RECYCLING COAL COMBUSTION BYPRODUCTS: A LABORATORY STUDY TO EVALUATE GROUT FORMULATIONS FOR USE IN THE KEMPTON MINE COMPLEX, WESTERN MARYLAND

Over 10E8 tons of coal combustion byproducts are produced annually by American power generating utilities. One option for disposal of this material is placing it back in the mine environment in an economically and environmentally favorable fashion. The goal of this project is to develop a grout that: 1) uses a large component of coal combustion by-products; 2) is economical; 3) is rheologically capable of retaining sufficient flowability (to be poured into the mine), and yet harden sufficiently to attain and retain high strength; and, 4) serve as a neutralizing agent for acidic mine waters. We have generated grouts in the lab, and four have been studied in detail. The mineralogical composition and strength have been monitored over approximately a 90 day period. The grouts were formulated using Fly Ash [FA], Flue Gas Desulfurization Products [FGD], and Lime Kiln Dust [LKD]. The composition of the grouts studied in detail are (reported as FA, FGD, LKD, water/solid): grout A (40%,15%,45%,0.48); grout B (60%,20%,20%,0.47); grout C (60%,10%,30%,0.47); and, grout D (60%,0%,40%,0.51). Strength measurements were obtained at 7, 14, and 68 days; the 68 day strength of all four grouts exceeded 1700 psi, with grouts A, B and C approaching 3000 psi. Mineralogical composition of the grouts was determined using XRD at approximately 1, 7, 14, 28, 56 and 90 days. All grouts were found to contain quartz, mullite, calcite, gypsum, portlandite and ettringite, in addition to glass, in concentrations that varied over the 90 days of analysis. Ettringite concentrations increase monotically in all four of the grouts with time, and the concentrations of the other phases decrease (with the exception of calcite and gypsum in one run, each). These grouts will be evaluated by the Power Plant Research Program (Maryland Department of Natural Resources) for their possible use in the Kempton Mine in western Maryland. The PPRP hopes to place a grout in the mine environment during the Spring of 2001.