With the growth of population, a rising quality of life and subsequent increasing demands for energy, our fossil fuels and natural resources are diminishing in a faster rate than they were created. Moreover, energy consumed from fossil fuels to produce virgin materials is contributing to global warming due to greenhouse gas emissions. A promising solution to slow down consumption of natural resources and global warming is recycling. Recycling is the third component of the “Reduce, Reuse, Recycle” waste management hierarchy. Recycling is the reprocessing of materials into new products.
According to the US Environmental Protection Agency (EPA) recycling gives the following benefits: protects and expands US manufacturing jobs and increases US competitiveness, reduces the need for landfilling and incineration, prevents pollution caused by the manufacturing of products from virgin materials, saves energy, decreases emissions of greenhouse gases that contribute to global climate change, conserves natural resources such as timber, water, and minerals, and helps sustain the environment for future generations. Recyclable materials, also called “recyclables,” may originate from a wide range of sources including the home and industry.
There are many types of recyclable materials including plastic, paper, glass, textile, asphalt, aluminum and industrial by-products. Materials to be recycled are either brought to a collection center or picked up from the curbside, then sorted, cleaned and reprocessed into new materials for manufacturing or can be used directly in a variety of high volume engineering applications.
The UW-Madison has initiated research programs and construction practice to promote use of recycled materials. The Recycled Materials Resource Center (RMRC) in the department of civil and environmental engineering, conducts research on identification of different types of recycled materials and assessment of their performance in a variety of civil engineering applications.
Professor Tuncer Edil, is the director of the RMRC-3rd Generation (3G). “The Recycled Materials Resource Center-3G, similar to the earlier center’s aims at promoting applied research and providing outreach to remove barriers to wider use of recycled materials and industrial byproducts in highway construction. Such use promotes sustainable construction by reducing greenhouse gas emissions and energy consumption in highway construction where vast amounts of materials are used,” Edil says. The role of recycled materials in a sustainable design and construction includes reduction of consumption of natural resources, energy, and water by reducing demands for raw materials.
Examples of recyclable materials that have been used for engineering applications and RMRC has conducted research on, includes: shredded automobile tires from discarded tires, fly ash and bottom ash from burning the coal in electrical power plants, foundry slag from melting iron ore, foundry sand from metal molding industry, crushed glass, reclaimed asphalt pavement (RAP) from excavating surface pavement, recycled concrete aggregate (RCA) from demolition of concrete structures, recycled asphalt shingle (RAS) from roofs of the houses, and rice husk ash.
When these waste products are used in place of conventional aggregates in high volume applications like highway embankments or backfills, natural resources and energy are preserved and potentially harmful waste disposal is avoided. Use of recyclable materials in diverse civil engineering applications helps a sustainable development. Extensive laboratory and field research activities are being conducted to verify suitability and assess environmental impacts of different recycled materials.
Federal and state initiatives have promoted use of recycled materials in common engineering practice. The use of recycled materials is now required for some federally funded projects, and many states and municipalities offer economic incentives encouraging the use of these materials in new transportation projects. The Wisconsin Department of Transportation has initiated conducting research to make the use of recycled materials cost competitive for Wisconsin highway construction. Two examples for use of recycled materials in real engineering practice include asphalt shingles, Bottom ash, and Fly ash.
Asphalt shingles cover nearly four out of five homes in the US. Demolition or renovation of houses produces about 12 million tons of asphalt shingle waste in the US of which over 400 thousand tons belong to the state of Wisconsin. The majority of the shingle waste is dumped into the landfills. Recent research identified use of shredded shingles in asphalt concrete industry to benefit from the oil content in the shingles, in cold patch for rapid repair of the surface pavement, as supplemental fuels in cement kiln dust industry and as structural fill for highway construction.
Bottom ash and Fly ash remain after combustion of coal in power. Bottom ash, a brown material similar to sand, is collected in the bottom of the boilers. Fly ash, ranging in color from tan to black, is a very fine powder-like particles collected before the flue gases reach the chimneys of coal-fired power plants. About 17 million tons bottom ash and 63 million tons fly ash have been produced in 2009. The majority of bottom ash and fly ash were used to be dumped into landfills. However, results of extensive research resulted in use of 44% of the produced bottom ash and 39% of fly ash in different applications in 2009 including concrete products, embankment fills, road base/sub-base, soil modification/stabilization, waste stabilization, shingle manufacture and landfill cover.
Recycled materials have been used in a number of UW-Madison construction projects to provide more sustainable or “green” campus. Angela Pakes Ahlman is the technical director of the RMRC-3G center and former manager for campus construction projects. “For all our UW major construction projects, we support sustainability in a variety of ways, with each project having some unique aspects of the age-old reduce-reuse-recycle. Some of our projects have won significant awards to recognize these achievements such as the new Biochemistry Building which achieved over 97% recycling, and the demolition of the Health Services Building which achieved 96% recycled and the Daily Reporter’s ‘Big Diverter Award’ for diverting 10,601 tons of material, equaling 13,869 yards in volume, from the landfill” she says. The new Union South is another example in the campus where recycled materials were used. “Plastics from used water and pop bottles were diverted from the landfill and “upcycled” into carpet. Post-consumer salvaged materials were used throughout the project such as wood salvaged from Wisconsin barns in Varsity Hall and recycled Kohl Center floor in the Lower Sett Rec space” she continues.
Current impediments for vast use of recycled materials include uncertainty about their performance and lack of standard specifications and guidelines. Research on different types of recycled materials is being conducted by various institutions and research centers throughout the US as well as the RMRC-3G in the civil and environmental engineering department at UW-Madison to identify and address such issues.