Rigid Foam
Not Just for Insulation
The same material that many contractors use to insulate walls and roofs—expanded polystyrene (EPS)—can help reduce lateral loads on building foundations and retaining walls. EPS geofoam is a lightweight fill that allows for the use of thinner walls, with less material, as well as a reduction in labor needed for concrete forming or the installation of segmented retaining wall blocks.
EPS geofoam has the same composition as EPS insulation, but is formed into blocks, rather than sheets. As a fill material, a key advantage of EPS is its ultra low weight—approximately 100 times lighter than soil (one to three pounds per cubic foot compared to 110 to 120 pounds for soil). EPS geofoam enables contractors to backfill against walls and foundations, replacing the heavy soil wedge customary with traditional fill materials.
Substantially lighter fill can mean a reduction in the amount of excavated soils, simpler wall designs including less structural steel and concrete because of the thinner wall thickness and reduced footing size. EPS geofoam can also reduce or eliminate the need for geogrids or mechanical tie-backs typically used with segmented retaining walls. As a result of using geofoam as a lightweight fill, contractors can build using much less costly fascias that act more like a fence than a retaining wall.
It addition to allowing for more cost-effective walls, EPS geofoam is easy for crews to install by hand. This can simplify construction staging and reduce equipment costs, especially on tight job sites.
| OTHER USES FOR GEOFOAM |
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EPS geofoam has been used for a wide range of architectural and infrastructure applications given its lightweight, durable nature. Applications include structural void fill, garden roofs and concrete forming. Common architectural void fills using geofoam include stadium seating in theaters and sports arenas, stairways, podiums, loading docks and pool decks. Manufacturers can provide custom-cut blocks in various shapes and sizes to enable contractors to quickly build up these and other similar features. EPS geofoam also works well for forming concrete walls of various types. For example, the contractors for a new water treatment plant in California used geofoam fill in place of traditional fills within three 7-foot by 7-foot by 50-foot concrete walls used to channel water. Typical construction of such walls entails two-sided forming, then filling the void with soil, sand or concrete slurry and completing a second concrete pour for a topping slab. With geofoam, blocks made-up half of the form, which served as a void fill and support for a concrete topping slab. This method enabled crews to pour the topping slab and channel walls at the same time, which significantly reduced forming labor, material costs and accelerated the concrete pouring schedule. In garden roofs, geofoam provides a lightweight, water-resistant, supportive base for liners, soil, irrigation systems and plants. |
ENGINEERS ENABLE
Engineers often specify EPS geofoam where underlying soils have low bearing capacity, which would cause unacceptable soil settlement and potentially damage nearby structures.
EPS geofoam is durable, does not decompose and is not adversely affected by freeze-thaw cycles. These attributes mean EPS geofoam works well in climates all across North America. Depending on the density of geofoam used, water absorption limits range from 2 percent to 4 percent by volume making it suitable for below-grade applications. Compressive resistance values range from 316 to 2,678 psf at 1 percent deformation. Contractors have used the material in numerous load-bearing applications, including as a sub-base under pavements supporting locomotives and jet aircraft. The loads on most backfills adjacent to buildings and retaining walls are substantially less.
Some examples of projects that used EPS geofoam as a backfill on foundation walls or retaining walls include:
- McDonalds Restaurant, Fairmont, W. Va.
- KBS Hospital, Dixon, Ill.
- West Virginia University student housing, Morgantown, W. Va
- Numerous highway embankments
At the Fairmont McDonalds, a retaining wall was needed that could accommodate the change in grade, as well as reduce the load over extremely soft soils. Typical soil fill would have caused unacceptable settlement of the retaining wall. The use of EPS geofoam allowed the owner to incorporate the traditional keystone retaining wall while eliminating the need to use the typical geogrid material to reinforce the retaining wall.
To determine if EPS geofoam is suitable for your project, consult a qualified civil or structural engineer or a geofoam manufacturer. A range of background information also is available from the Syracuse University Geofoam Research Center (http://geofoam.syr.edu) and the EPS Industry Alliance (http://epsindustry.org/other-applications/geofoam).
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