New Effective Medium Theory for the Diffusivity or Conductivity of a Multi-Scale Concrete Microstructure Model.
New Effective Medium Theory for the Diffusivity or
Conductivity of a Multi-Scale Concrete Microstructure
Model.
(965 K)
Garboczi, E. J.; Berryman, J. G.
Concrete Science and Engineering, Vol. 2, 88-96, June
2000.
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Website:
http://ciks.cbt.nist.gov/garbocz/paper119/p119monograph.
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Keywords:
concretes; diffusivity; conductivity; differential
effective medium theory
Abstract:
To attempt to represent concrete properly as a composite
material, one must consider at least three phases:
matrix, aggregates, and the interfaclal transition zone
(ITZ), a thin shell of altered matrix material
surrounding each aggregate grain. Assigning each of
these phases a different transport parameter,
diffusivity or conductivity, results in a complicated
composite transport problem. Random walk simulations can
be performed for this system, but are time-consuming,
hence the anticipated usefulness of effective medium
theory. Previous applications of differential effective
medium theory were plagued by the need to use an
arbitrary parameter chosen to fit the simulation
results. A new kind of differential effective medium
theory presented in this paper removes this need for a
fitting parameter. An aggregate particle with a
surrounding ITZ is mapped onto an effective particle of
uniform conductivity, which is then treated in usual
differential effective medium theory. The results of
this theory compare favorably to random walk simulations
for multi-scale concrete models with varying aggregate
size distributions.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899