Many engineers are familiar with using geosynthetics such as expanded polystyrene (EPS) geofoam in infrastructure projects, but might not have considered the applications and benefits of the material in building construction. In the same way that geofoam's light weight, strength, and consistency help simplify and improve construction of roadways and other infrastructure, those same benefits apply to building applications ranging from soft soil remediation to construction of stadium seating and landscaped roofs.
Geofoam performance attributes
A defining feature of EPS geofoam is its ultra-light weight compared to other fills. Geofoam weighs approximately 0.7 to 2.85 pounds/cubic foot, depending on the product type, compared to 110 to 120 pounds/cubic foot for soil. It even weighs much less than other low-weight fills such as cellular concrete (35 to 100 pounds/cubic foot) and wood chips (15 to 30 pounds/cubic foot). Unlike other fills, it offers predictable engineered values, which simplifies design and construction.
Common infrastructure applications for geofoam, which also work well for various building needs, include:
- use as lightweight structural void-fill for numerous concrete and landscaping applications;
- create a zero loading factor for soft soil remediation;
- eliminate or reduce lateral loads on structures;
- lighten the driving block for slope stabilization; and
- reduce lateral and dead loads over existing or newly buried utilities.
Although it is light weight, EPS geofoam has better bearing capacity than most foundation soils. The material's compressive resistance ranges from about 317 to 2,678 pounds/square foot at a 1 percent strain. As long as combined dead/live loads do not exceed 1 percent strain, the material will not creep or experience plastic yield.
With a closed-cell structure, EPS geofoam is hydrophobic and dries quickly. As a result, little, if any, weight gain is expected due to water absorption.
Following are several examples of building projects in which geofoam figured prominently.
Landscaped roofs — In 2015, Facebook opened a 430,000-square-foot office building in Menlo Park, Calif., that features a 9-acre landscaped roof. Reminiscent of a city park, the roof of the MPK 20 building includes 400 trees, a half-mile walking trail, and hills and berms.
Creating the landscape contours with soil would have imposed prohibitive dead loads, so the project team instead specified EPS geofoam. The designers were able to create natural looking ground contours at a fraction of the weight of soil. The geofoam also provides supplemental protection against water intrusion into the roof assembly and additional thermal insulation.
Likewise, the design team for the new 20-acre Maggie Daley Park on Chicago's Lake Michigan shoreline used 65,000 cubic yards of EPS geofoam to form landscape contours. Much of the park overlies the East Monroe Street Parking Garage, which lacked sufficient structure to hold earthen landscape features. "[Geofoam] allows you the freedom to be creative," said Peter Schaudt, FASLA, partner with Hoerr Schaudt Landscape Architects, as quoted in the Chicago Sun-Times.
Soft soil remediation — In the same way that engineers have used EPS geofoam to remediate soft soils for roadway projects, the material works well for solving challenges with poor load bearing soils in building projects.
One example is a renovation of the city hall in Renton, Wash., that required installation of new handicap ramps. Located near the glacier-formed Lake Washington, the building sits on soft glacial till. To avoid post-construction settlement, the project team specified EPS geofoam as a void fill in the ramps. Crews installed 5,000 cubic yards of EPS geofoam, which played a role in helping complete the project two months ahead of schedule and nearly $600,000 under budget.
Swimming pools — In another building application where reducing dead loads is crucial, design professionals are specifying geofoam for swimming pools in hotels, schools, and community centers. Project teams can order geofoam blocks pre-cut to precise dimensions or can easily cut them to size and shape onsite. This simplifies the concrete-forming process and greatly reduces weight for construction of rooftop pools or sites with poor load-bearing soils. Once crews form the pool basin and decks with geofoam, they can apply shotcrete directly to the foam.
Stadium and theater seating — Geofoam provides a fast and simple way to create tiered seating for auditoriums, movie theaters, gymnasiums, and places of worship. For such stadium-style seating, crews hand place row upon row of geofoam blocks to achieve the necessary profile. They can then either place concrete over the geofoam as shotcrete or as precast panels. Using geofoam greatly simplifies the forming process and eliminates the need for complex tiered compacting of soil to form the stepped profile of stadium seating.
Slope leveling — An inverse type of project to constructing stadium seating is to convert an existing sloped space into a level one. For example, the University of Washington wanted to convert a sloped floor lecture auditorium into a surgical suite at Northwest Hospital in Seattle. The project engineers specified Insulfoam GF geofoam as a structural void fill to reverse the slope. The EPS supplier custom factory cut the blocks to minimize field fabrication on the job site. Because the enclosed auditorium did not have space to accommodate heavy equipment, and as noise from mechanical compaction of soil would have disrupted hospital patients and staff, geofoam was an ideal alternative. The lightweight structural fill provided a strong, stable subbase for the new, level concrete floor slab.
Among the above projects, and others, key applications and benefits of EPS geofoam for building applications include its use as:
- slab infill under concrete topping slabs to reduce labor and aggregate base used in traditional fill scenarios and to reduce compaction testing;
- a soil remediation to reduce weight on certain subgrades; and
- backfill in retaining walls to reduce lateral load pressure.
Other applications include rooftop infill material such as for air handler voids and as a sandwiched material between precast concrete panels.
Tom Savoy is the technical director of Insulfoam (insulfoam.com).