PSI - Issue 78

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

1921

al. (2019); Pipistrelli et al. (2025). In the Middle Eastern contexts, raw earth-based materials, Cluni et al. (2023, 2025); Gomes et al. (2019) have been used for similar purposes since ancient times, Biscontin and Driussi (2021). Raw earth, either alone or combined with other sustainable materials (e.g. canvas, straw, rice husk, etc.), can in fact be employed in the form of plasters, earthenware, and bricks for new constructions as well as restoration and finishing interventions.

2. The experimental campaign 2.1. The set-up

There are no specific construction standards regulating the production, repair, or restoration of decorative elements such as stuccoes or precious plasters. Consequently, recognising that these elements fall within the category of artificial stone materials, the authors opted to conduct an experimental campaign in accordance with European, European Committee for Standardization-CEN (1999), and British Standards, British Stan dards Institution (2019), which governs the geometry, preparation criteria, and testing methods for mortars. This approach aims to ensure repeatability and scientific rigour throughout the experimental campaign, which, by way of comparison, will involve specimens incorporating different mix designs. The mechanical tests will include a three-point bending test to assess the elastic and post-peak behaviour of the specimens. Looking ahead, at least three specimens per category will be subjected to testing. The data acquired – including displacement, load, and damage evolution – will be evaluated with reference to all samples, which will differ only in their mix design, while curing times, specimen geometry, and testing conditions will be kept constant across all tests, Fig. 1. Each prism will be positioned in the testing machine with one side resting on two support rollers spaced 10 cm apart, with its longitudinal axis perpendicular to these supports. The load will be applied vertically via the central roller, which will bear on the side face opposite the supported one. The servo-hydraulic testing machine operated in displacement control. Accordingly, the test will be conducted at a slow and constant speed; based on previous experience, a rate of 0.1 mm per minute will be adopted. The results will be evaluated in terms of force-displacement behaviour and critically analysed by comparing the different load–displacement responses, as well as the initiation and propagation patterns of the observed cracks. 2.2. The artificial stone prototypes The experimental tests will be conducted on prismatic specimens with a square cross-section, each mea suring 16 x 4 x 4 cm. Historical mortars are composite materials comprising a binder (or a mixture of binders), various inert materials (predominantly inorganic compounds, not necessarily crystalline in na ture), and certain additives – often organic – added in appropriate quantities to reduce shrinkage cracking (e.g. natural fibres) or to enhance the mechanical performance of the mixture (e.g. pozzolana), as well as its adhesion, workability, or compatibility characteristics. In this field, technological innovations concern the raw materials employed, lime technology (burning temperature, slaking time, water proportion), produc tion techniques (binder-to-aggregate ratios and granulometry), and, not least, the craftsmanship expertise involved. Various mix designs differing in type and size of natural additives and aggregates are analysed. For each mixture to be tested, Table 1, the specimens will be prepared simultaneously with all prototypes allowed to cure for at least 28 days: • A. Gypsum+sand. Proportions: 3 parts sand to 1 part gypsum (volume ratio 3:1). Mineralogical type: river/siliceous sand and gypsum (soft mineral composed of calcium sulphate dihydrate mixed with rock flour). Grain size: sand 0–3 mm. • B. Gypsum+black pozzolana. Proportions: 3 parts black pozzolana to 1 part gypsum (volume ratio 3:1). Mineralogical type: gypsum combined with natural siliceous or siliceous–aluminous materials derived mainly from ashes and lapilli emitted during eruptions in the Naples area. Grain size: gypsum < 0.2 mm; pozzolana 0–6 mm.