Development of Accelerated Test Methods for Ettringite Related Damage

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Development Of Accelerated Test Methods for Ettringite Related DamageNSF Proposal No. 9988725 (UM No. 990928-8477)ABSTRACT The study will evaluate expansion rate measurement as a possible rapid test method for delayed ettringite formation (DEF). Concrete specimens with different amount of potassium will be cast and stored under high moisture conditions to accelerate DEF. The measured expansion rate data will be analyzed using nonlinear curve fitting algorithms based on the Incomplete Gamma function in order to extract characteristic expansion parameters. These parameters will then be correlated with time-resolved measurements of the amount of ettringite formed, which will be determined through a combination of scanning electron microscopy, quantitative X-ray diffraction, synchrotron radiation energy dispersive diffraction, and other means. In addition, computer tomography will be used for 3D imaging of crack propagation. Weight gain as a function of humidity cycling will also be explored as a possible alternative rapid test method. The formation of ettringite or ASR gel involves the uptake of water, which results in a permanent weight, or mass, gain of the sample. Since mass can be measured more sensitively and conveniently than length change, this suggests the possibility of replacing the expansion measurement with a weight change measurement that is more directly related to DEF. The study will contribute to the understanding of the cause for the distress mechanism in DEF, and will contribute to the development of a rapid test method for DEF.