Drying shrinkage of portland cement pastes I. Microcracking during drying

The occurrence of microcracking of portland cement pastes during drying has been studied by comparing the effects of specimen thickness on shrinkage and cracking using light microscopy. Increases in specimen thickness tended to impede drying and wetting, but there were only slight changes (less than experimental errors) in total and reversible shrinkage once equilibrium was attained. Although microcracking occurred at the beginning of drying whenever the thin specimen (thickness <2mm) was suddenly exposed to low relative humidity (～50%), the cracks eventually closed up. It was concluded that no matter whether or not this microcracking happened, the shrinkage of the specimen after reaching equilibrium was unrestrained.