With the advent of green building and more immediate prospect of summer rains has come a heightened interest in pervious concrete pavements. Two recent
With the advent of green building Û and more immediate prospect of summer rains Û has come a heightened interest in pervious concrete pavements. Two recent demo installations and a new publication attest to a growing commitment to environmental stewardship through effective stormwater management.
MICHIGAN CONCRETE ASSOCIATION
More than 250 builders, developers, architects, engineers and contractors learned firsthand about the benefits of using pervious concrete during a late-spring pavement demonstration at the Michigan Concrete Association headquarters in Lansing. Supporting the event and formulating the pavement’s mix design were local producer Builders’ Redi-Mix, a U.S. Concrete Inc. company, and Degussa Admixtures, Cleveland.
Pervious concrete placement can be difficult if the mix isn’t optimized for the application, notes U.S. Concrete – Michigan’s Reid Goniwiecha, Technical Services manager. It can be a harsh mix that creates rapid and premature moisture loss, resulting in a very narrow working window. Without proper admixtures, the low water-to-cementitious materials ratio and lack of fines in pervious concrete make discharging the material difficult and slow. Placing and compacting can also be labor-intensive if the mix isn’t designed to overcome these obstacles.
Pervious concrete mixes combine portland cement, coarse aggregate, water and admixtures. Due to the lack of fine aggregate, the pore structure contains many voids allowing water to pass through. The mix design used in the MCA demonstration incorporates Degussa’s Polyheed 1025 polycarboxylate-based, mid-range, water-reducing (MRWR) admixture; Delvo Stabilizer hydration-controlling admixture (HCA); and, Rheomac VMA 362 viscosity-modifying admixture. The use of Polyheed 1025 assists in achieving the desired strength by creating a strong paste to coarse aggregate bond and maximizing cement hydration. The Delvo agent creates a longer working window for placement, and eliminates the need to retemper the mix. With the absence of fine aggregate, Rheomac VMA 362 admixture adds body and helps lubricate the mix.
The demonstration area was an 11,000-sq.-ft. parking lot, requiring over 175 yd. of pervious concrete mix. The association needed a new parking lot and was able to double parking capacity with the concrete spec, while adhering to all storm water requirements set forth by the Local Drain Commission in Ingham County.
Utilizing pervious concrete allowed us to maximize our parking lot while minimizing land use, says MCA Director of Marketing Bernie Cawley. We met all local, state and federal storm water requirements without the use of a retention pond which will allow us enough vacant land to expand our building at a later date.
KENTUCKY READY MIXED CONCRETE ASSOCIATION
Architects, engineers, developers and contractors on hand for the mid-June installation of a new parking area at the Girl Scouts Program and Learning Center in Louisville, Ky., were introduced to the environmental benefits of pervious concrete, including improved water quality. Partnering with the organization on its new headquarters project were the Kentuckiana Concrete Promotion Group, Kentucky Ready Mixed Concrete Association, American Concrete Institute-Kentucky Chapter, Ohio Valley Concrete Promotion Group, and Indiana Ready Mixed Concrete Association.
This new section to our parking area provides visitors a safe area on which to park and walk, as well as an environmentally sound paving solution, notes Girl Scouts Program CFO Lyndy Alexander. Valuable as a storm water management system, she adds, pervious concrete offers engineers, architects and those interested in soil, water and environmental responsibility an alternative to traditional systems, such as retention ponds, currently utilized in storm water management.
An environmentally-safe, soybean oil-based water-repellent, the Bean, was applied to the pervious concrete after placement to help protect the surface, especially during the curing period. The Bean is manufactured in Indiana from Indiana soybeans and is safe for plants and animals. As hosts noted during the installation, pervious concrete is essentially structural concrete pavement that drinks water. Rather than run off into storm drains carrying oil and other pollutants with it, rainwater penetrates pervious concrete’s porous structure, traveling through the pavement directly into an underground stone storage layer, then into the soil naturally. Thus, pervious concrete filters and cleans storm water before it reaches water stored beneath the surface.