Papers by Author: Teresa Rivas

Abstract: This paper presents the evaluation of the efficacy of the removal of biological crust from ornamental granites. The removal was made applying different procedures and the efficiency was evaluated by means of optic and scanning electron microscopy (SEM), Fourier Transformed Infrared spectrometry (FTIR) and colour measures (CIE-L*a*b* colour spaces). Among the cleaning procedures, an abrasive cleaning method, several chemicals-based methods applied by brush in aqueous media (using acids, bleach, benzalkonium chloride, ethanol and others) and laser (Nd:YVO4 at 355 nm) were used. This last method was previously found very efficient in removing graffiti and biological crusts in other granites. The present study was conducted on a granite of great commercial value from Galicia (NW Spain) and traditionally used on construction of historical buildings in this region and abroad. Slabs of this granite with an intense biological crust were used. Before the cleaning procedures, the biological crust was characterized by the same techniques to establish the comparison between Pre and Post cleaning. The efficacy in the crust removal was evaluated with optic and electronic microscopy; the best cleaning methods were the acid-based methods and laser. In both cases, no biological remains were found on the cleaning surfaces. Hydrogommage (the abrasive cleaning method) obtained intermediate results, and benzalkonium chloride cleaning showed the worst effectiveness. FTIR technique helped to identify the presence of organic signals of biological crust; and also, it provided useful information on the contaminant remains on the stone after cleaning and on mineral damages. Colour differences after cleaning gave additional information about the efficiency of the cleaning.

Abstract: This work presents 3-D Finite Element Model of the heat transfer inside granite during pulsed laser ablation with the aim of achieving laser cleaning treatment without damaging the stone surface. The model is focused on biotite, the most affected granite-forming mineral, owing to its low melting temperature. The model predicts sizes of the molten region that are consistent with experimental results. Moreover, the effects of different irradiation parameters; i.e., fluence, laser repetition frequency, and speed of scan have been investigated through the size of the biotite molten region. This model may be considered as the first stage of a comprehensive model of the laser ablation process in granite.

Abstract: The sol-gel process has been found to be successful in applications for the conservation and restoration of stone. However, a well-known drawback of the materials obtained by this process is their tendency to crack during drying inside the pores of the treated stone. In this article, we present an overview of our current research centred on producing crack-free sol-gel materials for consolidating and protecting building stone. A novel synthesis, in which a surfactant acts as a template to make the pore size of the gel network coarser and more uniform, is shown to provide an effective alternative for preventing the cracking of consolidants. We also highlight an alternative pathway, in which we add an organic component to the silica precursor in the presence of the surfactant. The hybrid organic-inorganic gel prepared in our laboratory provides excellent waterproofing to the stones under study.