High volume-high value usage of flue gas desulfurization (FGD) by-products in underground mines: Phase 2 -- Field investigations. Quarterly report, January 1--March 31, 1998
Description: The factors that control the strength of FBC ash grout were the focus of work during this quarter. Samples were prepared at different water contents and placed into cylindrical PVC molds. At specified curing intervals, the grout cylinders were subjected to unconfined compressive strength testing as per procedures described in previous reports. Chemical, mineralogical, and microscopical analyses were also conducted on the samples. It was found that higher curing temperatures significantly increase the strength gain rate of the FBC ash grout, in agreement with earlier results. As expected, water content also exerts a strong influence on the strength of the grout. The compressive strength data obtained for the laboratory-prepared samples are in excellent agreement with strength data obtained on grout placed in auger holes during the field demonstrations. The data also indicate that the field samples suffered negligible deterioration over the course of the curing period in the auger holes. Analysis of the laboratory prepared grout samples using XRD revealed a mineralogy similar to the field samples. A correspondence between ettringite abundance and compressive strength was observed only during grout curing. The formation of minerals such as ettringite is apparently a good indication that curing reactions are progressing and that the grout strength is increasing, but mineral distribution by itself does not explain or predict final strength. The microscopy data, in combination with geotechnical and XRD data, suggest that the strength of the grout is largely a function of the density of an amorphous (or finely crystalline) material that comprises the majority of the cured grout. Therefore, an increase in density of this material results in an increase in grout strength.
Date: September 1, 1998
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