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Bricks manufacturing technologies to increase built heritage resilience and to raise common identities of peoples

Periodic Reporting for period 1 - CLAYONRISK (Bricks manufacturing technologies to increase built heritage resilience and to raise common identities of peoples)

Reporting period: 2019-04-15 to 2021-04-14

Interdisciplinary studies of bricks shaping historical structures provide a knowledge base loaded with heritage and technological value. Hence, the manufacturing processes are meaningfully linked with the cultural identity and improve the understanding of bricks physical performance and resistance over time (durability), that could be applied to current ceramic industry in order to produce quality bricks by means of eco-innovative and sustainable processes. Such topics are important for society because: a) the knowledge attained represents a heritage resource that confers special cohesion and identity, b) comprehensive studies of ancient bricks represents a preventive measure to increase built heritage resilience towards earthquakes and climate changes, and c) outputs should be transferred to new bricks production in order to achieve eco-friendly solutions.

The CLAYONRISK project has addressed ancient brick resistance over time from the manufacturing process via three main objectives: a) to perform a multianalitical study of the ancient bricks that shape the built heritage of the city of Padua (Veneto region, Northern Italy) belonging to Roman, Late Antiquity, Medieval and Renaissance times, b) to state the influence of the manufacturing on bricks physical (mechanical and hydric) behaviour and durability, and c) to highlight the data to transfer to current ceramic industry regarding to sustainable raw materials supply and environment protection.

The main conclusions are: a) clayey bricks shape the image of Padua, with colour changes from yellowish to beige and to reddish hue from Roman to Renaissance times, b) even though a low vitrification degree was achieved, the bricks have been rather resistant over time, c) the diverse sintering of the yellowish-beige and the reddish hue bodies -that has led differential mechanical and hydric performances- and the high humidity of the city -that allows that the humid conditions within the bodies remain fairly constant- have turned out beneficial for the conservation of bricks and structures, and d) the use of local clays may reduce the transport costs and may allow the production of quality bricks without requiring very high temperatures, so the consume of energy and CO2 would be decreased.

The CLAYONRISK project has entailed a major impact on the career development of the MSCA fellow, that has worked in an independent way, has strengthened her research profile, has extended her professional network and has enlarged her future prospects.
The multianalitical study has comprised spectrophotometry, X-ray fluorescence, X-ray powder diffraction, polarized optical and scanning electron microscopies (environmental, field emission and cold field emission) with EDS microanalysis, Mössbauer spectroscopy and laser granulometric analysis. Bricks resistance to seismic activity has been inferred from the assessment of the mechanical behaviour -velocity of the ultrasonic waves and anisotropy measurement and compressive tests performance-. The pore system -by means of hydric tests and mercury intrusion porosimetry- and bricks durability to moisture, frost and salt crystallization action were determined.

The results achieved pointed out that: a) Mg-rich calcareous clays and illitic clays were used, in concordance with the composition of the local clays, and temperatures of 800-850 °C or over 900 °C were reached, b) melilites, clinopyroxene-type, anorthite, Mg-silicates and hematite were the high-temperature phases and secondary phases were calcite and zeolite, c) a lesser calcareous content on the base clays and the decrease of the firing temperatures were the main technological modifications accomplished on bricks manufacturing along the history of Padua, yielding colour changes of the ceramic bodies from yellowish to beige and to reddish hue, d) the reuse of Roman bricks during the Late-Antiquity and Medieval times, confirmed by means of scientific data, has allowed to observe that high humid conditions enhance its conservation, d) the good resistance over time shown by bricks and fabrics is mainly because of the high stable microtexture developed within the ceramic bodies by the high-temperature phases, the better distribution of loads and efforts inside the fabrics due to the slightly differential mechanical behaviour of the bricks, and the low moisture gradient between bricks and the nearby environment largely due to the high humidity conditions of the city and e) the use of local clays may reduce the transport costs and allows the production of quality bricks without requiring very high temperatures, so the consume of energy and CO2 would be decreased.

The present MSCA was characterized by the publication of 2 scientific papers (+3 in progress) -all available in Open Access-, dissemination at 5 international conferences, 1 invited talk and 1 workshop. Data were also submitted to open access repositories (IT SYGMA tool and IRIS Institutional Archive of UNIPD and Open Research Europe platform). In addition, 6 outreach activities were performed by the fellow with the support of the International Research Office of UNIPD. The European Union funding has been acknowledged in all the dissemination activities developed under the project.
To further advance the understanding of the connection among bricks manufacturing technologies, built heritage resilience and environment protection, the CLAYONRISK project has shown that: a) the colour of bricks entails an identifier both of the manufacturing technologies and of a specific period of the city, b) the sintering degree of the ceramic bodies can be used as quality marker of bricks physical performance and durability, in order to infer the potential impact of earthquakes and extreme weather events on bricks and historical structures and c) if new quality bricks that preserve the aesthetical values of the city were produced, the use of local clays may provide eco-innovative and sustainable solutions.

The data achieved build the ground for future comprehensive studies of ancient bricks towards the understanding of their mechanical behaviour and resistance over time from the manufacturing process. The knowledge attained strongly relies on the importance to address such issues considering ancient bricks as systems within an entire structure that are continuously interacting with the surrounding environment.

Thinking of restoration purposes, new quality bricks that would increase the built heritage resilience against earthquakes and climate change considering at the same time eco-friendly solutions would be produced through the knowledge base generated. Sustainable raw materials supply and eco-friendly production entails a direct industrial application of the project, being of special interest for the ceramic industry of Northern Italy. Such regional industry represents the main potential user of the results, as the current understanding could be implemented into new bricks production that would preserve the aesthetical values of the city and would be especially suitable for the conservation of the built heritage placed at high humid environs. Considering that the largest part of world heritage sites is exposed to natural hazards and climate changes, and the use of clay bricks worldwide, the results arisen bring also an important benefit for society as a whole.
Zeolite secondary phases (hydration products) formed within pristine carbonate inclusions observed b
High temperature phases formed during the firing process observed by SEM-SE (a) and FESEM-BSE (b and