## 3 Results and Discussion
### Microstructural Characteristics
#### 3.3.1 SEM/EDS Analyses  
Figure 14a-d presents the morphology of the control AAECs (B1, B2, T1, and T2). As expected, the PVA fibers embedded in the AAEC matrix remained intact without any rupture or breaking in the failed cube specimens tested under compression. The morphology of the binary mixes appears to be denser, with a smaller number of unhydrated/partially hydrated fly ash particles than their ternary counterparts, as shown in Figure 14a,c. The fly ash particles are embedded in the matrix of ternary mixes, as indicated in Figure 14b,d. This can be attributed to the relatively lower reactivity of fly ash class F particles. Figure 12: Influence of (**a**) MWCNTs, (**b**) rGO, and (**c**) MgO on 28-day UPV of AAEC mixes with reagents 1 and 2. Figure 13: Correlation between (UPV) and compressive strength at 28 days. The MgO-added mix exhibited the highest compressive strength (as described in the previous section, Figure 11a) and showed a denser morphology than the control mixes. The MgO-added mixes appeared to be the most compact among all the mixes, with some of the particles acting as inert material, filling up the void spaces, as noted in Figure 15a-d.  
Figure 14: Morphology of the control mixes: (**a**) B1, (**b**) B2, (**c**) T1, (**d**) T2. Figure 15: _Cont._  
Good dispersion can be seen in Figure 15e,f, and individual MWCNTs are distributed throughout the matrix uniformly. In addition to filling pores and voids, the MWCNTs bridge hollow spaces and micro cracks. MWCNT bridging was observed, as shown in Figure 15e, in a 2000k zoom picture from the SEM test. The crack-bridging effect of MWCNTs contributes to the deacceleration of the initiation and extension of cracks [35]. The mechanical properties of MWCNT-incorporated AAEC mixes are better (especially the compressive strength and UPV for 0.3% wt. MWCNT dosage, as discussed in the previous section, Figures 11b and 12a) than those of their control counterparts. The propagation of micro cracks and branching must pass the nanotubes or occur in areas with a weak matrix-MWCNT interaction bond state, which is essential to the macro properties of AAECs. The absence of a prominent interfacial layer between the MWCNTs and the geopolymer matrix, as can be inferred from the microstructure, demonstrates a healthy bond, indicating the chemical stability of MWCNTs under geopolymerization. Figure 15g,h shows the good morphology of the rGO-incorporated AAEC mixes (B2R3, B2R6) with uniform dispersion. The main reaction product for binary mix B1 consisted of C-A-S-H and calcium-rich N-C-A-S-H acute phases with traces of MgO, as indicated in the SEM/EDS graphs presented in Figure 16a Their presence can be confirmed from the elements (Ca = 10.8%, Si = 8.3%, Al = 5.6%, C = 14.7%, Mg = 5.5%, Na = 1.5%, and O = 53.6%) noted in the EDS graph. The partially hydrated round fly ash class C and angular GGBFS particles can be observed in the SEM micrograph. The dominant reaction product for binary mix B2 consisted of C-A-S-H, as shown by the elements (Ca = 17.9%, Si = 7.7%, Al = 4.1%, C = 12.8%, O = 48.8%) with higher percentages in the EDS analysis presented in Figure 16b. An additional binding phase composed of C-S-H can be observed in the SEM micrograph because of the higher calcium content in the system (for B2 with reagent 2) than that in mix B1. The higher calcium content is attributed to the higher calcium content in reagent 2 (Ca(OH)2:Na2 SO4 = 2.5:1) compared to that in reagent 1 (Ca(OH)2:Na2 SO3:5H2O = 12.5). The higher calcium content in reagent 2 resulted mainly in the formation of C-A-S-H/C-S-H gels and comparatively less dissolution of silicate and aluminum ions, which are responsible for polymerization/alkali activation. As a result, the reagent 1 mixes developed lower strengths than their reagent 2 counterparts. The binary and ternary mixes developed C-A-S-H, N-C-A-SH, and C-S-H reaction product combinations depending on whether they incorporated reagent type 1 or 2.