Geofoam is a term, originally coined by Dr. Dawit Negussey of Syracuse University, to describe block or planar foam plastic insulation used below-grade. After several years of research, this technology was brought to the United States, via a research project conducted by the Foamed Polystyrene Alliance (FPSA), then a business unit of the Society of the Plastics Industry (SPI). All current members of XPSA participated in FPSA and co-sponsored this research.

Geofoam can be used as a lightweight-fill soil substitute; or as insulation beneath highways or airport runways. XPS is typically used in the latter two categories due to its excellent ability to withstand freeze-thaw cycles and its higher long-term insulating power. The power is not compromised when it gets wet.

Case Study

Airport Runway Insulation—Newton Field, located in Jackman, Maine, was Maine’s first public airport to insulate under its runway. Half-a- million board feet of extruded polystyrene (XPS) insulation was used to carry out the project.

Jackman is cold. Frost penetrates eight to ten feet into the ground. Despite frigid winter weather, real pavement problems do not begin until spring, when thaws trigger frost heaving and paving deterioration. Other than the obvious safety hazards that this presented, it also meant additional maintenance expenses.

Traditionally, freeze/thaw problems have been solved by a deep layer of gravel under the pavement. It would take 118 inches of gravel to prevent the subgrade from freezing and the Federal Aviation Administration requires native soils to be replaced with granular soils to two-thirds of the frost depth. For Jackman, the FAA estimated depth of frozen soil was 72 inches, requiring 48 inches of pavement and base section.

At Newton Field, however, it was decided to use an alternate technique: extruded polystyrene insulation placed under the roadbed. This application can not only prevent those problems associated with frost heave, but can also save money in the initial construction because less aggregate is needed for the base. In this case, the use of insulation saved 36 inches of gravel subgrade—more than 19,000 cubic yards of gravel and the excavation to fill it.

The specification for Newton field called for a high compressive strength insulation board, leveled on a minimum 1-inch layer of supporting granular material, covered with 12½ inches of gravel and two inches of bituminous pavement. The thickness of the board depends on severity of the frost. About ½ inch of board thickness is recommended for each 500 freezing index days. Two-inch board was specified for Jackman with its freezing index of 2200.

According to a spokesman for the Maine airport, it was necessary that the insulation withstand a loading of 40lbs. per square inch, had a high insulating factor and a low water absorbency. The water absorbency, in particular, was very important. If the insulation absorbed too much water, it would freeze and be useless as an insulator. They tested XPS as specified in ASTM C 578 2001, Type VI, and it met all the requirements, including a competitive price.

The Newton Field project used XPS as specified in ASTM C 578 2001, Type VI boards 8-feet long, 24-inches wide and 2-inches thick. XPS, made by UC Industries, Inc., is a 40 psi high density, closed cell foam panel with continuous skin surfaces for water resistance and a long term R-value of 5 per inch of thickness. XPS is lightweight and easy to handle, weighing about 400 lbs per 1,000 square feet in the 2-inch thickness. It meets AASHTO Spec-M230, Federal Spec HH-I-524C, Type VI, ASTM C 578-87a and other cold weather specs.

Because Newton Field is the first U.S. airport where extensive use has been made of insulation under the runway, the project is being monitored by the U.S. Army’s Cold Regions Research & Engineering Laboratory, which hopes to use the data to validate and refine airport designs and procedures for frost-prone areas.

XPS in Highway Applications—Highway frost heave is a major factor responsible for the distress of pavement in Colorado and other states. The phenomenon presents a problem both from the standpoint of safety and costly, repeated repairs. Three things must be present for frost heaves to occur: freezing and thawing temperature ranges, free flowing water and permeable soils. When the frost penetrates deep, ice lenses form in the roadway foundation. As a result, the pavement surface is thrust upward into the hump we call “frost heave.” The key to frost heave is soil temperature — by insulating the roadway, frost is prevented from cycling in the ground.

In the summer of 1988, two roadway upgrading projects were done by the Colorado Department of Highways (CDOT), in mountainous terrain, on the approach to the Eisenhower Tunnel. In both cases Type VI XPS as specified in ASTM C 578 2001 was used to help control chronic frost heave. One project used about 300 linear feet of XPS, the other, a 10 mile stretch of I-70, had eight areas where frost heave problems had been experienced. XPS was used in sections ranging from 85 to 500 ft. — a total of about 1900 linear feet of insulated roadway.

Traditionally, depending on analysis of soil, excavation is to a depth of 10 inches — 6 inches of base course and 4 inches of asphalt. The department added another 8 inches to accommodate insulation, excavating to about 18 inches total. Then 2 inches of base for a leveling course is placed. Next the 2 inch XPS panels are positioned. Workers stagger the joints of the panels in a brick pattern. This helps interlock them — a standard insulation practice originally developed on flat roof applications. Fine sand is shoveled over each joint and scattered over the boards holding the panels in place. Then an 8 in. base (crushed gravel) is followed by plant mix, leveling coat, and seal coat.

The work is all standard except for a minimum of extra care required when applying gravel on top of the XPS panels. It’s a simple technique, and the crews of both contractors picked it up easily.

Wendell Upright, CDOT Project Engineer, said, “The key is to go deeper with roadbed excavation in order to include insulation. If there’s a drainage problem, it gets solved by adding filter material and perforated pipe, so that water can get out again. Workers place insulation over the pipe to keep cold air from penetrating upward to the road.”

Engineers decided that use of a few hundred feet of extra XPS would be a good investment to avoid future problems. So wherever plans called for installation of perforated pipe to drain water, they insulated the pipe with the same 2-in XPS as specified in ASTM C 578 2001, Type VI extruded polystyrene being used under the roadbed.;

The Colorado Department of Highways now insulates all pipes when building new roads or when installing or replacing pipes in existing roads.

As Wes Goff, Resident Engineer puts it, “We would no longer contemplate a sizable project without applying insulation where frost heave problems would be anticipated. The experimental projects gave us confidence to go ahead. Extruded polystyrene insulation is no longer experimental — it’s the approved, standard technique.”


About XPSA

The Extruded Polystyrene Foam Association (XPSA) is a trade association representing manufacturers of Extruded Polystyrene Foam (XPS) insulation products and the industry's raw material suppliers. XPSA members collectively manufacture more than 95% of all XPS destined for use in the North American market. XPSA promotes the benefits that accrue to society from appropriate use of XPS foam insulation applications.

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