Geofoam is expanded polystyrene (EPS) or extruded polystyrene (XPS) manufactured into large lightweight blocks. The blocks vary in size but are often 2 m x 0.75 m x 0.75 m. The primary function of geofoam is to provide a lightweight void fill below a highway, bridge approach, embankment or parking lot. EPS Geofoam minimizes settlement on underground utilities. Geofoam is also used in much broader applications, the major ones being as lightweight fill, green roof fill, compressible inclusions, thermal insulation, and (when appropriately formed) drainage.[1]
The area of geofoam can nicely segue into geocombs, previously called ultralight cellular structures which Horvath [2] defines as “any manufactured material created by an extrusion process that results in a final product that consists of numerous open-ended tubes that are glued, bonded, fused or otherwise bundled together.” The cross-sectional geometry of an individual tube typically has a simple geometric shape (circle, ellipse, hexagon, octagon, etc.) and is of the order of 25 mm across. The overall cross-section of the assemblage of bundled tubes resembles a honeycomb that gives rise to its name. Presently, only rigid polymers (polypropylene and PVC) have also been used as geocomb material.
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The first use of EPS Geofoam was in Olso, Norway in 1972. Geofoam was used in the embankments around the Flom Bridge in an effort to reduce settlements. Prior to installing Geofoam, this area experienced 20-30 centimeters of settlement annually causing extreme roadway damage.[3]
Due to the success of the Oslo Geofoam project, the first International Geofoam Conference was held in Oslo, Norway in 1985 so engineers could exchange knowledge, research results, share new applications, and discuss case histories. Since then, two more conferences were held in Tokyo, Japan and Salt Lake City, USA 1996 and 2001, respectively. The next conference is planned for June 2011 in Lillestrom, Norway.[4]
Between 1985 to 1987, Japan used over 1.3 million cubic meters of Geofoam in 2,000 projects. Testing and use of Geofoam in these projects demonstrated the potential advantages of Geofoam as a light-weight fill. For example, Geofoam was placed beneath runways in Japanese airports, proving the material can sustain heavy and repeated pressure.[3]
Geofoam was first used in the United States was in 1989 on Highway 160 between Durango and Mancos, Colorado. An increase in rainfall caused a landslide, destroying part of the highway. Geofoam was used to create highway side slope stabilization to prevent any similar issues. The use of Geofoam in this project versus conventional restoration resulted in a cost savings of 500%.[5]
The largest Geofoam project in the United States lasted from 1997 to 2001 on Interstate 15 in Utah. Geofoam was chosen to minimize that amount of utilities that would need to be relocated or remodeled for the project. A total of 3.53 million cubic feet of Geofoam was used, and approximately $450,000 was saved by not needing to relocate utility poles.[6] Geofoam was also used in embankments and bridge abutments for base stability.[5]
Slope Stabilization is the use of Geofoam in order to reduce the mass and gravitational force in an area that may be subject to failure, such as a landslide. Geofoam is up to 50 times lighter that other traditional fills with similar compressive strengths. This allows Geofoam to maximize the available right-of-way on an embankment. Geofoam’s light weight accompanied by its ease to install reduces construction time and labor costs.
Embankments using Geofoam allow for a great reduction in necessary side slopes compared to typical fills. Reducing the side slope of the embankment can increase the usable space on either side. These embankments can also be built upon soils affected by differential settlement without being affected. Maintenance costs associated with Geofoam embankments are significantly lower when compared to embankments using natural soil.
Retaining Structures using Geofoam have a reduction in lateral pressure as well as prevent settlement and improve water proofing. Geofoam light weight will reduce the lateral force on a retaining wall or abutment. It is important to install a draining system under the Geofoam to insure that you don’t have problems with built up hydrostatic pressure or buoyancy.
Utility Protection is possible by using Geofoam to reduce the vertical stresses on pipes and other sensitive utilities. Reducing the weight on top of a utility by using Geofoam instead of a typical soil prevents utilities from potential issues, such as collapses.
Pavement Insulation is the use of Geofoam under pavement where pavement thickness can be controlled by frost heave conditions. Using Geofoam as a sub-grade insulation element will decrease this differential thickness. Geofoam is 98% air by volume, making it an effective thermal insulator. Proper installation of Geofoam is especially important as gaps between Geofoam blocks will work against Geofoam insulating effects.
Advantages of using Geofoam include:
Disadvantages of using Geofoam include:
| Physical Properties of EPS Geofoam | |||||
|---|---|---|---|---|---|
| TYPE - ASTM D6817 | EPS12 | EPS15 | EPS19 | EPS22 | EPS29 |
| Density, min. kg/m3 | 11.2 | 14.4 | 18.4 | 21.6 | 28.8 |
| Compressive Resistance @ 1% deformation, min., kPa | 15 | 25 | 40 | 50 | 75 |
| Flexural Strength min., kPa | 69 | 172 | 207 | 276 | 345 |
| Water Absorption by total immersion, max., volume % | 4.0 | 4.0 | 3.0 | 3.0 | 2.0 |
| Oxygen Index, min., volume % | 24.0 | 24.0 | 24.0 | 24.0 | 24.0 |
| Buoyancy Force kg/m3 | 952 | 955 | 958 | 961 | 969 |
| Physical Properties of EPS Geofoam | |||||
|---|---|---|---|---|---|
| TYPE - ASTM D6817 | EPS12 | EPS15 | EPS19 | EPS22 | EPS29 |
| Density, min. lb/ft3 | 0.70 | 0.90 | 1.15 | 1.35 | 1.80 |
| Compressive Resistance @ 1% deformation, min., psi | 2.2 | 3.6 | 5.8 | 7.3 | 10.9 |
| Flexural Strength min., psi | 10.0 | 25.0 | 30.0 | 40.0 | 50.0 |
| Water Absorption by total immersion, max., volume % | 4.0 | 4.0 | 3.0 | 3.0 | 2.0 |
| Oxygen Index, min., volume % | 24.0 | 24.0 | 24.0 | 24.0 | 24.0 |
| Buoyancy Force lb/ft3 | 59.4 | 59.6 | 59.8 | 60.0 | 60.5 |