Much construction demolition debris consists of wastes with little recycling value for highways, such as wood and plaster. However, demolition debris also includes concrete, glass, metal, brick, and asphalt, most of which can be reused in highways as aggregate. In order to be a viable resource and meet the standard specifications as aggregate when crushed, the construction and/or demolition rubble must be separated from the other debris and cleaned of detritus. Construction wastes generated and the associated annual tonnage produced are presented below. Tonnage estimates were collected from numerous sources and summarized in NCHRP Synthesis 199.
Reclaimed Asphalt. Asphalt pavement from the demolition of parking lots, roads, and highways can be reclaimed. Most states are making at least some use of reclaimed asphalt pavement (RAP) in highways, with use within asphalt pavement as the most prevalent use. Estimated tonnage of available RAP is 50 million tons annually. Because the use of RAP interferes with the ability to control hot-mix temperatures during formulation, asphalt mixtures can contain only between 20 and 50 percent RAP. Achieving 50 percent RAP content is practical only in a laboratory setting, where thorough blending of the RAP and new aggregate can be controlled. When plant efficiency is a concern, 50 percent RAP in hot mix is not practical. The differential between the temperature of the discharged gases and the discharged asphalt mix reaches 70° F (21°C). High exhaust gas temperatures can lead to premature corrosion of plan equipment. Thus the percentage of RAP that can be incorporated efficiently is based on the plant efficiency that can be maintained. (U. S. Army Corps of Engineers, Hot-Mix Asphalt Paving Handbook, AC 150/5370-14, July 1991, Appendix 1, pp. 1-21, and 2-45.)
Reclaimed Concrete Pavement (RCP). The recycling of concrete pavement began in this country many years ago, first as unbound aggregate, then in asphalt-wearing surfaces, and later as concrete aggregate. Improved methods of breaking up concrete and separating out the rebar have made the use of RCP more cost-competitive. Many states now recycle concrete pavements either as new concrete or as aggregate in subbase material or base course. This does not include demolition debris of concrete structures.
Roofing Shingles. Scrap and leftover materials from composite shingle manufacturing operations results in a large quantity of waste annually. The waste includes fragments, asphalt binder, and granules. These wastes can be recycled as asphalt paving material. Shingle waste from roofing contractors and demolition operations is less viable because of possible contamination.
Sandblasting Residue. Many uses of sandblasting grit are possible if the removed paint was not lead based. If the paint was lead based or contained other metals, the debris would have to be analyzed to determine if it was nonhazardous before suitable use.
Demolition Debris. Demolition debris is a major component of waste. Much of this debris can not be received in municipal landfills. To be viable for recycling, the debris has to be separated into homogeneous materials. Rubble material has many recycling uses in highways. Wood debris can be chipped and used for lightweight fill and mulch, but only if it is untreated. Disposing of asbestos-containing material (ACM, prevalent in buildings constructed before 1979) is difficult because chrysotile asbestos fibers are known to increase cancer risk if inhaled. If demolition of buildings with ACM from state transportation right-of-way is required in a project, it is possible in some states to arrange for on-site disposal in a state-monitored landfill.
