Thesis Defense – Ghida Karbala

Thesis Defense – Ghida Karbala

Ghida Karbala, PhD student in the Multi-Scale team at the Navier laboratory, will defend their thesis entitled “Hydromechanical Behavior of Earthen Plasters Containing Swelling Clays during Drying” on Friday, October 02, 2026 at 2:00 PM, at Cécile Poisson Auditorium at the Georges Perec Library.

The defense will be held in english.

The defense will be broadcast at the following link: https://univ-eiffel.zoom.us/j/81614159284?pwd=pRLye1SFUNnkcog742lYYM4Q0kU5Nk.1

Thesis Jury

The thesis jury is composed of the following members:

  • Paulina Faria, NOVA University Lisbon, Reviewer
  • Antonin Fabbri, Lyon University, Reviewer
  • Myriam Duc, Gustave Eiffel University, Examiner
  • Stefano Dal Pont, Université Grenoble Alpes, Examiner
  • Anh-Minh Tang, Ecoles national des ponts et chausses, Invited
  • Patrick Belin, Gustave Eiffel University, Invited

Thesis Abstract

Earthen plasters are sustainable construction materials, but their use is limited by water sensitivity, shrinkage, cracking, and fresh-state instability. These challenges increase when swelling clays are present, due to their strong interaction with water and highly shrinkage behavior. This thesis, therefore, examines how montmorillonite affects the drying, shrinkage, and cracking behavior of earthen plasters.
The earth plaster formulations covered montmorillonite contents from 5% to 100%. Drying experiments under controlled airflow, combined with Magnetic Resonance Imaging (MRI), showed that the formulations follow a classical porous-media drying behavior, with a constant rate regime followed by a falling-rate regime. This transition is linked to the development of water content gradient across the sample height. As montmorillonite content increases, drying becomes more heterogeneous and internal liquid transport becomes limited from earlier stages.
An MRI-based inverse method was developed to quantify effective permeability during drying by combining MRI water content profiles, capillary pressure measurements, and Darcy’s law. This approach extends permeability measurements beyond conventional methods to lower water contents. The results show that permeability decreases strongly with water loss and is further reduced as the montmorillonite content increases.
Shrinkage of thin plaster slabs was then investigated during drying. The slabs exhibited a curling sequence, favored by higher montmorillonite content and faster drying, whereas sand addition reduced this deformation. This behavior was attributed to internal pressure gradients and the material’s evolving viscoelastic properties.
Cracking experiments showed that the addition of montmorillonite increased shrinkage and cracking sensitivity. The local slab thickness influenced crack development, while clay-rich formulations produced denser crack networks.
During the drying experiments, bleeding was observed in fresh earthen plasters. This phenomenon was therefore investigated using X-ray radiography, and the associated settlement behavior was interpreted within a self-weight consolidation framework. This analysis made it possible to distinguish the deformation caused by settlement from the shrinkage induced by capillarity.
Overall, this thesis shows that montmorillonite plays a central role in controlling the fresh-state stability and drying behavior of earthen plasters. By linking drying kinetics, internal water transport, permeability, shrinkage, curling, cracking, and bleeding, this work provides a physical framework for understanding the behavior of clay-rich earthen materials and supports the future development of more controlled and durable earthen plaster formulations.

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