In the study of ancient mortars, important archaeometric informations concern the investigation on the production technologies with particular care to the raw materials utilized. As regards the aggregate, it’s easy to recognize the kind, amount and granulometry, but in the case of binder, the characterization and the individuation of the limestone used in the production of the lime is quite difficult. This problem was afforded in the study of the mortars used in the Roman bridge called Ponte di Augusto (Narni, Umbria-Italy) which crossed the valley of the river Nera. This bridge, built in the 27 b.C, is one of the widest ever erected by the Romans. It was 170 m long and probably it had four spans. At present only one arch is standing which should not be the widest. Its chord is 20 m long and its height at the intrados is 27 m. The arches, the piers and the abutments were made by a framework of well cut travertine ashlars filled with a mortar that shows a really strong cohesion with mechanical characteristics similar to that of the modern concrete. Mineralogical (XRD), and petrographical analyses (OM) were carried out on the whole sample, while chemical-microchemical (XRF and ESEM-EDS), physical (TG-DTG) analyses were carried out on the binder itself. It is well known that the Romans were able to produce high-quality mortars of relatively low porosity, strong mechanical characteristics and high hydraulicity by adding pozzolane. The mortars used in the Ponte di Augusto show these good characteristics and a binder of high hydraulicity, but the analytical data exclude the use of any particular additive like pozzolane. The chemical data obtained by XRF analyses of the lumps and by ESEM-EDS analyses of the binder reveals a high Si content and low Al2O3/SiO2 and K2O/Al2O3 ratios; this is not compatible with the burning of marly limestones, rather with the use of cherty limestones: a possible stone chemically compatible with the observed data could be the cherty limestones whose fragments are widespread in the mortar mixture and that widely outcrop around Narni. The high hidraulicity in the Roman mortar was not always obtained only by the use of additives like pozzolane.
Hydraulic roman mortars: not always pozzolanic / Cantisani E.; Fratini F.; Pecchioni E.; Rescic S.. - ELETTRONICO. - (2004), pp. 1-1. (Intervento presentato al convegno 32th IGC Florence Italy tenutosi a Firenze nel 20-28 Agosto 2004).
Hydraulic roman mortars: not always pozzolanic
PECCHIONI, ELENA;
2004
Abstract
In the study of ancient mortars, important archaeometric informations concern the investigation on the production technologies with particular care to the raw materials utilized. As regards the aggregate, it’s easy to recognize the kind, amount and granulometry, but in the case of binder, the characterization and the individuation of the limestone used in the production of the lime is quite difficult. This problem was afforded in the study of the mortars used in the Roman bridge called Ponte di Augusto (Narni, Umbria-Italy) which crossed the valley of the river Nera. This bridge, built in the 27 b.C, is one of the widest ever erected by the Romans. It was 170 m long and probably it had four spans. At present only one arch is standing which should not be the widest. Its chord is 20 m long and its height at the intrados is 27 m. The arches, the piers and the abutments were made by a framework of well cut travertine ashlars filled with a mortar that shows a really strong cohesion with mechanical characteristics similar to that of the modern concrete. Mineralogical (XRD), and petrographical analyses (OM) were carried out on the whole sample, while chemical-microchemical (XRF and ESEM-EDS), physical (TG-DTG) analyses were carried out on the binder itself. It is well known that the Romans were able to produce high-quality mortars of relatively low porosity, strong mechanical characteristics and high hydraulicity by adding pozzolane. The mortars used in the Ponte di Augusto show these good characteristics and a binder of high hydraulicity, but the analytical data exclude the use of any particular additive like pozzolane. The chemical data obtained by XRF analyses of the lumps and by ESEM-EDS analyses of the binder reveals a high Si content and low Al2O3/SiO2 and K2O/Al2O3 ratios; this is not compatible with the burning of marly limestones, rather with the use of cherty limestones: a possible stone chemically compatible with the observed data could be the cherty limestones whose fragments are widespread in the mortar mixture and that widely outcrop around Narni. The high hidraulicity in the Roman mortar was not always obtained only by the use of additives like pozzolane.
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