Numerical and experimental study of desiccation cracks formation during convective drying of porous materials: application to geomechanics and chemical engineering

PhD researcher: J. Hubert

Promotor: F. Collin 

 

Abstract

This PhD project aims to improve our understanding of the mechanisms behind cracking/fracturing of porous deformable materials during convective drying or desiccation.  Its strength lies in the collaboration of teams from the geomechanical (Geo³) and chemical engineering (LGC) departments.

 

For geomaterials, Boom Clay is studied in the in the context of nuclear waste disposal in excavated damage zones. Given the importance of insuring good sealing conditions, the potential host rock - Boom clay - response to the stresses induced by the excavation of the galleries and the storage of high activity waste has been thoroughly studied. Yet more work is needed to characterize the drying behavior, a coupled thermo-hydro-mechanical process between the host rock and the ventilation air, in order to guarantee the storage capability of the host rock.

 

Indeed, the ventilation needed during the construction and operation phases could induce a desaturation of the host rock and, in turn, lead to cracking and thus to the loss of the sealing properties. The goal is, thus, to study the behavior of geomaterials under forced flow circulation and to be able to predict cracks occurrence.

 

For chemical engineering applications, tests will be performed on resorcinol-formaldehyde resins, following previous works from the LGC. The objective is to establish a link between manufacturing parameters, microstructure, drying conditions and product final quality, defined by the absence of cracks.

 

An experimental campaign based on the use of 3D images acquired by X-ray microtomography is conducted to characterize textural changes during convective drying. This requires the development of accurate and robust image analysis methods to highlight the links between microstructure, effective mechanical properties, and crack susceptibility.

 

From a modelling point of view, constitutive laws must first be established to incorporate cracking phenomena in the thermo-hydro-mechanical models developed in the finite element code LAGAMINE.

 

 

 

 

 

 

 

 

 

 

Figure 1 : Cracks formation and propagation as observed using an X-ray microtomography during the convective drying of Boom Clay sample

 

Partners

  • Main research team:
    • Equipe de géomécanique du département ArGEnCo, secteur Geo³, ULg
    • Field: geomechanics : experimental and numerical modeling of geomaterial behavior and geotechnical work.
    • Specialty: Development of the finite element framework LAGAMINE which allows for multiphysics and coupled modelization.
  • In collaboration with:
    • Laboratoire de Génie Chimique, Department of Chemical Engineering, ULg.
    • Field : Chemical engineering,

Specialty: Convective drying of porous material with study of the textural changes (shrinkage, cracking) using X-ray microtomography.

 

Funding

The thesis is funded by the F.R.S-FRNS (PDR T.1094.14). This PhD research is part of the projet intitled "Etude expérimentale et numérique de la fissuration lors du séchage de matériaux poreux : applications dans les domaines du génie chimique et de la géomécanique" (Frédéric Collin, Angélique Léonard).

 

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