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Geofoam Technical Bulletin
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EPS Geofoam
Materials used in construction engineering are changing rapidly. Structural steel and concrete are stronger than even just a few years ago. And new “geosynthetic” materials such as inorganic fibers, composites and plastics are being used more frequently, and with greater results, than ever before.

As part of this evolution, the use of EPS geofoam in engineered construction is growing fast and furious. But just what exactly IS geofoam? What does it DO? And how is it USED?

Hany L. Riad, Ph.D., P.E., an engineer currently using geofoam in Boston’s Big Dig, comments, “In civil engineering applications, the use of EPS typically translates to benefits to construction schedules and savings in overall cost of construction. EPS is unaffected by occurring weather and is environmentally safe. Its service life is comparable to other conventional construction materials and will retain its physical properties under engineered conditions of use.”

EPS Geofoam 101
“EPS Geofoam” describes low-density cellular plastic foam solids used in geotechnical applications such as lightweight fill for construction on soft ground, for slope stabilization, and retaining wall or abutment backfill; as well as for roadway and runway subgrade insulation and foundation insulation.

Polystyrene is the main polymer used to produce EPS geofoam. Expanded Polystyrene (EPS) geofoam is created in a two-stage, molded bead process. EPS geofoam is typically produced in blocks that can be cut into various shapes and sizes to suit specific projects. It can also be produced in a range of densities to meet varying project needs.

EPS geofoam is produced from expandable polystyrene resin beads that contain microscopic cells filled with a blowing agent (usually pentanes or butanes). The resin is exposed to steam under controlled pressure, which softens the cell walls. The blowing agent expands - causing individual resin beads to increase in volume by up to forty times – and “pre-puff” is formed. After a brief holding period to allow stabilization, the pre-puff beads are poured into a large rectangular mold cavity, or block mold. Steam is injected into the mold, and heat and pressure further expand the beads to fuse them into a molded block.


Doing More with Less
The philosophy of “less is more” has permeated almost every facet of modern life – construction engineering notwithstanding. EPS geofoam is a perfect fit, giving designers a unique product that works in conjunction with other, more traditional materials to solve construction problems with unprecedented strength and flexibility.

EPS geofoam enables engineers, architects, builders and other industry professionals to design by function, that is, to focus on the key geosynthetic functions they’re looking for in an particular project, then select the best combination of products to achieve the goals most cost efficienty.

EPS geofoam provides several unique functions not available with other types of geosynthetic materials. This multi-functionality replaces the need for many different products to achieve the desired results, making EPS geofoam highly cost effective.

At the same time, EPS geofoam products work very well as a complementary resource, with EPS geofoam-based composites and new synergies enabling end users to design with even greater flexibility and more options, not to mention unique results that would not be otherwise attainable.

EPS geofoam products help reduce and absorb the impacts of naturally occurring forces such as gravity and earthquakes rather than trying to strengthen or stiffen a structure to resist the forces. By working with, rather than against these forces, EPS geofoam gives engineers more flexible solutions to construction challenges.

Inside Geofoam
The two key properties that make EPS geofoam so attractive in design and construction are its low density for stress and deformation-related construction problems, and its thermal insulation properties that help combat frost-heave problems.

The density of EPS geofoam is controlled during the manufacturing process, and ranges from 15 to 22 kg/m3 for lightweight fill applications. This low density is only about 1 to 2% of the density of soil and rock, making EPS geofoam a superior, ultra lightweight fill material that significantly reduces the stress on underlying subgrades. The lighter load reduces settlements and boosts stability against bearing and slope failures.

Because it is approximately 98% to 99% air by volume, geofoam is a very efficient thermal insulator. EPS geofoam can be produced with higher densities to obtain the higher R-values preferred for insulation purposes, as well as to achieve lower deformation. EPS geofoam has been used in road and airfield pavements and railway track systems, beneath refrigerated storage buildings, sports arenas and storage tanks to prevent ground freezing and heaving, and in below-ground building segments to reduce seasonal heating and cooling requirements.

Other notable geofoam properties include:

• High compressive strength – makes EPS geofoam durable and resistant to damage over time
• Low moisture absorption – moisture absorption rates increase as density increases, but are still minimal
• Low interface friction – in direct shear tests, the interface friction between sand and EPS geofoam is comparable to the internal friction of sand alone

Applications of EPS Geofoam
The two main uses of EPS geofoam are for lightweight fill and insulation applications. Outlined below are specific applications of EPS geofoam in geotechnical construction.

