Date of Award

Spring 1-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Yunping Xi

Second Advisor

Edward Garboczi

Third Advisor

Jeong-Hoon Song

Fourth Advisor

Mija Helena. Hubler

Fifth Advisor

Yida Zhang

Abstract

Frost attack can heavily damage concrete materials and concrete structures. Therefore, it is important to predict the service life of concrete structures considering the effect of the deterioration process. A theoretical model based on Mori-Tanaka micromechanics method was developed to estimate the deterioration of elastic properties of concrete under low temperatures. The model took into account a continuous pore size distribution for cement paste, freezing temperatures with different pore sizes, and damage development in cement paste. The model was able to characterize the stiffening effect due to the formation of solid ice and the weakening effect of the damage development due to excessive ice formation. The accuracy of model predictions was validated with published experimental data. Moreover, the effective diffusivities of concrete under low temperatures were predicted based on a multiple-scale generalized self-consistent (GSC) model. The results show that the diffusivities of concrete under low temperatures vary based on the amount of ice formation and the extent of damage production. An experimental study was conducted to determine the coupling parameter for the effect of thermal gradient on moisture transfer. The theoretical models for the elastic and transport properties and the coupling parameter were implemented in a finite element code. The estimations of temperature distributions by the finite element code were compared with the experimental data, and a good agreement was obtained. In order to mitigate the frost damage, nano-silica was incorporated in concrete mix design to optimize the pore structure of cement paste and thus to improve the mechanical properties of concrete. A comprehensive experimental study was conducted to evaluate the effect of nano-silica on mechanical and durability properties of the concrete, particularly on its low temperature resistance. The results indicated that nano-silica can be used as an effective additive to improve the resistance of concrete to the frost attack.

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