The binder of the roman concrete of Ponte di Augusto in Narni (Italy)

The main aim of this work was to study the characteristics of the mortar binder used in the building of the bridge called “Ponte di Augusto”, erected over the river Nera (Narni, Italy) in 27 B.C.. Mineralogical, chemical, physical, micropaleontological, granulometric and petrographical analyses were carried out on whole samples and on the binder itself, particular care being devoted to lumps. In the past, the Romans were able to create high-quality mortars of relatively low porosity, with strong mechanical characteristics and high hydraulicity. The mortars used in the “Ponte di Augusto” also show the same characteristics and are excellently conserved. Preliminary results ascribe these good characteristics to the use of a binder of high hydraulicity, obtained by calcinating local impure limestone and not by inserting any particular additives.