An assessment of different alkali-activated cements as stabilizers of sulfate-bearing soils

Abstract

The stabilization of sulfate-bearing soils with traditional calcium-based stabilizers is not recommended, as reactions between the calcium and sulfates in the presence of water could lead to soil heave. Alternative stabilization methods are therefore required, and this paper proposes innovative alkali-activated cements (AACs), whose use for soil stabilization and especially sulfate-bearing soils is little researched. To fill this knowledge gap, AAC systems with a ground granulated blast-furnace slag precursor and different alkaline activators, including commercial lime, wastepaper sludge ash (PSA), potassium hydroxide (KOH) and potassium carbonate (K 2 CO 3 ), were used to treat an artificial sulfate-bearing clay. AAC-treated clay specimens cured for 7 and 28 days, respectively, were soaked in water for 45 days; their one-dimensional swelling, unconfined compressive strength (UCS), pH and ultrasonic pulse velocity (UPV) were measured and compared to those of specimens not exposed to water. Material characterization (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR)) was performed to attest cementation and detect ettringite. In AAC systems, CaO/Ca(OH) 2 did not lead to specimen heave and damage, and developed the highest strengths. Potassium-based activators performed less well but combined PSA–K 2 CO 3 in time led to strength gain. Overall, AACs lead to greater strengths than lime only or lime and admixtures, and show promise as sulfate-bearing soil stabilizers. Thematic collection: This article is part of the Leading to Innovative Engineering Geology Practices collection available at: https://www.lyellcollection.org/topic/collections/leading-to-innovative-engineering-geology-practices