Effect of cyclic wetting and drying on microstructure, composition and length changes of lime-based plasters

Abstract

Plasters as surface layers of building structures are often exposed to cyclic wetting and drying during their service life. In this paper, the impact of cyclic wetting and drying on microstructure, composition, and length changes of lime-based plasters is investigated using mercury intrusion porosimetry, optical microscopy, qualitative and quantitative X-ray diffraction analysis, simultaneous thermal analysis, and contact dilatometry. Lime-cement- and lime-metakaolin plasters as typical representatives of this group are saturated by water at first and then subjected to five consecutive drying-wetting cycles. Hydration processes, together with carbonation and possible partial dissolution of portlandite and calcite after immersion of samples in water, are identified as the most important reactions affecting the microstructure and composition of the lime-cement plaster, while for the lime-metakaolin plaster the pozzolanic reaction resulting in monocarbonate production, together with possible portlandite and calcite dissolution, are probably the most significant factors. The measurements of hygric strain show that the wetting-drying process is near-reversible since the beginning of the second cycle, whereas capillary pressure is the dominant shrinkage/swelling mechanism.