Pietro Lura, Ye Guang, Kyoji Tanaka, and Ole Mejlhede Jensen Microcrack Detection in...
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![Page 1: Pietro Lura, Ye Guang, Kyoji Tanaka, and Ole Mejlhede Jensen Microcrack Detection in High-Performance Cementitious Materials.](https://reader036.fdocuments.net/reader036/viewer/2022062322/56649f4d5503460f94c6d6e0/html5/thumbnails/1.jpg)
Pietro Lura,Ye Guang, Kyoji Tanaka,and Ole Mejlhede Jensen
Microcrack DetectionMicrocrack Detectionin High-Performance in High-Performance
Cementitious MaterialsCementitious Materials
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Early-age crackingEarly-age cracking
Tokyo Institute of Technology, Yokohama, Japan
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MicrocrackingMicrocracking
(Bisschop & van Mier 2002)
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DefinitionsDefinitions
(Jensen & Hansen 2001)solid
water
air
Chemicalshrinkage
Autogenousshrinkage
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Autogenous shrinkage in Autogenous shrinkage in HPCHPC
- Less water
- More cement
- Silica fume
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Internal microcrackingInternal microcracking
• Does autogenous shrinkage lead to internal cracks?
• How to detect them?
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Superabsorbent polymers Superabsorbent polymers (SAP)(SAP)
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Autogenous relative humidityAutogenous relative humidity
Paste C (w/c 0.30 + 20% SF +0.6% SAP)
Paste A (w/c 0.35)
Paste B (w/c 0.30 + 20% SF)
75
80
85
90
95
100
0 7 14 21 28
Time (days)
Rel
ativ
e h
um
idit
y (%
)
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-3000
-2000
-1000
0
1000
0 7 14 21 28
Time (days)
Au
tog
en
ou
s s
tra
in (
µm
/m)
Autogenous strainAutogenous strain
Paste C (w/c 0.30 + 20% SF +0.6% SAP)
Paste A (w/c 0.35)
Paste B (w/c 0.30 + 20% SF)
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Samples for crack detectionSamples for crack detection
Stainless steel rod
12 m
m
10 mm
- 3 cement pastes- 1.5, 3, and 6-mm rods- sealed at 32C
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Properties of GalliumProperties of Gallium
- melting point 29.8 C- does not wet cement paste- nontoxic
0.01
0.1
1
10
0.1 1 10 100
Intrusion pressure [MPa]
Po
re d
iam
eter
[µ
m]1.2 µm
1.6 MPa
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Gallium intrusionGallium intrusion
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Sample preparationSample preparation
- epoxy resin- grinding- polishing- crack examination: - optical microscope
- BSE - EPMA
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Crack detection (1)Crack detection (1)
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Crack detection (2)Crack detection (2)
Agglomerate
Gallium
Steel bar
CSH gel
Unhydrated cement Crack
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ConclusionsConclusions
• Cracks before intrusion can be distinguished
• High shrinkage, big rod Cracks
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Further researchFurther research
• EPMA
• Acoustic Emission
• FE calculations