*3.6. XRD Analysis*

Figure 8 presents XRD patterns of non-cement blended samples prepared using various S/FA ratios at 28 days. Hydration products appeared in various phases, including Ca(OH)2, Ca3SiO5, Ca6Al2(OH)12(SO4)3-26H2O and CaFe2O5. The non-cement blended specimens displayed roughly the same CaSO4-2H2O and Ca6Al2(OH)12(SO4)3-26H2O (ettringite) [31] peaks compared to the control groups. Note that the non-cement blended specimens also presented relatively small Ca(OH)2 peaks and slightly high Ca3SiO5 peaks compared to the P specimens. It also indicated that the hydration products of non-cement blended specimens were similar to the P specimens and almost less calcium hydroxide (Ca(OH)2) was found in non-cement blended specimens. It indicated that the quartz (SiO2) in the FA reacted with lime (CaO) and Ca(OH)2, resulting in the formation of C-S-H and C-A-S-H gel, which are the key factors in strength development in cementitious materials [32,33]. The FA also had higher proportions of f-CaO and CaSO4, which has been shown to activate cementing processes and hydration reactions [34]. It also confirmed that the strength of non-cement blended composites can be achieved to conventional cement-based materials at the age of 56 days.

**Figure 8.** XRD patterns of various samples at 28 days.
