Leaching of Lime from Fly Ash Stabilized with Lime and Gypsum

Stabilization of fly ash is one of the promising methods to transform the waste material into a safe construction material. The longevity of lime-stabilized fly ash is related to the amount of lime that remains in the matrix after leaching. This paper presents leaching test results of a class F low lime fly ash stabilized with varying percentages of lime (4, 6, and 10%) alone or in combination with gypsum (0.5 and 1.0%). Addition of gypsum has been found to be very effective in reducing the leaching of lime from fly ash stabilized with lime. The effects of factors like lime content, gypsum content, curing period, and flow period on leaching of lime from a compacted stabilized fly ash matrix are reported herein. Compacted specimens were cured for seven and 28 days. The concentrations of calcium in the effluent emanating from hydraulic conductivity test specimens were measured daily for seven days in succession. The concentration of calcium in the leachate was reduced to 80 from 540 ppm for addition of 1.0% gypsum to fly ash stabilized with 10% lime and cured for 28 days. Two nondimensional parameters αcoi and βcoi are presented herein to study the effect of gypsum on the total amount of calcium leached out from the compacted stabilized fly ash. A model is also presented to estimate the amount of calcium leached out from the stabilized fly ash.