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8/10/2019 Presentation 17102014
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Literature review on the study ofchanges in pore size distributionof clay upon loading
Jun Kang ChowSupervisor: Prof. YH Wang
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Interpret the changes in poresize distribution of clay
during the loading processes.
Preconsolidation
SEM MIP
Loading
Freeze drying
Washing
Adjust properties
Direct observation(from SEM)
Measurement (from MIP)+
Current stage of research(Wang, Y.H. & Xu, D., 2007; Wang, Y.H. & Yu, C.Y.,
(unpublished)) Sample : Speswhite
kaolin
Mechanical responses of kaolinite claydepend on cluster-to-cluster interactions
rather than particle-to-particle interactions
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Samples obtained before andafter loading for MIP test arenot identical .Freeze-drying process mayalter the pore sizedistribution of clayspecimens.
Preconsolidation
SEM MIP
Loading
Freeze drying
Washing
Adjust properties
Results of MIP test show thatlarger pores reduce in size after
loading.
This does not guarantee thepores involved are inter-aggregated pores .
PROBLEMS ?
Current stage of research(Wang, Y.H. & Xu, D., 2007)
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~ 0.42 m (pore C of pH 4 spec.)~ 0.18 m (pore B of spec. withsalt)
~ 1.22 m (pore D of spec. withsalt)
~ 0.42 m (pore B of pH 7.8spec.)
Existence of smaller/larger Types B, C and D pores than thesizes indicated.SEM image shows that particles that form aggregatedassociations can be unevenly arranged, creating larger intra-
aggregates pores .
Result of MIP test(Wang, Y.H. & Xu, D., 2007)
Figure is taken from Wang, Y.H. and Xu, D.(2007)
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We are unable to observe
the loading process.
We are unable to visualize
how the arrangement of clayfabric is altered due toloading.
To search the suitable method thatallows the visualization of changes
in clay fabric arrangement upon
loading
HOW?
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Methods to study pore sizedistribution of clay
Directobservation
Measurementtechnique
Scanning ElectronMicroscope (SEM)EnvironmentalScanning ElectronMicroscope (ESEM)X-ray computedtopography (CTscanning)
Mercury IntrusionPorosimetry (MIP)Nitrogen sorptionmethod
Non-polar liquiddesorptionWater-desorption
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Systematic errors due to:Inappropriate pore model (assuming cylindrical pore model)Variation in surface tension and contact angle
Measurement of pore size distribution of clay (Lawrence, G.P., 1977; Westermack, S., 2000)
Mercury intrusionporosimetry
Nitrogen sorption Non-polar liquiddesorption
Water desorption
Measure poresize of ~ 3 nm 200 mMeasure thepressure requiredto force mercuryinto poresErrors due to:distribution ofpore volume andpore collapse
Carried out atlow temperature(~ -196 C)Able todetermine rangeof pore size ~ 0.3- 300 nm
Interactionsbetween non-polar liquidsand claysurfaces are
weakEquilibriumtimes are long
Most fine-textured soilsshrink andparticlerearrangement
takes placeStresses onpore wallsduring anincrease insuction cause a
reduction inpore size
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A pore system cannot be adequatelycharacterised by the use of only onemethod.Combine both methods to measure thepore size distribution of clay. (Sills, I.D. etal. 1973a, 1974)
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Technology available
At this T, only a modest gas pressure isrequired to stabilize water (achieve saturation)
Method
Focus
Type of samples
Sample Size
Preparation
Resolution
Workingtemperature
SEM
Morphology ofmaterials
Dry samples(Absence of water)
~ few mm indiameter
Freeze-drying &coating of samples
are required
~
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An electron beam is emittedtowards a conductive sample inhigh vacuum conditions .
Secondary electrons are releasedfrom the sample, collected bydetector and amplified to producean image.
The conductive coating of sample(gold) improves the image quality.
The vacuum ensures the effectiveoperation of the electron gun.
Working principle of SEM
(Absence ofwater)
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Working principle of ESEM When electrons are emitted, theyhave to travel through the ga s .
Secondary electrons (with lowenergies) have a high collisioncross-section with the gas
molecules.Ionizing collisions lead to thegeneration of addition daughterelectrons a cascadeamplification . At the same time, positive ions arealso produced.
These ions drift down towards thesample compensate the chargebuild-up at the surface of insulators.
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ESEM Quanta 250 FEI NanoCharacterization
Metals & alloys,magnetic &superconductingmaterials
Ceramics, composites,plasticsFilms/coatingsGeological materials
mineralsSoft materials polymers, gels,tissues, plant
Particle, porousmaterials fibers
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Application of ESEM Journal Description
Montes-H, G. et al.(2005) To study the swelling-shrinkage behavior of compactedbentonite submitted to hydration/dehydration conditions
Vaunat, J. et al. (2007) To study the residual shear strength of a plastic clay(Boom clay) under high suction
Zhang, G. et al. (2004) To study how Fe oxides alter the soil structure of a
highly weathered oil alluviumSelvam, A. &Barkdoll, B. (2005)
To observe changes in clay fabric using ESEM &correlate it to the permeability changes occurring in clay
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One Sample
Preparation Stage:WashingAdjusting
PropertiesPreconsolidation
Loading
ESEM
Varyloading
Many Samples
Preconsolidation
SEM MIP
Loading
Freeze drying
Washing
Adjust properties
Future work/Challenge:
Design of cellDigital imageanalysis