## 3 Results and Discussion  
The Gladstone FA-based GP samples exhibited higher density readings compared to Gladstone/Callide FA-based specimens. For example, the former set of samples had density values ranging from 2396 kg/m\({}^{3}\) and 2154 kg/m\({}^{3}\), and for the latter set, it was between 2059 kg/m\({}^{3}\) and 1870 kg/m\({}^{3}\). It was also found that the most-dense Gladstone FA-based GP paste was GP 10, and the most-dense Gladstone/Callide FA-based GP paste was GP 05. When considering the setting times, it was observed that Gladstone FA-based GP pastes remained in liquid state for about 30 min, whereas the other category of pastes set quicker than 30 min. The initial setting times for samples such as GP 01, 02, and 03 of the Gladstone/Callide FA-based GP pastes were between 2 and 4 min, and hence cubes of these samples could not be cast. Figure 3 shows a comparison of the morphology of Gladstone FA-based GP 01 and Gladstone/Callide FA-based GP 01 samples 5 min after casting. This could be attributed to the changes in the pH value of the solution with the addition of NaOH. A higher hydroxide content has the ability to increase the alkalinity of a solution, thus, increase the pH value of a solution, and vice versa. In the case of GP-based materials, it was previously reported that at lower values of pH, the GP mixture exhibited enhanced fluidity (i.e., more workable), while at relatively higher pH values, the mixtures exhibited increased viscosity, thus resulting in the accelerated setting [55]. This could explain why GP 01, 02, and 03, which had a decreasing ratio of Na\({}_{2}\)SiO\({}_{3}\) to NaOH (i.e., a higher hydroxide content), thus having an increase in pH, set quicker than GP 04 and 05. Figure 3: A picture indicating the morphological features of the mixtures: Gladstone FA GP01 (**left**)/Gladstone/Callide FA GP01 (**right**). It was interesting to note that the above effect did not occur in the case of Gladstone FA-based matrices. They in fact exhibited longer setting times even with the variation in the ratios of Na\({}_{2}\)SiO\({}_{3}\) to NaOH. This can be attributed to the difference in amounts of the oxides of aluminum and silicon in the formulations of the two FA materials. It was reported that aluminum can exert a significant influence on the setting times of the GP pastes [56]. For instance, it is established with lower SiO\({}_{2}\):Al\({}_{2}\)O\({}_{3}\) ratios produced shortened setting times, and that slight variations in the Si and Al concentrations can result in substantially different setting times for the GP mixtures. As given in Table 1, Gladstone FA had a slightly higher ratio of approximately 2.0 as opposed to 1.8 for Gladstone/Callide FA, which indicates a longer setting time in the latter case. It was also reported [57] that a higher silica content in geopolymers necessitated a higher water content. In addition to this, presence of a higher content of aluminum within the matrix can initiate quick condensation and thus accelerate the geopolymerization reaction [58; 59]. This supports the findings from the present study, as Gladstone/Callide FA does indeed have a higher silica and aluminum content compared to Gladstone FA. In Table 3, a comparison of the initial compressive strengths among the sealed and unsealed Gladstone FA-based GP specimens are tabulated and are graphically presented in Figure 4. It can be seen that unsealed specimens produced strengths ranging from approximately 15 to 58 MPa, while sealed specimens recorded much higher strengths ranging from approximately 23 to 74 MPa, with the highest strength recorded from GP05 for both sealed and unsealed specimens. An average initial strength increase of approximately 25% was recorded in the sealed specimens compared to unsealed specimens, where sealed specimens exhibited initial strength readings of up to approximately 74 MPa. This constitutes a direct evidence that initial surface evaporation plays a crucial role in the development of strength of GP pastes.