d'Aniello, Francesca (2024) Study of compatibility criteria for the formulation of restoration mortars. [Tesi di dottorato]

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Abstract

Abstract This study enhances the understanding of compatibility criteria for restoration mortars, crucial for the preservation of ancient and traditional buildings. It focuses on the formulation of lime-pozzolana mortars that are compatible with ancient mortars and traditional substrates. Following Vitruvius' recommendations, a 1:2 binder-to-aggregate ratio was used to compare a pozzolana from the historic site of Fondi di Baia, the area referenced by Vitruvius, with a commercially available pozzolana from the Phlegraean Fields. The mortar constituents were thoroughly characterised using mineralogical, chemical, and physic techniques to establish correlations between the materials and mortar properties. The comparison between two reference mortars, M0L (using pozzolana from Baia) and M0C (using commercial pozzolana), was made through characterisation at 28 and 90 days of curing using PLM, FESEM-EDS, FTIR, XRPD, XRF, and TG-DSC. Physical and mechanical properties, such as compressive and flexural strength, hydric properties, and density were measured according to UNI EN standards. Additional tests included UPV on dry and wet samples, and MIP. The outcomes demonstrated similar physical and mechanical properties after 90 days of curing, validating the use of commercial pozzolana as a reliable alternative for producing restoration mortars, particularly since quarrying is no longer permitted at the historical source in Fondi di Baia. The performance of M0C was further assessed on substrates typical of ancient constructions, limestone, bricks, and tuff, revealing significant differences in mortar behaviour depending on the substrate. Adhesion tests highlighted these variations in physical-mechanical performance, stressing the importance of substrate-specific testing in conditions similar to those of the real world. Six additional mortar formulations were developed by adjusting the binder-to-aggregate ratio and the granulometry of pozzolana. These formulations were characterised after 28 days using the same analytical approach as M0L and M0C. Fresh-state properties, such as apparent density and consistency, were also measured according to UNI EN 1015-2-3:2007. Aesthetic compatibility was assessed through colorimetric analysis. This approach confirmed the potential of traditional materials, such as lime putty and pozzolana, in creating mortars tailored to diverse restoration needs, achieving a range of physical-mechanical properties without relying on cementitious binders or synthetic additives. In the final phase, composite samples simulating masonry structures (substrate-mortar-substrate) were subjected to hydric and salt crystallisation tests to evaluate compatibility and long-term durability. The results highlighted that while finer pozzolana offered better individual mechanical performance, coarser pozzolana displayed improved resistance to salt crystallisation in composite samples, underlining the importance of optimising formulations based on specific restoration requirements. This research contributes to bridging the gap in the literature on restoration lime and pozzolana mortars from the Phlegraean Fields and offers practical guidance to restorers and producers. By focusing on the compatibility, durability, and mechanical performance of mortars, the study provides an evidence-based approach to developing tailored restoration materials that respect both the authenticity of ancient techniques and the demands of modern conservation projects.

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