Characterization of historical mortars from the bell tower of St. Nicholas church (Pisa, Italy)

The aim of this research is to characterize the binder and aggregate fractions of sixteen mortar samples from the bell tower of the St. Nicholas church at Pisa, using X-ray fluorescence (XRF), X-ray powder diffraction (XRPD), simultaneous thermogravimetric/differential scanning calorimetry analysis (TG/DSC), optical microscopy (OM) and electron microscopy equipped with a microanalysis system (SEM/EDS). The analytical procedure used for studying the mortars is based on TG/DSC analyses performed on the binder fractions, obtained by disaggregation of the mortar samples, and on micro-analytical data directly collected on the mortar binders combined with chemical, mineralogical (qualitative composition) and petrographic (modal composition) data measured on the bulk mortar samples. The collected data indicate that the examined samples are hydraulic lime mortars with natural river sands (average binder/aggregate ratio 1:1), except for two of them which are artificial pozzolanic mortars with cocciopesto. The most probable raw materials used to produce the mortars are the binding materials obtained by firing carbonate rocks locally available, cherty limestone and subordinately Mt. Pisano marble, and the Arno River sands or, more likely, natural admixtures of Arno and Serchio River sandy sediments.