Critical examination of drying damage to cement pastes

Abstract

Several methods of drying cement paste prior to determining its physical properties, for example pore size distributions, are critically studied. Phase-pure preparations of ettringite and calcium monosulfoaluminate are used as sensitive indicators of damage. Oven drying at 105°C and drying over strong desiccants, for example MgClO₄, is damaging. D-drying for 2–3 h is recommended as a robust but relatively non-damaging treatment. D-drying reduces the water content of ettringite to ∼30 H₂O per formula unit, but removal of its zeolitic water, ∼1·7 H₂O, does not degrade the structure. Monosulfoaluminate, AFm, is reduced from 12 to 10 H₂O with shrinkage of its basal spacing from ∼9·0 to ∼8·2 Å. However, D-drying of pastes from commercial calcium sulfoaluminate rich in AFm usually gives mixtures of the ∼9·0 and ∼8·2 Å phases.