Potential Alkali-Carbonate Rock Reactivity of Some of The Aggregate Used in Fishtrap Dam.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MISS
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Two samples of carbonate rock coarse aggregate were obtained from the quarry that furnished some of the coarse aggregate for Fishtrap Dam. These materials were subjected to petrographic examination. Small rock cores were prepared from some of these aggregate particles and tested for length change in sodium hydroxide solutions. Five concrete mixtures were made in the laboratory using these aggregates specimens from these mixtures were tested for length change during moist storage or during storage in laboratory air followed by moist storage other specimens were tested for compressive strength. Six concrete cores from the spillway portion of Fishtrap Dam were received in the laboratory. They were inspected and photographed. Thin sections were made and selected specimens were tested for length change during moist storage. It was concluded that an alkali-carbonate rock reaction had occurred at Fishtrap Dam. There was no indication that this was a deleterious reaction. It is likely that the use of low-alkali portland cement and relatively small aggregate size served to keep the reaction at a safe level. It is also possible that natural dilution of the reactive rock by innocuous rock had a moderating effect on the reaction.
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