Inhomogeneous interfacial transition zone model for the bulk modulus of mortar

The macroscopic bulk modulus of mortar and concrete is modeled by assuming that each inclusion (fine or coarse aggregate) is spherical, and is surrounded by an interfacial transition zone (ITZ) in which the elastic moduli vary smoothly as a power-law function of radial distance from the center of the inclusion. The exponent in the power law can be chosen based on the estimated thickness of the ITZ, or by fitting the power law to measured porosity profiles. For this model, an analytical expression has been found by Lutz and Zimmerman (J. Appl. Mech., 1996) for the macroscopic bulk modulus. The macroscopic bulk modulus depends on known properties such as the elastic moduli of the bulk cement paste and the inclusions, the volume fraction of the inclusions, the elastic moduli at the interface between the cement paste and inclusion, and the thickness of the ITZ. In this paper the inhomogeneous ITZ model is used to analyze the data of Wang et al. (Gem. Cone. Res., 1988) on the bulk modulus of mortar containing sand inclusions. By fitting the measured moduli to the model predictions, we can estimate, in a non-destructive manner, the elastic moduli within the ITZ. For Wang's specimens, it is inferred that the elastic moduli at the interface with the inclusions is 30-50% less than in the bulk cement paste. (C) 1997 Elsevier Science Ltd.