TECHNOLOGY FOR USING SULFATE WASTE IN ROAD CONSTRUCTION

Mixtures of fly ash, lime and sulfate waste were examined for their potential use in highway construction. Initially, pure calcium sulfate componds such as gypsum were used as the source of sulfate. In most cases, gypsum were found to increase the compressive strength of lime-fly ash-water mixtures. During this initial phase of the project, variables such as fly ash source, form of calcium sulfate, lime type, mixture consistency, curing temperature, admixtures and impurities expected in waste sulfates were examined. Also, studies of compound development in selected mixtures were performed. The second phase of the study was designed to obtain strength-compositional relationships for samples prepared with actual waste sulfates. These waste sulfates included neutralized acid mine drainage, titangypsum, hydroflouric acid by-product, gas scrubber waste and neutralized steel pickling liquor. Results of this phase were used for the selection of mixtures for engineering evaluation. These mixtures were examined for compressive and tensile strength, freeze/thaw resistance, wet/dry stability, California bearing ratio, permeability and leachability. Finally, the possibility of reparing aggregate from mixtures containing waste sulfate was examined. The aggregate, as well as portland cement concrete and asphaltic concrete prepared with it, was tested using standard techniques.