What Compressive Strength Do You Really Need?

What Compressive Strength Do You Really Need?
Many projects design & build for higher load bearing densities then are required, thus costing significantly more time and money than is necessary.  ASTM’s D6817 is the specification for rigid cellular polystyrene geofoam. Designing to this standard not only helps engineers meet technical specifications, but also helps save money and time by using EPS (expanded polystyrene) geofoam, which is listed by the standard, as a structural void fill.  Geofoam has the compressive strength to bear heavy loads like concrete slabs, soil overburden, highway trucks and even airplane traffic and has gained widespread acceptance in load-bearing applications with federal and state entities like DoTs, airports and commercial projects.  
Similarly referring to ASTM C578 (Specification for Rigid Cellular Polystyrene Thermal Insulation) while selecting your below-grade insulation products, not only helps you design the right product for the job, but also helps avoids unnecessary costs associated with over engineering. 
ASTM C578 publishes compressive strength, deformation and dimensional stability values for both EPS & Extruded Polystyrene – XPS. Insulfoam’s wide range of plain and coated-facer insulation products meet ASTM C578 specifications, providing the same compressive strengths and long-term moisture prevention as competing below-grade insulations. But Insulfoam products come at a lower cost to the building owner, helping deliver significant savings in project costs.
  • Project:  San Francisco 49er’s New Football Stadium
  • Location:  Santa Clara, CA
  • Product:  Insulfoam GeoFoam 2,500 cubic feet of EPS39 and 25,000 cubic feet of EPS15
  • Application:  Below grade structural void fill to support foundation for the fan seating areas
EPS Geofoam

EPS Geofoam

The contractors (Conoco Company of Concord and Turner & Devcon Construction) chose EPS Geofoam due to it’s extremely low weight and high load-bearing capacity to support the dimensional stability required for concrete topping slabs.  Insulfoam’s multiple manufacturing locations in California and nearby states provided just-in-time deliveries direct to the job site, which was a welcome bonus.

The single largest benefit to concrete contractors when using EPS is the ability of the material to constitute half of the form and the fill simultaneously, which completely eliminates the concept of a two pour operation. Read the full project profile here:  San Francisco 49er’s Find EPS Geofoam Useful In Future Home.



  • Geofoam is 98% lighter than traditional fill
  • Geofoam does not settle
  • Geofoam eliminates lateral stresses from retaining structures
  • Geofoam can be designed for seismic forces


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