Sustainability from The Ground Up By Fariborz M. Tehrani
The ground supporting a structure plays an essential role in what is pos- sible for that project. The stability of soil can determine a structure’s height, weight, and even how sustainable or resilient its construction can be. This vitality can be especially true for projects requiring ground improvement, retaining systems, and other ground and foundation sta- bilization forms. These projects may incorporate more raw materials in their planning and may also need heavier-duty foundation systems to provide an adequate base. Both needs can potentially enlarge a project’s carbon footprint or make sustainability benchmarks difficult to achieve. However, for structures built on soft soils, engineers and building professionals can reduce a build’s ecological impact by considering what materials are used as geotechnical backfill. For example, light - weight aggregates made from expanded shale, clay, or slate (ESCS) significantly reduce structural demands and possess a high internal friction angle, further reducing lateral loads. This reduction, in turn, eases material needs for foundation support. Due to their low density, ESCS lightweight aggregates can also reduce transportation costs—fi - nancially and ecologically. In fact, from mining to placement, ESCS presents a sustainable option for projects that require soil remediation or ground improvement with substantial needs for moving the earth. Responsible mining and low-impact manufacturing Sustainable construction encompasses more than the use phase of a building product—it stretches into a product’s future with end-of- life considerations and into its past to the extraction of the very raw materials it is made from. This consideration can include responsible mining practices. Responsible mining involves determining if a mine is an appropriate use of land and if its development is environmentally responsible, beneficial to workers and affected communities and other societal and ecological considerations. For ESCS, the mining process can benefit local environments and communities by slowing the rate at which ma- terials are taken from one area and transported to another. For example, naturally occurring geotechnical fill materials such as gravel or limestone require a one-to-one ratio between extraction and use—every cubic yard or meter of specified material requires an equal amount to be extracted from the earth. This ratio can easily exceed the unit value when considering waste and losses associated with un- processed mining materials. Hence, this approach can quickly strip an area of resources and profoundly impact local ecosystems. However, because shale, clay, and slate are expanded two to three times their original volume, they can reduce the speed at which a mine extracts materials without reducing the total amount of geotechnical fill provid -
ESCS lightweight aggregate reduces lateral loads on MSE walls. Photo: Courtesy of ESCSI
ed to job sites. Further, the engineered process technology minimizes waste and recycles losses in production to maximize productivity and reduce mining footprints. While ESCS requires rotary kiln firing to expand the raw materials, the energy and carbon emissions represented in this process are offset by the reduction of raw material needed as well as the other sustainable benefits across the material’s life and how it reduces material needs in adjacent and complementary building systems. Reduce fuel needs and emissions caused by transportation In addition to needing to extract fewer materials from mines, engineers who utilize ESCS lightweight aggregates as a geotechnical backfill can also expect to see significant reductions in transportation costs compared to other materials. This saving is due to the low density of the aggregate. Whereas traditional quarried materials have a typical dry loose bulk density of 95 – 135 pounds per cubic foot (1500 – 2200 kilogram per cubic meter), ESCS aggregates land between 35 – 55 pounds per cubic foot (560 – 880 kilogram per cubic meter).
Figure 1. ESCS reduces transportation footprints to one-sixth of those for conventional backfills. Photo: Courtesy of ESCSI
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csengineermag.com
April 2023
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