About 90 samples of mortars from Pisa historical buildings have been analysed and compared with some samples of ancient mortars characterized by pozzolanic aggregates. Chemical (XRF), mineralogical (XRD) and petrographical (optical microscopy) data have been collected on bulk samples. An X-ray energy-dispersive system (EDS) attached to a SEM was used to determine the chemical compositions of binder, clots and pozzolanic grains (whenever present). The binder components which couldn't be directly assessed (CO2 , H2O+) have been indirectly derived through a computation method. Data collected suggest that the main stock of analysed samples (mortars from Pisa monuments) contains two principal types of binder: the first type corresponds to a common carbonated lime; the second type is a hydraulic lime, where the carbonate component is associated to an important silicate fraction, which ranges from 13 to 89 % by weight of total binder (on average 47%).This hydraulic type had a widespread application in the construction of Pisa ancient monuments; for example, it was constantly employed in the building of the famous "Leaning Tower". It is here shown that the silicate fraction of such hydraulic mortar, which is amorphous to X-ray diffraction, is made up by a hydrated calcium alumino-silicate having a very low Al2O3 / SiO2 ratio (on average 0.125). On the basis of chemical and optical characteristics of hydraulic mortar binders from Pisa and the results of laboratory tests, as well as through comparison with the characteristics of ancient hydraulic mortars having pozzolanic aggregates, it is concluded that such mortars were prepared most likely by mixing slaked lime with a reactive, highly siliceous material such as a diatomaceous earth.
On the binder of some ancient mortars
FRANZINI, MARCO;LEONI, LEONARDO;LEZZERINI, MARCO;SARTORI, FRANCO
1999-01-01
Abstract
About 90 samples of mortars from Pisa historical buildings have been analysed and compared with some samples of ancient mortars characterized by pozzolanic aggregates. Chemical (XRF), mineralogical (XRD) and petrographical (optical microscopy) data have been collected on bulk samples. An X-ray energy-dispersive system (EDS) attached to a SEM was used to determine the chemical compositions of binder, clots and pozzolanic grains (whenever present). The binder components which couldn't be directly assessed (CO2 , H2O+) have been indirectly derived through a computation method. Data collected suggest that the main stock of analysed samples (mortars from Pisa monuments) contains two principal types of binder: the first type corresponds to a common carbonated lime; the second type is a hydraulic lime, where the carbonate component is associated to an important silicate fraction, which ranges from 13 to 89 % by weight of total binder (on average 47%).This hydraulic type had a widespread application in the construction of Pisa ancient monuments; for example, it was constantly employed in the building of the famous "Leaning Tower". It is here shown that the silicate fraction of such hydraulic mortar, which is amorphous to X-ray diffraction, is made up by a hydrated calcium alumino-silicate having a very low Al2O3 / SiO2 ratio (on average 0.125). On the basis of chemical and optical characteristics of hydraulic mortar binders from Pisa and the results of laboratory tests, as well as through comparison with the characteristics of ancient hydraulic mortars having pozzolanic aggregates, it is concluded that such mortars were prepared most likely by mixing slaked lime with a reactive, highly siliceous material such as a diatomaceous earth.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
