NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD

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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

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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)

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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

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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

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Resonance cross section
1H(15N,ag)12C
Energy (MeV)
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Resonant Reaction Depth Profiling
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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

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Sample Preparation

• Saturated Ca(OH)2 Solution ( pH12.5)
• 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

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Typical Experimental Plan

• Temperature Number of Pellets Time
  Span oC Hrs
• 10 10 21
• 20 4 5.5
• 30 10 2.5

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Measurements

• Typical scan takes about one hour
• Chamber vacuum lt 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

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Beam Energy Resolution
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Time Progression
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Typical Scan at Early Times
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C3S at 30 oC
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Temperature Dependence of Induction Time
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Hydrogen Profile Pre-breakdown
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Hydrogen Profile Post-breakdown
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H Concentration with Retarder and Accelerator
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Comparison of Profiles
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Comparison with Belite
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Time Dependence of Belite Hydration Profiles
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Highly Accelerated
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Lightly Accelerated
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Ternary Diagram of Glass Composition
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Glass Hydration Procedure

• Saturated Li(OH)2 Solution ( pH12)
• N2 purge to prevent carbonation
• Specimens removed at 72 hours
• Hydration stopped using methanol rinse
• Specimens dried in 10-6 Torr vacuum

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NRRA Results of FF Series
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NRRA Results of Low-Ca CF
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NRRA Results of High-Ca CF
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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

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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