*3.3. XRF Analysis*

The results of the XRF analysis are shown in Table 5; the main chemical components of the cementless materials were found to be CaO, SiO2 and Al2O3. The proportions of the mentioned oxides were similar among the groups of specimens, which also indicated that the hydrated products should be C-S-H or C-A-S-H. It was noticed that the specimens all had a high content of SO3, which quickly formed well-crystallized calcium-alumina crystals or ettringite in the voids of the specimens and helped to improve the hydrated bulk densities of the microstructures [12]. It may also be the leading cause of the higher compressive strength of G5 and G6 specimens (60% and 55% of co-fired fly ash). Moreover, the ratios of Ca/Si and Ca/Al in the air-cured and water-cured specimens were similar. The higher Ca/Si and Ca/Al specimens corresponded to better compressive strengths and represented more crystallization and gelation.

