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Grid Pavers: Uses and Limits

By Richard Bodie, Vice President of Commercial Sales, Pavestone Company






Having a stable paving surface that vegetates is desirable in today's efforts to develop sustainable projects. Infiltration of on site precipitation reduces stormwater runoff quantity. Vegetated surfaces also slow sheet flow drainage.


Open celled concrete "grass" pavers have been used successfully for a variety of paving treatments for many years. Most applications are performing to their design intent and are providing a structural-ecological benefit to the user.

The goal of this article is to provide the reader with some simple and practical guidelines for the product. Please note that when grass pavers are expected to carry automobile traffic the user should consult with a local engineering firm familiar with the product and local building codes.

Grasstone pavers, grid paving, and open cellular concrete paving grids typically are all one in the same. Dry cast concrete grass pavers are made to 4000 psi compressive strength. The unit's surface area sizes range from one to two total square feet. The product is typically available in three, four and six inch thicknesses. Unit shapes are either rectangular or geometric interlocking "figure eights". The latter is preferred for vehicular traffic as it may restrict lateral creep of individual units. The principle use has been to provide a stable surface that is capable of growing grassy plant species in the open cells within the body of the unit. It is accurate to consider the product as a surface stabilization element for the development of grassy vegetative growth.






As with any living area, irrigation and maintenance are required to keep plantings green. Regionally appropriate grassy species selection, frequent watering, fertilizers and weed control are required if the objective is to have a successful grassed area.







The unit's surface area sizes range from one to two total square feet. The product is typically available in three, four and six inch thicknesses. Unit shapes are either rectangular or geometric interlocking "figure eights". The latter is preferred for vehicular traffic as it may restrict lateral creep of individual units.


Residential and Commercial uses

The product has a multitude of uses from residential to commercial. Most residential use has been driveway "runners" where the units are placed in two parallel bands that support the vehicle directly underneath the wheel paths.

Miscellaneous uses have been from refuge can platforms to small paved areas under exterior hose bibs. Commercial use has been applications involving emergency access paving such as fire lanes. Other areas commonly used are overflow parking lots for public use facilities. Designers and end user are able to have required "access" pavements that, when irrigated and maintained, look just like grassed areas.

Pedestrian use and access is great for areas where the application involves high foot traffic and reliable footing. Vehicular use and access have been viable uses provided appropriate civil engineering has been provided. Like any other paving surface material, civil engineering considerations have to be taken into account. Considerations such as existing soil strength, sufficient dimensions of structural base materials for the traffic design loads and site specific environmental conditions have to be addressed for the product to perform structurally.






Thermal heat reduction of paved areas having more vegetated area, in lieu of monolithic paved areas, means receiving waters are less subject to damaging heated water runoff, which is also environmentally friendly. The product should not be used in significant hydraulic flow volume applications and not be used on slopes greater the 3:1.


Sustainability

The product, when engineered, can be a vehicular pavement that is suited to light duty traffic. Having a stable paving surface that vegetates is desirable in today's efforts to develop sustainable projects. Infiltration of on site precipitation reduces stormwater runoff quantity. Vegetated surfaces exhibit a higher Manning's coefficient, which also slows sheet flow drainage. Thermal heat reduction of paved areas having more vegetated area in lieu of monolithic paved areas means receiving waters are less subject to damaging heated water runoff, which is also environmentally friendly.

For the product to perform, proper design and construction must be employed. The product's limitations are high repetition single axle trafficking and or any tandem axle traffic. In these cases unit cracking and vertical deflection are probable. Cracking is a sign of failure and may be a sign of future pavement degeneration. Incidental hairline cracking should not be considered grounds for rejection. Onsite inspection may be required.

The ability to have a stable grassy surface capable of sustaining light traffic has far reaching applications.






Grid pavers are perfect for areas where the application involves high pedestrian foot traffic requiring reliable footing. They also work well for areas involving vehicular use and access. However, it is important to make sure appropriate civil engineering has been provided, as it should be with any paving surface material.


Erosion Control

There have been uses of the product for erosion control purposes with limited success. There has been limited hydraulic stability testing of these products and therefore it is difficult to analyze and design the products for erosion protection. The product should not be used in significant hydraulic flow volume applications and not be used on slopes greater the 3:1.

As with any living area, irrigation and maintenance are required to keep plantings green. Appropriate grassy species selection, frequent watering, fertilizers and weed control are required if the objective is to have a successful grassed area. Partial defoliation from repetitive traffic and high ambient temperatures can be expected.

Grass pavers continue to serve a variety of design solutions for designers, contractors and end users alike. The ability to have a stable grassy surface capable of sustaining light traffic has far reaching applications. Knowing the product features, benefits and limitations will insure continued satisfaction.



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December 8, 2019, 7:59 am PDT

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