Autiero, Francesca (2021) Multiscale approach toward the assessment and conservation of archaeological heritage at Pompeii. [Tesi di dottorato]

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The protection and promotion of heritage structures must be addressed by following fundamental principles of compatibility, reversibility, distinguishability, and minimum intervention for the protection of both the material asset and intangible values. To do that, conservation, reinforcement, and restoration interventions of architectural heritage require multi-disciplinary approaches. Indeed, the achievement of comprehensive and detailed knowledge of the structural behavior and material characteristics of heritage structures is an essential part of the conservation and restoration process. The archaeological site of Pompeii was listed as a World Heritage Site for the outstanding value of its tangible and intangible heritage. The protection of this exceptional site set special challenges related to its great extension, the fragility of its built asset, and a large number of visitors hosted every day. Moreover, from a structural point of view, technical and conservation restrictions limit the possibility to perform extensive and in-depth investigation campaigns to characterize basic mechanical properties. This study was based on scientific cooperation between the Department of Structures for Engineering and Architecture (DiSt), of the University of Naples Federico II, and the authority of the Archaeological Park of Pompeii (PAP). The research programme developed in this thesis aimed at providing fundamental mechanical information, which was still lacking in the literature, and suitable diagnostic methodologies, mainly based on non-destructive techniques and correlations with destructive test outcomes, to support structural assessment and conservation. For this purpose, the study was developed through multiscale diagnostic approaches and involved different types of activities and methodologies: extensive surveys; archival research; in situ inspections; in situ and laboratory testing involving both non-destructive and destructive methods; and numerical simulations. The research mainly focused on two typical constructive elements of ancient Pompeian architecture, among those most representative and vulnerable of the site: rubble stone masonry structures, traditionally known as opus incertum; and free-standing multridrum tuff columns. The study of rubble stone masonry was developed through three main stages from the scale of the building materials to the scale of the masonry assemblages: i) the mechanical characterization of typical building materials (i.e. archeological stone units and mortars), which involved destructive tests (i.e. compression tests) and non-destructive tests (i.e. sclerometric tests and ultrasonic pulse velocity tests) performed on the stone units; ii) the characterization of archaeological masonry structures through in situ non-destructive tests, namely sonic pulse velocity tests; iii) the construction and characterization through non-destructive (i.e. sonic pulse velocity tests) and destructive tests (i.e. in situ diagonal compression tests and laboratory axial compression tests) of masonry panels reproducing the archaeological opus incertum. These were constructed by carefully following the ancient technique found at Pompeii and using original stone units and compatible mortar. Considering the impossibility of performing minor destructive tests or destructive tests on the archaeological materials, the extended and articulated investigation programme provided unique information on a very common masonry typology in heritage contexts. As regards the study of the multidrum columns, it involved two main stages: i) extensive surveys and analyses of their geometrical features and the most widespread forms of degradation, affecting their stability and seismic response, which included an analysis of past structural interventions and their effects on the current state of preservation of the columns; ii) the numerical modeling of these elements and simulation of their seismic response, under different real seismic inputs. Systematic and detailed knowledge of the geometrical properties and state of preservation of a considerable number of free-standing multidrum columns allowed identifying columns being potentially more vulnerable than others; moreover, approximate formulations for a primary estimation of the stability of multidrum columns towards the seismic risk were derived from the numerical simulations. In addition to that, a comprehensive and accurate research programme was developed for the design and characterization of a suitable repair mortar for structural interventions on archaeological structures. This part of the research was developed within a research visit at the University of Minho (Guimaraes, Portugal), Institute for Sustainability and Innovation in Structural Engineering (ISISE), and the research stay was coordinated and supervised by Prof. Eng. Miguel Azenha and Prof. Eng. Paulo B. Lourenco for ISISE. The mixture was prepared following traditional mix design and using raw materials as similar as possible to the ancient ones. In particular, precious and rarely available natural pozzolan from the Phlegrean area (i.e. the same volcanic region where the ancient Roman builders collected their pozzolan) was used. The experimental programme and the adopted methodologies were accurately controlled to monitor fundamental mechanical and physical properties of the mortar from the first days after the preparation up to 200 days, to provide useful information which is still lacking in the literature. This study aimed at supporting the conservation and valorization of heritage assets of immeasurable value, by contributing to achieving adequate knowledge from a structural point of view. The attainment of that objective was intended based on the development of investigation approaches that are: i) compatible with conservation requirements; ii) repeatable and comparable with experimental campaigns carried out in other contexts; iii) representative of the vast built heritage of the site. The achieved information could represent a useful tool for the definition of appropriate choices and new methodologies for the design and planning of suitable interventions on the heritage structures.

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