By Tom Savoy
Expanded polystyrene (EPS) Geofoam (GF) is a rigid, engineered fill material that is widely known for its lightweight composition, predictable performance, and simplified installation process. The effective fill solution is frequently employed by engineers and project designers to optimize labor resources, speed up construction timelines, and address a variety of geotechnical challenges, including:
- lightening loads on structures, utilities, or underlying soils
- remediating soft soils and minimizing differential settlement
- stabilizing steep slopes and embankments
- reduce lateral load behind retaining structures
- serving as a structural void fill for concrete or landscaping applications
EPS GF has been used as a geotechnical material since the 1960s. One of the first documented projects in North America that utilized EPS GF was during the installation of the Trans-Alaska Pipeline. Thanks to its thermal insulation properties, EPS GF was employed to provide effective utility protection. Decades later, it’s still being successfully utilized in the field. Just a few years ago, the rigid foam material was used to accelerate construction timelines and effectively stabilize the eastbound lanes of U.S. 36 between Boulder and Denver, Colorado. The material’s lightweight composition made it possible for crews to quickly unload over 200 flatbed trucks and install the product with ease. More recently, engineers and architects utilized EPS GF to build up a quarter-mile bridge across Tampa Bay that leads to the newly renovated St. Pete Pier waterfront park on Florida’s West Coast. The lighter load reduces settlements and boosts stability against bearing and slope failures to successfully support the largest waterfront park in the Southeast region.
Project cost-savings, galore
In application, EPS GF’s combination of lightweight yet load-bearing properties can support overall project cost-savings. For example, the geosynthetic fill’s lightweight composition lends a quick, efficient installation process, which in turn can reduce hours spent on the jobsite. While lightweight, the rigid foam material is engineered to demonstrate exceptional compressive resistance to support high loads. With this level of brawn, one flatbed of custom-made EPS GF can accomplish what would otherwise require approximately 12 dump truck loads of soil fill. Less material in play helps simplify construction logistics, minimizing labor and material costs in twofold. Thoughtfully engineered to maximize efficiencies, EPS GF’s lightweight composition, compressive strength and customization capabilities can support generous cost-savings across a project’s bottom line.
A defining feature of EPS GF is its lightweight composition. Composed of 98 percent air voids by volume, EPS GF weighs approximately 0.7 to 2.85 pounds per cubic foot. It’s approximately 100 times lighter than most soil types, and 20 to 30 times lighter than concrete. This extreme difference in unit weight is the defining feature of EPS GF, making it an attractive solution over traditional fill materials. Because EPS GF is so lightweight, large earthmoving equipment is not required during installation. Instead, custom-cut blocks of EPS GF can be installed easily and efficiently by hand—an ideal solution for accelerating construction schedules. Because the pieces of rigid foam are designed to lock in place, much like stacking blocks or assembling a puzzle, smaller crews are freed up to focus on other, more time-consuming tasks on the job site. In application, the material helps keep projects on budget by decreasing upfront material costs and reducing the number of hours crews spend on the job site.
As mentioned earlier, EPS GF’s lightweight composition was a defining feature for the St. Pete Pier project engineers and designers, who were able to apply 700,000 board feet of the rigid foam material across the concrete deck of the bridge. Because the material is so lightweight, there is significantly less stress applied to the underlying substrate.
“It’s a quarter-mile deck over water, and you don’t want additional weight over water,” said Dave Hall, a territory manager for Insulfoam, the leading manufacturer of EPS products. “Ground with soft soil makes building construction notoriously difficult. If you place something heavy on soft soil, it will place pressure on the underlying soil. The soil will inevitably compress with time, putting the structural integrity of the system at risk.”
To its benefit, lightweight blocks of EPS GF can sideline this problem and lighten the load on the substrate. What’s more, the material is also designed in such a way that it does not degrade—a key factor to withstanding Florida’s low sea levels and high precipitation rate.
Strength to boot
Although lightweight, EPS GF is designed to exhibit exceptional strength. As an engineered material, manufacturers can customize EPS GF blocks to offer enhanced compressive strength, with values ranging from approximately 2.2 psi to 18.6 psi (317 to 2,678 pounds per square foot) at a 1 percent strain. Assuming combined dead/live loads do not exceed the 1 percent strain designation, the material will not creep or experience plastic yield. With this assurance, EPS GF offers improved stability against bearing and slope failures. And because the material is engineered to disperse loads evenly across a surface, it minimizes post-construction settling, which again supports a more stable foundation. This is not the case with soil and related fill materials, as their inconsistent compositions can lead to non-uniform load transfer and differential settlement. This can cause dangerous, uneven settling and lead to permanent structural damage. By employing the EPS GF approach, engineers and project designers will proactively avoid these risks and ultimately extend the lifespan of the complete building system.
Although EPS GF can be manufactured in many sizes and shapes, standard blocks are typically 40″ x 48″ x 96″. These oversized puzzle pieces can fill massive volumes, reducing upfront material and labor costs. For custom projects, the rigid foam material can be cut on the factory floor to meet exact specifications. For example, engineers and project designers can use EPS GF to simplify the construction of commercial and institutional swimming pools. The blocks of material can be pre-cut to create virtually any shape or slope, which eliminates separate concrete pours for vertical wall sections and topping slabs. EPS GF can also be tailored to accommodate intricate landscaping features or utilities around the pool deck. This level of customization eliminates much of the field-cutting, which again supports material and labor cost-savings.
While traditional fills have, and likely will continue to have their place across civil and structural applications, EPS GF offers engineers and project designers an efficient, cost effective fill alternative. The rigid foam material enables professionals to design by function, that is, to focus on addressing key geosynthetic challenges within a particular project. The material exhibits several special characteristics—a lightweight composition, compressive strength and easy customization—that truly sets it apart from traditional fill options. This inherent multi-functionality replaces the need to employ a host of building materials and tools to achieve project goals. Because EPS GF takes the “less is more” approach to address void fill needs, it can support generous labor and material cost-savings—keeping project budgets in the black.
Tom Savoy is the technical director for Insulfoam, a division of Carlisle Construction Materials. He has worked in the EPS Industry for 34 years and in construction materials (manufacturing and testing) for 40 years. Tom actively participates in many trade organizations including ASTM, SPRI and EPS IA. He can be reached at email@example.com.