LP
Leo Pel
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6 records found
1
In this article, we study the self-weight consolidation behavior of kaolinite suspensions with different concentrations in deionized water using nuclear magnetic resonance (NMR). NMR enables the direct assessment of density distributions and pore size within the consolidating suspensions. The results show that electrochemical conditions (pH and ionic strength), arising from ion leaching from the kaolinite, influence the consolidation dynamics, in agreement with previous studies. The evolution of the density profile over time is interpreted using a large-strain consolidation model based on the Gibson–Merckelbach formulation. The model is implemented in both Eulerian and Lagrangian frameworks, allowing a comparison between these two approaches. A key observation from the NMR measurements is that the solid volume fraction reaches a maximum value at the base of the column. This behavior is not captured by the classical Merckelbach–Kranenburg constitutive model, highlighting its limitations in highly compacted regimes. To account for this effect, a simple modification based on a reduction in permeability is introduced. This modification can be interpreted as a hydraulic limitation, as it leads to vanishing fluid fluxes and prevents further densification. The comparison between experimental and numerical results shows that this approach improves the agreement with the measured density profiles. In addition, the model captures the main trends of the pore size distribution measured by NMR, although some discrepancies remain in magnitude. Overall, the combined experimental–numerical approach provides new insight into the applicability and limitations of Gibson–Merckelbach consolidation models for fine-grained suspensions.
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In this article, we study the self-weight consolidation behavior of kaolinite suspensions with different concentrations in deionized water using nuclear magnetic resonance (NMR). NMR enables the direct assessment of density distributions and pore size within the consolidating suspensions. The results show that electrochemical conditions (pH and ionic strength), arising from ion leaching from the kaolinite, influence the consolidation dynamics, in agreement with previous studies. The evolution of the density profile over time is interpreted using a large-strain consolidation model based on the Gibson–Merckelbach formulation. The model is implemented in both Eulerian and Lagrangian frameworks, allowing a comparison between these two approaches. A key observation from the NMR measurements is that the solid volume fraction reaches a maximum value at the base of the column. This behavior is not captured by the classical Merckelbach–Kranenburg constitutive model, highlighting its limitations in highly compacted regimes. To account for this effect, a simple modification based on a reduction in permeability is introduced. This modification can be interpreted as a hydraulic limitation, as it leads to vanishing fluid fluxes and prevents further densification. The comparison between experimental and numerical results shows that this approach improves the agreement with the measured density profiles. In addition, the model captures the main trends of the pore size distribution measured by NMR, although some discrepancies remain in magnitude. Overall, the combined experimental–numerical approach provides new insight into the applicability and limitations of Gibson–Merckelbach consolidation models for fine-grained suspensions.
This study presents a method to determine surface relaxivity in soft sediments by combining one-dimensional Nuclear Magnetic Resonance (NMR) imaging with particle size and shape estimates. In order to determine the surface relaxivity up to now often methods like Mercury Intrusion Porosimetry or Brunauer–Emmett–Teller (BET) are used which where drying steps are involved which can alter material properties during analysis, particularly in highly deformable materials, making these techniques unreliable for soft soils. By combining NMR relaxometry and estimates of particle sizes and shapes of a soft soil, this new approach provides accurate, non-invasive surface relaxivity measurements. This method is demonstrated on kaolinite, glass beads, and natural soils, showing that this method supports detailed assessment of pore size distributions in soft sediments, benefiting geotechnical and environmental research where soil stability is critical.
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This study presents a method to determine surface relaxivity in soft sediments by combining one-dimensional Nuclear Magnetic Resonance (NMR) imaging with particle size and shape estimates. In order to determine the surface relaxivity up to now often methods like Mercury Intrusion Porosimetry or Brunauer–Emmett–Teller (BET) are used which where drying steps are involved which can alter material properties during analysis, particularly in highly deformable materials, making these techniques unreliable for soft soils. By combining NMR relaxometry and estimates of particle sizes and shapes of a soft soil, this new approach provides accurate, non-invasive surface relaxivity measurements. This method is demonstrated on kaolinite, glass beads, and natural soils, showing that this method supports detailed assessment of pore size distributions in soft sediments, benefiting geotechnical and environmental research where soil stability is critical.
