2018 – 2020
What is the challenge?
Natural stone is one of the most widely used geological construction materials. Although stone masonry structures have the potential to survive over centuries, they may be subject to significant damage and deterioration. Various conservation treatments have been explored for modifying the characteristics of stone, often in the layer closer to the surface. However, treatments may limit the breathability of the material triggering further damage.
Why is it important for society?
Microbially induced carbonate precipitation by bacteria is a promising breathable alternative for the protection of building stone from deterioration. The mineralogical composition and pore structure of most stone types used in construction are favourable for the growth of bacterial communities. However, the protection layer will deteriorate in the same manner as the host material, and although it will give enhanced protection of the stone, it is not infinitely durable. By giving this microbiological protection system the ability to ‘self-heal’ (i.e. respond automatically to heal damage and deterioration, without human intervention), it has the potential to considerably extend the durability of masonry protection.
What are the overall objectives?
During the GEOHEAL project, our objectives focused on the development, application and assessment of biological healing and self-healing mechanisms for repairing and preventing damage in cementless construction materials, such as natural stone. The direct compatibility of the biological healing products, such as calcite, with stone materials, enables their application in heritage conservation, and significant reduction of maintenance costs in both existing and new structures. There is the potential for other minerals to act in a similar way, and which may be more durable (e.g. oxalates).
The work has produced working healing and self-healing systems for application in masonry and similar materials, as described above, and has led to a number of developments.
Collaborations between Cardiff School of Engineering and Cadw, the Welsh Government’s historic environment service, were established to deliver research impact through testing on heritage masonry materials. A heritage site in Wales which exhibits masonry deterioration was identified and following site visits and investigations representative stone types from the site were selected and subjected to experimentation which proved the efficiency of the developed biological system to change the microstructure of the materials exposed to weathering. Yet, the applied treatment did not seem to alter the treated zone of the stone specimens to an extent that could be proven incompatible with the substrate or any adverse aesthetic impact (extremely important in heritage structure management).
The developed biological system was also investigated as a method for repairing and preventing further damage on sedimentary stone-built heritage that has been impacted by ballistics. The biological treatment was applied on stone specimens previously subjected to simulated ballistics under laboratory conditions with the resulting biomineralisation sufficient to significantly reduce water absorption, improving durability and suggesting that the method can be considered to sensitively repair structures without necessarily obscuring the damage, considered part of the history in regions that experienced armed conflict. See Figure: Microbially induced healing in limestone.
The GEOHEAL project has attracted interest from wide ranging media sources such as BBC Wales, Forbes, The Engineer, New Civil Engineer, TECH Explorist and others. The GEOHEAL research work has been widely disseminated through articles, workshops, seminars, international conference presentations, invited lectures and Youtube videos.
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The GEOHEAL project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 745891.