Fifteen Interstate bridges in Virginia were constructed within the same time period in the same general locality and with the same materials and engineering design, except for differences in the lithologies of the coarse aggregate. In 9 of the structures an argillaceous dolomitic limestone was used, in 6 a crystalline dolomite. Both aggregates meet abrasion and soundness specifications. The limestone has a rock prism expansion in alkaline solution of 1 percent at 6 months; the dolomit under the same conditions shows no expansion. Recent surveys of the 15 bridges, opened to traffic in July 1960, show 90 percent of the slabs of the 6 containing dolomite to be free of pattern cracking and scaling, but only 15 percent of the slabs of the 9 bridges containing limestone to be free of these defects. The 15 structures have the same exposure and maintenance history, and there are no differences in the air void system characteristics of the hardened concrete that could explain the differences in pattern cracking and scaling frequency. Petrographic examination reveals that the argillaceous dolomitic limestone has the fabric of a prototypical alkali-reactive carbonate rock, and the concrete containing this stone has abundant hairline cracks propagating through both the paste and the aggregate. The other stone is a mosaic of equigranular, interlocked dolomite subhedra, and the concrete containing it is virtually free of distress. Tests using a nonreactive aggregate as a diluent and cement with varying percentages of alkalies show increasing freeze-thaw distress with increasing alkalies or with increasing reactive aggregate at constant cement alkali content.

Media Info

  • Media Type: Print
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 55-63
  • Monograph Title: Cement-aggregate reactions
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00097200
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Sep 30 1975 12:00AM