Pietro Lura,Ye Guang, Kyoji Tanaka,and Ole Mejlhede Jensen

Microcrack DetectionMicrocrack Detectionin High-Performance in High-Performance

Cementitious MaterialsCementitious Materials

Early-age crackingEarly-age cracking

Tokyo Institute of Technology, Yokohama, Japan

MicrocrackingMicrocracking

(Bisschop & van Mier 2002)

DefinitionsDefinitions

(Jensen & Hansen 2001)solid

water

air

Chemicalshrinkage

Autogenousshrinkage

Autogenous shrinkage in Autogenous shrinkage in HPCHPC

- Less water

- More cement

- Silica fume

Internal microcrackingInternal microcracking

• Does autogenous shrinkage lead to internal cracks?

• How to detect them?

Superabsorbent polymers Superabsorbent polymers (SAP)(SAP)

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 (%

)

-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)

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

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

Gallium intrusionGallium intrusion

Sample preparationSample preparation

- epoxy resin- grinding- polishing- crack examination: - optical microscope

- BSE - EPMA

Crack detection (1)Crack detection (1)

Crack detection (2)Crack detection (2)

Agglomerate

Gallium

Steel bar

CSH gel

Unhydrated cement Crack

ConclusionsConclusions

• Cracks before intrusion can be distinguished

• High shrinkage, big rod Cracks

Further researchFurther research

• EPMA

• Acoustic Emission

• FE calculations