Impact of the urban heat island on freeze-thaw risk of natural stone in the built environment, a case study in Ghent, Belgium.

Freeze-thaw cycles are important in the weathering behaviour of natural building stones in humid, cold to temperate climates. It is expected that the elevated air temperatures in urban environments, the so-called urban heat island (UHI), will have an impact on freeze-thaw weathering. In this study, the impact of the urban heat island on the potential freeze-thaw risk is assessed by parameterization of climatic data of 1 year (07/2016-06/2017) from the MOCCA (Monitoring the City's Climate and Atmosphere) project, which studies the urban heat island in Ghent, Belgium. The dose-response of Savonnières, a French limestone often used as building stone, is investigated in laboratory and by HAM simulations. Analysis of the MOCCA data demonstrates that the urban heat island phenomenon decreases the number and intensity of freeze-thaw cycles in an urban environment with 42% and 41% respectively for the studied year in Ghent. This decrease suggests a mitigation of frost risk in urban environments. Laboratory tests and computational simulations confirm that this leads indeed to a decreased freeze-thaw risk in urban landscapes compared to the surrounding rural environment.