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The concrete in Martin Dam, an arch-gravity hydroelectric power dam in Alabama, completed in 1926, was sampled by three 152-mm (6-in.) cores drilled in the crest of the dam to the foundation. Samples taken from these cores were examined petrographically, tested ultrasonically to measure compressional- and shear-wave velocities, tested in unconfined compression, tested in triaxial loading in groups of three cores each at three confining pressures, and tested for strength in direct tension.
The petrographic examination yielded evidence of the occurrence of alkali-silica reaction in concrete from all three drill holes; however, alkali-silica reaction gel was not found in the lower part of one hole. The core from this zone contained large flakes of tetracalcium aluminate monosulfate-12-hydrate (C4 A¯SH12). No reference to the presence of this compound in concrete in crystals large enough to be visible to the naked eye was found in the literature. Although the evidence of alkali-silica reaction is clear, it did not extend to cracks in the mortar except to a minor extent. The mechanical tests indicated concrete in good physical condition. Despite the presence of alkali-silica reaction, the Martin Dam concrete appears to be in acceptable condition and in better condition than some younger structures that are still in service.
Special technical assistant, Structures Laboratory, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Miss.
Stock #: CCA10202J