For decades the Ohio Department of Transportation (ODOT) has used by-product aggregates such as iron and steel slag, slacker aggregate, and steam-boiler slag for highway subbase courses. These aggregates are cost-competitive with natural aggregates in areas near their production sources. The department recently used recycled concrete pavement as subbase on two projects and in-place rubblized concrete pavement as subbase on several others. The use of these by-product aggregates does pose some risk. Steel slags, slacker aggregate, recycled concrete, and rubblized concrete pavement have been identified as sources of tufa precipitate, which builds up in pipe underdrains and storm sewer systems on highway projects. Tufa is a porous calcium carbonate deposit that forms as water drains through aggregate containing free lime. Based on research conducted in the 1980s, the Ohio DOT prohibited the use of slag and slacker aggregate as subbase material for backfill for underdrain trenches, as well as the use of recycled concrete as subbase material, and has limited the use of rubblized in-place concrete pavement as subbase. Researchers at Toledo University recently developed testing procedures to quantify free-lime content of steel slag and recycled concrete aggregates. Using these tests and previous site performance, ODOT hopes to identify specific sources of these aggregates for which indications of precipitate potential are minimal. Aggregates from those sources may then be used as subbase material. Further research has been proposed to identify measures of economically reducing this precipitate potential. It is hoped that the results of this work will lead to a solution that allows broader use of these waste aggregates without compromising drainage systems. (Edited Article)


  • English

Media Info

  • Pagination: p. 26
  • Serial:
    • TR News
    • Issue Number: 184
    • Publisher: Transportation Research Board
    • ISSN: 0738-6826
  • Publication flags:

    Open Access (libre)

Subject/Index Terms

Filing Info

  • Accession Number: 00723804
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Jul 10 1996 12:00AM