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Plastics hold a unique perception in society. On one hand, they are embraced as the convenience material of the century; on the other, they are demonized as ocean-polluting and habitat-destroying forces of anti-nature. But plastics are like many other human inventions. Its existence is neither inherently good nor evil, and its ultimate impact depends on usage.
For those in industry, plastics exist beyond grocery bags and six-pack rings (single-use plastics). Their unique physical and chemical properties afford many benefits to projects that must contend with water, chemicals, and containment. However, what isn’t widely known or discussed is its relative carbon footprint or sustainability versus other more traditional construction materials.
In this article, we will explore the carbon footprint of geosynthetics versus traditional construction materials and summarize the benefits of geosynthetics.
Calculating the carbon footprint of geosynthetics vs. traditional construction materials
A carbon footprint is defined as the measure of the total amount of carbon dioxide (CO2) and other carbon compounds emitted by a system within a timeframe (1). While it is a simple calculation to sum the carbon footprint of a typical passenger vehicle (4.6 metric tons, 2), the terminology does not apply as easily to things like 10 m of concrete pipe or a square foot of geosynthetic liner. In these cases, the carbon emissions during manufacturing, transporting, and end of life activities must be considered. As such, the term embodied carbon (EC) is used.
The EC measurement includes the cumulative carbon emissions required to produce, deliver, and use a material. The calculation includes material-specific processes. For instance, the EC in concrete includes the emissions derived from the extraction, processing, and transportation of cement and its aggregate constituents. A similar calculation is done for steel, which includes the emissions from mining iron ore, transportation and processing of the ore into steel, plus further transportation and processing of the steel on-site. For geosynthetics, the EC calculation includes the emissions from capturing oil or gas, transporting to a refinery, processing into resin, manufacturing into a synthetic product, and transporting to the site. Finally, the EC measurement in all cases includes the carbon emissions derived from actual construction activities (3).
Table 1. Table of case study results adapted from 3.
|Case Study||Traditional Approach||Geosynthetic Approach|
|Cost (K)||CO2 Footprint (tons)||Cost (K)||CO2 Footprint (tons)|
|Sheet Piling Wall||$246||433||$121||69|
Five case studies, each comparing the total carbon footprint (including EC) of a project using the traditional approach vs. the geosynthetics approach, demonstrates the relative sustainability of geosynthetics in practice. The first case study compared a slope stability project using traditional gabion wall design and quarry imported gravel with a reinforced soil slope (site-available soil) and geogrids. The traditional approach cost about $571,000 and carried a total carbon footprint of about 157 tons of CO2. In contrast, the geosynthetic approach cost less than $50,000 and carried a total carbon footprint of about 21 tons of CO2. The other case studies showed similar cost and carbon footprint savings (see Table 1). What makes geosynthetics useful as a construction material?
Summarizing the benefits of geosynthetics
The key benefit of geosynthetics can be boiled down to one word: options. There are geosynthetic options to solve an array of problems in just about any construction project.
As a whole, geosynthetics are products made with polymers and typically include geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells, and geocomposites. Because geosynthetics are made with the same class of material, most products share similar physical traits such as a high degree of durability while maintaining a relatively light weight. Additional advantages can be seen in geosynthetics made with specific kinds of polymers. For instance, geomembranes made with high-density polyethylene (HDPE) are typically more rigid and durable than a liner made with linear low-density polyethylene (LLDPE). HDPE is also known for its relatively high resistance to long-term ultraviolet (UV) light and chemicals such as acids, bases, and hydrocarbons.
Geosynthetics can be extruded into various shapes. Geomembrane liners, for instance, can be extruded using a technique called flat die extrusion. Flat die extrusion enables a high degree of consistency when creating asperities or other physical features on the liner, which can go on to solve specific project problems such as improving slope stability or improving drainage.
Results from various case studies have not only demonstrated how geosynthetics can be relatively more sustainable than traditional construction materials, but also offer unique benefits that can enhance the way engineers solve application-specific problems.
- 1. https://www.researchgate.net/publication/275035331_’Carbon_footprinting’_Towards_a_universally_accepted_definition
- 2. https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
- 3. https://geosynthetic-institute.org/papers/paper41.pdf
- 4. Brown and X. Lu, “PENT-Universal Test for Slow Crack Growth in Plastics,” in Limitations of Test Methods for Plastics, ed. J. Peraro (West Conshohocken, PA: ASTM International, 2000), 146-154. https://doi.org/10.1520/STP14348S. Accessed online at https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP14348S.htm.
- 5. http://www.plasticspipe.com/docs/41