CONSOLIDATION OF CARBONATE AND SILICATE STONES: A STUDY ON COMBINED TREATMENTS WITH DIAMMONIUM PHOSPHATE AND LIME-BASED NANOMATERIALS

Abstract

Historic stone materials used in Cultural Heritage undergo different weathering process that lead to a loss of physical-mechanical properties. Consolidation treatments have the aim of restoring these properties but must also satisfy conditions of chemical-physical compatibility, absence of damaging byproducts, harmlessness of the involved substances. Innovative suitable products have been recently introduced, such as nano-structured consolidants and diammonium hydrogen phosphate (DAP). The latter acts as a consolidant in the form of hydroxyapatite, an insoluble phosphate, that is a product of the reaction between DAP and calcium ions provided by the treated calcareous substrate. The combination of DAP with calcium-based nanoconsolidants promotes such reaction, allowing its application also on siliceous substrates. In this study, this approach has been tested on biocalcarenite and sandstone samples. The treatments were evaluated by observing morphology and distribution of consolidants inside the pore space by means of scanning electron microscope, and by measuring different parameters, such as those related to pulse ultrasound transmission, variation of colour and capillary water absorption. For this latter parameter a mathematical model has been proposed in agreement with Italian, Austrian and European regulation.