Cohesion Gain Induced by Nanosilica Consolidants for Monumental Stone Restoration

Mineral nanoparticle suspensions with consolidat-ing properties have been successfully applied in the restoration ofweathered architectural surfaces. However, the design of theseconsolidants is usually stone-specific and based on trial and error,which prevents their robust operation for a wide range of highlyheterogeneous monumental stone materials. In this work, wedevelop a facile and versatile method to systematically study theconsolidating mechanisms in action using a surface forcesapparatus (SFA) with real-time force sensing and an X-ray surfaceforces apparatus (X-SFA). We directly assess the mechanicaltensile strength of nanosilica-treated single mineral contacts andshow a sharp increase in their cohesion. The smallest usednanoparticles provide an order of magnitude stronger contacts. We further resolve the microstructures and forces acting duringevaporation-driven, capillary-force-induced nanoparticle aggregation processes, highlighting the importance of the interactionsbetween the nanoparticles and the confining mineral walls. Our novel SFA-based approach offers insight into nano- and microscalemechanisms of consolidating silica treatments, and it can aid the design of nanomaterials used in stone consolidation.