## 3 Results and Discussions
### Microstructural Analysis  
The morphology and microstructural characteristics of the mortar specimens were studied under a scanning electron microscope (SEM) at 28 days. The reaction prod  
Figure 8: Yield stress versus slump flow. Figure 7: Shear stress–strain relationship: (**a**) binary mortars; (**b**) ternary mortars. ucts/elemental compositions determined using EDS analysis are discussed to relate their influence on fresh state and rheological properties. The morphology of the binary (CS) mortars appears to be denser with a smaller number of un-hydrated/partially hydrated fly ash particles than their ternary (CFS) counterparts, as shown in Figure 9a,b. The fly ash particles are seen to be embedded in the matrix of ternary CFSM2 mortar, as indicated in Figure 9b. This can be attributed to the relatively lower reactivity of fly ash class F particles in CFSM2. The control mortar (FP\({}_{\text{C}}\)M) exhibited the highest compressive strength of 43.5 MPa (Table 3), and its matrix appeared to be the most compact among all the mortar specimens, with some of the FA-F particles acting as inert material filling up the void spaces, as noted in Figure 9c. The dominant reaction product for binary CSM2 mortar with reagent two consisted of C-A-S-H as evidenced by the presence of higher percentages of elements (Ca = 17.9%, Si = 7.7%, Al = 4.1% and O = 48.8%) in the EDS analysis presented in Figure 10a. Additionally, the high calcium content in reagent two (Ca(OH)\({}_{2}\):Na\({}_{2}\)SO\({}_{4}\) = 2.5:1) led to the formation of Portlandite (Ca(OH)\({}_{2}\)), which facilitated the synthesis of additional C-S-H gel. The formation of these gels (C-A-S-H/C-S-H) was also identified in fly ash/slag-based binders from previous research studies [38]. Figure 9: Morphology of the mortars at 28 days: (**a**) CSM2; (**b**) CFSM2; (**c**) FP\({}_{\text{C}}\)M.  
A mix of amorphous and crystalline products can be observed from the SEM micrograph of ternary mortar CFSM2 with reagent two presented in Figure 10b. The main reaction product consisted of C-A-S-H gel as determined from major elements (Ca = 17.5%, Si = 14.3%, Al = 10.4%, Na = 2.2% and O = 36.3%) in the EDS analysis. The higher calcium content in the CFSM2 composition facilitated silicate and aluminum ions' dissolution from fly ash. This enhanced dissolution of ions led to an improved alkali activation with addi  
Figure 10: (**a**): SEM micrographs and EDS analysis of the binary mortar CSM2; (**b**): SEM micrographs and EDS analysis of the mortar CFSM2; (**c**): SEM micrographs and EDS analysis of the mortar \(\text{FP}_{\text{C}}\text{M}\). tional binding phases (C-S-H and N-C-A-S-H/N-A-S-H) responsible for higher strengths (Table 3) than their ternary counterpart with reagent one. The formation of only crystalline C-A-S-H/C-S-H in binary (CS) mixes led to higher 28-day compressive strength (Table 3) than their ternary (CFS) counterparts, where a blend of crystalline (C-A-S-H) and amorphous (N-C-A-S-H/N-A-S-H) reaction products are formed with comparatively more un-hydrated or partially hydrated fly ash grains (Figure 10a,b). The production of C-A-S-H and C-S-H with shorter Si-Al linkages in both binary/ternary mixes with reagent two (Figure 10a,b) produced lower viscosity and yield stress with a higher slump flow (as confirmed from the fresh state and rheology test results presented earlier) compared to their reagent one counterparts, where the formation of N-C-A-S-H and N-A-S-H gels with comparatively longer polymeric chains in addition to C-A-S-H were found to be dominant as confirmed from authors' previous research [23]. The partially hydrated fly ash class F (FA-F) particles observed as embedded in the control mortar matrix (FP\({}_{\text{C}}\)M) shown in Figure 10c facilitated the densification of the matrix by filling up the void spaces.