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
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
Outline Concrete deterioration mechanisms Neutron tomography DEF case study Results Calibration methods Conclusions
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 = 4-22 y = 5-10 Freeze-thaw cycles F-T Ice H2O Rebar corrosion - Rust Fe2O3·nH2O, FeO(OH) or Fe(OH)3
Single Spherical Aggregate Model E. Garboczi, CCR, 1997
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
Conventional Analytical Methods X-ray diffraction Thermal analysis Scanning electron microscopy Fracture surface Polished section
Neutron vs X-ray Attenuation
Comparison of X-ray and Neutron Radiographs Neutrons
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 1254.62 0.051 1.77 0.0903 4.675 ASR gelb Na2O∙xSiO2∙y H2O 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 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
NIST Neutron Imaging Facility
Neutron Camera n Converter screen Target hn Mirror Rotating stage CCD Camera hn
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 ~ 70°C In the field ambient moisture causes ettringite to reform → DEF
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
Concrete Test Prism Measurement point
Simulated Steam Curing
Initial Thermal Cycling
Water Storage
Expansion of Concrete Prisms High Potassium Control
Drilling of 2 inch Cores
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
Tomographic Image of Core Bright rims around aggregates 5 cm
Tomographic Image of Core Bright rims around aggregates 5 cm Ca S Al O
Segmentation of Tomographic Slice Grayscale 2-D slice through tomographic volume Histogram of grayscale values segmented by concrete phase.
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
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
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 = 4-22 y = 5-10 Freeze-thaw cycles F-T Ice H2O Rebar corrosion - Rust Fe2O3·nH2O, FeO(OH) or Fe(OH)3
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
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