Browsing by Author "David W. Johnston, Ph. D., Committee Member"

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    Estimating Crack Growth in Temperature Damaged Concrete
    (2009-12-18) Recalde, Juan Jose; David W. Johnston, Ph. D., Committee Member; James M. Nau, Ph. D., Committee Member; T. Matthew Evans, Ph. D., Committee Member; Michael L. Leming, Ph. D., Committee Chair
    Evaluation of the structural condition of deteriorated concrete infrastructure and evaluation of new sustainable cementitious materials require an understanding of how the material will respond to applied loads and environmental exposures. A fundamental understanding of how microstructural changes in these materials relate to changes in mechanical properties and changes in fluid penetrability is needed. The ability to provide rapid, inexpensive assessment of material characteristics and relevant engineering properties is valuable for decision making and asset management purposes. In this investigation, the effects of changes in dynamic elastic properties with water content and fluid penetrability properties before and after a 300 °C exposure were investigated as they relate to estimates of the crack density parameter, developed from the work by O’Connell and Budiansky (1974; 1977) on dry and saturated crack media. The experimental and analytical techniques described in this dissertation allow calculation of a value for the crack density parameter nondestructively from differences in wet and dry dynamic shear modulus of relatively thin disks. The techniques were used to compare a conventional concrete mixture and several mixtures with enhanced sustainability characteristics. The analysis provided quantitative assessment of changes with high temperature damage and autogenous healing, and provided estimates of increases in mean crack trace lengths. The three enhanced sustainable materials investigated were a very high fly ash mixture (mixture F), a magnesium phosphate cement based mortar (mixture M), and a magnesium phosphate cement based concrete (mixture G), and were compared to a conventional concrete mixture (mixture C). The results showed that water interaction, deterioration due to damage, and autogenous healing recovery were different for mixtures G and M than the concrete mixtures C and F based on portland cement. A strong correlation was found between log(API), Gd and crack density parameter. The findings imply that the test method and related analysis can be used to evaluate the validity of current standard test methods to new “green†construction materials and therefore be a useful screening tool as well as providing important insight into microstructural changes in concrete under various exposures.