Conservation of Cultural Heritage Building: Evaluation of Ca[Zn(OH)3]2•2H2O Nanoparticles Coating Behavior Under Salt Crystallization Cycles

Calcareous stones are composed of a mixture of minerals and different cementing agents. Due to their heterogeneity, they are sensitive to the action of multiple environmental factors, including temperature, relative humidity, solar radiation, microorganisms, and salt crystallization processes that are the cause of degradation, inducing changes in their physical and chemical properties. Then it is desirable to account for specific studies on new nanomaterials that improve stone characteristics to extend its performance for long periods. In Yucatan, the calcareous stone is a traditional building material used since the prehispanic period, however, its susceptibility to deterioration has created a demand to elaborate protective treatments that improves its consolidation. This work shows the performance of new nanomaterials synthesized via sol-gel, based on calcium and zinc hydroxide dihydrate, with the formula Ca[Zn(OH)(3)](2)center dot 2H(2)O (CZ) and applied on three Yucatan calcareous stones Calcehtok, Chichen Itza and, Mayapan, and further evaluated under the sodium sulphate crystallization aging test. Results indicated that after applying CZ nanoparticles (NPs) to stones, physical and mechanical properties like capillarity, colour, propagation of ultrasonic velocity, and structure improved as they showed a decrease in stone cracks, cavities, and pores. The salt crystallization tests indicate significant changes in the control properties of untreated stones when compared to those specimens coated with CZ. In addition, a better performance was observed for the stones from Calcehtok, followed by Mayapan and Chichen Itza, respectively.