An assessment of different alkali-activated cements as stabilisers of sulphate-bearing soils

The stabilization of sulphate-bearing soils with traditional calcium-based stabilisers is not recommended, as reactions between the calcium and sulphates in the presence of water could lead to soil heave. Alternative stabilization methods are therefore required, and this paper proposes innovative alkali-activated cements (AAC), whose use for soil stabilisation and especially sulphate-bearing soils is little researched. To fill this knowledge gap, AAC systems with ground granulated blastfurnace slag precursor and different alkaline activators including commercial lime, wastepaper sludge ash (PSA), potassium hydroxide (KOH) and potassium carbonate (K2CO3) were used to treat an artificial sulphate-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, pH, and ultrasonic pulse velocity were measured and compared to those of specimens not exposed to water. Material characterisation (SEM-EDS, Raman spectroscopy and 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-K2CO3 led to strength gain in time. Overall AAC led to higher strengths than lime only or lime and admixtures and show promise as sulphate-bearing soil stabilisers.