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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

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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

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

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Major Deterioration Processes in Concrete Mechanism Abbrev- iation Expansive Phase Formula Delayed Ettringite Formation DEFEttringite(CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) 32 Alkali Silica ReactionASRASR Gel Na 2 OxSiO 2 yH 2 O x = 4-22 y = 5-10 Freeze-thaw cyclesF-TIceH2OH2O Rebar corrosion-RustFe 2 O 3 nH 2 O, FeO(OH) or Fe(OH) 3

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Single Spherical Aggregate Model E. Garboczi, CCR, 1997

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Signatures of Expansion Types Based on the Garboczi Model Expansion TypeMechanismCrack TypeGap Thickness Uniform matrixDEF? F-T?Circumferential Aggregate radius Rim onlyDEF?Circumferential Aggregate radius Aggregate onlyASR, F-T?RadialNone

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

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Neutron vs X-ray Attenuation 8

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

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Neutron Attenuation Coefficients of Common Phases in Concrete PhaseFormula Molecular weight g/mol H fraction Density g/cm 3 H density Atoms/cm 3 Attenuation coefficient* cm -1 QuartzSiO 2 60.0902.6500.284 LimestoneCaCO3100.0902.7200.258 CSH gel a (CaO) 1.7 (SiO 2 )(H 2 O) 1.8 187.830.0192.610.04992.731 Calcium hydroxide Ca(OH) 2 74.080.0272.230.06023.193 Ettringite(CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) 32 1254.620.0511.770.09034.675 ASR gel b Na 2 OxSiO 2 y H 2 O x = 4-22 y = 5-10 214.08 - 1563.78 0.012 - 0.032 1.93 2.46 0.0314 - 0.0631 1.833 - 3.355 Water iceH2OH2O18.000.1110.90.10005.081 a Allen et al. 2007 b Broeckmann, 2012 *Attenuation for bound H at 0.18 nm wavelength 10

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NIST Neutron Imaging Facility 11

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n Target Rotating stage Converter screen Mirror CCD Camera h Neutron Camera

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Steam Curing and DEF Primary ettringite forms during early hydration Normal concrete curing temperatures 30 - 40 C Steam curing at pre-cast plant 80 90 C Hypothesis Ettringite decomposes ~ 70C In the field ambient moisture causes ettringite to reform DEF

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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

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Concrete Test Prism Measurement point

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Simulated Steam Curing

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Initial Thermal Cycling

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Water Storage

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Expansion of Concrete Prisms 19 High PotassiumControl

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Drilling of 2 inch Cores 20

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Raw Neutron Image Scan Image Capture Pixel Pitch = 25 m 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 10 7 cm 2 /s 6 cm 7 cm

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Bright rims around aggregates 5 cm Tomographic Image of Core 22

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Bright rims around aggregates 5 cm Ca SAl O Tomographic Image of Core 23

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

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Areal Fractions of Concrete Phases % Porosity14.0 Aggregates70.0 Paste22.0 Ettringite3.0 Sum100 False Color Image 25

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Internal H Standard Cement Phase Attenuation Coefficient cm -1 Plastic Attenuation Coefficient cm -1 CSH Gel2.73Polycarbonate3.31 Calcium hydroxide3.19Polystyrene3.96 Ettringite4.67Polyethylene6.86

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Major Deterioration Processes in Concrete Mechanism Abbrev- iation Expansive Phase Formula Delayed Ettringite Formation DEFEttringite(CaO) 3 Al 2 O 3 (CaSO 4 ) 3 (H 2 O) 32 Alkali Silica ReactionASRASR Gel Na 2 OxSiO 2 yH 2 O x = 4-22 y = 5-10 Freeze-thaw cyclesF-TIceH2OH2O Rebar corrosion-RustFe 2 O 3 nH 2 O, FeO(OH) or Fe(OH) 3

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Conclusions Neutron imaging can identify concrete hydrous phases Neutron tomography can capture 3-D spatial relationships among phases at 20 m 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

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Richard A. Livingston: rliving1@umd.edu Thank you for your attention!