Nanolime deposition in Maastricht limestone

Abstract

The development of nanomaterials is growing exponentially in the last decade. New discoveries and their applications have taken place in different fields, such as electronics, chemistry, biology and physics. Some innovative nanoproducts have become available also for the conservation of cultural heritage (e.g. nano-Ca(OH)2, nano-SiO2, nano-TiO2, CNTs, etc.), showing interesting potentialities and advantages. However, there are also drawbacks. Extensive literature is available on nanolimes, i.e. colloidal alcoholic dispersions of Ca(OH)2 nanoparticles, which are promising materials for the consolidation of lime-based plasters and calcareous stone, often present in ancient masonry structures. Nanolimes have several advantages such as high stability, fast carbonation rate and good chemical and physical compatibility with calcareous stone and lime-based plasters. However, in comparison to other existing consolidant products, like TEOS-based (Tetraethylorthosilicate), the penetration depth of nanolime is often limited, which may consequently result in a low effectiveness. The research presented in this paper aimed at understanding the penetration and deposition process of nanolime when applied in Maastricht limestone, a soft, highly porous substrate, widely used in the Dutch and Belgian provinces of Limburg. This research focused on the nanolime transport process to clarify whether nanolime is able to penetrate and deposit in depth in the material or if it simply accumulates near the surface. In order to investigate the distribution and particle size of nanolime deposited in the stone, next to simple phenolphthalein tests, optical microscopy, AFM and SEM-EDS were used. On the basis of the obtained results, the transport and deposition of a commercial nanolime in Maastricht limestone has been elucidated. The comprehension of the nanolime transport mechanism (penetration and distribution) within the treated material is crucial for improving the effectiveness of this consolidation treatment.