A practical method for preparing Ca(OH)2 nanodispersions for the consolidation of archaeological calcareous stones

Abstract

Exposure to atmospheric conditions results in considerable deterioration of calcareous building stones, lime mortars and plasters in archaeological monuments, requiring several conservation treatments. During the consolidation treatments of the deteriorated calcareous stones, compatibility can best be achieved by introducing a material that would have similar chemical composition and mineralogical structure with the original stone. In recent years, studies on the preparation of Ca(OH)2 nanodispersions for the consolidation of limestone and marble have increased but the preparation processes of these nanodispersions are usually complicated and time consuming. This study aimed to prepare Ca(OH)2 nanodispersions in ethyl alcohol at sufficient concentration levels with a practical method for the consolidation of calcareous archaeological materials. The preparation of higher concentrations of Ca(OH)2 nanodispersion in ethyl alcohol was done by using nano sized CaO and its dispersion in ethyl alcohol. Deteriorated marble pieces from Roman Marble Quarry near Pessinus Archaeological site (Ballıhisar, Turkey) were treated with the prepared Ca(OH)2 nanodispersion and kept at high relative humidity (~90%) at room temperature in the laboratory. Efficient penetration of the nanodispersion, and increase in the physicomechanical properties of treated marbles were followed by examinations with polarizing microscope, SEM, XRD and ultrasonic pulse velocity measurements. Carbonation of the dispersion was followed by titrimetric analysis. Calcite was the main polymorph observed after carbonation. The results showed that consolidation treatments with Ca(OH)2 nanodispersions similar to the one prepared in this study can be used for all calcareous archaeological materials that need improvements in their physical and mechanical properties. © 2018 MAA.