Hygric Swelling of Portland Brownstone

摘要

Portland Brownstone (PB) is a widely used building material, particularly in New York City, that is susceptible to severe deterioration from weathering. This stone contains clays that may cause damage by dilating during wetting/drying cycles. We have measured the swelling strain of PB in aqueous solutions to determine the effect of ionic strength (of KCl and CaCl_2) and water activity (in isopropanol solutions). We have also measured the stress exerted during swelling when the expansion is constrained. These data permit calculation of the stresses produced during wetting/drying cycles, which are found to be comparable to the tensile strength of the stone.