ALKALI REACTIVITY OF CARBONATE ROCKS - EXPANSION AND DEDOLOMITIZATION

ALTHOUGH UNSATISFACTORY PERFORMANCE OF LIMESTONE AND DOLOMITE AGGREGATES IN CONCRETE IS RELATIVELY RARE, CERTAIN CARBONATE ROCKS HAVE BEEN FOUND TO EXPAND RAPIDLY IN SOLUTIONS OF THE ALKALI METAL HYDROXIDES. THESE REACTIVE ROCKS CAN BE CATEGORIZED ON THE BASIS OF MINERAL COMPOSITION AND TEXTURE, ALL BEING ARGILLACEOUS DOLOMITIC LIMESTONES. IN TERMS OF TEXTURE, THE ROCKS ARE BEST DESCRIBED AS PARTIALLY DOLOMITIZED CALCILUTITES; THAT IS, SMALL DOLOMITE CRYSTALS SCATTERED THROUGH A MATRIX OF EXTREMELY FINE GRAINED CALCITE AND CLAY. A SIMPLE AND RAPID LABORATORY TEST FOR THE EXPANSIVE REACTION IN ALKALI HAS BEEN DEVELOPED. THE EXPANSION OF THESE ROCKS ACCOMPANIES THE FOLLOWING CHEMICAL REACTION BETWEEN THE ALKALIES AND THE MINERAL DOLOMITE: CALCIUM: MAGNESIUM CARBONATE PLUS 2(M HYDROXIDE) YIELDS M CARBONATE PLUS MAGNESIUM HYDROXIDE PLUS CALCIUM CARBONATE, WHERE M STANDS FOR POTASSIUM, SODIUM OR LITHIUM. IN CONCRETE, THE ALKALI CARBONATE PRODUCED IN THE DEDOLOMITIZATION REACTION WILL REACT WITH HYDRATED CEMENT PRODUCTS AND THE ALKALIES WILL BE REGENERATED, PERMITTING A CONTINUING REACTION WITH THE DOLOMITE. THE RATES OF BOTH EXPANSION AND DEDOLOMITIZATION ARE FUNCTIONS OF THE CALCITE-DOLOMITE RATIO AND TEXTURE OF THE ROCK. ALTHOUGH SINGLE CRYSTALS OF DOLOMITE WILL SLOWLY DEDOLOMITIZE AND EXPAND IN ALKALINE SOLUTIONS, MAXIMUM REACTION OCCURS WHEN CALCITE AND DOLOMITE ARE PRESENT IN APPROXIMATELY EQUAL AMOUNTS, AND WHEN BOTH ARE EXTREMELY FINE GRAINED. /AUTHOR/

  • Supplemental Notes:
    • Vol 40, pp 462-474, 11 FIG, 2 TAB, 16 REF
  • Authors:
    • Hadley, D W
  • Publication Date: 1961

Media Info

  • Monograph Title: Proceedings of the Fortieth Annual Meeting of the Highway Research Board, Washington, D.C., January 9-13, 1961.
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00217883
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Jun 5 1972 12:00AM