From Roman knowledge to conservation of built heritage: advances in sustainable pozzolanic mortars

The integration of natural pozzolanic materials into Roman mortar formulations represents a remarkable milestone in ancient construction technology. Volcanic sands from the Somma-Vesuvius area, in particular, played a key role in the production of hydraulic mortars, enabling the development of highly resilient materials. When combined with hydrated lime, these pozzolans triggered pozzolanic reactions that lead to the formation of calcium silicate hydrates, compounds known for their mechanical strength and chemical durability (Jackson et al., 2014). This Romans’ deep understanding of local geo-resources allowed them to optimize the longevity and structural stability of their constructions, providing a valuable model for sustainable material use in modern conservation practices. Despite their durability, natural pozzolanic mortars remain susceptible to deterioration due to environmental exposure and intrinsic factors such as porosity and mineralogical composition. Consequently, effective preservation strategies must be guided by both historical knowledge and scientific analysis to ensure that new restoration materials are compatible with the originals, not only chemically, but also in terms of mechanical and physical properties (Moropolou et al., 2000). This study focuses on developing conservation mortars inspired by Roman techniques, using hydrated lime paste, raw volcanic materials and advanced admixtures to produce formulations that are sustainable and compatible with ancient substrates (Spadavecchia et al., 2024). The research includes the design of various mortar mixes: reference mortars incorporate volcanic aggregates from different Vesuvian eruptions (Avellino, Pompeii, Pollena), simulating the composition of the ancient mortars discovered in the archaeological sites of the area, while experimental mixes include pozzolanic additives such as metakaolin, nano-silica, silica fume, and volcanic ash. Specimens were prepared following ancient methodologies and subjected to extensive laboratory testing. Analytical techniques included X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Laser Diffraction, Thermogravimetric Analysis (TGA), and Mercury Intrusion Porosimetry (MIP). Mechanical properties, such as compressive strength, porosity, and water absorption, were evaluated at multiple curing stages (28, 90, 180 days), while durability included resistance to salt crystallization and freeze- thaw cycles after 90 days of curing. The findings of this research contribute to the development of restoration mortars that are both technologically advanced and historically respectful, offering practical solutions for the sustainable conservation of built heritage (Collepardi, 2003).