Geofoam has been used as a lightweight construction material in the United States since the 1980s. With almost 40 years since its first use, you wouldn’t expect innovation. It works so well that new uses are still being studied and developed.
Geofoam is expanded polystyrene (EPS) or extruded polystyrene (XPS). It is 98% to 99% air by volume and can either be pre-shaped/cut or shaped/cut onsite. Installing the EPS blocks doesn’t require skilled training; the blocks are easy to carry and place by hand. Geofoam is often used as road fill in areas with poor subsoil. No surcharging, preloading, or staging is necessary – making it easier to use than other fill material. It has compressive resistance values of 2 to 15 psi at 1% strain – it is strong enough to support traffic and landscaping equipment loads.
This has made it an integral part of many civil engineering and architectural projects. It was first used in Norway in 1972 as a fill for a roadway project. Since then it has been used for roadway widening, compensating foundations, retaining and buried wall backfill, slope stabilization, foundations for lightweight structures, and many other projects.
A study conducted in 2019 by Al Ashar University in Cairo, Egypt looked at the best technique for reducing the stress acting on buried pipes using EPS geofoam. In addition to an all sand fill control, four variations of the geofoam/sand fill techniques were tested. The embankment: a three block geofoam overburden layer (Figure 2), the imperfect ditch: a one block geofoam layer embedded in sand above the pipe (Figure 3), the embracing EPS block: a block of geofoam cut to encase the upper part of the pipe (Figure 4), and the EPS encasement block with head void: geofoam blocks encasing the upper part of the pipe (Figure 5). Sand filled the voids above and below the pipe when necessary.
A jack was used to apply a compressive load and dial gauges measured the vertical settlement and pipe deformation. The EPS encasement block with head void protected the buried pipe from the stress the most – reducing the vertical and horizontal deformations by 95% to 99%. The study shows that all four methods protect the pipe when compared to the sand only fill, with the exception of the imperfect ditch. There was a 0% reduction of vertical deformations with the imperfect ditch method. While this isn’t a new use for geofoam, this study gives designers more confidence when using it and better direction on the optimal method.
Landscaping, Architectural, Green Roofs
Green roofs have been gaining ground, especially in Asia and Europe. For good reason – they help with the urban heat island effect, reduce runoff, improve local air quality, and better building aesthetics. The problem is they are heavy. All the different layers in a green roof can put a huge load on the underlying structures. When a green roof is being added to an existing building the building wasn’t originally designed to handle the load. This can lead to failure if the design isn’t accurate, as demonstrated by the University of Hong Kong collapse in 2016.
Geofoam is 100 times lighter than soil; it doesn’t create an additional load to underlying structures. Geofoam can fill voids and create interesting terrain without adding to the axial loading on structures. There is no struggle to get the geofoam to the roof of tall buildings. They can be easily cut to any shape and create unique designs. Green roofs are still struggling to take off in North America. Hopefully, with geofoam making them easier to design and install, builders in North America will give green roofs another look.