75 research outputs found
The San Saturnino Basilica (Cagliari, Italy): An Up-Close Investigation about the Archaeological Stratigraphy of Mortars from the Roman to the Middle Ages
The manufacturing technology of historical mortars from the Roman to Medieval period apparently has not undergone evolutions. As reported in the literature, a quality decrease in the raw material occurred after the fall of the Roman Empire. During the Roman Age, the mortars presented the requirements of long durability due to hydraulic characteristics, and in later times, the production has only partially maintained the ancient requirements. To focus on the different production technologies between Roman and Medieval mortar, this research presents the case study of San Saturnino Basilica (Italy), where an archaeological mortar stratigraphy from Roman to Middle Ages is well preserved. An archaeometric characterization was performed to compare the mortars of the Roman period with the mortars of the Medieval period collected from the case-study monument. This comparison was carried out by measuring some physical-mechanical, mineralogical, petrographic and thermal features that give more information about the durability and resistance to mechanical solicitations and weathering. After the characterizations, contrary to what is reported in the bibliography, a better quality of Medieval materials than Roman ones is pointed out. This has been highlighted by higher hydraulicity, mechanical performance, and a more appropriated particle-size distribution of aggregates
Monitoraggio del degrado e conservazione del Patrimonio monumentale della Regione Sardegna attraverso caratterizzazione geochimica, petrofisica e micro-fotogrammetrica di superfici lapidee
Cultural Heritage of Sardinia (Italy) consists of a large number of historical monuments belonging to different cultures (e.g. Nuragic, Roman, Phoenician-Punic, Romanesque, Aragonese), from 1800 BC to 1700 AD. Some of these buildings, nowadays in a poor state of conservation, are subject to management and monitoring plans.
In this research, four representative archaeological sites from Roman to Romanesque cultures are the topic of an in-depth study.
The project focuses on ancient mortars, stones and paintings.
An integrated and multi-scale approach proposed in this project, combines classical physical-mechanical, petrographic and geochemical investigations (archaeometry) with accelerate aging tests (AAT).
Optical mineralogy observations (OM) on stones permit the rock classification and the identification of ancient supply quarries. In the case of marbles, the provenience of the rocks was established by cross-analysis OM and isotope-ratio 13C vs 18O.
OM on mortars identifies the environment origin and typology of aggregates.
Both mortars and stones are subject to physical-mechanical tests in order to obtain densities, porosities, imbibition and saturation indices, tensile and compressive strengths.
In addition, the particle-size distribution (PSD) of mortar aggregates points out information about the production methodology.
A XRPD diffraction associated with SEM-EDS and TGA-DSC analysis on mortar binders recognized alteration mineral phases and established the hydraulicity degree.
In addition μXRD with associated μRaman spectroscopy and μFT-IR have been carried out on the fresco to characterize the pigments and their binder.
By in-situ observations and digital image reconstruction, decay mapping of some building portion highlight the diverse alteration forms of the stone.
Accelerated aging tests on samples with analogue lithology to the one used in the selected monument, try to reproduce these alteration forms in laboratory. The aging tests, conducted by climatic chambers, faithfully reproduce the temperature, humidity, capillary rising, CO2 air content and solar radiation of the environment context where the monuments are located.
All macroscopic morphologic modifications have been represented before and after the aging tests by 3D photogrammetric modelling (online available).
Furthermore, before, after and in some case during the aging tests, a wide series of physical-mechanical parameters (e.g. linear roughness, mass, color changes, mechanical strengths, densities, P ultrasonic speeds.) and chemical parameters (e.g. efflorescences characterization) have been evaluated. Traditional applied petrography approach allows to observe the actual decay state and accelerated aging tests predict the modalities of decay development in the future
Climate Change and Cultural Heritage: From Small- to Large-Scale Effects—The Case Study of Nora (Sardinia, Italy)
Rising sea levels are mainly due to increases in environmental temperatures that are causing ice to melt. The weathering of geomaterials is mainly due to the increase in the concentration of greenhouse gases in the atmosphere. This research addresses current and future sea level rises and their weathering effects on the building stones in the Phoenician–Punic archaeological area of Nora (Sardinia, Italy). Some forecasting models, selected according to real-world scenarios (shared socioeconomic pathways—SSPs), give a definitive overview of both the rising sea levels and stone weathering conditions in Nora. The year 2100 A.D. was selected as the base of our investigations because the SSPs are scenarios of projected socioeconomic global changes up to 2100 A.D. The data on the expected alteration of geomaterials were reconstructed by considering the temperatures, the rainfall amount, and the atmospheric CO2 of every scenario. This was made possible by knowing the current degree of alteration of the geomaterials and their weathering resistance. The rising sea level models were obtained through the SSPs scenarios data and built using geographic information systems software. The projections show a slowing down of the weathering degrees of the stone materials in Nora. This is due to the increase in the average annual temperature and the decrease in the average annual rainfall. However, it is shown that some other factors, such as the marine spray in the area, could accelerate the decay. Projections of the rising sea levels show how the settlement will be partially submerged, losing between 3.54% and 8.49% of the emerged land. The models provided a maximum ingression of the coastline, ranging from 23.7 m to 29.5 m, based on the severity of the scenarios. Coastline-shifting maps indicate the flooding of some buildings located on the western coast of Nora, the most sensitive part of the territory
K/Na-silicate, ethyl-silicate and silane nano-molecular treatments in the restoration of high porous limestone
Carbonate sedimentary rocks (i.e., limestones) have been frequently used in historical times due to easy availability and workability. These latter depend primarily by petrophysical characteristics (porosity, bulk density) that influence the mechanical strength. However, the limestones with high porosity (>30%) and a poorly cemented carbonate-matrix show chemical alteration (i.e., dissolution) and physical decay (e.g., decohesion).
