The goal of research is the mineralogical-petrographic study of the mortars used in some medieval fortification walls of XVI century located in the Siena and Cagliari cities. In the first case, the mortars of the walls designed by Baldassarre Peruzzi were studied, while in the second case the mortars used in the Santa Croce's walls (within the "Castello" district) were studied. From the beginning of the sixteenth century until the end of XVI and the XVII centuries, these two ancient fortifications were affected by different masonry transformations, which resulted in different mortar types. The compositional characterization of the entrapment mortars of the historical buildings can be a particularly significant tool for: i) the definition of the construction phases of a ancient yard site and its transformations over time, ii) the realization of data-base timescales valid for local level but also on a national scale, iii) the possible identification, in a synchronic dimension, of mortars selected for specific building types. Therefore, the final purpose of the research is to compare the mortars of the XVI century with those used in the wall circles dating back to previous periods (XIV and XV century) and located in different Italian territories (i.e., Tuscany and Sardinia), to understand the variations of the processing technologies of the raw materials for the production of the mortars. The research at the moment focuses attention on the entrapment mortars of brick walls taken from different portions in Peruzzian walls of the Siena fortifications. The samples were chosen according to their representativeness but above all on the basis of the chronological significance. Preliminary investigations have highlighted the use of different types of mortar compared to previous ones, characterized by high hydraulicity indexes and a greater care in the selection and treatment of raw materials for the aggregates. In fact, the mortars show a narrow dimensional distribution of aggregate (referable to a use of sands with a grain size from very fine to fine) and the little presence of silty or coarser components. Among the constituents of the aggregate are mainly quartz granules (both in monocrystals and in polycrystalline aggregates), belonging to the typical Pliocene marine sands on which the historical centre of Siena is located. The binding / aggregate ratios are usually higher (1/1) in mortars of the sixteenth century compared to mortar three-fifteenth century (around 1/2). These evidences, taken from the compositional point of view, between the mortars of the XIV and those of the following centuries suggest a deliberate choice of new materials, more technologically advanced, in the context of major upgrades to the city defenses implemented at the beginning of the sixteenth century.
Mineralogical-compositional variations in the production technologies of mortars used in some Italian medieval fortifications located in different territorial and historical contexts
Columbu Stefano
Primo
Writing – Original Draft Preparation
;
2018-01-01
Abstract
The goal of research is the mineralogical-petrographic study of the mortars used in some medieval fortification walls of XVI century located in the Siena and Cagliari cities. In the first case, the mortars of the walls designed by Baldassarre Peruzzi were studied, while in the second case the mortars used in the Santa Croce's walls (within the "Castello" district) were studied. From the beginning of the sixteenth century until the end of XVI and the XVII centuries, these two ancient fortifications were affected by different masonry transformations, which resulted in different mortar types. The compositional characterization of the entrapment mortars of the historical buildings can be a particularly significant tool for: i) the definition of the construction phases of a ancient yard site and its transformations over time, ii) the realization of data-base timescales valid for local level but also on a national scale, iii) the possible identification, in a synchronic dimension, of mortars selected for specific building types. Therefore, the final purpose of the research is to compare the mortars of the XVI century with those used in the wall circles dating back to previous periods (XIV and XV century) and located in different Italian territories (i.e., Tuscany and Sardinia), to understand the variations of the processing technologies of the raw materials for the production of the mortars. The research at the moment focuses attention on the entrapment mortars of brick walls taken from different portions in Peruzzian walls of the Siena fortifications. The samples were chosen according to their representativeness but above all on the basis of the chronological significance. Preliminary investigations have highlighted the use of different types of mortar compared to previous ones, characterized by high hydraulicity indexes and a greater care in the selection and treatment of raw materials for the aggregates. In fact, the mortars show a narrow dimensional distribution of aggregate (referable to a use of sands with a grain size from very fine to fine) and the little presence of silty or coarser components. Among the constituents of the aggregate are mainly quartz granules (both in monocrystals and in polycrystalline aggregates), belonging to the typical Pliocene marine sands on which the historical centre of Siena is located. The binding / aggregate ratios are usually higher (1/1) in mortars of the sixteenth century compared to mortar three-fifteenth century (around 1/2). These evidences, taken from the compositional point of view, between the mortars of the XIV and those of the following centuries suggest a deliberate choice of new materials, more technologically advanced, in the context of major upgrades to the city defenses implemented at the beginning of the sixteenth century.
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