Robert Grupe / October 2019
Q: What are the current trends construction and demolition waste?
A: Depending on where a project is located, governing regulations construction and demolition waste may have little to major impact on the contractor. Regardless of its impact, there is a trend and, therefore, an entire growing industry to effectively capture this mineral-rich waste and convert it into new products.
Construction and demolition waste is essentially the waste generated during both the demolition phase of an existing structure and the erection of a new building. Controlling how this material is disposed has become global concern; therefore, restrictions are becoming more prevalent. New regulations are being administered, and interesting new technologies are being advanced. The building materials of interest to a contractor are cold-formed steel framing, gypsum and concrete. One of the main reasons for the focus on these materials is their inherent material properties, which make them highly desirable for creating a closed-loop cycling or can be effectively repurposed for a new use. A closed loop is when a material such as steel or gypsum can, after a service life as a product, be recovered and cycled back to be used in a similar product. Repurposing a material after a product’s service life is when the gypsum core in drywall can be repurposed for an agriculture product to enhance soil conditions and increase product yield.
One of the main drivers for stricter regulations on construction waste is to minimize the impact of this waste in a landfill. A midwestern survey cited that almost a quarter of the materials going into a landfill are generated from construction sites. Along with that tremendous amount of waste is also the increased potential for certain building products that are normally benign to exhibit undesirable, hazardous results in certain environmental conditions. As a result, both the European Union and countries within North America are adopting stricter guidelines.
In the recycling industry there are four recognized phases for material recovery. These stages are sourcing, collection, sorting and recovery. The source for steel, the mineral gypsum and the components within concrete can be captured at the construction job site. The collection then becomes the diversion of these materials and collection by third-party companies specializing in this endeavor. This phase is experiencing technical enhancements like specialized smart containers. Highly efficient documentation using electronic information is becoming the norm. New companies focused specifically on collection are providing value-added services.
The waste material then goes through a sorting procedure. Here is where technology advances are being made. The traditional method for sorting construction waste was to place it on a conveyor belt where the various materials, including gypsum concrete, steel, wood and non-ferrous metals, were separated by hand. This could soon be replaced by the combination of artificial intelligence and robotics. This is the result of a joint venture between two companies. One is based in the United States while the other is in Japan. The artificial intelligence uses optics technology to scan the waste on the belt and subsequently “tells” the robotic component which waste to select, pick up and place in a specific location for material recovery. The AI has the ability to “learn,” which means it can adapt to new materials to sort. This is a fast and accurate solution that can sort up to 25 tons of waste per hour. A material recovery is where the desired minerals are obtained through specialized processing.
Steel recycling begins with shredding it into more manageable sizes, and it then goes through a process called “pyrometallurgy.” This is commonly done in an electric arc furnace with the result being new steel ready for fabrication. New technology has made its mark here as well, resulting in higher efficiencies and increased quality control.
Processing of concrete starts with the removal of rebar, a ferrous reinforcement. Then the concrete will go through a crushing cycle. The remains can then be used as a roadbed aggregate or as a base for asphalt. In a different facility, newer technology allows for silica sand to be extracted from the waste concrete.
Gypsum panels undergo a crushing process. The recovered gypsum can then be introduced into the production of new panels. In Europe, some gypsum panel manufacturers have partnerships with recycling companies where the recovered gypsum is processed at the gypsum panel plant and placed directly into the feedstock. New technology is in evidence here as well. One global gypsum panel recycling company has developed a process in which 100 percent of the gypsum panel is captured, including the paper facers. This process also removes contaminants from the gypsum waste, which allows for greater quantities of the captured mineral to be mixed into the gypsum panel mix.
The directive to divert construction demolition and waste from landfills may seem to be a needless burden on the contractor, but it has led to the growth of an industry that focuses on recovering finite minerals and materials for reapplication elsewhere. This industry is complete with a supply chain that starts at the job site and flows from new businesses catering on collection to new companies that specialize in material recovery. This is a win for both industry and sustainability.
Robert Grupe is AWCI’s director of technical services. Send your questions to firstname.lastname@example.org, or call him directly at (703) 538.1611.