Calcium Hydroxide Crystal Evolution upon Aging of Lime Putty

Aging of lime putty, by storing slaked lime under excess water for extended periods of time, has been recognized for centuries as a means to improve the quality of hydrated lime as a binder in lime-based mortar and plasters. How-ever, there is limited, and at times contradictory, evidence about the effect of the extended exposure of portlandite (Ca(OH)2) to water. Our data from X-ray diffraction, ni-trogen adsorption, and scanning electron microscopy stud-ies indicate that portlandite crystals undergo both an im-portant size reduction and a significant morphological change, developing submicrometer, platelike crystals upon aging. A model for portlandite evolution is proposed and discussed, based upon (a) differences in solubility between {0001} basal pinacoid faces, and {1010} prism faces, and (b) heterogeneous secondary nucleation of nanometer-scale platelike portlandite crystals. I