Restoration feasibility study by using alkali activated mortars based on Mt. Etna volcanic ash: The case study of Monreale Cathedral (Palermo, Italy).

• Volcanic-ash AA mortars, have been tested on damaged mosaics of Monreale Cathedral. • Bedding AA mortars have been applied for the reposition of detached tesserae. • Replicates of the mosaic decorations engraving and painting AA mortars were tested. • Pre-casted colored alkaline activated mortars have been created. • Colorimetric differences between original tesserae and new AAMs have been evaluated. This paper describes for the first time a case-study regarding the applicability of alkali activated mortars based on volcanic-ash (Mt. Etna) directly on-site on a UNESCO Heritage site known worldwide, the Monreale Cathedral (Sicily, Italy). In the perspective of "Advanced Green Materials for Cultural Heritage" project, small damaged areas of the mosaics were selected to test the application of bedding mortars for the filling of lacunae and the repositioning of detached original tesserae , as well as the replication of the mosaic decorations by engraving and painting on the finishing mortars or by the realization of new pre-casted tesserae. Both the critical aspects of preparation and the steps taken to improve operative conditions (e.g. use of Ca-additive) have been highlighted. The monitoring of results over time confirms the intervention's success, representing in this way a pioneering on-site cultural heritage application of these materials. [ABSTRACT FROM AUTHOR]