AN INTERPRETATION OF SOME PUBLISHED RESEARCHES ON THE ALKALI-AGGREGATE REACTION PART I - THE CHEMICAL REACTIONS AND MECHANISM OF EXPANSION PART II - A HYPOTHESIS CONCERNING SAFE AND UNSAFE REACTIONS WITH REACTIVE

RESEARCH RESULTS ARE INTERPRETED AS HAVING THE FOLLOWING INDICATIONS: THE RELATIVE REACTIVITY OF A GIVEN FORM OF SILICA IS DETERMINED BY THE NUMBER OF INTERRUPTED SILICON- OXYGEN-SILICON LINKAGES, A MATTER OF SPECIFIC SURFACE AND 'HOLES' DUE TO DISORDERLY ATOMIC ARRANGEMENTS. CAUSTIC ATTACK ON REACTIVE SILICA IN THE PRESENCE OF EXCESS LIME PRODUCES A NONSWELLING LIME-ALKALI-SILICA COMPLEX IF CHEMICAL EQUILIBRIUM IS REACHED. ABNORMAL SWELLING IN CONCRETE IS DUE TO THE FORMATION OF AN ALKALI-SILICA COMPLEX WHICH IS NOT IN EQULIBRIUM WITH LIME, DUE TO THE INABILITY OF LIME TO DIFFUSE INTO THE REACTIVE PARTICLE WHERE THE ALKALI-SILICA COMPLEX HAS FORMED. EXPANSION IS PROBABLY DUE TO THE SWELLING OF SOLID ALKALI-SILICA COMPLEX, BUT IT MAY ALSO BE DUE TO HYDRAULIC PRESSURE GENERATED BY OSMOSIS OR BY BOTH MECHANISMS. ENLARGING ON CONSIDERATIONS SET DOWN IN PART I, A HYPOTHESIS IS DEVELOPED CONCERNING REACTIONS BETWEEN REACTIVE SILICA, CALCIUM HYDROXIDE, AND ALKALI IN CONCRETE. THE HYPOTHESIS ASSUMES THAT THE REACTION PROCEEDS SAFELY OR UNSAFELY ACCORDING TO THE RELATIVE AMOUNTS OF CALCIUM HYDROXIDE AND ALKALI ADSORBED IN THE OUTER PART OF THE REACTED LAYER OF THE OPAL PARTICLES. SEVERAL CONCLUSIONS ARE DRAWN ON RESULTS OF PUBLISHED EXPERIMENTAL DATA BEARING ON SAFE LIMITS OF ALKALI CONTENT AND SAFE SILICA-ALKALI RATIOS. /AUTHOR/

  • Supplemental Notes:
    • Vol 26, No 6, PP 497-516, 12 REF
  • Authors:
    • Powers, T C
    • Steinour, H H
  • Publication Date: 1955-2

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  • Accession Number: 00212669
  • Record Type: Publication
  • Source Agency: Highway Research Board Bibliography
  • Files: TRIS
  • Created Date: Jun 18 1994 12:00AM