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Utilization of Recycled Materials in Illinois Highway Construction
According to the Illinois Environmental Protection Agency's (IEPA) 2000 Annual Landfill Capacity Report "as of Jan. 1, 2001, 53 landfills reported having a combined remaining capacity of 743.4 million gate cubic yards, or 49.3 million gate cubic yards less than on Jan. 1, 2000, a decrease of 6.2 percent." Also, at current waste generation rates "landfill life expectancy in Illinois [is] 15 years barring capacity adjustments." As waste continues to accumulate and availability and capacity of landfill spaces diminish, agencies are increasing application and use of recycled materials in highway construction.
The Illinois Department of Transportation utilizes millions of tons of highway materials annually. The basic building materials in roadway and bridge construction are primarily aggregate, cement, and asphalt. The annual usage of recycled materials is over 1.5 million tons. The educated use of recycled materials can result in reduced cost potentials and may enhance performance; however, not all recycled materials are well suited for highway applications. The two main reasons for not utilizing a reclaimed material are 1) addition of material is a detriment to highway performance, and 2) excessive cost. This report reviews current usage of various recycled materials, as well as discusses reclaimed materials not currently being utilized by the Department.
Eleven recycled materials that the Department has found to perform favorably as valuable supplements or substitutes for conventional materials include: air-cooled blast furnace slag, by-product lime, fly ash, glass beads, granulated blast furnace slag, microsilica, reclaimed asphalt pavement, recycled concrete pavement, steel reinforcement, steel slag, and wet-bottom boiler slag. The information provided for each material outlines the origin, physical properties, engineering value, present use, annual quantities used, and economic impact.
Five additional materials experimented with by other states but are currently not viable resources in Illinois highways, for economic or technical reasons, are the following: bottom ash, crumb rubber, glass aggregate, waste foundry sand, and roofing shingles. Each material's origin, physical properties, potential engineering value, potential application, and departmental concerns regarding each non-utilized material are outlined herein.
The quantities of reclaimed materials used-tonnage, in general-indicated within the report and summarized by the appendix are based on materials use as reported to the Materials Integrated System for Test Information and Communication (MISTIC) for the year 2001. The MISTIC database provides materials quantities according to contracted use, testing and inspection data, as well as construction pay items, all by major materials categories, such as aggregate, concrete, paint, etc. All quantities have summarily been converted to English units as referenced within the report.
Use of recycled materials varies from year to year depending on construction activity as well as type of construction projects in a given season. Also, the ability to use recycled materials relies on their use economically-depending on availability or feasibility under unique contract circumstances. In 2001, the Department used nearly 1.4 million tons (2.8 billion pounds) of recycled materials in highway construction. That is, based upon the federal EPA's estimates of individual waste generation, usage equivalent to nearly one third of the waste generated annually by individuals in the City of Chicago.