## 1 Introduction  
The underground mining methods with cemented backfill have key advantages in controlling ground pressure, realizing the absence of waste mining, and the efficient utilization of mineral resources [1; 2]. However, the high cost of cementitious materials used in the mine backfill operations has exerted tremendous economic pressure on the mining industry [3]. Indeed, cemented tailings backfill (CTB) or cemented paste backfill (CPB) represents nearly 50-85% of the total operating costs when considered for a cement content of 3.5-9% used in the backfill mix. CTB allows mining companies to extract more ore in a secure manner, while simultaneously improving working and environmental conditions [4; 5]. As a result, the use of solid wastes is an effective approach to reduce mining costs, improve operational safety, and develop a new type of cementitious material with a relatively low cost and high mechanical strength. CTB is a composite matrix of the total filtrated processing tailings (containing 70-85 wt% solid content), hydraulic binder, and mixing water. The physicochemical and mineralogical properties of these ingredients (tailings, binder, and water) have a key influence on strength, stability, transport, curing, and placement performance of CTB materials [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Binders are used to ensure the strength and durability of CTB mass. The most commonly used binder type in the mine sites is ordinary Portland cement (OPC), which is costly and prone to acid and/or sulfate attacks when sulfide-rich processing tailings are used for the manufacture of CTB mass [16]. For that reason, utilization of efficient cost control and highly durable alternative cement types is required for the CTB mixes containing such tailings [17]. [PERSON] et al. [18] demonstrated that the use of pozzolanic mineral and chemical additives as an alternative binder in CPB drastically prevented the mechanical strength losses, even at lower cement contents. It is well known in the concrete industry that alkali-activated slag cement provides a high mechanical strength and stability under aggressive conditions [19]. Some researchers also reported that the cost of alkali-activated slag cement could be as little as a half of that of OPC, ensuring its potential as an alternative binder to be used within CTB or CPB samples containing sulfidic mine tailings [20; 21]. Numerous researchers have conducted extensive research on the activation of slag powder and new filling materials. [PERSON] et al. [22] reported that the cement-related costs were significantly reduced (35%) to achieve an equal strength of 1 MPa for 28-day cured CPB samples, increasing the corresponding mechanical strength gain. [PERSON] et al. [23; 24] also reported that the addition of a proper amount of an alkali activator such as sodium silicate could improve the backfill's strength, drainage, and microstructural properties. Addition of sodium silicate to the CTB mix can reduce the total porosity and the required setting time of the backfill, contributing to an increase in the backfill strength and ore production. In addition, [PERSON] et al. [25] developed concrete mixtures with granulated blast furnace slag as an aggregate, and their results demonstrate that alkaline solution can activate slag effectively. [PERSON] et al. [26] believed that the hydration process and mechanical properties of slag cement are highly dependent on type and dosage of alkaline catalysts. Sodium hydroxide (SH) and sodium silicate are the most commonly used activators. Sodium silicate is indeed a viscous material that is usually used to activate pozzolanic materials such as slag and fly ash. The chemical compound has many applications, namely, in waste treatment [27], mine tailings [28; 29; 30; 31], sand fill [32], and other construction materials [33; 34; 35]. Moreover, [PERSON] et al. [36] analyzed the micromechanical properties of slag binder and found that the strength of sodium hydroxide-active slag cement is higher than that of the surrounding non-reacted slag cement.