## 1 Introduction
As a rule, lower values for static yield stress were observed for higher flow spreads, irrespective of the mortar type. A sharp decline in static yield stress values was noted for all the mortars at the specified L/S ratios before entering the plastic state (flow spread ranged between 140 mm and 190 mm) [9]. The slag-based mortars developed by [PERSON] and [PERSON] [10] exhibited a lower flow spread and higher initial torques than OPC and AAFA-based mortars at a specified L/S ratio. OPC mortars exhibited a substantial decrease in torque development initially from 115 to 9.94 N.mm when the L/S ratio was increased from 0.13 to 0.20 due to the decrement in inter-particle frictional forces. After the initial decline, the torque remained constant exhibiting thixotropic behavior till the test completion [10]. Another study reported a similar demonstration of thixotropic characteristics by AAS and AAFA-based mortars with slight deviations. Additionally, a reduction in torques was observed with an increase in the water to cement ratio (W/C) for OPC-based mortars. Similarly, at higher L/S ratios, lower values for torques were obtained for AAS and AAFA-based mortars. The addition of sand led to higher torques [11]. A similar observation was made in another study where the amount of liquid needed to obtain a required consistency was increased when a more significant amount of fine aggregates was used, as it led to higher yield stresses [12]. All the mortar mixes (AAS, AAFA and OPC), irrespective of reagents, fitted the Bingham model as per the rheological data [12; 13; 14]. However, an investigation by [PERSON] et al. revealed that slag-based mortars activated with WG better fit the Herschel-Bulkley model for rheological characteristics [15]. The other research studies [16; 17] also reported that the activation of slag using WG followed the Herschel-Bulkley model for rheological parameters. The slag-based mortars activated using sodium hydroxide (NaOH) [15] or a combination of NaOH and sodium carbonate (Na\({}_{2}\)CO\({}_{3}\)) [18] fitted the Bingham rheological model [15; 18]. The dynamic yield stress (\(\gamma\)) and plastic viscosity (\(\eta\)) of the Bingham model were reduced with an increased L/S ratio. This is due to reduced inter-particle frictional forces with decreased solids concentration because of the higher liquid content in the system. The fly ash-based mortars exhibited low plastic viscosity values, while the highest plastic viscosity was observed for OPC and slag-based mortars at the lowest L/S ratios. The slag-based mortars activated with WG demonstrated a higher viscosity value of 2.92 than the slag-mortars activated with NaOH and OPC mortars (0.72) at an L/S ratio of 0.15 [9; 15]. The influence of water-reducing admixtures (WRAs) on the rheological characteristics of alkali-activated fly ash binders (AAFA) was investigated in another study [19]. The fly ash-based binders were synthesized by mixing fly ash with the alkaline reagent consisting of 12.5 M NaOH (85%) and Water glass (15%). Lignosulphonates, melamines (first and second generation) and polycarboxylates (latest generation) were used as WRAs. A carboxylate-based superplasticizer was determined to be the most effective based on flowability results. The fly ash-based binders with 0.8% WRAs exhibited similar flow curves in the ascending branch (when the shear stress increased) and the descending side (the shear stress was decreasing). A similar observation about flow curves was made in another study, reflecting that these alkali-activated mortars or pastes are not influenced by the de-clustering of flock particles, a typical phenomenon in cement-based binders [20]. The flow curves for fly ash-based binders had a straight lower branch, indicating that these binders comply with the Bingham model. This means that these binders tend to flow when a slight initial force is applied. The binders with WRAs exhibited lower plastic viscosity values than the fly ash mixes without these admixtures.