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Vegetation of ACBs and Grid Pavements

by Robert Parker, Pavestone Company

While the urban sprawl has brought economic prosperity, it has not been without some detriment to the American landscape. The fragmentation and destruction of wildlife habitats, discharge of pollutants to streams and lakes and a higher concentration of thermal heating have created problems for major metropolitan areas. Two such hardscape solutions are articulating concrete blocks (ACBs) and grid pavements.

Each of these individual grids exhibits two interlocking ears and two interlocking sockets shaped to allow for positive interlocking of all grids within the matrix. This interlocking design provides for omni-directional terrain surface contouring and a continuous interlocked field matrix. This system exhibits a continuous interlock and co-planar surface when encountering most all grade contours such as domes, depressions or channel constrictions.

The Earth Science Enterprise of NASA, in fulfilling their mission "to understand and protect our home planet," has used satellite collected data as a means to get vital earth science information into the hands of local and regional decision makers. As city planners began to learn of the long-term environmental negative impact of urbanization, engineers and manufacturers teamed together to create viable solutions used as BMPs. ACBs and grid pavement products are produced in an interlocking design with a surface areas open cellular structure allowing for vegetative growth. By reestablishing a natural habitat environment in developments, it delivers a landscape with aesthetic value, is eco-friendly and decreases stormwater runoff pollutants.

Grid pavements and ACBs are ideal for intermittent vehicular loading applications such as overflow parking, fire lanes, roadway shoulders, medians and crossovers along highways. The softer green landscape provided by the open cell concrete paving material allows storm water runoff to flow through the pavement system.

For erosion control where higher flow water might be present in channels, ACBs provide a similar solution. They increase vegetation and the systems are designed to work well as non-erosive boundaries in storm channels, rivers, streams, lakes and detention ponds. The common thread with all of the applications would be a desire to keep them from becoming a large area of cast in place (CIP) concrete. Poured concrete is subject to thermal shrinkage/expansion cracking, soil heaving and or settlement. Overall, as it is not eco-friendly, CIP leads to the diminishment of wildlife habitats. Also, as with grid pavements, due to the fact that our population and cities are growing so rapidly, storm water run off rates are at an all time high and can cause loss of property and life. Government regulations, such as NPDES, require permeable and green solutions erosion control. This is where ACBs have a distinct advantage over cast in place concrete rip rap. The designer has the ability to use open cells that allow you to backfill and place vegetation to gain the greener solution.

The single cable design of this ACB provides an economical and high performance mattress system.

A large part of this type of project will be in or around residential areas, where aesthetics will be an issue. The ability to have a softer or green friendly look to the project is a way to get the local residents and government entities to be behind your project. The design of most of the systems on the market, allow for you to adjust the unit surface open area. Depending on the amount of flow, you can have a wider opening allowing for more area to backfill and vegetate. Grid pavements are also designed with open cells to allow for planting. The cells of both products can be planted with a variety of vegetation. A few planting options are veining plants when on a slope, to different types of grasses when in flat areas or less severe slopes. Native plants are preferred when using for channel vegetation.

The purpose of using ACBs is to prevent the applied areas from becoming large sections of cast in place concrete as it is subject to thermal shrinkage/expansion cracking, soil heaving and/or settlement. ACBs have an advantage over cast in place concrete by giving designers the ability to use open cells which allow for backfilling and placement of vegetation to gain the greener solution.

One of the problems when planting this type of system is making sure the vegetation you have chosen can stand up to the conditions. Using grasses that cannot stand up to heat is one of the most common problems. In hotter ambient temperatures, concrete generates a large amount of radiant heat. You need to choose a type of grass that is deep rooting that does well in drought and heavy rain. Several types of grasses fit this description Bahiagrass, Common Bermuda and Hybrid Bermuda to name a few. Once you have selected the type of grass, you need to determine the method of application. The most common method for applying seed grasses is hydro-seeding. Hydro-seeding uses water, seed, fertilizer and wood fiber mulch. The mixture is blended in a tank then applied by a hose and nozzle to the desired area. The mulch helps protect the seed as well as helping with erosion control until the grasses have a chance to take root. It is also important to note that on steeper slopes the mulch can also be applied with tack to help it stay in place during rain events.

For erosion control where higher flow water may be present in channels, ACBs increase vegetation and the systems are designed to work well as non-erosive boundaries in storm channels, rivers, streams, lakes, and detention ponds.

It is important with both grid pavements and ACBs that there is a maintenance program started. As with any vegetation habitat, proper maintenance will insure the finished project continues to work as designed and maintain the desired green friendly appearance. It is important to water the new seed - if left to dry out the seed will die. It is also important to mow new turf. If not, mowed weeds will choke out the new grass. Just as your lawn it is important to fertilize the project every six to eight weeks. If the project cannot be maintained by the owner, there is the option of filling the cells with aggregate. While you will lose the softer look, the system will still help with storm water runoff problem.

Discharge of pollutants to streams and lakes and a higher concentration of thermal heating have created problems for metropolitan areas. The open cellular structure of ACBs allows for vegetative growth, which helps to reestablish a natural habitat environment in developments, as well as being eco-friendly by decreasing storm water runoff.

ACBs and grid pavement systems made by Pavestone Co. and others offer you an ecologically sound alternative to standard concretes. They combine the protection of a hard surface such as concrete or asphalt combined with the environmental benefits of a soft, permeable cover. It is important to remember with ACBs that most of the products have been tested in full-scale hydraulic flumes. This data, along with design guidelines from The Hydraulic Circular 23 - July 97, will give you the design information to choose the proper ACB for your project. A good reference for your grid pavement design would be Tech Spec number 8 through the Interlocking Concrete Pavement Institute.

Sources: Hydropave Engineering and & Technical Manual. Hydropave Company, Grapevine TX. 2003. Tech Spec Number 8. Interlocking Concrete Pavement Institute.

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June 18, 2019, 6:40 pm PDT

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