###### Abstract  
This study investigates the effects of clay content on the strength and microstructural mechanisms of artificially prepared low-liquid-limit clay solidified with SSGM binder, composed of salt sludge (SAS), steel slag (SS), ground granulated blast-furnace slag (GGBS), and light magnesium oxide (MgO), and the law of influence of viscous particles content on the strength of the solidified low-liquid-limit clay and its microscopic mechanism were investigated through a freeze-thaw cycle test and microscopic test. The results indicate that, under freeze-thaw cycles, both the mass and unconfined compressive strength of the solidified soil decrease with increasing cycle number. At the same number of cycles, samples with lower clay content exhibit smaller mass loss rates and unconfined compressive strength loss rates. Microstructural tests reveal that the hydration products of the binder, including C-S-H, C-A-S-H, C-A-H, and AFt, not only cement soil particles and fill internal pores but also interconnect to form a mesh-like structure, enhancing internal stability. However, as freeze-thaw cycles progress, the structure of the solidified soil deteriorates, with an increase in large pores and the formation of penetrating cracks and voids, leading to reduced strength. The SSGM binder demonstrates excellent freeze-thaw resistance for solidifying low-liquid-limit clay and improves the utilization rate of industrial waste, showing promising application potential in permafrost regions. freezing-thawing cycles; solid-waste-based binders; steel slag; microscopic structure +
Footnote †: journal: Applied Sciences  
0000-0001-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-5000-50000-50000-50000-50000-50000-50000-50000-50000-50000-5  
damage, and environmental pollution [9]. Salt sludge is a solid byproduct generated during the ammonia-soda process for alkali production [10]. Its disposal primarily involves stockpiling, landfill, or sea reclamation by damming. However, these methods can lead to the formation of \"white seas\", causing soil and water alkalization [11]. Currently, the resource utilization of salt sludge primarily focuses on the recovery and extraction of NaCl [12], and limited research has been conducted on its application as an alkali activator. The CaO and MgO present in salt sludge can provide alkaline environments by releasing alkali metal cations such as Ca\({}^{2+}\) and Mg\({}^{2+}\) during hydration reactions [13]. Steel slag, a byproduct of the steel industry, contains cementitious components and exhibits potential as a cementitious material [14; 15], but due to its own low early hydration activity [16] and constraints on its stability [17], its performance as a supplementary cementitious material in cement-solidified soil is not ideal when used alone [18]. However, studies have shown that steel slag, when combined with ground granulated blast-furnace slag as a cementitious material, can exhibit excellent synergistic hydration reactions [19; 20]. In the alkaline environment provided by soda residue [21], the alkali activator induces the dissociation of vitreous phases in steel slag and ground granulated blast-furnace slag during the early stages of hydration. This process significantly influences the structure of hydration products [22], further activating their reactivity and leading to the formation of cementitious materials [23]. Due to its insufficient alkalinity, salt sludge cannot fully activate the reactivity of steel slag-ground granulated blast-furnace slag. Adding chemical additives such as MgO can effectively enhance the alkalinity of the hydration environment. Furthermore, studies have found that reactive MgO-magnesium carbonate composite cementitious materials generate low-crystallinity brucite [24] during hydration, which effectively improves their strength [25; 26].