PSI - Issue 78

Riccardo Liberotti et al. / Procedia Structural Integrity 78 (2026) 1919–1926

1920

in the event of seismic activity. This jeopardises not only the conservation of artefacts but, in some cases, even human safety. Similarly, environmental factors determine the occurrence of material degradation phenomena affecting these artworks, processes which are often accelerated by climate change or extreme events such as earthquakes, with tragic consequences beyond the mere material loss. To this, human responsibility must also be added, which may manifest as negligence when maintenance is lacking, or as criminal actions in the destruction of cultural identities during wartime. The most common degradation phenomena affecting heritage, which cannot be described exhaustively here for reasons of brevity, are correlated in the following sections with their causes and material specificities, in view of designing a consolidation intervention based on nanomaterials with a preventive character, while ensuring full respect for the material integrity and intrinsic value of the architecture. Particular attention is dedicated to decorative apparatuses, plaster casts, and natural stone elements, introducing in brief the essential notions regarding their geological and stereometric aspects (e.g. cutting and workability of quarried materials, physical, commercial, and usage characteristics) and, above all, providing an overview of the chemical-physical processes concerning artificial stone materials, which represent the main focus of this research as they constitute the decorative apparatuses themselves. By way of comparison, the most significant results from experimental mechanical tests are presented here, comparing materials with and without the application of both commercial and innovative consolidants. In the field of heritage conservation, a consolidant is a substance or formulation specifically designed to penetrate and strengthen deteriorated materials without altering their original appearance or compromising their authenticity. Its primary purpose is to restore or improve the mechanical cohesion of weakened substrates – such as stone, plaster, stucco, or mural surfaces – by binding disaggregated particles and enhancing structural integrity, while respecting the material, historical, and aesthetic values of the artefact. 1.1. Material degradation Once the construction phase is completed, all buildings inevitably undergo physical deterioration, decay, and the disintegration of material molecules into smaller molecules or fragments. Degradation may be initi ated by external factors such as heat, moisture, chemicals, UV exposure, fungi, or bacteria – to name but a few – and is further exacerbated by mechanical stresses, for example those induced by seismic events, El-Gohary (2017). From a phenomenological perspective, it is important to distinguish between: • Alteration – a change occurring in a material which, while modifying some of its characteristics, does not necessarily undermine its conservation. • Degradation – a gradual and irreversible process that causes an architectural or structural element to lose its defining characteristics of shape, colour, resistance, reliability, and durability, ultimately rendering it unfit for its original purpose. Alterations are often physiological and do not necessarily compromise the architectural or structural integrity of an artefact; in some cases, they may even enhance its expressive potential. Conversely, interventions become mandatory when past or ongoing degradation phenomena have caused irreversible damage that compromises material properties. The complex interplay between these processes must therefore be critically analysed within a comprehensive framework by professionals operating in the heritage conservation field. In general, the deterioration of architectural surfaces is categorised according to UNI 11182:2006, Ente Italiano di Normazione (2006), which provides guidelines for recognising and classifying forms of decay in different stone materials. These materials can be divided into two macro-categories: • Natural materials – e.g., marble, limestone, granite, sandstone, onyx, alabaster, gneiss, etc. • Artificial materials – which are often multi-phase and obtained through chemical-physical processes from natural rocks, e.g., concrete, stuccoes, ceramics, bricks, bedding mortars, plasters, and so forth. The present contribution focuses on the second category of materials, particularly those used in the realisa tion of heritage decorative apparatuses, such as stuccoes, plasters, and bas-reliefs. Historical and iconographic research shows that although various natural additives of plant origin – such as hemp, flax, or broom – or animal origin – such as casein, animal gelatines, or egg yolk – were used in ancient stuccoes, the most com monly recurring binders were undoubtedly hydraulic lime and gypsum in Europe, Ronca (1994); Galassi et