Strength and Electrochemical Properties of Alkali-Excited Coal Gangue-Slag Co-Solidified Sludge

Abstract

To address the issues of low strength, poor economic efficiency, and high carbon emissions associated with traditional sludge solidifiers, this study employs coal gangue (CG), a byproduct of coal production, and granulated blast furnace slag (GBFS) to prepare geopolymer cementitious materials for sludge solidification. The effects of the solidifier mix ratio, coal gangue calcination temperature, and alkali activator modulus on the unconfined compressive strength of the stabilized soil after 7 and 28 days of curing were investigated. Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) tests were conducted on the stabilized soil to explore the relationship between strength, electrochemical parameters, and microstructure. The results indicate that when the ratio of coal gangue to slag is 2.5:7.5, the calcination temperature of coal gangue is 750 °C, and the modulus of water glass is 1.1; meanwhile, the stabilized soil exhibits high strength. The electrochemical parameters were used to qualitatively characterize the ionic concentration in the pore solution as the degree of soil adhesion and the hydration level during the solidification process. Stabilized soil with higher hydration and strength exhibited a distinct capacitive arc, with deeper hydration resulting in a rightward shift of the curve’s intercept on the horizontal axis. This study demonstrates the applicability of electrochemical impedance spectroscopy in evaluating the solidification effectiveness of alkali-activated calcined coal gangue-blast furnace slag sludge.

Keywords

coal gangue / slag / sludge / solidification / electrochemical impedance spectroscopy

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