Critical examination of drying damage to cement pastes

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-dryingfor 2-3 h is recommended as a robust but relatively non-damaging treatment. Ddrying 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 A. However, D-drying of pastes from commercial calcium sulfoaluminate rich in AFm usually gives mixtures of the ~9.0 and ~8.2 A phases.