QUANTIFICATION OF PORE STRUCTURE CHARACTERISTICS FOR DETERIORATED MORTAR DUE TO CALCIUM LEACHING BY SYNCHROTRON MICROTOMOGRAPHY

Transcription

1 QUANTIFICATION OF PORE STRUCTURE CHARACTERISTICS FOR DETERIORATED MORTAR DUE TO CALCIUM LEACHING BY SYNCHROTRON MICROTOMOGRAPHY Takafumi SUGIYAMA (Hokkaido Univ.) Michael A. B. PROMENTILLA (Hokkaido Univ.) Takashi HITOMI (Obayashi Co. ) Nobufumi TAKEDA (Obayashi Co. )

2 Material Degradation in Long Term Service Calcium leaching Degrading mechanical and transport properties Ro ck Bent nit e Sand and Clay Wast e Concret e Change of pore structure characteristics Cementit ious barrier Radioactive Waste Repository

3 Development for calculation model of ion transport in hydrated cement system (SiTraM in 23) Cl - C s C b Steady-state migration test τ δ ε Pore structure characteristic K + Ca 2+ J i n OH - s = D j= 1 ij C x Ion-Ion Interaction in pore solution j Na + C Ion-Solid Interactions C f Ca 2+ leaching Cl - binding Φ L Φ R Membrane potential Na + Na + Ca Ca 2+ K + Cl - Cl - Cl K + Electrical double layer

4 Significance of pore structure characteristics for material properties Strength Performance of Cement-based Materials Transport Properties of Cement-based Materials Pore Structure Characteristics 3D Micro-geometry Porosity, Diffusion Tortuosity

5 Pore Structure Characteristics of Cement-based Materials estimated from 3D Micro-geometry using Synchrotron Microtomography Methodology: Synchrotron microtomography Random Walk Simulation Application to deteriorated mortars and cement pastes Accelerated electrical tests for calcium leaching

6 Synchrotron Microtomography Bentz et al 2, Helfen et al. 25, Lu et al. 26, Burlion et al. 26, Koster 26, Gallucci et al. 27 SPring-8 (Japan) Same principle as medical CT scan Creates X-ray image of slice through object that can make 3D volume But higher-energy, more focused Synchrotron-based X- rays (higher spatial resolution) X-ray source is tunable, X-ray radiation is monochromatic, and X-ray beam is flat Applications Geology, Anthropology, Biology, Medicine, Engineering Advantage and Disadvantage 6/38

7 X-ray imaging of specimen SPring-8 3D reconstruction of image Pixel size =.5 micron 3D Image processing Extraction of 3D pore space Mathematica program (Nakashima et al.27) SLICE (Nakano et al., 27) Pore segmentation Pore cluster multiple labeling Visualization and quantification of porosity Quantification of tortuosity based on random walk simulation (RWS) 7/38

8 X ray Scanning of Specimen BL47XU X-Ray source Beam energy: 15 kev 2x13 px CCD 15 projections (18 rotation) Specimen CCD 1μm Rotating Stage 8/38

9 Mortar before deterioration Water to cement ratio:.5 Sand to cement ratio :2. Curing periods: 238days SLICE 4 1 µm

10 Extraction of 3D image (VOI) 3 x 3 pixels in 2D 3 x 3 x 3 pixels (VOI) Based on REV (Representative Elementary Volume) analysis 15 µm

11 Accelerated Electrical Method Direct current voltage Cathode Ca 2+ Anode Electrode (Pt) Cement paste Electrode (SUS) Ion-change water Ca 2+ Ion-change water Schematic diagram for accelerated electrical test Acceleration test underway using Acrylic cell 11/38

12 Distribution of CaO/SiO 2 ratio in cement hydrate (obtained by EPMA) EPMA) According to Saito et al. ACI Materials J Diffusion test Inner side After 2,days Surface Acceleration test After 2months under 5 V/cm Inner side Cathode side 2mm 8mm 6mm

13 Specimens under investigation W/C Cement Sand Chemical admixture Mortar.5 OPC Sieved under 21µm (S/C:2.) Super-plasticizer Cement paste.5 OPC Non Viscosity agent (cellulose-ether type) OPC: Ordinary Portland Cement JIS R521 Non-deteriorated mortar: 3 weeks in curing Deteriorated mortar: 2weeks in curing followed by acceleration test for 13weeks Cement paste: 2weeks in curing followed by acceleration test for13weeks 13/38

14 Deteriorated Mortar Non deteriorated Mortar 15 µm SLICE 5 SLICE 5

15 Porosity-Threshold dependency curve of VOI Deteriorated Mortar 1..1 segmented porosity At this transition point, the segmented porosity started to increase rapidly wherein the boundary between pore and the solid matrix is most likely to be segmented as pore space. Threshold value for segmentation norm. frequency GSV. 15/38

16 Deteriorated Mortar (D.M.) 16/38

17 (a) Grayscale image (b) Segmented image D. M. 15μm (White for Solid, Black for Pore) Non D. M.

