Characterization of a Newly Synthesized Calcium Oxalate-Silica Nanocomposite and Evaluation of Its Consolidation Effect on Limestones

A novel biomimetic nanocomposite was synthesized by the sol gel process in order to reduce the main drawbacks of tetraethoxysilane (TEOS)-based consolidants, such as crack formation upon the drying process and insufficient bonding to carbonaceous substrates. The reaction route involves the addition of a colloidal solution of synthesized nano-calcium oxalate to TEOS producing a crack-free mesoporous xerogel with pore radius of approximately 15 nm, with application to stone conservation. Calcium oxalate which is the main component found on the patinas, was synthesized by the reaction of calcium hydroxide with oxalic acid in the presence of isopropanol. Finally, n-octylamine was added to the mixture, as surfactant. The effectiveness of the new consolidant was evaluated on bioclastic limestones, which are frequently found in historic and modern architectural structures in the Mediterranean basin. The hygric properties and tensile strength of treated samples were improved without affecting either microstructural characteristics or causing phenomena of overstrengthening.