Road Embankments
Geotechnical engineers have long recognized the usefulness of lightweight fill to reduce load strain. Traditional lightweight materials used in embankment construction include chipped bark, sawdust, dried peat, fly ash, slag, cinders, cellular concrete, lightweight aggregates, shredded tires, and seashells. A major advantage of using geofoam as fill material in embankments is that it is up to 50 times less massive than other lightweight fills, thus providing:

• Maximum available right-of-way
• Faster construction schedule
• Lower traffic impact
• Comparatively clean construction near waterways
• Reduced labor
• Minimal future maintenance

Retaining Wall or Abutment Backfill
Placing EPS geofoam behind retaining structures and below-grade walls reduces lateral pressure, lowers settlements, improves waterproofing and provides better insulation. The low density and relatively high compressibility of EPS geofoam also limit horizontal forces against retaining structures during earthquakes.

Slope Stabilization
Because the density of EPS geofoam is 50 to 100 times lower than soils, geofoam is highly effective in improving the stability and safety of slope construction by minimizing the potential of failure surfaces between driving blocks and resisting blocks in a slope.

Pavement Insulation
EPS geofoam is used successfully as highway and airport pavement subgrade insulation to reduce subgrade stress and deformation as well as to protect against frost heaving.

Frost Protected Shallow Foundations
In cold climate regions, building foundations are required to extend below depths of expected frost penetration. This typically requires housing construction with basements or crawl space below floor grade. By using EPS geofoam, homes can be built in cold climates with slab-on-grade support. Frost protected shallow foundations significantly reduce construction costs as well as energy costs.

Boston’s Big Dig
The Central Artery/Third Harbor Tunnel (CA/T) Project, also referred to as the a.k.a. ‘Big Dig’, in Boston, Massachusetts, has utilized many innovative terhnologies in the rebuilding of interstate highways I-90 and I-93 through the heart of the city. Among such innovations are eight (8) EPS geofoam transition structure and ramps located on the I-93 Northbound and Southbound mainlines. These structures are constructed primarily of expanded polystyrene geofoam lightweight fill material for highway embankments.

The sue of EPS as a geofoam lightweight fill was an outcome of a cost and schedule initiative to replace precast concrete girder bridges, elebated slabs and regular fill on both sections, and all supported on pile foundations and drilled shafts. Construction using EPS has resolved the primary technical challenge of constructing a finished roadway elevated above existing grade in a congested urban area underlain by extremely soft and compressible soils. The heights of the CA/T – EPS geofoam ramps vary, with a maximum height of the finished roadway pavement above existing grade of approximately 8 meters or 25 feet.

The CA/T embankment structures represent on of the largest EPS construction of its kind in the United States and some of the highest freestanding EPS structure in the world. Considerable experience has been acquired on this technology with the assistance and support from the Federal Highway Administration (FHWA).

Geofoam Project Receives National Recognition
The American Society of Civil Engineers (ASCE) named Salt Lake City’s Interstate 15 (I-15) geofoam project the 2002 Outstanding Civil Engineering Achievement (OCEA). Past OCEA winners include the Whittier Access Project, the relocation of the Cape Hatteras Light Station, the Denver International Airport and the World Trade Center.

The I-15 project is the largest public works project ever undertaken using the engineering and construction method known as 'design/build.' Design/build can shorten the time needed to complete a project, but its success requires highly effective project management.
The award presented to the Utah Department of Transportation recognizes the project for its significant contribution to civil engineering progress and to Salt Lake City's community. I-15 was selected from among six outstanding project finalists throughout the United States. In total, there were 33 entries submitted for consideration.

"The I-15 project has contributed greatly to Salt Lake City's ability to stage the successful Salt Lake 2002 Winter Olympic Games, and will continue to serve the area's residents for years to come," said H. Gerard Schwartz, Jr., P.E., ASCE president. "The Interstate exemplifies the ideals of innovation, technical excellence and community benefit."

In announcing the selection of the I-15 project, the jury noted that the project was completed in just four years, half the time that would have been needed using traditional approaches, and came in $32 million under budget. Jurors also noted the innovative use of materials, such as lightweight expanded polystyrene geofoam in the embankments. The Utah Section of the American Society of Civil Engineers on behalf of the Utah Department of Transportation nominated the project.

Since 1960, ASCE has named a project as an Outstanding Civil Engineering Achievement. The prestigious national award recognizes civil engineering projects that contribute to community well-being, demonstrate resourcefulness in planning and solving design challenges, and use innovative construction methods.