Applications for reuse of lime sludge from water softening

Lime sludge, an inert material mostly composed of calcium carbonate, is the result of softening hard water for distribution as drinking water. Representatives from eight Iowa cities representing 23% of the state\u27s population, estimated that they collectively produce 64,470 tons of lime sludge (dry weight basis) per year, and they currently have 371,800 tons (dry weight basis) stockpiled. The research goal was to find useful and economical alternatives for the use of lime sludge. Feasibility studies tested the efficacy of using lime sludge in cement production, power plant SO[subscript x] treatment, dust control on gravel roads, wastewater neutralization, and in fill materials for road construction. Since the fill material application showed the most promise in accomplishing the research goal, it was chosen for further investigation. Lime sludge is classified as inorganic silt with low plasticity. Since it only has an unconfined compressive strength of approximately 110 kPa, lime sludge mixed with fly ash and cement was developed to obtain higher strengths. When fly ash was added at a rate of 50% of the dry weight of the lime sludge, the unconfined strength increased to 1600 kPa. Further, friction angles and California Bearing Ratios were higher than those published for soils of the same classification. However, the mixtures did not survive freeze/thaw and wet/dry tests without excessive mass and volume loss. Thus, fill composed of these mixtures must be placed at depths below the frost zone