Page E3.2 . 24 October 2001                     
ArchitectureWeek - Environment Department
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    Recycling Construction Debris

    (continued)

    As an additional benefit, regular recycling pick-up of material at the site can keep the site cleaner and increase work efficiency and safety, while helping builders comply with mandates to reduce landfill disposal.

    C&D Debris Recycling magazine estimates there are now more than 3,500 C&D debris recycling facilities in operation, and this number is growing rapidly.

    The following table from World Wastes Magazine* shows the average composition of construction and demolition debris:


    Type of Material Percent of Total Debris
    Wood 27.4
    Asphalt/Concrete/Brick/Dirt 23.3
    Drywall 13.4
    Roofing 12.0
    Miscellaneous Mixed 11.9
    Metal 8.8
    Paper 2.7
    Plastics 0.5

    Materials Most Frequently Recycled

    Metals: Metals have the highest recycling rates among materials recovered from C&D sites. Good markets for ferrous metals, as well as copper and brass, have existed for years. The Steel Recycling Institute estimates the recycling rate for C&D steel is about 85 percent.

    A 1997 survey of North American aggregate producers by Vanderbilt University and C&D Recycling found that the markets for waste rebar removed from the concrete rubble appear to have increased from 1994 to 1997.

    Concrete: The primary use of crushed concrete is as a replacement for road-base gravel. Other applications include use as an aggregate in asphalt or concrete. Concrete recycling is practiced in most areas of the country, and is most prevalent in areas where landfill tipping fees are high or aggregate is in short supply.

    Based on data collected for the State of Washington from waste concrete processors and recyclers, it has been estimated that 1.4 to 1.5 million tons (1.3 to 1.4 million tonnes) of waste concrete in that state are recovered, crushed, and recycled annually.

    In California, the estimated generation of "inert solid waste," which consists of concrete, asphalt, dirt, brick, and other rubble, is 8.2 million tons (7.4 million tonnes) per year. The estimated recycling rate for inert solid wastes is 57 percent.

    Wood: Wood waste produced at construction sites generally has better potential for reuse than wood from demolition sites due to the ease of separating the materials. Wood processing facilities have sprung up in many areas of the United States in recent years, particularly in areas with high landfill costs.

    Processed (chipped) wood is used as mulch, composting bulking agent, animal bedding, and fuel. Wood waste from construction or demolition is attractive as a fuel because of its low moisture content.

    Asphalt Shingles: According to the National Association of Home Builders, about two-thirds of the U.S. residential roofing market is made up of asphalt shingles. Common uses for recycled roofing asphalt include hot mix asphalt for paving, cold mix asphalt paving product, and new roofing materials.

    For now the challenge of meeting specifications for paving and roofing materials poses a limit to the growth of these applications. Preconsumer manufacturing scrap (approximately one million tons (0.9 million tonnes) per year) is currently being used in hot mix asphalt.

    Drywall (Sheetrock, Gypsum): Drywall is recycled by first separating the paper backing, which is recycled into new paper backing, and then remixing the gypsum and using it in the manufacture of new drywall. Recovered drywall is also used as animal bedding, cat litter, and as a soil amendment.

    Deconstruction

    "Deconstruction" refers to selective dismantling or removal of some of the more valuable materials from buildings before, or instead of, demolition. Examples include electrical and plumbing fixtures that are reused, steel, copper, and lumber that are reused or recycled, wood flooring that is remilled, and doors and windows that are refinished for use in new construction.

    This process is labor intensive and may require more time than traditional demolition. However these extra costs may be offset by a higher market value for the recovered materials, especially since they tend to be less contaminated.

    Demolition contractors have been practicing deconstruction in varying degrees for a number of years. This activity, along with recovery of demolition materials after the building has been knocked down, has increased significantly since the 1980s.

    Although the increasing trend towards C&D recovery suggests the environmental and economic advantages of recovery are becoming more widely understood, a number of economic barriers persist.

    The up-front cost of collecting, sorting, and processing C&D material may deter recovery. The low value of the recycled-content material in relation to the cost of virgin-based materials may mean the time and cost of recovery shows little return. And the relatively low cost of C&D debris landfill tipping fees provides little incentive to reduce waste.

    Landfills and incinerators for postconsumer waste materials are becoming more expensive to site and operate due to the high cost of control technologies necessary to minimize groundwater and air pollution. It can been expected that, as these costs increase, so too will the financial advantage of recovery over disposal.

    Adam Davis is a principal of Natural Strategies, a management consulting firm that helps organizations achieve "bottom-line" results through the application of sustainability principles.

     

    AW

    ArchWeek Image

    Old industrial doors become room dividers in the Ecotrust Building.
    Photo: Breese Watson

    ArchWeek Image

    Old fir flooring, recovered from a demolished building, finds new life as wainscot in the Ecotrust Building, Portland, Oregon.
    Photo: Breese Watson

    ArchWeek Image

    Construction and demolition debris compose up to 30 percent of materials disposed of in California landfills. But recovered concrete can be crushed and used as road gravel or aggregate.
    Photo: Alameda County

    ArchWeek Image

    An old mounting face plate for a boiler door is reborn as a frame for a recycled-wood commemorative plaque in the Ecotrust Building.
    Photo: Breese Watson

    ArchWeek Image

    Metal grating that was once the floor surface around machinery is now cleaned up and serving as a decorative wall covering for Ecotrust Building doorways.
    Photo: Breese Watson

    ArchWeek Image

    Demolition waste, if not sorted and salvaged for reuse, will become more fodder for landfills.
    Photo: Alameda County

    ArchWeek Image

    Salvage operations sort and collect construction debris for reuse.
    Photo: Alameda County

    ArchWeek Image

    Mixed debris that can't be easily sorted on a demolition site can still be mechanically sorted for recycling.
    Photo: Alameda County

     

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