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Borehole Geophysical Investigation: Seminoe Dam, WY Characterization of Internal Fracturing and Dynamic Moduli Reduction of Mass Concrete Undergoing Aar
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 23rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 2010, cp-175-00010
Abstract
Alkali aggregate reaction (AAR) is the general term for a slowly occurring chemical reaction in which highly alkali cement paste reacts with concrete aggregate. AAR is a common problem in concrete poured prior to the 1950’s. The reaction leads to the formation of an alkali silicate gel at the interface of the aggregate and cement. This gel product is less dense than the reactants, causing expansion. The gel product also increases in volume with water. During July of 2009, five six-inch diameter boreholes with varying depths were drilled into Seminoe Dam. Down hole optical and acoustic imaging tools were utilized to locate and characterize fractures within the concrete surrounding the borehole. Data collected from sonic and density logging tools were used to calculate the in-situ dynamic modulus values of the concrete surrounding the borehole wall. Imaging data was analyzed for fracture dip, orientation and frequency. Sonic data was analyzed for the concrete’s compression and shear wave velocities. Concrete density was computed from gamma ray logging data. In-situ shear, bulk and Young’s modulus values were determined throughout the depth of the boreholes. Characterization of the fractures and in-situ dynamic modulus values of the concrete are used in comparison with past investigations of Seminoe Dam to gauge the progression and effects of AAR throughout the structure.