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Evaluation of effect of sulfate on class c fly ash and lime stabilized expansive soil

As, Mehme
In this study, effect of sulfate on expansive soil treated with Class C Fly Ash was investigated. Also, lime was used for comparison purposes. The swelling soil was prepared at laboratory environment by mixing kaolinite and bentonite. Class C Fly Ashes obtained from Soma and Sivas-Kangal Thermal Power Plants were used as main additives for stabilization. Na2SO4 and CaSO4.2H2O were used as sulfate sources with different concentrations (3000ppm to 40000ppm). Optimum fly ash content was chosen as 15% and 10% for Soma (SFA) and Sivas-Kangal Fly Ash (KFA) respectively. Index tests, swelling and unconfined compressive strength tests were performed to understand the effect of fly ash on sulfate bearing soils. XRD analysis, zeta potential tests and scanning electron microscope were also used to see the effect of treatment on chemical structure and microstructure. Sulfate addition affected the swell potential of each treated specimen differently. Swell potential of 15% SFA treated specimen was positively affected from sulfate addition. Although not dramatic, general increase was observed in the swell potential of 4% lime treated specimen after sulfate addition. Swell potential of 10% KFA treated specimen was not affected much from the sulfate addition, especially for CaSO4.2H2O. The strength of fly ash and lime treated specimens was generally affected negatively from Na2SO4 addition however, CaSO4.2H2O addition had no significant effect. A dramatic decrease was observed in strength of 40000ppm Na2SO4 added fly ash treated specimens that were cured at 10⁰C as a result of the probable salination and ettringite formation.