In this work it was taken as case study a biomicritic limestone belonging to the carbonatic miocenic series (lower Tortonian) of Cagliari (southern-Sardinia, Italy). This limestone has a low-medium cementing matrix containing hygroscopic clay and sea-salt phases, which make the rock degradable. To limit the decay it can intervene with consolidating products (K-Na-silicate, ethyl-silicate) and protective-chemicals (silane nano-molecular gel-coat) to reduce the porosity and permeability to the liquid aqueous phase. Results highlight an increase of strength after consolidation and a decrease of gas-permeability after protection-treatment, maintaining in both cases a good permeability to the vapor-phase
Building pathology and environment: Weathering and decay of stone construction materials subjected to a Csa mediterranean climate laboratory simulation
Building stone materials have to satisfy long-term durability requirements in different environments in terms of mechanical strength and resistance to aggressive conditions. Several studies and field observations show that weathering on geo-materials is related to average annual precipitation and temperature.
The decay also depends on salts air/soil concentrations and biological agents, but the more harmful impact is given by greenhouse gas (e.g. CO2, SOX, NOX, O3). These last induce the acidification of the rain and runoff waters. Nowadays, decay prediction is required in order to estimate the behaviour of stone materials over time. This research represents a second part of a previous work where the response to weathering of some construction materials used in ancient and contemporary architecture and cultural heritage has been evaluated by a labo- ratory simulation of hot-summer Csa Mediterranean climate. Simulation consists of accelerate ageing test on climate chamber by reproducing macro (e.g. daily and seasonal cycles of temperature, relative humidity, CO2 air concentration) and micro (e.g. rain, soil capillary rising) environments. Some non-destructive testing were executed to evaluate some physical–mechanical “decay markers” before and after the ageing. Test caused both decreasing and increasing of Leeb D hardness, decreases of permeability and a general decrease of ultrasonic speed, mainly due to the formations of patinas, crusts and efflorescences on the surfaces
The ancient pozzolanic mortars and concretes of Heliocaminus baths in Hadrian s Villa (Tivoli, Italy)
The aim of this work is the physical and mineralogical-petrographic characterization of the mortars from the Baths with Heliocaminus, a special and unique ar- chitectural building in the complex of the Hadrian’s Villa in Tivoli. Thirty samples were investigated for composition and physical properties (density, porosity, water absorption, me- chanical strength, particle size distribution of aggregate, etc.), representative of eight mortar groups: cubilia bedding mortar, brick bedding mortars, floor-coating and wall-coating bedding mortars, floor (rudus) and wall conglomerates (trullisatio), vault concretes, and lime plasters (arriccio). Physical param- eters, together with the microscopic analysis and binder/ aggregate ratio determined in three ways using image analysis (on thin sections and on specimens) and weight-data from dissolution of binder, have shown an interesting relationship between the physical-compositional characteristics and the function of mortars within the structure of the Heliocaminus baths. To identify the minerals and the reactant phases be- tween binder and aggregate, as well as the hydraulic degree, selected samples were analyzed with x-ray powder diffraction, thermogravimetry, and differential scanning calorimetry tech- niques. The obtained results provide a close relation between
pozzolanic characteristics and physical-mechanical properties of the mortars (i.e., punching strength index)
Origin of Roman worked stones from St. Saturno christian Basilica (south Sardinia, Italy)
The work aims to define the origin of the architectural stone elements worked by Romans and reused in the St. Saturno Basilica, between the late Antiquity and Romanesque periods. Thus, different rocks (marbles, various facies of limestones, volcanic rocks) used to construct the ancient building were sampled and analysed. All the different kinds of stones were sampled from the Basilica, taking precise reference to the various construction phases and structural changes of the monument occurred in the centuries. The sedimentary and volcanic lithologies belong to the local outcrops of Cagliari Miocenic geological formation (e.g. limestone) and to other volcanic outcrops of south Sardinia, respectively. By means of a multi-method archaeometric study (mineralogical-petrographic observations on thin sections and O-18 vs C-13 stable isotope ratio analysis), the provenance of classical marbles used for manufacturing Roman architectural elements (column shafts, bases, capitals, slabs, etc.) were defined, which are thought to come from extra-regional sources. The results show that the marbles come mainly from Apuan Alps (Italy) and subordinately from Greek quarrying areas
Mineralogical-chemical Alteration and Origin of Ignimbritic Stones Used in the Old Cathedral of Nostra Signora di Castro (Sardinia, Italy)
The pyroclastic rocks belonging to the Late Eocene-Miocene volcanic activity that occurred in Sardinia between 38 and 15 Ma ago were widely used as construction materials in several Romanesque churches of the easternmost Logudoro area, as well as in large parts of the Sardinia territory. In this work, the ancient Cathedral of Nostra Signora di Castro (twelfth century) was taken as a representative case study. There is no historical or archaeological evidence of ancient quarries. Based on the geochemical, petrographic, and volcanological data on several samples from an extensive field area (approximately 150km2), a geographical zoning of the volcanics has been recognised. In the Oschiri sector, there are three different sub-zones, which can be identified with different volcanic rocks: less fractionated rocks (Differentation Index ∼70–78); intermediately fractionated rocks (D.I. ∼76– 79); and more fractionated rocks (D.I. ∼77–82). To identify the origin of the ignimbrite rocks of the Church of Nostra Signora di Castro, two statistical methods were used: stepwise linear discriminant and canonical analysis. Moreover, to define the geochemical transformation processes induced by the alteration, a comparative study of concentrations of major and trace elements measured by XRF and SEM-EDX analyses on the surface portion and the innermost areas of the stone was made
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