Cohesion Gain Induced by Nanosilica Consolidants for Monumental Stone Restoration

Abstract

Mineral nanoparticle suspensions with consolidating properties have been successfully applied in the restoration of weathered architectural surfaces. However, the design of these consolidants is usually stone-specific and based on trial and error, which prevents their robust operation for a wide range of highly heterogeneous monumental stone materials. In this work, we develop a facile and versatile method to systematically study the consolidating mechanisms in action using a surface forces apparatus (SFA) with real-time force sensing and an X-ray surface forces apparatus (X-SFA). We directly assess the mechanical tensile strength of nanosilica-treated single mineral contacts and show a sharp increase in their cohesion. The smallest used nanoparticles provide an order of magnitude stronger contacts. We further resolve the microstructures and forces acting during evaporation-driven, capillary-force-induced nanoparticle aggregation processes, highlighting the importance of the interactions between the nanoparticles and the confining mineral walls. Our novel SFA-based approach offers insight into nano- and microscale mechanisms of consolidating silica treatments, and it can aid the design of nanomaterials used in stone consolidation.

Evaluation of Eco-Friendly Consolidating Treatments in Pugliese Tuff (Gravina Calcarenite) Used in Italian Heritage Buildings

“…The average values of the results obtained indicate that all treatments, except lime water, improved the compressive strength and DRMS resistances (Figure 18). These high improvements in mechanical resistance coincide with the results shown by other authors who have tested the effectiveness of this type of consolidants on calcarenites [27,32,35,50,53,54,56,57,76]. The results obtained with ultrasound have been heterogeneous, although with the exception of lime water, the other treatments slightly increased the speed of wave transmission, which implies improvements in the cohesion between particles.…”

“…The surface of the stone has been completely covered by a crackle layer. This behavior is common in this type of treatment, as reported in other research works [27,35,56,57].…”

“…Nanosilica is also selected only to serve as a comparative reference in terms of results. It has been widely demonstrated that nanosilica usually generates improvements in resistance [27,56,57], although in the case of calcarenites it introduces compounds very different from the nature of the stone itself.…”

From Nanoparticles to Gels: A Breakthrough in Art Conservation Science

“…Another fundamental class of colloidal materials largely adopted in stone consolidation is silica and its derivatives to strengthen silicate rock or buildings degraded by erosion and weathering. Commercial coatings based on colloidal silica were already used since the 1970–1980s, − and cohesion gain induced on stone by nanosilica was also proved recently, while the most popular consolidants on the market are traditionally based on alkoxysilanes . However, the latter form networks in the stone that tend to crack, diminishing their effectiveness.…”