This study introduces a fast 1D nuclear magnetic resonance (NMR) imaging method based on multi-slice imaging with a stepper motor to study sedimentation dynamics of clayey soils. Traditional NMR is limited by long acquisition times due to water’s T1 relaxation time. Our approach combines multi-slice imaging with a stepper motor and frequency-based selection, reducing measurement time while maintaining sub-millimeter resolution, at the same time overcoming the limitations by the slow relaxation of water. This nondestructive method provides detailed insights into the sedimentation and consolidation of suspensions, including pore size distribution and density profiles within a single measurement. The technique is demonstrated with kaolinite clay suspensions, highlighting the technique’s ability to capture the dynamics of gravity-driven systems rapidly and accurately, even for fast-sedimenting soils such as kaolinite in the first hours of sedimentation. This advancement is valuable for geotechnical and environmental applications where understanding sedimentation is crucial.
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This study introduces a fast 1D nuclear magnetic resonance (NMR) imaging method based on multi-slice imaging with a stepper motor to study sedimentation dynamics of clayey soils. Traditional NMR is limited by long acquisition times due to water’s T1 relaxation time. Our approach combines multi-slice imaging with a stepper motor and frequency-based selection, reducing measurement time while maintaining sub-millimeter resolution, at the same time overcoming the limitations by the slow relaxation of water. This nondestructive method provides detailed insights into the sedimentation and consolidation of suspensions, including pore size distribution and density profiles within a single measurement. The technique is demonstrated with kaolinite clay suspensions, highlighting the technique’s ability to capture the dynamics of gravity-driven systems rapidly and accurately, even for fast-sedimenting soils such as kaolinite in the first hours of sedimentation. This advancement is valuable for geotechnical and environmental applications where understanding sedimentation is crucial.
Dewatering, which is the process of separating (colloidal) suspended particles from a solvent (usually water), is used in many engineering applications (sanitary engineering, dredging engineering…). Key questions associated with dewatering in the context of the reuse of dredged sediment are (1) what is the process kinetics, (2) how can these processes be optimized and (3) can the dewatered sludge be reused and for which application? Dewatering and consolidation are functions of the suspended particles’ size and type, and their solvent-mediated interaction. In this presentation, some examples will be given about the dewatering of suspensions and slurries as found in engineering applications. The presentation will focus on the behaviour of mineral clay suspensions (kaolinite, montmorillonite, illite…) composed of particles of different particle sizes. We will show that, depending on the particle size distribution and solvent properties, the system is either undergoing a slow sedimentation dominated by thermodynamic forces or a rapid sedimentation dominated by gravity. The sedimentation is followed in time using NMR and inferential image analysis, and the particles are characterized by size, density and electrokinetic charge. We show that the time evolution of the sedimentation behaviour can be modelled using an advection-diffusion equation. The advective term is a function of gravity, whereas the diffusion term represents either a hard-sphere repulsion or an effective stress, depending on whether thermodynamic forces dominate the system. We show that after solving this advection-diffusion equation numerically, the results based on the theory of Gibson does match the experimental data collected from NMR in the phase of slow kinetics. For the early stages of settling and consolidation, where the system kinetics are fast, we show that the data are contaminated by artifacts due to the limited time of signal acquisition imposed by the NMR method. We show that is possible to overcome those limitations by either sacrificing some information related to particle’s sizes using the NMR or by combining the NMR method with excess pore pressure measurements along the height of the settling columns.
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Dewatering, which is the process of separating (colloidal) suspended particles from a solvent (usually water), is used in many engineering applications (sanitary engineering, dredging engineering…). Key questions associated with dewatering in the context of the reuse of dredged sediment are (1) what is the process kinetics, (2) how can these processes be optimized and (3) can the dewatered sludge be reused and for which application? Dewatering and consolidation are functions of the suspended particles’ size and type, and their solvent-mediated interaction. In this presentation, some examples will be given about the dewatering of suspensions and slurries as found in engineering applications. The presentation will focus on the behaviour of mineral clay suspensions (kaolinite, montmorillonite, illite…) composed of particles of different particle sizes. We will show that, depending on the particle size distribution and solvent properties, the system is either undergoing a slow sedimentation dominated by thermodynamic forces or a rapid sedimentation dominated by gravity. The sedimentation is followed in time using NMR and inferential image analysis, and the particles are characterized by size, density and electrokinetic charge. We show that the time evolution of the sedimentation behaviour can be modelled using an advection-diffusion equation. The advective term is a function of gravity, whereas the diffusion term represents either a hard-sphere repulsion or an effective stress, depending on whether thermodynamic forces dominate the system. We show that after solving this advection-diffusion equation numerically, the results based on the theory of Gibson does match the experimental data collected from NMR in the phase of slow kinetics. For the early stages of settling and consolidation, where the system kinetics are fast, we show that the data are contaminated by artifacts due to the limited time of signal acquisition imposed by the NMR method. We show that is possible to overcome those limitations by either sacrificing some information related to particle’s sizes using the NMR or by combining the NMR method with excess pore pressure measurements along the height of the settling columns.
