30. Characterization and Properties of Silicate and Nanocomposite Coatings for the Protection of Dolomite Marble Against Weathering

Moisture presence, salt precipitation and crystallization, temperature and ultraviolet radiation are main environmental factors of deterioration of the building materials of historic monuments. The presence of moisture in a material is due to rising and falling damp. Many commercial stone consolidation and water-repellent products contain tetraethoxysilane (TEOS). Synthesis of composite and nanocomposite coatings is an important method to improve the protective properties of these products. In this work composite coatings by adding silica nanoparticles to TEOS-based commercial products were synthesized. TEOS-based commercial products were RC-70 and RC-90. The type of silica nanoparticles used was Aerosil 200. As substrate dolomite marble specimens were used. The protective properties of the coatings were examined by water capillary absorption tests, salt spray tests and ultraviolet radiation tests. Coating characterization, the study of the morphologies of the surfaces and the investigation of the coatings behaviour in weathering conditions, was carried out by SEM, AFM, gravimetric measurements, optical observation and measurements of colour variation, contact angle and porosity. The protective properties of the coatings depended on the type of the polymeric material and the addition of silica nanoparticles. All coatings used protected marble against salt weathering and ultraviolet radiation. Polymeric coatings decreased porosity, surface roughness, water absorption, salt crystallization and the height of the capillary rise and increased contact angle values. Exposure in ultraviolet radiation conditions decreased in all cases contact angle values. Better protective properties were observed in the case of RC-90 in comparison to RC-70. This can be attributed to the increased elasticity of the structure of RC-90, due to the presence of the methylphenyl component. The addition of silica nanoparticles decreased porosity and improved the protective behaviour of the coatings against salt weathering and ultraviolet radiation.