Modeling the Elastic Properties of Concrete Composites: Experiment, Differential Effective Medium Theory and Numerical Simulation.
Modeling the Elastic Properties of Concrete Composites:
Experiment, Differential Effective Medium Theory and
Sun, Z.; Garboczi, E. J.; Shah, S. P.
Cement and Concrete Composites, Vol. 29, No. 1, 22-38,
concretes; microstructure; interfacial transition zone;
numerical simulation; differential effective medium
theory; dynamic elastic moduli; mechanical properties;
elastic properties; mortar; composite materials;
cements; raw materials; aggregates
Concrete is a mixture of cement, water and aggregates.
In terms of microstructure, besides the cement paste
matrix and aggregate inclusions, there is a third phase,
which is called the interfacial transition zone (ITZ),
which forms due to the wall effect and can be
thought of as a thin shell that randomly forms around
each aggregate. Thus, concrete can be viewed as a bulk
paste matrix containing composite inclusions. To compute
the elastic properties of a concrete composite, a
differential effective medium theory (D-EMT) is used
in this study by assigning elastic moduli to
corresponding bulk paste matrix, ITZ and aggregate. In
this special D-EMT, each aggregate particle, surrounded
by a shell of ITZ of uniform thickness and properties,
is mapped onto an effective particle with uniform
elastic moduli. The resulting simpler composite, with a
bulk paste matrix, is then treated by the usual D-EMT.
This study shows that to assure the accuracy of the
D-EMT calculation, it is important to consider the
increase in the water:cement mass ratio (w/c) of the ITZ
and the corresponding decrease in w/c ratio of the bulk
matrix. Because of this difference in w/c ratio, the
contrast of elastic moduli between the ITZ and the bulk
paste matrix needs to be considered as a function of
hydration age. The Virtual Cement and Concrete Testing
Laboratory (VCCTL) cement hydration module is used to
simulate the microstructure of cement paste both inside
and outside the ITZ. The redistribution of calcium
hydroxide between ITZ and bulk paste regions can further
affect the elastic contrast between ITZ and bulk paste.
The elastic properties of these two regions are computed
with a finite element technique and used as input into
the D-EMT calculation. The D-EMT predictions of the
elastic properties of concrete composites are compared
with the results measured directly with a resonant
frequency method on corresponding composites. This
comparison shows that the D-EMT predictions agree well
with experimental measurements of the elastic properties
of a variety of concrete mixtures.