CHEMISTRY OF RETARDERS AND ACCELERATORS AND APPENDIX

EXPERIMENTAL WORK IS REPORTED ON ACCELERATORS AND RETARDERS FOR PORTLAND CEMENT. WHEN PORTLAND CEMENT REACTS WITH WATER THE COMPONENTS ENTER INTO SOLUTION IN THE SAME STOICHIOMETRIC PROPORTIONS AS THE WATER-FREE COMPONENTS, FORMING SOLUTIONS WHICH ARE SUPER-SATURATED WITH RESPECT TO HYDRATES AS SOLIDS. THE HARDENING OF CEMENT IS A RESULT OF A CONTINUOUS DISSOLVING OF THE SILICATE COMPOUNDS AND THE FOLLOWING PRECIPITATION OF THE HYDRATE, WHICH ACTS AS A GLUING AGENT. AT NORMAL SET THE SOLUTION CONTAINS LARGE AMOUNTS OF CALCIUM HYDROXIDE AND THE SOLUBILITY OF THE ALUMINATES IS GREATLY DECREASED. THE REACTIONS ARE RETARDED BY A PROTECTIVE FILM CONTAINING TRICALCIUM ALUMINATE DOUBLE SALT WITH CALCIUM SALT OR TETRACALCIUM ALUMINATE. RETARDERS ARE COMPOUNDS THAT GIVE RISE TO SUCH PRECIPITATES THAT DECREASE THE SOLUBILITY OF THE ALUMINATES AND FORM A SEMI- PERMEABLE MEMBRANE AROUND THE CEMENT GRAINS. ACCELERATORS HASTEN THE DISSOLUTION OF THE SILICATES BY DECREASING BY PH AND INCREASING THE CALCIUM ION CONCENTRATION--WITHOUT DISSOLVING THE ALUMINATES. DESTROYERS ARE SUCH COMPOUNDS AS SUGAR, BORAX AND HUMUS WHICH DISSOLVE THE ALUMINATES AND CAUSE QUICK SET. THE ALKALIS CAUSE QUICK SET AND LOWERED STRENGTH, BUT THE ACTION CAN BE GREATLY REDUCED BY CALCIUM AND MAGNESIUM SALTS THROUGH NEUTRALIZATION TO ALKALI SALTS. BASIC BLAST-FURNACE SLAG REACTS LIKE PORTLAND CEMENT IF THE SOLUBILITY OF THE ALUMINATES IS REDUCED BY THE ACTION OF RETARDERS. A SHORT REVIEW IS PRESENTED OF THE LITERATURE ON THE SUBJECT. TEST RESULTS ARE PRESENTED IN TABULAR FORM IN THE APPENDIX.

  • Supplemental Notes:
    • pp 298-394, 20 FIG, 65 TAB, 53 REF, 1 APP
  • Corporate Authors:

    Intl Symp On Chemistry of Cement Proc

    /Stockholm
    ,   United States 
  • Authors:
    • Forsen, L
  • Publication Date: 1938

Subject/Index Terms

Filing Info

  • Accession Number: 00212691
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 1 1994 12:00AM