Thaumasite formation in Portland-limestone cement pastes

Small cylinders (10-mm diameter x 10-mm height) made at a water:solids rati o of 0.5 from Portland cement with 0, 5, 15, and 30% limestone additions we re cured in water at room temperature for 28 days. They were subsequently s tored in various solutions at 5 degrees C for periods of up to 420 days. Th e pastes were inspected visually and examined by X-ray diffraction every 28 days. Selected samples were also examined by thermal analysis and scanning electron microscopy. Pastes containing fine limestone additions were susce ptible to formation of thaumasite after only a few months of exposure to su lfate solutions. The extent of thaumasite formation was greater with increa sing limestone additions and when magnesium sulfate was present in the solu tion. Thaumasite formation was then accompanied by formation of brucite and secondary gypsum. Calcium hydroxide was a reactant rather than a reaction product and C-S-H gel was also consumed. (C) 1999 Elsevier Science Ltd. All rights reserved.