Construction researcher Hannelore Derluyn wants to identify the mechanisms that cause the rocks used in construction to degrade. The key: extending the life of materials or even preserving architectural heritage.
Her lab colleagues like to describe Hannelore Derluyn as a reserved person. Paradoxically, they also admire his speech ” honest and direct “, “who does not bother with meanderings“. This researcher of geomechanics and porous media, within the Laboratory for Complex Fluids and Their Deposits (LFCR), would still have something to show, because there are not many scientists capable of competing in her specialty, that is, the study of building materials.
Hannelore Derluyn is particularly interested in external phenomena that lead to changes in porous building materials, such as natural stone or brick: water, salt, ice, bacteria… the agents of degradation are potentially numerous, reasons and multiple scenarios. In order to understand these phenomena in detail, the researcher uses tomography, an imaging technique that produces a three-dimensional image of an object from a series of X-rays.
Witness the invisible
A scientist can thus observe, on a microscopic level and in real time, phenomena invisible to the human eye and see what is happening at the heart of matter:Now we can see the formation of certain crystals or the circulation of certain fluids in matter in real time. This is impossible with traditional scanners“, she explains. These discoveries have multiple uses: preserving historic buildings, improving civil engineers’ modeling, or even preventing global warming damage to our structures.
Examples of salt-induced damage: (A) salt crystallization on the surface of a masonry facade causing efflorescence (white spots) and scale formation (Huesca City Hall, Spain), (B) scale (Oita Motomachi Buddha, Japan) (C) alveolization (Paphos Castle , Cyprus).
Originally from Flanders, more precisely from Roeselare, a town only thirty kilometers from Lille, Hannelore Derluyn became interested in the influence of moisture on textiles inside a building while studying civil engineering at the Catholic University of Louvain. In 2009, she flew to the Swiss Federal Institute of Technology in Zurich, Switzerland, where she obtained her PhD in 2012 on the topic of salt transport and crystallization in porous media. “In my thesis, I wanted to focus on natural stone, a material very present in historical buildings, potentially strongly affected by possible damage.“, she explains.
Now we can see the formation of certain crystals or the circulation of certain fluids in matter in real time.
His interest in the subject may have been sparked much earlier, through his grandfather, an enthusiast in the field who built his own house and that of his children. “When I was little, during family gatherings, the adults would talk about their construction projects with pencils all the time.“, she recalls. Her father also played an important role in her career choice. For his part, she remembers visiting as a child the ancient ruins of Vaison-la-Romaine, not far from Mont Ventoux, a place famous for its wealth of Roman mosaics.
Hannelore Derluyn still remembers this floor that was decorated with it and in which she saw “a history that unfolds over centuries“. “This feeling also occurs in my research», recognizes the one who defines herself as »the witness of the invisible” and for whom to observe these degradation mechanisms at the microscopic level in real time, “it’s a bit like discovering a hidden world“.
Observe the buildings to take better care of them
The researcher says that she likes, during her Sunday walks, to look at the extraordinary buildings that surround her. Recently, she recorded panels that talked about the desalination of the vaults of Notre-Dame de Paris. Her conservative friend Julie Desarnaud then explained to her that this phenomenon appeared after the 2019 fire.During the intervention of the firefighters, a large amount of water was applied to the roof. The sulfate present within the plaster that covered the outside of the vaults was exposed to moisture and the sulfate salts present within crystallized. Without prompt corrective action, this could permanently damage the linings.», explains Hannelore Derluyn.
Salt crystallization in a porous medium at different scales.
The scientist regularly observes similar phenomena in her laboratory using a tomograph. “I’m a bit like a doctor looking at the human body using medical imaging, but I do it for buildings to take better care of them. I observe the water that penetrates the rock, where it lingers, into which hollows it rushes, etc. When I studied textiles, it was the same. I saw the wires, how they were stretched and how their arrangement changed every time the water hit them.“, she describes.
Bringing researchers and construction experts into dialogue
Her position as a woman in a discipline dominated by men is not the only trait that distinguishes her within her laboratory. Before arriving in France and joining the CNRS in 2016, as a research fellow at the LFCR, Hannelore Derluyn worked in Belgium and German Switzerland. Two countries in northern Europe where customs regarding the organization of academic research differ from the south, and thus from France. There, most of the time, there is a researcher at the head of the laboratory around whom all other scientists gravitate. In France, the directors are not attached to the laboratory, they change every five years. A peculiarity that at first sight may prove destabilizing, the researcher recognizes, even if it does not have the shadow of an academic tenor, can offer a form of freedom in approaching subjects. “On the other hand, I come from an area where if you want to do something, you work, work, you get there and you don’t need a paper to prove it.“, she jokes.
In the future, the work that Hannelore Derluyn and her team are doing in the PRD-Trigger project funded by the European Research Council will be decisive. They should enable the refinement of certain mathematical models that reproduce the phenomenon of rock degradation. “Tomography allows you to see where crystals and liquids are located in matter. But that doesn’t tell us the concentration of salt in the crystals or the temperature of the ice. This information is provided by mathematical models.», the researcher points out. Another challenge in this area of research remains better collaboration between researchers and construction professionals. “This dialogue is necessary so that we know what we can do as researchers and so that we do not get lost in non-operational solutions.“, she concludes. Cooperation, which could therefore be the key to a well-preserved heritage. ♦