Many of Europe's most famous buildings are over a thousand years old. Although this shows how robust are the materials used by our ancestors (ancient Romans above all), the preservation of historic buildings is an increasingly demanding and costly problem.
A solution can be found in several recent advances in self-healing concrete. These include a self-healing bacterial paste, which has the potential to save historic buildings and ancient stone structures. This is what we read on Horizon Magazine, body funded by the EU Commission.
The promises of self-healing cement
In the European Union alone, bridge maintenance costs from 4 to 6 billion euros every year. Their replacement would cost over 400 billion euros.
Huge sums, which inspired the scientists in this recent study to look for a method that would see bridges and other historic buildings heal themselves: their investigations led them to develop a bacterial paste that becomes self-healing cement.
A study of Bath University showed that concrete mixed with bacterial spores eventually hardens into the calcite, creating a self-healing concrete that heals cracks in old historic buildings.
Can stone buildings also regenerate?
While this is a great advance for concrete structures, what about historic stone buildings?
The team of a European project called Geoheal has recently developed a technique that allows users to spray or brush the stone with a bacterial paste that begins to heal damage as soon as it occurs.
"Stone and geological materials are naturally bio-receptive," he says Michael Harbottle by Geoheal, professor of geoenvironmental engineering at Cardiff University.
The bacteria we used can live happily in such environments and lead to the formation of new minerals, as long as they have access to water, oxygen and nutrientsMichael Harbottle, Geoheal
The tests show the improvement of the microstructure of the masonry
Geoheal researchers tested their bacterial paste at Tintern Abbey in Monmouthshire, Wales, a historical landmark founded in 1131.
Using two types of bacteria, sporosarcina pasteurii e sporosarcin ureae, they found that this paste actually improved the microstructure of the masonry without changing the external appearance or the transpiration of the stone.
Not just historic buildings
Treatments with self-healing bacteria have the potential to greatly improve the safety of critical infrastructure and prevent catastrophic events such as the 2018 collapse of the Morandi Bridge in Genoa, Italy, which resulted in the deaths of 43 people.
The self-healing properties of the bacterial paste have an effect, in this sense, not only on the "underground" concrete (that of the foundations of a structure) but also on the iron kept inside.
In addition to more solid historic buildings, we will have bolder and more sustainable future buildings
Moisture and soil chemicals can gradually weaken steel over many years, leading to weakened structures and potential disasters. This is why methods such as those of bacteria-based self-healing cement are incredibly valuable.
Magdalini Theodoridou, Newcastle University engineer who worked on the Geoheal project, says: "In historic buildings, self-healing structural materials and elements would provide stability. In new buildings it would allow for bolder and more sustainable designs."
And he's right. The future could bring us futuristic stone buildings. Exciting new construction methods and forms of architecture which could remain robust for centuries.