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چکیده
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The cement-based stabilization/solidification (S/S) is commonly used to remediate heavy-metal-contaminated clayey soils. Two mechanisms of solidification and stabilization in this method include the formation of cementation products (such as C-S-H) and achievement of alkaline condition for development of pozzolanic interactions. Determining the effecting mechanisms of heavy metal immobilization in the cement- based stabilization/solidification process and the long-term efficiency of stabilization/solidification materials, is the most important aspect of research in this field. Still, the major problem associated with this method is heavy-metal precipitation, which retards cement hydration. The objectives of this research are to determine the influence of pH-dependent lead solubility patterns on the stabilization/solidification of contaminated bentonite and to overcome the problems associated with cement hydration in this process through NaOH treatment. In addition, due to the pozzolanic properties of fly ash, in order to investigate the effect of fly ash on the optimum amount of required cement at different concentrations of contaminants, several mixtures of cement-fly ash were used to solidify the contaminated bentonite. Finally, the long-term performance of Pb stabilization and solidification mechanisms in cemented stabilized/solidified materials and the role of each mechanism on heavy metal immobilization are investigated. In order to achieve the above-mentioned objectives a series of physicochemical experiments were performed. The mention section includes a laboratory study of the interaction of fly ash with bentonite and the interaction of fly ash with cement in the presence and non-presence of lead nitrate contamination. Macro-structural experiments such as unconfined compressive strength, atterberg limits, hydrometer test, compressive strength of mortars and measurement of setting time have been performed on these samples. In addition, a series of X-ray diffr
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