# Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars
## 3 Results and Discussion
### Dry Unit Weight  
The test results of the dry unit weights of the geopolymer mixes are shown in Figure 7. As can be observed from the figure, the mixes with a 10 molar NaOH solution developed lower unit weights in comparison with those prepared with a 15 molar NaOH solution. The lower unit weight of the mixes having lower activator concentrations agrees with previous research on FA-based geopolymer mortar [50], FA-based geopolymer concrete [60] and geopolymers having zeolitic tuff and marble waste [51,61], and this was because the densification between the particles of the mixes increased with the increasing activator concentration [50]. The 10 molar NaOH mixes with 50% and 70% FA had 4-11% and 8-14% lower unit weights compared with the companion mixes with 15 molar NaOH solution, respectively. For a given vermiculite content and NaOH concentration, increasing the FA content resulted in a decreased unit weight of the geopolymers. The lower unit weight of the mixes with a higher content of FA agrees with previous research on concrete with recycled concrete fine aggregate [52] and gypsum composite [53,54], and this was due to the less specific gravity of FA in comparison with that of sand, which was replaced with FA. For the 10 molar NaOH solution, the 70% FA mixes containing 0%, 10% and 30% vermiculite had 13%, 7% and 10% lower unit weights, respectively, and for the 15 molar NaOH solution, they had 3%, 4% and 9% lower unit weights compared with the companion 50% FA mixes, respectively.  
As shown in Figure 7, the incorporation of expanded vermiculite led to a decrease in the unit weights of the mixes for a given FA content and NaOH concentration. It can also be seen that increasing the content of vermiculite caused a decrease in the unit weights of the mixes. These results agree with previous research on conventional mortar [12,25,26,28,62], conventional concretes [63,64], metakaolin-based geopolymer concrete [57], slag-based geopolymer mortar [65] and fibrous gypsum plasters [66], and they happened because of the lower specific gravity of expanded vermiculite in comparison with the sand [26]. This could also be due to the existence of voids in the structure of the expanded vermiculite, as was reported by [PERSON] et al. [12]. At 50% FA, the mixes containing 15% and 30% vermiculite exhibited approximately 7% and 10% lower unit weights, respectively, and at 70% FA, they experienced approximately 5% and 12% lower unit weights than the companion mixes with 0% vermiculite, respectively. It was reported by [PERSON] et al. [19] that mortar mixes containing 100% expanded clay and pumice as the other types of lightweight materials exhibited dry unit weights of higher than 1800 kg/m\({}^{3}\). As was  
Figure 7: Dry unit weights of the geopolymer mortar.  
reported by [PERSON] et al. [28], the dry unit weight of cement-based mortar containing 30% expanded vermiculite was 1774 kg/m\({}^{3}\). However, the dry unit weights of the mortar of this study were less than 1500 kg/m\({}^{3}\) with up to 30% of expanded vermiculite, which is lower than the existing studies with clay, pumice and expanded vermiculite.