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GENERAL DISCUSSION BY TWO CONTRIBUTORS

THE SPEAKER DISCUSSED THE MECHANISM BY WHICH DIRECT ENLARGEMENT OF THE CRYSTALS OF DOLOMITE IS BELIEVED TO BE RESPONSIBLE FOR MUCH, IF NOT ALL, OF THE EXPANSION OBTAINED WITH CARBONATE ROCKS. PREVIOUS DISCUSSIONS HAVE EXPLAINED WHY THE ALKALI-DOLOMITE REACTION CAN CAUSE EXPANSION OF CONCRETE, BUT DOES NOT EXPLAIN WHY SAMPLES OF ROCK IMMERSED IN SOLUTIONS OF DIFFERENT ALKALI HYDROXIDES SHOW DIFFERENT AMOUNTS OF EXPANSION. FOR AN EXPLANATION OF THIS, THE MECHANISM INVOLVED WHEN AN IONIC COMPOUND DISSOLVES IN WATER MUST BE EXAMINED. RESULTS SHOW THAT CALCITE CAN REACT WITH ALKALI HYDROXIDES. AS WATER IN THE CEMENT PASTE IS USED UP BY REACTION WITH THE CEMENT MINERALS AND AS WATER EVAPORATES FROM THE CONCRETE, THE CONCENTRATION OF THE ALKALIS IN THE SOLUTION IN THE PORES OF THE HARDENED CEMENT PASTE AND IN THE PORES OF THE AGGREGATE BECOMES RATHER HIGH. THEREFORE IT IS CONCLUDED THAT THE CALCITE FRACTION IN THE FINE-GRAINED REACTIVE DOLOMITIC ROCKS MAY CONTRIBUTE TO THE EXPANSIONS IN CONCRETE. THE SECOND SPEAKER PURSUES FURTHER THE QUESTION REGARDING THE REGENERATION OF ALKALI AFTER THE DEDOLOMITIZATION REACTION. REPORTS CONCERNING THE OCCURRENCE OF NEW TYPES OF REACTION RIMS IN ROCKS WITH LOW DOLOMITE CONTENT PLUS THE PREVIOUS QUESTION MAKE IT DESIRABLE TO CONSIDER THE STABILITY OF SOLID CALCIUM CARBONATE /CALCITE/ IN THE PRESENCE OF CEMENT HYDRATION PRODUCTS. FROM REASONS DESCRIBED, IT IS BELIEVED THAT CONSIDERABLE REGENERATION OF ALKALI CAN OCCUR AND THAT IN THE ATTAINMENT OF EQUILIBRIUM CONSIDERABLE REACTION CAN OCCUR BETWEEN CALCITE AND CEMENT HYDRATION PRODUCTS.

Media Info

  • Media Type: Print
  • Features: References; Tables;
  • Pagination: pp 110-113
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00212315
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Dec 2 1994 12:00AM