Abstract: The oxygen-containing functional group in organic matters of sludge is prone to combine with the aluminum and calcium produced by the hydration of cement, thus delaying the hydration process and hindering the hardening of cement. To eliminate the adverse impact of organic matters on cement hydration, we select potassium ferrate as an admixture for the pretreatment of sludge, and examine the changes in the strength of cement-stabilized sludge via unconfined compressive strength and direct shear strength tests; furthermore we look into the microstructure of cement-stabilized sludge using scanning electron microscope. Research findings suggest that pretreating by adding potassium ferrate could effectively improve the unconfined compressive strength and shear strength of cement-stabilized sludge because the organic matters in sludge are oxidized by potassium ferrate, which ensures the full progress of cement hydration reaction and volcanic ash reaction.Besides, potassium ferrate is reduced by organic matters. The adsorption of free Fe(III) onto clay particles surface thins the diffusion layer and gives rise to the flocculation of clay particles.In conclusion, potassium ferrate pretreatment improves the strength of cement-stabilized sludge by changing the microstructure of cement-stabilized sludge.

Key words: cement-stabilized sludge, organic matters, potassium ferrate, unconfined compressive strength, shear strength, scanning electron microscope