Sustainable restoration mortars in a circular economy perspective

The present research focuses on one of the most complex and challenging applications of 'sustainable' mortar use in restoration. The study stems from the context of the PNRR NODES project – Spoke 2, coordinated by the University of Turin and promotes sustainable development and technologies for a “greener” future. In modern construction, the use of mortars demands a finished product that is suitable for its use, with good aesthetic properties and durability over time. These characteristics are even more crucial in a restoration project, where compatibility with the old material comes into play. The sustainability of 'raw' materials, in this case secondary raw materials, is an issue that characterises the current historical moment. In this context, the characterisation of ancient mortars plays a fundamental role in establishing correlations with their sources and for the creation of new formulations. The sustainability of 'alternative' mortars refers to the valorisation of local products, the use of waste materials and fully recyclable compounds, and reduced impact on human health and the environment. One of the potential compounds to use for mortar production can be collected from extractive waste associated to marble and limestone exploitation. Indeed, lime is alkaline and non-toxic, well-known as antiseptic and disinfectant. In addition, due to the low burning temperature and partial reabsorption of carbon dioxide during setting, lime, especially quicklime, is characterised by lower permanent CO2 emissions. In this study different protocols are carried out, compared, and analysed in detail, with the aim of systematising 'alternative' restoration mortar formulations. These are based on the use of 'geomaterials', like waste from mining industry and construction and demolition. In particular, the lime-based binder is obtained from the calcination of white marble waste (quarry sludge, sawdust, etc.) from two different quarries located in Tuscany and Val d'Aosta. The aggregate used for the skeleton of the mortars can be obtained from quarry waste in Piedmont and Val d'Aosta (e.g. gneisses, granites, marbles, limestone, etc.) and/or concrete selected from treatment plants that recycle construction and demolition waste. Finally, each formulation is evaluated regarding performance, compatibility with historic mortars and potential contribution to the circular economy. The results of this research activity are an example of a multidisciplinary approach to the conservation and sustainable management of cultural heritage sites, where issues of scientific research, art, green building and circular economy are intertwined.