This study is part of a wider research on construction techniques of the coastal towers of Sardinia. It examines the three towers on the Asinara Island with the aim to identify the construction techniques and technologies through the characterization of stone materials and through subsequent identification and dating of the different phases of construction. In order to rationalize and optimize data collection and processing it was helpful to set up and test a common protocol to all buildings which is also applicable to a larger scale. The first phase of the protocol involved the archival research, mainly carried out in the Cagliari archives (Archivio di Stato, Archivio Storico, Archivio di manoscritti della Biblioteca Universitaria), and the documentation on the many bibliographical sources. The next steps, carried out directly on the site, have allowed the metric and / or photogrammetric survey of the three towers, and reasoned sampling of interstitial mortars, plasters, waterproofing materials and stones used. The absence of recent interventions or their easy location and demarcation, as well as the advanced state of decay has facilitated the retrieval of historical materials attributable to the original building. The analysis of the samples was set by observing the following steps: execution of photos of the samples with digital camera; macroscopic analysis, performed in situ, in order to obtain information on the stratigraphic position of the sample, the characteristics of the color, the texture and the way of working; petrographic analysis of thin section in transmitted light polarized (OM) and X-ray diffraction of samples such as to characterize the mineralogical composition of the aggregates and the binder; disintegration of mortar sample in order to define the size distribution and the proportions of the binder/aggregate; X-ray diffraction analysis (XRD) to define the mineralogical-petrographic composition of the binder, aggregates separated by particle size, partially burnt limestone and lumps of lime. The synthesis of the tests carried out made it possible, through the comparison of results obtained with the historical sources, to deliver an exact determination of important data on the construction techniques used in the three towers and on their chronological articulation and also to deliver a first indication of degradation and the causes that originated them. This constitutes a valuable basis on which to set appropriate readings of the historical text and make appropriate proposals for the restoration originated from a deep knowledge of historical materials and their application.
The characterization of stone materials in the study of historic building techniques: the case of the Asinara towers
MURRU, STEFANIA;GRILLO, SILVANA MARIA
2013-01-01
Abstract
This study is part of a wider research on construction techniques of the coastal towers of Sardinia. It examines the three towers on the Asinara Island with the aim to identify the construction techniques and technologies through the characterization of stone materials and through subsequent identification and dating of the different phases of construction. In order to rationalize and optimize data collection and processing it was helpful to set up and test a common protocol to all buildings which is also applicable to a larger scale. The first phase of the protocol involved the archival research, mainly carried out in the Cagliari archives (Archivio di Stato, Archivio Storico, Archivio di manoscritti della Biblioteca Universitaria), and the documentation on the many bibliographical sources. The next steps, carried out directly on the site, have allowed the metric and / or photogrammetric survey of the three towers, and reasoned sampling of interstitial mortars, plasters, waterproofing materials and stones used. The absence of recent interventions or their easy location and demarcation, as well as the advanced state of decay has facilitated the retrieval of historical materials attributable to the original building. The analysis of the samples was set by observing the following steps: execution of photos of the samples with digital camera; macroscopic analysis, performed in situ, in order to obtain information on the stratigraphic position of the sample, the characteristics of the color, the texture and the way of working; petrographic analysis of thin section in transmitted light polarized (OM) and X-ray diffraction of samples such as to characterize the mineralogical composition of the aggregates and the binder; disintegration of mortar sample in order to define the size distribution and the proportions of the binder/aggregate; X-ray diffraction analysis (XRD) to define the mineralogical-petrographic composition of the binder, aggregates separated by particle size, partially burnt limestone and lumps of lime. The synthesis of the tests carried out made it possible, through the comparison of results obtained with the historical sources, to deliver an exact determination of important data on the construction techniques used in the three towers and on their chronological articulation and also to deliver a first indication of degradation and the causes that originated them. This constitutes a valuable basis on which to set appropriate readings of the historical text and make appropriate proposals for the restoration originated from a deep knowledge of historical materials and their application.
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