1. Neutron Tomography Measurement of Delayed Ettringite Formation in Concrete
Richard A. Livingston
Materials Science & Engineering Dept
University of Maryland
14th ISNDCM
Marina del Rey, CA, June 24, 2015

2. Co-Authors
Amde M. Amde & Serge Feuze Civil Engineering Dept., U. of Maryland Daniel Hussey & David Jacobson Physical Measurement Laboratory, NIST Acknowledgements John Newman, Laser Technologies, Inc Stewart Sherman, National Ready Mix Concrete Association

3. Outline Concrete deterioration mechanisms Neutron tomography
DEF case study
Results
Calibration methods
Conclusions

4. Major Deterioration Processes in Concrete
Mechanism
Abbrev- iation
Expansive Phase
Formula
Delayed Ettringite Formation
DEF
Ettringite
(CaO)3∙Al2O3(CaSO4)3∙(H2O)32
Alkali Silica Reaction
ASR
ASR Gel
Na2O∙xSiO2∙yH2O
x = y = 5-10
Freeze-thaw cycles
F-T
Ice
H2O
Rebar corrosion -
Rust
Fe2O3·nH2O, FeO(OH) or Fe(OH)3

5. Single Spherical Aggregate Model
E. Garboczi, CCR, 1997

6. Signatures of Expansion Types Based on the Garboczi Model
Mechanism
Crack Type
Gap Thickness
Uniform matrix
DEF? F-T?
Circumferential
≈ Aggregate radius
Rim only
DEF?
≠ Aggregate radius
Aggregate only
ASR, F-T?
Radial
None

7. Conventional Analytical Methods
X-ray diffraction
Thermal analysis
Scanning electron microscopy
Fracture surface
Polished section

8. Neutron vs X-ray Attenuation

9. Comparison of X-ray and Neutron Radiographs
Neutrons

10. Neutron Attenuation Coefficients of Common Phases in Concrete
Formula
Molecular weight
g/mol
H fraction
Density g/cm3
H density Atoms/cm3
Attenuation coefficient*
cm-1
Quartz
SiO2
60.09
2.65
0.284
Limestone
CaCO3
100.09
2.72
0.258
CSH gela
(CaO)1.7(SiO2)(H2O)1.8
187.83
0.019
2.61
0.0499
2.731
Calcium hydroxide
Ca(OH)2
74.08
0.027
2.23
0.0602
3.193
Ettringite
(CaO)3∙Al2O3(CaSO4)3∙(H2O) 32
0.051
1.77
0.0903
4.675
ASR gelb
Na2O∙xSiO2∙y H2O
x = y = 5-10
0.032
1.93 – 2.46
0.0631
3.355
Water ice
H2O
18.00
0.111
0.9
0.1000
5.081
aAllen et al. 2007
bBroeckmann, 2012
*Attenuation for bound H at
0.18 nm wavelength

11. NIST Neutron Imaging Facility

12. Neutron Camera n Converter screen Target hn Mirror Rotating stage
CCD Camera hn

13. Steam Curing and DEF Primary ettringite forms during early hydration
Normal concrete curing temperatures ° C
Steam curing at pre-cast plant 80 – 90° C
Hypothesis
Ettringite decomposes ~ 70°C
In the field ambient moisture causes ettringite to reform → DEF

14. Sample Preparation Two batches of concrete from same mix
Control
Potassium added, 1.2% as K2CO3
Cast as prisms 3” x 3” x 11”
Two curing conditions
Room temperature
Steam cured
J. Newman, FHWA SBIR, 2011

15. Concrete Test Prism
Measurement point

16. Simulated Steam Curing

17. Initial Thermal Cycling

18. Water Storage

19. Expansion of Concrete Prisms
High Potassium
Control

20. Drilling of 2 inch Cores

21. Raw Neutron Image Scan Image Capture Pixel Pitch = 25 μm
Rotation step = 0.1°
Range = 180°
Image scan time ~15 sec.
Replicate scans = 3
Total acquisition time = 26 hrs
Neutron Beam
L/D = 450
Fluence = 1.3 x 107 cm2/s
7 cm
6 cm

22. Tomographic Image of Core
Bright rims around aggregates
5 cm

23. Tomographic Image of Core
Bright rims around aggregates
5 cm Ca S Al O

24. Segmentation of Tomographic Slice Grayscale
2-D slice through tomographic volume
Histogram of grayscale values segmented by concrete phase.

25. Areal Fractions of Concrete Phases
False Color Image
Areal Fractions of Concrete Phases
%  
Porosity
14.0
Aggregates
70.0
Paste
22.0
Ettringite
3.0
Sum
100

26. Internal H Standard Cement Phase Attenuation Coefficient cm-1 Plastic
CSH Gel
2.73
Polycarbonate
3.31
Calcium hydroxide
3.19
Polystyrene
3.96
Ettringite
4.67
Polyethylene
6.86

28. Major Deterioration Processes in Concrete
Mechanism
Abbrev- iation
Expansive Phase
Formula
Delayed Ettringite Formation
DEF
Ettringite
(CaO)3∙Al2O3(CaSO4)3∙(H2O)32
Alkali Silica Reaction
ASR
ASR Gel
Na2O∙xSiO2∙yH2O
x = y = 5-10
Freeze-thaw cycles
F-T
Ice
H2O
Rebar corrosion -
Rust
Fe2O3·nH2O, FeO(OH) or Fe(OH)3

29. Conclusions Neutron imaging can identify concrete hydrous phases
Neutron tomography can capture 3-D spatial relationships among phases at 20 μm resolution
Exhaustive volumetric sampling enables highly precise materials characterization
Nondestructive nature makes it possible to observe reactions among phases over time
Limitations include scarce beam time at neutron facilities

30. Thank you for your attention!
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