Three-Phase Model of the Elastic and Shrinkage Properties of Mortar.
Three-Phase Model of the Elastic and Shrinkage
Properties of Mortar.
Neubauer, C. M.; Jennings, H. M.; Garboczi, E. J.
Advanced Cement Based Materials, Vol. 4, 6-20, March
mortar; building technology; cement paste; composite
materials; drying; elastic; interfacial zone; shrinkage
Mortar and concrete are composite materials with overall
properties that are influenced by the arrangement and
characteristics of each constituent in the
microstructure. Elastic shrinkage, like other properties
of mortar and concrete, must be described by a
three-phase model: aggregate, bulk cement paste, and
interfacial transition zone (ITZ) cement paste. A
simple two-dimensional digital-image-based model of a
mortar is developed based on the hard core/soft shell
percolation model. Specific attention is given to the
properties of the ITZ between cement paste and
aggregate. The elastic shrinkage properties of this
model are computed numerically, using a specialized
finite-element technique. The effects of varying the
elastic moduli and shrinkage properties of the ITZ and
buld cement paste are examined in parameter studies,
both analytically, for low aggregate content, and
numerically, for arbitrary aggregate content. Special
attention is given to the effect that the topology of
the ITZ has an overall shrinkage. A comparison is made
betwwen model predictions and the limited available
experimental results (0.35 w/c, 65% hydration), assuming
an ITZ width of 20 mu m. Based on this comparison, this
paper introduces the prediction that the Young's modulus
of the ITZ is one third to one half of the modulus for
bulk cement paste and that the unrestrained shrinkage of
the ITZ material is close to the shrinkage of bulk
cement paste when both are averaged over a 20-mu m ITZ.
This finding is supported by further analysis of a
three-dimensional microstructural model of cement paste.