Suitability of silica nanoparticles for tuff consolidation

In this study, the suitability of a nano-silica based consolidant for the conservation of a volcanic tuff was evaluated. The consolidant consists of an aqueous suspension of nano-silica particles (diameter of 10 divided by 20 nm) and despite its lower penetration capacity than ethyl-silicate-based consolidants, takes advantage of less toxicity, a fast-enough setting time. Moreover, it induces not-relevant chromatic alterations on specimens' surface. For this purpose, two series of specimens have been dipped one or two times in the consolidating solution (1:1 dilution). After treatment by immersion, a considerable amount of solvent evaporated, but a continuous silica gel film permeated the pores of stone surface layers, thereby reducing the stone susceptibility to decay mechanisms related to the action of water, mainly the water absorption by capillarity and permeability. The consolidating action promoted also a moderate strengthening effect, increasing the cohesion of tuff as evidenced by unconfined compressive and flexural strength tests. Finally, ageing tests (freeze-thaw cycles) have provided additional data that support the suitability of silica nanoparticles for conservation/restauration of tuff. (C) 2019 Elsevier Ltd. All rights reserved.