Journal article
(2017)
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Robert J. Flatt, Nevin Aly Mohamed, Noushine Shahidzadeh, Michael Steiger, Francesco Caruso, Hannelore Derluyn, Julie Desarnaud, Barbara Lubelli, Rosa Maria Espinosa-Marzal, Leo Pel, Carlos Rodriguez-Navarro, George W. Scherer
Salt crystallization represents one of the major causes for the degradation of building and ornamental stone. As such, it has attracted the attention of researchers, who over the years have progressively unraveled most mechanisms involved in salt damage. Despite this mechanistic understanding, many questions subsist about how to quantitatively predict damage or its progression, and in particular how to relate performance on site to that in laboratory tests.
In this context, a new RILEM TC 271‐ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage.
This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo‐mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial “induction” phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed “damage onset” is reached. Beyond this point, during the “propagation phase”, the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions. ...
In this context, a new RILEM TC 271‐ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage.
This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo‐mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial “induction” phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed “damage onset” is reached. Beyond this point, during the “propagation phase”, the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions. ...
Salt crystallization represents one of the major causes for the degradation of building and ornamental stone. As such, it has attracted the attention of researchers, who over the years have progressively unraveled most mechanisms involved in salt damage. Despite this mechanistic understanding, many questions subsist about how to quantitatively predict damage or its progression, and in particular how to relate performance on site to that in laboratory tests.
In this context, a new RILEM TC 271‐ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage.
This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo‐mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial “induction” phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed “damage onset” is reached. Beyond this point, during the “propagation phase”, the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions.
In this context, a new RILEM TC 271‐ASC has been started with the objective of defining laboratory tests that deliver more reliable predictions of field behavior. One deliverable of this TC is to provide a theoretical insight into this question based on recent progress on the understanding of salt damage.
This paper presents a summary of this work, highlighting key aspects relating to crystallization pressure, chemo‐mechanics and mass transport. Implications are discussed in relation to the most used accelerated salt crystallization tests in an attempt to better define which field exposure conditions that these tests best represent and may be used for, or define effective test procedures representing specific field conditions. A simple conceptual model for the development of salt damage is introduced. During an initial “induction” phase, transport of ions and accumulation of salt in the porous materials occurs without causing detectable damage until a critical point, termed “damage onset” is reached. Beyond this point, during the “propagation phase”, the material degrades, typically losing strength and cohesiveness. The implications of these two phases are discussed in relation to the selection of appropriate salt weathering tests and conservation interventions.
The aim of this study is to investigate the effect of water migration from cracks into the bulk paste on autogenous self-healing. Nuclear magnetic resonance (NMR) technique was utilized to monitor water migration from cracks into the bulk paste during the process of autogenous self-healing. NMR results show that initially the water in the crack migrates into the bulk paste and the water content of the bulk paste increases significantly. However, after 5-h autogenous self-healing, the amount of non-chemically bound water in the bulk paste (adjacent to the crack surfaces) determined by NMR decreased instead. It indicates that some of the water coming from the crack was used for additional hydration of unhydrated cement particles in the bulk paste (during the process of autogenous self-healing). Before this study, in term of autogenous self-healing only the recoveries that related to the filling of cracks were concerned. The observation and quantification of densification of cement paste adjacent to the crack surfaces provides a new insight into autogenous self-healing.
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The aim of this study is to investigate the effect of water migration from cracks into the bulk paste on autogenous self-healing. Nuclear magnetic resonance (NMR) technique was utilized to monitor water migration from cracks into the bulk paste during the process of autogenous self-healing. NMR results show that initially the water in the crack migrates into the bulk paste and the water content of the bulk paste increases significantly. However, after 5-h autogenous self-healing, the amount of non-chemically bound water in the bulk paste (adjacent to the crack surfaces) determined by NMR decreased instead. It indicates that some of the water coming from the crack was used for additional hydration of unhydrated cement particles in the bulk paste (during the process of autogenous self-healing). Before this study, in term of autogenous self-healing only the recoveries that related to the filling of cracks were concerned. The observation and quantification of densification of cement paste adjacent to the crack surfaces provides a new insight into autogenous self-healing.