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 efficiently.
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.
