SULFATE-BEARING PHASES IN STEAM-CURED CEMENT PASTES

CEMENT AND CEMENT-POZZOLAN PASTES CONTAINING ADDED GYPSUM ABOVE CERTAIN AMOUNTS, AND CURED AT TEMPERATURES ABOVE 120 DEGREES C., CONTAINED BOTH ANHYDRITE AND A SULFATE-BEARING APATITE MINERAL, ELLESTADITE. HYDROGARNET, WHEN PRESENT, MIGHT ALSO OCCUR IN A SULFATE-SUBSTITUTED FORM AS SUGGESTED BY VARIATION IN UNIT CELL DIMENSIONS. THE THIN SURFACE DEPOSIT ON TYPE I CEMENT PASTE EXPOSED TO CONCENTRATED SEA WATER AT 121 DEGREES CONTAINED MAGNESIUM HYDROXY SULFATE HYDRATE AS A MAJOR PRODUCT. TOBERMITE (11A) CONTAINED LATTICE SUBSTITUTED SULFATE, WHICH AMOUNTED TO 1.6% IN REFERENCE SPECIMENS PREPARED AT 175 DEGREES C. ETTRINGITE OR MONOSULFATE WAS NOT DETECTED.