Expanded Polystyrene (EPS): Some Basics

EPS, a versatile, ultra-lightweight material, is one of the most common types of rigid plastic foams (RPFs) in use today. EPS has been used for over 30 years in numerous and varied applications ranging from the ubiquitous "take out" coffee cups to cushion packaging, thermal insulation and, now, geosynthetics.

EPS: The Newest Geosynthetic
The Norwegian Road Research Laboratory (NRRL) deserves recognition for routine geosynthetic use of EPS block beginning with road insulation in the 1960s. EPS is more cost effective than XPS (and all other known RPFs as well) for use as lightweight fill.

Indiana Route 109 Bogged Down No More
The repair of Indiana Rt. 109 near Ft. Wayne in the fall of 1995 was the first use of EPS foam for road work in the State, and to date represents the single largest EPS fill in the Midwest. Polyfoam Packers provided 6,156 cubic yards of EPS that was assembled into a super-lightweight fill to raise an 1100- foot long section of road out of a peat bog and stabilize the road embankment. The project was completed during the first week of December, and the road was closed to traffic for only eight weeks.

Route 109 is a two-lane asphalt pavement running north approximately 11 miles from U.S. Rt. 30 at Columbia City to U.S. Rt. 33 at Wolf Lake. A few miles south of Wolf Lake, Rt. 109 had developed a large, ever-deepening dip that forced periodic closing of the road due to flooding. It's a common occurrence in this area of northeast Indiana where roads frequently must cross peat bogs: the wet peat -- in combination with clay and other organic soils -- is too weak to support the gravel and asphalt that make up a typical road pavement.

Proving the Concept
Polyfoam Packers previously had demonstrated that a relatively shallow excavation, followed by placement of EPS foam blocks topped with a slab of structural concrete, could correct sinking pavements and failing embankments for thousands of dollars less than conventional practices. The EPS construction method, as it is called, has been used successfully in Europe, Japan and Canada for 20 years or more, but has been slow to catch on the United States, where most civil and geotechnical engineers are unfamiliar with the technology.

In the fall of 1993, Polyfoam Packers supplied the EPS lightweight fill, the technical support and design parameters for the reconstruction of Atkinson Road in Grayslake, IL. From that experience, and after investigating several alternative designs, the Indiana DOT Division of Materials and Tests recommended the use of EPS for State Rt. 109. That recommendation was based on the ability of the EPS construction method to raise and stabilize the embankment-- something other constructions could not do for the same cost.

Building a Stable Road Base
Again with the design and technical support of Polyfoam Packers, Indiana DOT engineered a fill measuring l,100 feet long, up to 45 feet wide, and up to 5 feet thick. Like the Atkinson Road project, State Rt. 109 started with a stepped excavation, with the deepest portions at the weakest point of the bog. The EPS blocks were installed in layers with the joints staggered both vertically and horizontally throughout the fill. Double-sided timber fasteners were used between horizontal layers of blocks to prevent any lateral movement during construction. Cutting of foam blocks to accommodate culverts and other structures was done easily with a chain saw.

Polyfoam Packers' Waukegan, IL plant delivered the 6,159 yd3 of 1.5 pcf material on 66 flatbed and drop-deck trailers over the course of eleven days. Many of the blocks measured 16 feet long, by four feet high, by 40 inches wide, and weighed up to 320 lbs. Trucks loaded the night before left for the jobsite early in the morning to assure that material was available for the installation when the contractor's crew arrived.

Once the foam blocks were in place, a four-inch thick slab of reinforced, structural concrete was poured on top to distribute the road pavement and traffic loads over the foam. While the concrete was a standard 4,000 psi mix, it actually developed approximately 6,000 psi strength because of the improved cure that resulted from being set on the EPS insulation. A 17-inch thick drainage course of No. 8 stone was placed over the concrete, and 12 inches of low-volume asphalt material made up the road pavement.

Polyfoam Packers Works Hard to Make Geofoam Easy
Polyfoam Packers provided much more than the lightweight EPS blocks and timber fasteners for the Indiana Rt. 109 project. The company provided complete installation instructions, so there was never any confusion while constructing the fill. Delivery of the material was closely coordinated with the excavation, to keep the contractor's labor to a minimum.

Polyfoam Packers maintained on-site technical assistance for the contractor and the State's project engineers to help answer the range of questions this new construction method presented, everything from construction on slopes and curves to chemical compatibility of adhesives and concrete admixtures. It is too easy to view this kind of project as simply building with blocks when in fact each one is a geotechnically engineered solution for construction on unstable ground. Delivering that solution takes a thorough understanding of the material as well as careful planning and execution by the engineers, contractors and supplier. With everyone's cooperation the reconstruction of Indiana Rt. 109 was finished well ahead of schedule.

After just eight weeks of construction, Rt. 109 was reopened to traffic. There has been no settlement of the pavement since completion of the project.

Post Script
Since the completion of the Indiana Rt. 109 job, Polyfoam Packers has taken on several additional geofoam projects. One of them, the approach ramps for the Great Western Bike Trail overpass at Interstate 355, was recently completed in Lombard, IL. Nearly 3,000 cubic yards of Polyfoam EPS block were placed in these embankments to protect a 48" diameter water line below.

For additional information on this exciting geotechnical material or to consult on your next geofoam project, contact Miles Ducore at 1-800-227-8865.