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NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD

NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD. Jeffrey S. Schweitzer Department of Physics University of Connecticut Storrs, Ct, USA 2nd International Symposium on Nanotechnology in Construction Bilbao, Spain November 2005. Collaborators.

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NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD

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  1. NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD Jeffrey S. SchweitzerDepartment of Physics University of Connecticut Storrs, Ct, USA 2nd International Symposium on Nanotechnology in Construction Bilbao, Spain November 2005

  2. Collaborators • Richard A. Livingston, FHWA • Claus Rolfs, Hans-Werner Becker, Ruhr Universität Bochum, Germany • Stefan Kubsky, Synchrotron SOLEIL, Saint-Aubin, Gif-sur-Yvette CEDEX, France • Timothy Spillane, University of Connecticut • Marta Castellote Armero, Paloma G. de Viedma, IETcc (CSIC), Madrid, Spain • Walairat Bumrongjaroen (University of Hawaii) • Supaluck Swatekititham (Chulalongkorn University)

  3. Study of the Induction Period • The details of the kinetics of the cement curing reactions are not known • The reactions appear to be initiated at the grain surfaces • Hydrogen plays a key role in the reaction process • Studying the change in hydrogen concentration as a function of depth and time will provide insight into the reactions

  4. Nuclear Resonant Reaction Analysis (NRRA) • Use of a narrow resonance (~ 1 keV) permits good spatial resolution • Use of inverse kinematics (a 15N beam) provide large dE/dx, which improves spatial resolution • A well isolated resonance provides the ability to have deep probing of the sample (~ 2-3 microns) • All of these are provided by the 6.4 MeV 15N(p,ag)12C reaction

  5. Resonance cross section 1H(15N,ag)12C Energy (MeV)

  6. Resonant Reaction Depth Profiling

  7. Pellet Preparation • Pure triclinic C3S powder • Pressed into 13 mm dia. ring molds • Fired at 1600 ºC to fuse upper surface • Epoxied to stainless steel backing or with no backing • Stored under nitrogen until used

  8. Sample Preparation • Saturated Ca(OH)2 Solution ( pH=12.5) • Isothermal (10, 20 or 30 °C ) • N2 Purge of solution • Specimens removed sequentially at specified times • Hydration stopped using methanol rinse • Specimens dried to 10-6 Torr vacuum

  9. Typical Experimental Plan Temperature Number of Pellets Time Span oC Hrs 10 10 21 20 4 5.5 30 10 2.5

  10. Measurements • Typical scan takes about one hour • Chamber vacuum < 10-6 • Use of two beam charge states to cover complete energy range to 11 MeV • Only background in gamma-ray spectrum is from cosmic rays • Beam-line cold trap minimizes carbon buildup

  11. Beam Energy Resolution

  12. Time Progression

  13. Typical Scan at Early Times

  14. C3S at 30 oC

  15. Temperature Dependence of Induction Time

  16. Hydrogen Profile Pre-breakdown

  17. Hydrogen Profile Post-breakdown

  18. Reaction zones in hydrating C3S during the induction period.

  19. H Concentration with Retarder and Accelerator

  20. Comparison of Profiles

  21. Comparison with Belite

  22. Time Dependence of Belite Hydration Profiles

  23. Highly Accelerated

  24. Lightly Accelerated

  25. Figure 5: Hydration profiles for C3A at various times. The 0 minute sample was not hydrated, but was treated with methanol and then stored in the vacuum with the others.

  26. Ternary Diagram of Glass Composition

  27. Glass Hydration Procedure • Saturated Li(OH)2 Solution ( pH=12) • N2 purge to prevent carbonation • Specimens removed at 72 hours • Hydration stopped using methanol rinse • Specimens dried in 10-6 Torr vacuum

  28. NRRA Results of FF Series

  29. NRRA Results of Low-Ca CF

  30. NRRA Results of High-Ca CF

  31. Future Research • Effects of Al2O3, Fe2O3 in alite • Effect of time-varying solution chemistry • Effects of accelerators & retarders • Relationship between surface layers and time of initial set • Effects of cement storage conditions, i.e. “dusting”

  32. Conclusions • NRRA is a powerful technique for understanding cement hydration and it can determine induction period with a precision of  4 minutes or  2% • Spatial resolution on the order of 2-3 nm can be achieved • A surface layer is formed during the induction period for C3S but not for C2S • Induction period determined by mechanical breakdown of surface layer ~ 10-20 nm thick. • Hydration involves concentration-dependent diffusion process • Further work is needed to determine the affects of accelerators and especially of retarders, and to understand hydration of other cement components

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