Microcrack detection in high performance cementitious materials
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Microcrack Detection in High-Performance Cementitious Materials. Pietro Lura, Ye Guang, Kyoji Tanaka, and Ole Mejlhede Jensen. Early-age cracking. Tokyo Institute of Technology, Yokohama, Japan. Microcracking. (Bisschop & van Mier 2002). Chemical shrinkage. Autogenous shrinkage.

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Microcrack Detection in High-Performance Cementitious Materials

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Microcrack Detectionin High-Performance Cementitious Materials

Pietro Lura,

Ye Guang, Kyoji Tanaka,

and Ole Mejlhede Jensen


Early-age cracking

Tokyo Institute of Technology, Yokohama, Japan


Microcracking

(Bisschop & van Mier 2002)


Chemical

shrinkage

Autogenous

shrinkage

Definitions

(Jensen & Hansen 2001)

solid

water

air


Autogenous shrinkage in HPC

  • Less water

  • More cement

  • Silica fume


Internal microcracking

  • Does autogenous shrinkage lead to internal cracks?

  • How to detect them?


Superabsorbent polymers (SAP)


Autogenous 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)


Autogenous 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)


Samples for crack detection

- 3 cement pastes

  • 1.5, 3, and 6-mm rods

  • sealed at 32C


10

1.2 µm

]

1

m

µ

[

r

e

t

e

m

a

i

d

e

0.1

r

o

P

0.01

1.6 MPa

0.1

1

10

100

Intrusion pressure [MPa]

Properties of Gallium

- melting point 29.8 C

  • does not wet cement paste

  • nontoxic


Gallium intrusion


Sample preparation

  • epoxy resin

  • grinding

  • polishing

  • crack examination: - optical microscope

    - BSE

    - EPMA


Crack detection (1)


Crack detection (2)


Conclusions

  • Cracks before intrusion can be distinguished

  • High shrinkage, big rod  Cracks


Further research

  • EPMA

  • Acoustic Emission

  • FE calculations


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