This research was based on a two-part basic research investigation studying the effects of cement paste-aggregate interfaces (or interfacial transition zones-HZ) on strength and durability of concrete. Part I dealt with the theoretical study and Part II dealt with the experimental. Part I, the theoretical part, illustrates the effect of ITZ on the concrete properties by assuming its elastic moduli to be varied continuously in the region. A four-phase composite model is employed and three functions are chosen to model the moduli variation in the ITZ. A theoretical solution for an n-layered spherical inclusion model is used to estimate the overall effective moduli of the modified four-phase model. The influence of material and geometric characteristics of the ITZ, as well as that of the aggregate on the overall effective moduli is investigated. The effects of three different moduli variations in ITZ on the overall moduli are compared. Their potential application is discussed. Finally, by comparing the prediction of the proposed models to a set of data on mortar, it is found that the elastic modulus at the interface is about 20-70% lower than that in the bulk paste for portland cement mortar, and 1040% lower for silica fume mortar. Part II, the experimental part, illustrates the relationship between the ITZ microstructure and the mechanical properties of the concrete. The mechanical properties studied included the dynamic modulus of elasticity, dynamic shear modulus, logarithmic decrement of damping, flexural tensile strength, and compressive strength. In addition, the effects of changing the water-tocementitious material ratio by mass, aggregate type, volume fraction of aggregate, and silica fume substitution, on these properties were investigated. A criterion based on water quantity and the specific surface area of aggregate by mass in a mixture was developed to eliminate biased date from the analysis process. This criterion was used to detect mixing and compaction problems that may have resulted in erroneous values of mechanical properties of specimen. In order to realize the compaction condition of the fresh mixture, an index of compaction (called gross porosity) was introduced. The three-phase model of Hashin-Shtrikman bounds was employed, tested, and validated with the experimental data from this research. A modification of this model linked the theory of Hashin-Shtrikman bounds to the results of this research on dynamic moduli of the transition zone. A form of optimal water content is recommended. This optimal water content may be used for a mixture to gain its possibly highest moduli, strengths and density. Thus, the rule of the optimal water content may potentially be applied to optimize the mixture design for conventional and high-strength concrete with consideration of ITZ.

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interface transition zone (ITZ), four-phase composite model, elasticity, effective moduli, elastic moduli, dynamic modulus, shear modulus, damping, flexural tensile strength, compressive strength, porosity, microstructure, Hashin-Shtrikman model, HPR-2071

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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