Lime based nanomaterials for the conservation of calcareous substrates in heritage structures

Nanolime is one of the most promising consolidation materials used in the conservation of historic calcareous substrates. Whilst the popularity of nanolime has grown significantly in the last two decades, its consolidation mechanism when applied to highly porous substrates still needs to be fully understood. The aim of this Ph.D. is to understand the consolidation mechanism of a number of nanolime products in highly porous substrates and to investigate new ways to improve nanolime consolidation effectiveness. The research consisted of six experimental programmes: 1) comparing the consolidation effectiveness of three available nanolime products (Nanorestore Plus®, Calosil® and nanolime synthesized following a method developed by researchers of the University of L'Aquila, Italy); 2) investigating the influence of different types of solvent on the consolidation effectiveness of nanolime; 3) investigating the influence of substrate pore structure and nanolime particle size on the consolidation effectiveness of nanolime; 4) investigating the consolidation effectiveness of nanolime on Biocalcarenite from Agrigento, Italy; 5) investigating the consolidation effectiveness of nanolime on Indiana limestone and weathered marble from the Smithsonian National Museum buildings, USA; and 6) investigating the use of additives to improve nanolime consolidation effectiveness. Nanorestore Plus® yielded the highest short-term consolidation effect, measured by means of a Drilling Resistance Measurement System, in both limestones and lime-mortars. However, L'Aquila nanolime showed a higher durability which was attributed to a better developed crystalline structure. A 50%-50% water-isopropanol solvent appeared to be the best option for dispersing nanoparticles synthetized through the L'Aquila's method as it yielded a higher consolidating effectiveness compared to other types of solvents. Results also suggest that due to the different size of their nanoparticles, Nanorestore Plus® could be more suitable to consolidate coarser substrates, while L'Aquila nanolime seems to be more suitable to consolidate substrates with a finer pore structure. Results also demonstrated that L'Aquila nanolime can be used effectively for the consolidation of the biocalcarenite from Agrigento and the weathered marble from the Smithsonian Museum. Furthermore, it was shown that the use of sticky rice in a combined treatment with L'Aquila nanolime improves the consolidation effectiveness although prolonged exposure to moisture can compromise treatment durability. Finally, results also showed that nanolimes yield a higher consolidation degree in substrates composed mainly of calcite (limestones) than in lime-mortars containing silica sand.