Geofoam FAQ
Expanded polystyrene (EPS) is a very common product that is widely used for packaging and in building construction. Manufacturing of EPS blocks begins with expandable polystyrene resin beads that are generally less than 3 mm in diameter and contain microscopic cells filled with a blowing agent. The usual blowing agents are pentanes or butanes and constitute about 5 percent of the bead weight. When exposed to steam under controlled pressure, the cell walls soften and the blowing agent expands. Individual resin beads enlarge by up to 40 times in volume to form pre-puffs. After a holding period to allow stabilization at room temperature, the pre-puffs are poured to fill a rectangular molding box. All six sides of the mold are fixed and more steam is injected through small perforations along the confining walls. The pre-puff in the molding box further expand and fuse to form a block.
ASTM C578 standard for EPS type I is 10psi or 1,440 pounds per square ft (1 square foot is equal to 144 square inches). One square inch of Type I EPS can support 10 pounds; however, set a one square foot board on the foam and it can support 1,440 pounds.
A car weighs approximately 4,000lbs that’s 1,000 lbs per tire, one tire sits on about 6” X 8” or 48 square inches Type I EPS foam in 48 sq inches can support 480 lbs, however drive the car on to 2 sheets of 4 x 8 OSB, 2 tires on each, now 32 square feet of foam is supporting the ½ the car or 2000lbs, 32 X 144 = 4,608 square inches or 46,080 lbs.
To stay at or below 1% deformation – 1lb foam supports 3.5 pounds per square inch. 10ft x 10ft slab of concrete weights 50lbs per square ft X 100 Square feet = 5,000 lbs. 100 square feet of Type I foam can support 50,400 pounds (100*144*3.5 lbs per sqin) at 1% deformation. One full size king cab 4 wheel drive pickup truck can weigh 12600 lbs. Parked on 10ft x 10 ft slab the total weight is 17,600 lbs well below the 50,400 lbs 100 square feet of 1 lb. EPS can support with 1% deformation or less.
Geofoam has been used for insulation and light weight fill applications for over 25 years. EPS blocks exhumed from a construction site in Norway after more than 20 years of burial were found to be in good condition and were re-used.
Geofoam blocks or boards are large but easy to handle. Construction with geofoam is rapid. For large volume applications, manufacturers may need adequate lead time to produce a sufficient quantity for a job. Geofoam shipments are usually installed on delivery without requiring on-site stockpiling or storage.Individual geofoam blocks or boards can be lifted by construction equipment and placed manually by a work crew. Smaller shapes and sizes required at the job site can be cut by either a chain saw or, more conveniently, by hot wire. The placement of geofoam blocks should be staggered to interlock and joints between block layers should not be made continuous. In handling and placement, care should be exercised to limit damage to geofoam blocks. Equipment that imposes high contact stresses should not be operated directly on the geofoam surface or over a thin lift above the geofoam.
EPS waste generated in manufacturing plants is shredded and added to pre-puff to make geofoam blocks. Shredded foam or re-grind may constitute about 5 percent or more of geofoam block content. This re-cycling does not involve chemical processing. It is also possible a greater percentage of re-grind may be allowed in making geofoam for some applications. So far, the extent of recycling has mainly involved use of re-grind or plant generated waste from cutting and trimming. EPS geofoam recovered from previous jobs has also been re-used.
Operation of machinery and haul trucks at construction sites may involve some amount of oil and fuel spilling. There would also be increased air pollution from both construction activity and traffic slow down. Soil embankments require construction in thin lifts with repeated compaction. There is no need for compacting geofoam and each block is equivalent to four or more lifts in height. Erosion by surface runoff and dust generated from the construction area would be reduced. Construction with geofoam is much shorter in duration and can occur in any season. Geofoam is not biodegradable and once installed below surface there are no adverse effects on soil and groundwater quality. The manufacture of EPS geofoam does not involve use of gases that are known to be harmful to the environment. Overall, there would be reduced environmental impact by using geofoam than would be with earth construction.