Discussion on “Stabilization of clay soil using alkali-activated sewage sludge” [J Rock Mech Geotech Eng 17 (2025) 3213–3224]

We read with great interest the investigations conducted by Pourakbar et al. (2024) on the “Stabilization of clay soil using alkali-activated sewage sludge.” The authors have investigated the feasibility of utilizing alkali-activated sewage sludge (AASS) as a binder for stabilizing the clayey soil. Sewage sludge (SS) in varying proportions of 1.5%, 2%, 2.5%, 3.5%, and 4.5% was utilized to prepare geopolymer binders using sodium and potassium-based alkali activators. Furthermore, unconfined compressive strength (UCS) and direct shear tests were conducted to examine the strength development of clayey soil stabilized with AASS. While the study presented some intriguing results, we have identified critical concerns regarding (i) the selection of SS as a precursor for alkali activation, (ii) technical inconsistencies associated with the compaction characteristics and microstructural analysis, and (iii) the feasibility of the proposed methodology for practical applications. Through our discussion, we seek to highlight these issues and provide constructive feedback to advance the understanding of alkali activation processes and their implications for soil stabilization.