Comparison of Latest and Innovative Silica-Based Consolidants for Volcanic Stones

This research explores the new perspectives in conservation and protection of two macroporous tuff stones, widely employed in the architectural heritage of Campania region, characterized by highly heterogeneous rock fabric and texture and a variable mineralogical composition that represent crucial factors responsible for their weak durability. The consolidation treatments were performed with a recently and widely used suspension of nano-silica crystals in water and with a lithium silicate solution that has received up to now scarce attention as a consolidant agent. Physical investigations (open porosity, Hg porosimetry, water absorption), morphological observations (SEM analyses) and visual appearance test (colorimetric measurements), along with assessments of performance indicators such as ultrasonic pulse velocity, surface cohesion test (peeling test) and durability test (salt crystallization), were carried out to investigate the consolidation effectiveness. Overall, lithium silicate consolidant showed a better behavior in terms of superficial cohesion, a most successful strengthening action and a considerable enhancement of salt resistance.Get more news about Inorganic Stone,you can vist our website!

The progressive and inevitable deterioration process of stone heritage and buildings went through a significant acceleration over the last century and is even expected to grow at a higher rate in the near future due to, among other things, increasing air pollution and enhanced deterioration due to deposition of soluble salts and/or aerosols or reactions of the stone with atmospheric pollutants, also associated with climate change . So, in the last decades, the increasing concern over the degradation of the worldwide cultural heritage has motivated researchers to find ever more innovative and effective solutions to preserve the integrity of the historical patrimony and at the same time to guarantee its continuing fruition.

In general, only the complete knowledge of the specific mechanisms responsible for the stone degradation, whether they are intrinsic properties of the stone (mineral composition, textural characteristics and pore/capillary structure, etc.) or extrinsic factors of decay (microclimatic conditions such as temperature and humidity changes, water/moisture transportation, air pollution, biological activities, etc.), enable planning the most appropriate strategies needed to reduce weathering of stone. The conservation of historic and culturally relevant stone artworks and buildings involves the on-site protection and/or restoration, usually achieved by re-establishing grain-to-grain cohesion of damaged stone through the application of organic polymers, alkoxysilanes or inorganic consolidant compounds . Moreover, one of the main purposes of consolidation treatments that cannot be overlooked is to avoid or reduce the water/moisture penetration in stones, in order to minimize the rate of stone decay due to freeze–thaw cycles inside the pore pattern or the intraporous crystallization of soluble salts transferred by the water . The improvement of the water repellence properties of deteriorated stone substrates is generally achieved using polymeric films to promote the reduction in the surface tension of the substrates, but the use of organic polymers presents several limitations and inconveniences, especially in terms of physical–chemical incompatibility. In addition, the same formation of polymeric protective films might cause further damage because of pore blocking, which negatively affects the water vapor transport mechanisms . On the other hand, inorganic consolidants, especially silicon-based compounds, have been extensively taken into consideration in the last years, especially because they offer a remarkable opportunity to design consolidants with higher compatibility with the original stone substrates . Consolidants are often alkoxysilane products, so much so that the tetraethoxysilane (TEOS)-based compounds are nowadays the most frequently and widely used for preservation in stone heritages.