18 Quantification of porosity Segmented porosity, ε t Connectivity γ Effective porosity, ε e ε t Total pore voxels Total voxels = ε e = ε t x γ No. of voxels of the largest percolating pore γ = 18/38 Total pore voxels

19 Pore Cluster Multiple Labeling Hoshen-Kopelman Algorithm Binary Image Matrix (Pore GSV = ) Labeled pore clusters /38

20 Diffusion Tortuosity and Random Walk Time-dependent diffusion coefficient of random Brownian motion of molecules To probe the geometry of porous media MSD 2 r = r t r 2 = 2dD t t () ( ) () For 3D random walk (d =3) Diffusion Tortuosity τ = D D( t) Free space (porosity = 1 %) D = 1 6 r t 2 Pore space (restricted diffusion) D( t) = 1 6 d r dt 2 2/38

21 Pore structural model: Capillary model Pore space : Diffusion tortuosity Le Tortuosity = Le L Tortuosity = D o D L Unidimensional: percolating in the x-direction τ f 1 MSD Unrestricted diffusion ( t) D D = ( t) D D < closed system Restricted diffusion open system τ f Le = L 2 time,t Mean square displacement vs time 21/38

22 Time-Dependent Diffusion Tortuosity 1 1 = Dt ( ) τ D Free space Open pore Closed pore t: diffusion time 22/38

23 Y 1 2 Y 1 2 Y Z 1 Z 1 Z X 1 2 τ = 1. = ( 2.4) 2 Le = 1 L -1-1 X 1 2 τ τ = ( 2.78) 2 Le = L X 1 2 Le =? L 23/38

24 Deteriorated Mortar A sample trajectory of a random walker in 3D pore space of DM -2 Y Z -2-2 X million time steps 5, walkers Percolating pore=.38 (98% of Porosity) Diffusion tortuosity: 4 24/38

25 Cement paste: Profiles for Ca and Si Ca 2+ Ca de1 de2 de unit:mm CaO% 5 Sliced samples for X ray CT SiO 2% Distance from cathode (m m ) Distance from cathode (m m ) 25/38

26 de1 SLICE3 15 µm

27 de2 SLICE3 15 µm

28 de3 SLICE3 15 µm

29 Reference OPC paste SLICE3 15 µm

30 Segmented pores de1 de2 de3 OPC

31 RWS de1 2 million time steps 5, walkers 6 Y 6 Y 6 X X X Z Z Y Ca 2+ Ca X 4 de1 de2 de3 unit:mm 31/38

32 RWS de2 2 million time steps 5, walkers 6 Y 6 Z 6 X X Y Z Z Y Ca 2+ Ca X 4 de1 de2 de3 unit:mm 32/38

33 RWS de3 2 million time steps 5, walkers 6 Y 6 Y 6 X X X Z Y Ca Z2 Ca X 4 de1 de2 de3 unit:mm 33/38

34 Cathode ε t ε e τ de1 de2 de Anode CaO/SiO

35 Segmented porosity, ε t Effective porosity, ε e Diffusion tortuosity, τ n/a

36 Conclusions 1/2 (1) The Synchrotron Microtomography technique can provide better understanding of the microstructure change in deteriorated mortar and cement paste. (2)The segmented porosity of the deteriorated mortar was increased by approximately ten times of that of non-deteriorated one. Especially the effective porosity was increased by approximately twenty times. The diffusion tortuosity was 4 for deteriorated mortar.

37 Conclusions 2/2 (3) For cement pastes as the CaO/SiO 2 ratio was reduced from 3.6 to 1.8 the effective porosity was increased from.14 to.33 while the diffusion tortuosity was reduced from 41 to 7. (4) Potential applications to predict transport properties such as diffusivity and permeability are being considered.

38 Acknowledgments Assistances from Dr. Nakashima and Dr. Nakano from AIST Dr. K. Uesugi and Dr. M. Uesugi from SPring 8, JASRI