Vidi grant: Understanding the behaviour of clays
Anne-Catherine Dieudonné receives a NWO Vidi grant to study the interaction between water and clays. Predicting the time-dependent behaviour of clays has been a major challenge so far. By focusing on the distribution and properties of water in clays, it will become clear how clays behave under stress with time.
Clays, widely present in the subsurface, are complex materials. Their high compressibility, sensitivity to water content changes (leading to swelling, shrinkage and cracking), and delayed response to stress changes pose challenges for construction projects and infrastructures. But the special properties of clays are also useful. Thanks to their low permeability and high retention capacity, clays act as effective barriers against the flow of water and the transport of pollutants. This is why it makes them essential components of dykes and landfills, and why the Dutch government is interested in disposing radioactive waste, from nuclear energy production and medical treatments for example, in a permanent underground facility.
Clay under stress
It is crucial to understand the behaviour of clay, now and in the long term. And there is still a lot to discover, according to Anne-Catherine Dieudonné, assistant professor at Geoscience & Engineering. To study the mechanical behaviour of clays, samples are loaded in the lab. “Clays have a very fine microstructure. So far, it is impossible to follow the physics of clay particles under stress on such a small scale.”
Static properties of clay cores are studied using CT scanning techniques.
Follow the shadow
Because clay particles are negatively charged, they attract water at their surface. This makes the density of the water much higher than that of tap water or water in sand. Dieudonné aims to study the distribution and properties of water molecules in clays and use this as a proxy for clay microstructure. Since the movement of the clay itself cannot be tracked directly, she therefore follows its shadow, so to say.
Anne-Catherine Dieudonné is excited: “We know that water behaves differently in clay. But for lack of better, we model with standard liquid water properties. Once we succeed in understanding the interaction between water and clay, we can reinterpret existing experimental results. This has the potential to yield groundbreaking new insights.”
Clay as an eternal repository?
Radioactive waste can be harmful to people and the environment for millennia. Therefore, it is crucial to design safe disposal facilities that can stand the test of time. Clay layers are interesting for several reasons. They have low permeability, high sorption capacity, and are self-healing.
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