Modification of Si-Based Consolidants by the Addition of Colloidal Nanoparticles: Application in Porous Stones

Abstract

Si-based consolidants, most widely used in the restoration of porous stones exposed to the environmental decay mechanisms, present some serious limitations, such as the tendency to crack and shrink during drying. This deficiency has been the focus of several studies with the objective of modifying and improving the above mentioned materials. The addition of nanoparticle dispersions into silica matrix has been found to enhance their effectiveness in several respects. Objective of the current research was to study the preparation of particle modified consolidants (PMC), consisting of an ethyl silicate matrix loaded with colloidal oxide titania (TiO2) particles and silica (SiO2) nanoparticles and the evaluation of their consolidation effect, applied to different porous limestones. Two compositions were prepared and then evaluated based on their stability in the liquid phase, the particle size, the% solids content and their morphological characteristics during the drying process. The characterization of the particles is made through dynamic light scattering (DLS). Penetration depth of the material is examined by scanning electron microscopy (SEM-EDAX). The color changes of the treated surfaces were measured by a portable spectrophotometer before and after treatment. Changes in the porosity and characteristics of the microstructure were determined by applying mercury porosimetry in untreated and treated samples. Based on the techniques applied, PMCs appear to be promising materials in stone consolidation, as they show a reduction of silicate network shrinkage and cracking during drying compared with the silicon-based consolidant. Treatment causes some changes in the properties of the substrate such as a reduction of the % water uptake (up to 15%) as well as an increase in the elastic modulus (up to 10%).