A multidisciplinary approach to the mortars characterization from the Town Walls of Gubbio (Perugia, Italy)

In the frame of the HERACLES (HEritage Resilience Against CLimate Events on Site) project, a set of cultural heritage sites was studied to improve their resilience against climate events. The mediaeval Town Walls of Gubbio, in the centre of Italy, are among these. Over the centuries, several factors including environmental actions and structural and material repairs have produced different criticalities, involving both structure and materials. A severe problem consists in the progressive degradation of the mortars binding the masonry. Since the wall body structure behaves/reacts properly only if the cohesion between mortar and stones is sufficiently large, it follows that mortars degradation represents a quite significant issue that deserves a special attention. The present work focuses on the characterization of the mortars sampled in various parts of the Walls, corresponding to different historical periods, restoration measures and interventions. They were characterized to determine the corresponding mineralogical and chemical compositions along with morphological features and to investigate their mechanical properties. For that purpose, penetrometric and sclerometric tests on site and ex situ laboratory techniques, such as X-ray diffraction, polarized light microscopy, scanning electron microscopy, thermogravimetry and differential thermal analysis, were used to examine the weathering effects on mortars and more generally their degradation state, in order to plan appropriate restoration and repair actions.