Surface characterization of consolidated earthen substrates using an innovative multi-analytical strategy

This study evaluates the combined use of innovative non-destructive methods and standard laboratory techniques for assessing the surface effects of various consolidation treatments (i.e., bacterial biomineralization, alkaline activation, colloidal dispersions containing nanolime or nanosilica, and ethyl silicate as a standard) on earthen building materials. It demonstrates that novel portable equipment (i.e., portable digital microscope, air permeameter, and mobile surface (contact angle) analyzer) and advanced strategies for the application and data interpretation of conventional analytical and testing methods (i.e., scanning electron and confocal microscopy, Leeb hardness testing, and visible light spectrophotometry) can yield complementary and extremely valuable quantitative results for the evaluation of consolidation treatments on such complex substrates. Our multi-analytical approach allows a detailed characterization of surface and near-surface features of treated earthen mock-ups. It is possible to disclose significant differences in the film-forming propensity and in-depth distributions of consolidants and their effect on key properties such as surface roughness and appearance, permeability, water behavior, and mechanical properties. Even though, the substrate's inhomogeneity and surface texture has proven to be especially challenging, this methodology offers a promising strategy for long-term in-situ monitoring of treatment performance and weathering behavior of built heritage materials.