## 3 Results and Discussions
### Fresh State and Rheological Characteristics
#### 3.1.2 Hysteretic Viscosity Behavior of Mortars  
Table 5 presents the shear rate (in RPM and 1/s) and the corresponding viscosity of different mix compositions with the increase followed by the decrease in RPM. The mortar (FP\({}_{\text{C}}\)M, CSM2, CSM2N, CFSM2 and CFSM2N) mixes regained their initial viscosity at 0.5 RPM exhibiting hysteretic loop characteristics (Table 5). The reduction in viscosity with an increase in shear rate (0.5 to 3.5 RPM) represented by a solid line (shear ramp-up) and the gain in viscosity with the decrease in shear rate (3.5 to 0.5 RPM) indicated by the dotted line (shear ramp-down) are presented in Figure 6a,b. The viscosity with shear rate plots indicates a rapid decrease in viscosity for all the mixes  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Speed**} & \multirow{2}{*}{ \begin{tabular}{c} **Shear Rate** \\ **(RPM/60)** \\ \end{tabular}  } & \multicolumn{6}{c}{**Mix-ID**} \\ \cline{3-10}  & & **CFM** & **CSM1** & **CSM1** & **CSM2** & **CSM2N** & **CFSM1** & **CFSM1N** & **CFSM2** & **CFSM2N** \\ \hline \multicolumn{1}{c}{**(RPM)**} & \multicolumn{6}{c}{**(\({}^{1}\)/s)**} \\ \hline
0.5 & 0.01 & 12.8 & 311.4 & 332.8 & 280.3 & 234.3 & 195.8 & 571.4 & 93.1 & 67.4 \\ \hline
1 & 0.02 & 8.0 & 173.9 & 156.8 & 142.8 & 122.5 & 114.5 & 344.0 & 48.2 & 36.4 \\ \hline
1.5 & 0.03 & 5.7 & 122.7 & 125.2 & 95.9 & 84.9 &with a more rapid decrease for mixes with reagent one till 0.02/s (1 RPM). This can be attributed to the higher degree dissolution potential of sodium metasilicate, which led to the faster release of water during the initial periods of the alkali activation process. All the mortar mixes showed decreased viscosity with an increase in shear rate up to 3.5 RPM depicting pseudoplastic behavior. The viscosity of different mix compositions followed the same path backward initially when the RPM started to reduce from 3.5 to 0.5 RPM, obtaining equal or higher final viscosities in all the mortar mixes at 0.5 RPM with few (lower final viscosity for mortar mix CSM2) exceptions. A similar trend was noted in a previous study where the two-part fly ash-based binders exhibited similar flow curves in both directions (shear ramp up and ramp down) [19]. This reflects that these alkali-activated pastes or mortars are not influenced by the de-clustering of floci, which is a typical phenomenon in cement-based materials [19]. Figure 6: (**a**): Viscosity versus the shear rate of binary mortars; (**b**): Viscosity versus the shear rate of ternary mortars. The control mortar mix (FPcM) obtained the same final viscosity of 12.8 Pa.s at 0.5 RPM, as indicated in Table 5. A lower final value of viscosity was observed for AAM mix CSM2. Almost similar final and initial viscosity values were observed for the mixes CSM2N and CFSM2. These mixes with reagent two exhibited a higher slump flow, lower viscosity and yield stresses than those with reagent one. This can be attributed to the dominant formation of cementitious reaction products (C-A-S-H/C-S-H) in mixes with reagent two (CSM2, CSM2N, CFSM2 and CFSM2N) having shorter chains than the Si-Al linkages in N-A-S-H/N-C-A-S-H gels being formed predominantly in the mortar mixes with reagent one (CSM1, CSM1N, CFSM1 and CFSM1N). All the mortar mixes with reagent one obtained higher final viscosity values at 0.5 RPM due to their faster reaction process owing to the system's high alkalinity. A similar observation was made in an earlier investigation on two-part fly ash-based geopolymer paste where sodium (Na) based activators resulted in considerably higher viscosities than potassium (K)-based activators with both a hydroxide and silicate-based solution [35]. Additionally, greater viscosity values were obtained for Na-based activators than their K-based counterparts due to the lower molecular weight of sodium. Consequently, more sodium silicate was needed than potassium silicate to achieve similar silica modulus and other ratios (Na\({}_{2}\)O/FA and K\({}_{2}\)O/FA).