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Effect of the Transition Zone on the Bulk Modulus of Concrete

Published online by Cambridge University Press:  21 February 2011

Melanie P. Lutz  and
Paulo J. M. Monteiro
Melanie P. Lutz
Affiliation:
Dept. of Materials Science & Mineral Engineering, Univ. of California, Berkeley, CA 94720
Paulo J. M. Monteiro
Affiliation:
Dept. of Civil Engineering, Univ. of California, Berkeley, CA 94720
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Abstract

In concrete, non-uniformities in the hydration process, due to the the “wall effect” produeed by the aggregate (inclusion) particles, lead to an interfacial transition zone (ITZ) that is characterized by an increase in porosity near the inclusions. This increase in porosity may in turn be expected to cause a local decrease in the elastic moduli. We have modeled the effect of the ITZ by assuming that the elastic moduli vary smoothly in the vicinity of the inclusions, according to a power law. The exponent in the power law is chosen based on the estimated thickness of the ITZ. For this model, a closed-form expression can be found for the overall effective bulk modulus. The predicted bulk modulus of the concrete depends on known properties such as the elastic moduli of the bulk cement paste and the inclusions, the volume fraction of the inclusions, as well as on the elastic moduli at the interface. By comparing the model predictions to measured data, we can obtain estimates of the elastic moduli at the interface. Application of this inverse procedure to a set of data from the literature on mortar containing sand inclusions leads to the conclusion that the modulus at the interface is about 15-50% lower than in bulk cement paste.

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 , 413
Copyright
Copyright © Materials Research Society 1995

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