Quantitative monitoring of superficial decay evolution in plastered and unplastered outdoors masonry

In masonry materials, the superficial decay is a widespread problem, both when the masonry is unplastered and with plaster. Aggressive environmental agents such as moisture and salts trigger the damage by propagating through the material capillary pores. Although studies have been carried out on salt crystallization and their damaging effects, for the preservation of masonry buildings, due to their high number and cultural importance, it is required to better investigate the phenomena on real cases in their specific microclimate. For these purposes, it would be important to have at disposal testing and monitoring tools capable of following the evolution of these processes since the beginning. Repeated visual inspections are commonly used to monitor the superficial decay but this is a subjective and qualitative technique. It would be important to apply image based diagnostic techniques capable of providing quantitative information. High-resolution laser scanning by triangulation technique of the masonry surface has the advantage of being contactless and rapid. In an experimental set up in Bologna, Italy, large-size brick masonry walls were built, stored outdoors and exposed to weathering over 2 summers. In a 2-header brick wall, one main face is unplastered and one plastered. Before the start of the second ageing season, moisture and salt capillary rise was simulated by low-concentrated sodium chloride solution (0.1% -wt). The aim was to favour solution evaporation and salt crystallization and to provoke material damage. 3D data acquisition by a triangulation laser scanning system was repeated at the end of both seasons. The meshes derived from point clouds data were compared. The proposed procedure successfully extracted quantitative information about areas of material spalling and detachment even in the initial phases of decay.