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Microstructure-Electrical Propertyrelationships in Cement-Based Materialss

Published online by Cambridge University Press:  21 February 2011

R.A. Olson ,
G.M. Moss ,
B.J. Christensen ,
J.D. Shane ,
R.T. Coverdale ,
E.J. Garboczi ,
H.M. Jennings  and
T.O. Mason
R.A. Olson
Affiliation:
Center for Advanced Cement-Based Materials, Northwestern University, Evanston, IL
G.M. Moss
Affiliation:
Center for Advanced Cement-Based Materials, Northwestern University, Evanston, IL
B.J. Christensen
Affiliation:
E. Khashoggi Industries, Santa Barbara, CA
J.D. Shane
Affiliation:
Center for Advanced Cement-Based Materials, Northwestern University, Evanston, IL
R.T. Coverdale
Affiliation:
MassterBuilders, Cleveland, OH
E.J. Garboczi
Affiliation:
NationalInstitute ofStandards and Technology, Gaithersburg, MD
H.M. Jennings
Affiliation:
Center for Advanced Cement-Based Materials, Northwestern University, Evanston, IL
T.O. Mason
Affiliation:
Center for Advanced Cement-Based Materials, Northwestern University, Evanston, IL
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Abstract

There has been much recent progress on the application of impedance spectroscopy (IS) to the study of microstructure and transport in cement-based materials. The IS spectrum allows for the precise determination of bulk resistance, which is a measure of the pore phase interconnectivity, and calculation of the relative dielectric constant, which is related to the capillary pore size and distribution. High values of the relative dielectric constant (σ105) observed in cement paste at early hydration times are the direct result of the microstructure inducing dielectric amplification. Solvent exchange and freezing experiments, combined with digital-image-based computer modeling, have confirmed the role of large capillary pores in the dielectric amplification in young pastes.

The conductivities (σ) and relative dielectric constants (εr) of ordinary portland cement (OPC) pastes were monitored during cooling and solvent exchange with isopropanol and methanol. Dramatic decreases in σ and εr, in some cases over two orders of magnitude, occurred at the initial freezing point of the aqueous phase in the macropores and large capillary pores. The same dramatic decreases in a and er were observed at the onset of solvent exchange. Both effects provide experimental support for the dielectric amplification mechanism within the microstructure on the μm-scale. A secondary dielectric amplification was observed in the frozen and solvent exchanged pastes, which produced dielectric constants on the order of 103. This effect is attributed to amplification on the nm-scale within the layered calcium silicate hydrate (C-S-H) gel microstructure. Additional insight into the variable nature of the C-S-H microstructure was obtained by comparing the dielectric behavior of methanol-exchanged OPC pastes to isopropanolexchanged OPC pastes.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 370: Symposia Va/Vb – Microstructure of Cement-Based Systems/Bonding and Interfaces in Cement... , 1994 , 255
Copyright
Copyright © Materials Research Society 1995

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