry’s needs have changed so have the means, methods, and materials used to solve challenges. Designers, engineers, and builders search for sustainable solutions to age-old considerations yet sometimes there is no substitute for tried and true, proven performance. When it comes to permeable paving systems, there is one proven product that is hard to beat. Used on projects around the country, Grasscrete offers a solid, drivable surface that can be planted with grasses or other vegetation to become completely and naturally concealed.
Spanning 1,300 acres, Orange County Great Park is a former Marine Corps Air Station in Irvine, California readapted to be one of the largest parks in the world. Meeting California’s landscaping water conservation requirements on that much property while creating the necessary vehicular accessibility was no small order. The requirements include establishing a maximum amount of supplemental site irrigation and encouraging 100 percent of groundwater capture and retention onsite. Florasource, Ltd. a California horticultural supply firm supported the buildout with a combination of materials ideally suited for the low-water climate and stormwater retention expectations.
“We provided UC Verde Buffalograss and Grasscrete,” shares Florasource founder, Tom Hawkins. “The grass is a great low-water lawn option that was bred specifically to grow well in drought-prone areas.” Requiring as little as 25 percent of the water of traditional turf grasses, UC Verde Buffalograss peaks at a growth height of just six inches. On the hardscape side, Grasscrete is a sustainable paving solution that was essential in meeting stormwater retention requirements.
“Grasscrete is an incredibly durable, permeable paving product that allows grasses or other vegetation to be planted within it,” says Hawkins. Manufactured by Sustainable Paving Systems, Grasscrete is a concrete lattice of solid and void that combines the strength and rigidity of a single, structural framework while providing access to soil, water, and sunlight to sustain vegetation. The result is a planted permeable surface that remains drivable when needed. In Irvine, Grasscrete was used to create hard, drivable surfaces for utility access roads, emergency vehicle fire lanes, and shoulders for roundabouts in bordering neighborhoods.
The key to Grasscrete’s durability is the molded pulp former. This third-generation product allows cast-in-place concrete to be continuously reinforced with #4 rebar. Grasscrete’s compressive strength is identical to other concrete flatwork, ranging from 45 psi to 6,000 psi depending on the specific mix. An important part of concrete’s strength is in the thickness of the slab; a minimum of 5.5 inches is recommended for Grasscrete.
Like the Orange County Great Park, at the Dr. Martin Luther King Jr. National Memorial in Washington D.C. Grasscrete created a solid, vehicle-accessible walkway as part of a design-build delivery. Builders installed paved and plantable access over a 2,000-SF route to the back of an auxiliary building housing the Memorial’s Ranger Station, bookstore, and restrooms. A ramp between the sidewalk and street lets Park Rangers, maintenance vehicles, and deliveries come and go freely while limiting visitor disruptions.
At the National Renewable Energy Laboratory (NREL) outside of Denver, Colorado, Grasscrete was incorporated in detention ponds to leverage the material’s permeability and durability differently. NREL’s mission is to research and develop clean energy and energy efficiency technologies and related sciences.
“As a research laboratory, NREL has been a testing ground for a wide range of pervious concrete systems,” says John Buteyn, Vice President and Technical Manager, at Colorado Hardscapes. “Improving a detention pond on this campus could have long-lasting implications for the way onsite water runoff is managed for generations to come.”
Generally integrated into campus settings, detention ponds detain water onsite to prevent heavy rains from overburdening municipal stormwater systems. Ponds are often planted with wetlands type vegetation to enhance their appearance. As water runs through the pond, a layer of sediment builds up and makes the pond less effective. Once enough sediment accumulates the pond must be scraped; a heavy-equipment process that generally destroys all existing vegetation leaving the need to completely replant the pond afterward.
“Grasscrete allows the vegetation to be planted into the concrete so the root systems form below the surface,” continues Buteyn. “When heavy equipment removes the sediment build-up, they can scrape it down to the surface and the plant’s root structures remain intact. This allows it to quickly regenerate without the need for new plantings.”
Uniquely, Grasscrete’s patented formers are made of recycled paper pulp. Rather than removing them after the concrete is cured, the 100 percent biodegradable pulp formers slowly begin dissolving after the pour starts. Despite being every bit as durable as a fully poured slab, the Grasscrete system results in 37.5 percent surface and effective void, meaning almost two-thirds of the entire pond surface is open space. This allows the vegetation to truly blanket the concrete surface. In the case of the NREL project, an integral color was added to the mix, making the structure largely disappear altogether.
In September 2008, Hurricane Ike destroyed the Town of Jean Lafitte, Louisiana auditorium while flooding thousands of homes and businesses in Jefferson Parrish. Despite the devastation, the town was determined to preserve the auditorium’s landmark location by rebuilding in place. Raising the site out of the floodplain required importing more than nine feet of soil while a pile-supported building was designed for the new 18,000 SF auditorium. Elevating the site so much caused some drainage complications along the parking lot where a steep embankment transitions down to a ball field at the original grade.
“The slope needed to be stabilized beyond the parking lot because of the steep grade and concerns about erosion,” says Robby Oswald, owner of Bomanite of New Orleans, the contractor hired to resolve the issue. Descending about 7 feet in just 12 feet of distance, rain runoff in Louisiana’s damp climate would likely erode the slope quickly. Once it did, the hill along the heavily trafficked route between Lafitte’s schools and the library would either be an eyesore, dangerous, or both.
“Grasscrete was the ideal solution because it allows vegetation to grow within the voids. In this case, it was covered with sod,” continues Oswald, who along with other Licensees across the country has exclusive rights to this innovative concrete system. “The product is backed by a great company that provides technical support whenever we need it,” says Oswald. “The ability to troubleshoot a project with other Licensed Contractors around the country is always there for us.”