Assessment of wind-driven rain impact, related surface erosion and surface strength reduction of historic building materials

Building surface erosion is a common phenomenon observed on historic building façades due to wind-driven rain (WDR) impact. Recently, studies on climate change and the effect this might have on increased extreme rainfall events has renewed the scientific interest on determining the risk of accelerated erosive effects. Given the fact that WDR loads on building façades is proportional to rainfall and represents the main moisture source and erosive physical impact for building façades, an assessment method that quantifies the severity of erosion is the first step towards recommending remedial measures. The paper discusses the major factors escalating the gradual loss of surface material, considering value, hazard, vulnerability and exposure in order to examine the WDR drop impact on the aesthetic significance and the structural integrity of heritage buildings, within a parametric framework. The study investigates the effects of different size water drops, with different impact speeds on a range of masonry materials with different surface asperities and varying moisture absorption features, at various impact angles. For the relative quantification of the long-term surface erosion, straightforward and globally adaptable experiments are proposed based on site-specific climatic data and materials. Finally, strength decline of exposed sample units proves the strength-degrading effect of erosive WDR.