Rigid-wall column tests are performed at a hydraulic gradient of100 on 21 compacted mixtures containing a Class F fly ash, sand, bentonite, and cement. Results indicate that combinations of the admixtures can lower the permeability of the fly ash by up to an order ofmagnitude. There appears to be an optimum percentage of fly ash that minimizes the permeability of fly ash-sand mixtures. Specimens from four mixtures as well as 100 percent fly ash, are tested at four hydraulic gradients to establish different flow rates. Tap water is used as the permeant fluid, and the effluent is sampled every quarterpore volume of flow and tested for 13 metal concentrations, pH, andelectrical conductivity. For most of the metals, most of the metal mass is leached within the first pore volume of flow. However, some metals (Ba, Ca and Sr) are not leached in significant quantities until two or three pore volumes of flow have passed through the test specimens. These two leaching behaviors suggest that there is dissolution competition between metal ions. No simple trend in leaching rateas a function of flow rate was observed for all mixtures and metals. However, for specific elements between different mixtures at approximately the same flow rate, an increase in the fly ash content tended to increase the leaching rate of most metals. A 2.5 percent cement content was more effective than a 10 percent bentonite content in reducing the leaching rate of metals for mixtures containing the same amount (75 percent) of fly ash
Samenvatting