Landscape Architect Articles

Foundation Innovation11-04-16 | Feature

Foundation Innovation
By Mike Dahl, LC/DBM

Bases for concrete pavers, porcelain tiles and natural stone can now be constructed without the use of a heavy layer of crushed stone thanks to the development of high-density manmade materials like the lightweight polypropylene panels made by Alliance Designer Products Inc. that were used in this pool deck installation.

Relatively new technology has given hardscape contractors an optional method of constructing bases for paver installations. The advancement involves replacing the crushed stone portion of a base with high-density, manmade materials.

One such product that does this is Gator Base, manufactured by Alliance Designer Products Inc. It was developed in 2012-2013 and first put on the market in the fall of 2013. Over one million square feet have been installed since then according to the manufacturer.

Made from polypropylene, the product comes in panels that are joined together with a tongue and groove system. Robert Cadieux, the sales and strategy development officer at Alliance says that the idea for the product can be traced to the practice started over 30 years ago of using expanded polystyrene, or EPS, geofoam as a base material in the construction of highways.

As he conveys, "This was developed foremost in Finland to reduce the freeze/thaw cycle and the movement caused by the cycle, and to save on the cost of construction because stacking up big blocks of foam is easier than having to excavate and backfill the hole with crushed stone."

As a comparison to stone, five panels weighing 6.6 pounds covers 28.9 square feet. The weight of the compacted stone needed to cover that area at a six-inch depth, a depth the manufacturer says the ???(R)???AE????-inch panels replace, is reportedly 1,440 pounds.

Besides that benefit, others cited by the manufacturer include reducing the amount of excavation needed, saving the cost of transporting stone to the worksite and then handling it at the worksite, reducing installation time and wear and tear on machinery.

To facilitate water drainage, the panels have evacuation channels built in. When asked if the product drains as well as crushed stone, Cadieux responded, "It will drain better because of the five weep holes every 16 square inches. Any water that accumulates below the paver will get evaporated right away into the native soil. We know that water in native soil will evaporate way faster than water on compacted surfaces."

The manufacturer asserts that the product itself will never leach chemicals or degrade in the ground for over 100 years, and that because the design distributes dynamic loads to a wide area (engineered to support up to 1152 pounds on a 12-inch by 12-inch paver), pressure on the ground is practically eliminated.

Though it is designed to replace six inches of crushed stone, its insulation value, or thermal resistance, is the equivalent to about three times that so freeze/thaw cycles can be significantly decreased. This was also the conclusion of an evaluation made in collaboration with the Université du Québec's engineering institute in the laboratory of their Pavements and Bituminous Materials department.

The tests found that the panels have a thermal resistance of nearly 15.7 inches of 3/4" dry stone, compacted to a porosity of 20 percent so there would be better frost protection with a single layer of the polypropylene product than with the usual 6-inch aggregate base. And similar movement for both of these systems would be observed after freeze-thaw cycles.

Another conclusion of the evaluation is that this system works best for patios and walking paths made with concrete pavers. The subgrade soil should be compacted to at least 95 percent of the modified proctor density (as with traditional applications), a geotextile fabric is needed on top of the subgrade and bedding sand should be used to ensure a smooth and uniform surface. The overall findings were that the system is equivalent to a traditional granular base under static and dynamic loads and therefore can replace a traditional base.

The manufacturer acknowledges that their product is for pedestrian use only, and promotes it as especially beneficial in areas difficult to access, in restricted construction zones where material storage is prohibited, and where construction speed is critical. Besides concrete pavers, it works well with ceramic tiles and natural stone according to Cadieux.

This new type of base construction is designed only for pedestrian use but because the inter-locking panels distribute all dynamic loads to a very wide area, one 12" x 12" paver can support a dynamic load of up to 1,152 pounds, it practically eliminates any pressure on the ground below the hardscaped area.

This is confirmed by contractors who have put it to use in the field.

Palmetto Paverstones of Myrtle Beach, South Carolina, which owner Bryon Fletcher says is "a 100 percent hardscapes company," has used it on a variety of projects and finds that it is easy to use and flexible.

"In my world, I'm looking at speed, versatility and the quality of the job," he says. "In the long run, it's allowing me to get a bigger number. The product does allow you to save a considerable amount of time."

Frank Canzeri of Floraval Landscaping in Laval, Quebec, describes the installation process as excavating five inches deep, leveling the ground, going over the area with a plate compactor, installing geotextile material, putting down one inch of sand and compacting it, installing the panels and then the pavers.

"I like it because it's less work to do the job," Canzeri adds. "And it's a good job."

Some of the installation tips from the manufacturer include making the total excavation width six inches wider on each side than the final paved area, ensuring a slope of at least one degree away from any structure, installing the panels on the extended excavation area, laying them out in a staggered pattern, trimming any visible curves or protruding angles with a utility knife, and adding a 1/2-inch layer of bedding sand on top of the panels for natural stone installations.

"It was just unbelievable how quickly and smooth it went," says the owner of Grass Masters in Lumberton, New Jersey. He points out that besides not having to haul away as much sod, soil, roots and such, the reduction in necessary excavation leads to "saving money, saving our backs and"?(R)? a lot less equipment at the jobsite. My guys appreciate us thinking out of the box and doing things that are alternative, and that are better."

As seen in LC/DBM magazine, October 2016.