Neutron Tomography Measurement of Delayed Ettringite Formation in Concrete

Transcription

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 DelayedEttringite Formation Abbreviation Expansive Phase Alkali Silica Reaction ASR ASR Gel Formula DEF Ettringite (CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) 32 Freeze-thaw cycles F-T Ice H 2 O Na 2 O xsio 2 yh 2 O x = 4-22 y = 5-10 Rebar corrosion - Rust Fe 2 O 3 nh 2 O,FeO(OH)orFe(OH) 3

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

6 Signatures of Expansion Types Based on the Garboczi Model Expansion Type Mechanism Crack Type Gap Thickness Uniform matrix DEF? F-T? Circumferential Aggregate radius Rim only DEF? Circumferential 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 8

9 Comparison of X-ray and Neutron Radiographs X-ray Neutrons 9

10 Phase Neutron Attenuation Coefficients of Common Phases in Concrete Formula Molecular weight g/mol H fraction Density g/cm 3 H density Atoms/cm 3 Attenuation coefficient* cm -1 Quartz SiO Limestone CaCO CSH gel a (CaO) 1.7 (SiO 2 )(H 2 O) Calcium hydroxide Ca(OH) Ettringite (CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) ASR gel b Na 2 O xsio 2 y H 2 O x = 4-22 y = Water ice H 2 O a Allenet al b Broeckmann, 2012 *Attenuation for bound H at 0.18 nm wavelength 10

11 NIST Neutron Imaging Facility 11

12 Neutron Camera Converter screen Mirror hν Target n Rotating stage CCD Camera

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

14 Sample Preparation Two batches of concrete from same mix Control Potassium added, 1.2% as K 2 CO 3 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 19

20 Drilling of 2 inch Cores 20

21 Raw Neutron Image Scan Neutron Beam L/D = 450 Fluence = 1.3 x 10 7 cm 2 /s 7 cm 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 6 cm

22 Tomographic Image of Core Bright rims around aggregates 22

23 Tomographic Image of Core Bright rims around aggregates O Ca AlS 23

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

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

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

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28 Major Deterioration Processes in Concrete Mechanism DelayedEttringite Formation Abbreviation Expansive Phase Alkali Silica Reaction ASR ASR Gel Formula DEF Ettringite (CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) 32 Freeze-thaw cycles F-T Ice H 2 O Na 2 O xsio 2 yh 2 O x = 4-22 y = 5-10 Rebar corrosion - Rust Fe 2 O 3 nh 2 O,FeO(OH)orFe(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! Richard A. Livingston: