Rubber, like other recycled industrial materials, has a number of uses in civil engineering applications, according to Michael Blumenthal of the Rubber Manufacturers Association (RMA). Blumenthal, along with other representatives of the National Recycling Coalition’s (NRC) Industrial Resources Council, presented at a session entitled “Industrial Recycling 101” at the NRC Congress held recently in Atlanta.
Because of its light weight and insulating properties, tire derived aggregate (TDA) has many useful applications, according to Blumenthal. Using the product as backfill, a medium for septic field drainage and for vibration attenuation on rail lines often provides a lower cost alternative to other materials, he said. TDA can also has applications in the solid waste industry and can be used as liner for certain types of landfills, cap closure and alternative daily cover (ADC).
According to Blumenthal, approximately 48 million tires were used in 2005 in civil engineering applications. While some states excel in putting the material to work, other lag behind, he said. The RMA is working to identify states whose current regulations do not permit the use of TDA and is targeting those state governments for education on the product’s benefits.
To illustrate TDA’s applications, Blumenthal recounted the use of tire shreds on the Dixon Landing Interchange in California. He said the regulatory climate introduced some obstacles to the product’s use, as some state agencies define tires as solid waste, which cannot contact groundwater. The short construction season also presented logistical challenges. However, studies have shown the use of tire shreds poses no significant environmental problems, Blumenthal said.
Regulations in some states also create barriers for the use of recycled products made from construction and demolition debris, according to William Turley, executive director of the Construction Materials Recycling Association (CMRA) and associate publisher of Construction & Demolition Recycling.
More than 325 million tons of C&D material is available for use, according to Turley. Recycled concrete is one of the most readily available commodities and has several reuse applications, including road and highway construction. However, some state Departments of Transportation have been reluctant to use recycled concrete because of fears of contaminants like lead-based paint, although Turley says studies have shown the material is safe.
Other C&D materials like asphalt shingles and gypsum wallboard face barriers to reuse because of similar contaminations fears. Asphalt shingles have reuse markets in roadbase, however, concern over asbestos contamination hampers some markets for the material, according to Turley.
Gypsum is “the toughest material in the stream to recycle,” Turley said. Virgin gypsum is cheap to mine and the recycled material has been linked to the generation of hydrogen sulfide gas emissions in landfills, which has had a negative impact on its use in ADC products.
Focusing on economics and opening profitable markets for the products made from recycling C&D material is the key to strengthening the industry, Turley said.
Byproducts from pulp and paper mills are another valuable recycled industrial material, according to Bill Thacker of the National Council for Air and Stream Improvement, who also addressed attendees at the session.
Materials like pulping rejects and scrap wood fiber have uses in the boiler fuel, composting, boxboard and landfill cover markets, Thacker said.