Comparison of the performance of a novel nanolime doped with ZnO quantum dots with common consolidants for historical carbonate stone buildings

Decohesion of building materials caused by weathering translates into the need for recurrent interventions with consolidating treatments that often turn out useless for desired long-term consolidation owing to their poor indepth penetration. Due to this, it is important to develop new products that allow evaluating their penetration in situ. In this work, three commercial consolidants (Estel 1200 (R), NanoEstel (R) and Nanorestore (R)) widely used in stone conservation were compared with a new consolidant nanocomposite (Nanorepair UV). This nanocomposite, which consists of calcium hydroxide nanoparticles doped with zinc oxide quantum dots, allows both consolidation and in situ evaluation of the penetration depth of the treatment, a key variable to assess effectiveness when an in-depth consolidation is required. The treatments were assayed on limestones from two quarries widely used in the construction of monuments in southern Spain. The development of new products devoted to our Cultural Heritage entails specific requirements such as effectiveness, durability and compatibility with the original materials without changing their aesthetic features. The compatibility was studied by colorimetric methods and SEM images to detect the formation of surface layers. The effectiveness of the treatments was quantified by both peeling test and ultrasound propagation speed. Finally, the durability was studied by an accelerated weathering test induced by salt crystallization. The results showed that nanolimes had higher effectiveness and better durability than silica treatments as consolidants for limestones. In addition, Nanorepair UV provided an additional functionality since it allowed measuring the treatment penetration depth in a simple and economical way, by means of ultraviolet illumination, while allowed to distinguish treated areas from untreated ones.