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NANOSCALE MEASUREMENTS OF CEMENT HYDRATION DURING THE INDUCTION PERIOD PowerPoint PPT Presentation


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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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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


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)


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


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


Resonance cross section

1H(15N,ag)12C

Energy (MeV)


Resonant Reaction Depth Profiling


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


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


Typical Experimental Plan

Temperature Number of Pellets Time SpanoCHrs

101021

20 45.5

30102.5


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


Beam Energy Resolution


Time Progression


Typical Scan at Early Times


C3S at 30 oC


Temperature Dependence of Induction Time


Hydrogen Profile Pre-breakdown


Hydrogen Profile Post-breakdown


Reaction zones in hydrating C3S during the induction period.


H Concentration with Retarder and Accelerator


Comparison of Profiles


Comparison with Belite


Time Dependence of Belite Hydration Profiles


Highly Accelerated


Lightly Accelerated


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.


Ternary Diagram of Glass Composition


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


NRRA Results of FF Series


NRRA Results of Low-Ca CF


NRRA Results of High-Ca CF


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”


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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