# Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars
## 4 Conclusions  
This paper has presented the first study on the properties of geopolymers containing expanded vermiculite as a sand material. The following conclusions can be made from presented results:  
* At a given FA and expanded vermiculite content, geopolymers prepared with a 10 molar NaOH solution developed a higher flowability (6-14%), apparent porosity (2-10%) and water absorption (4-25%), as well as a lower dry unit weight (4-14%), compressive strength (13-22%), ultrasound pulse velocity (3-11%) and thermal conductivity (1-8%) in comparison with those having a 15 molar NaOH solution. This observation was due to the more compact microstructures of the geopolymers with the 15 molar NaOH solution than those with the 10 molar NaOH solution;
* Geopolymers with a higher FA content exhibit a higher flowability, water absorption and apparent porosity, but a lower dry unit weight, compressive strength, ultrasound pulse velocity and thermal conductivity in comparison with those having a lower FA content for the same content of expanded vermiculite and NaOH concentration;
* For the same FA content and NaOH concentration, incorporating expanded vermiculite (15%) resulted in a decrease in the flowability (\(\sim\)6%), dry unit weight (\(\sim\)6%), compressive strength (\(\sim\)7%), ultrasound pulse velocity (\(\sim\)6%) and thermal conductivity (-18%), as well as increased water absorption (\(\sim\)9%) and apparent porosity (\(\sim\)6%) in the geopolymer. This is due to the porous structure of the expanded vermiculite;
* An increase in the content of expanded vermiculite (from 15% to 30%) resulted in a decrease in the flowability (\(\sim\)4%), dry unit weight (\(\sim\)5%), compressive strength (\(\sim\)9%), ultrasound pulse velocity (\(\sim\)13%) and thermal conductivity (\(\sim\)14%), as well as increased water absorption (\(\sim\)15%) and apparent porosity (\(\sim\)7%) in the geopolymer for a given FA content and NaOH concentration;
* The geopolymers prepared in this study containing 30% expanded vermiculite exhibited a lower dry unit weight compared with those prepared in previous studies [15; 24] containing 30% clay, pumice and expanded vermiculite. In addition, the geopolymer prepared with 30% expanded vermiculite developed a lower thermal conductivity than the concrete with 100% expanded polystyrene [80] and cement mortar with 40% expanded perlite [14] prepared in previous studies. These results indicate great potential for producing an eco-friendly and lightweight building material with excellent sound and thermal characteristics.  
**Author Contributions:** Conceptualization, O.G.; methodology, O.G. and H.T.; validation, O.G., A.G., H.T. and T.O.; formal analysis, A.G.; investigation, O.G. and H.T.; writing--original draft preparation, A.G.; writing--review and editing, O.G., A.G. and T.O.; supervision, T.O. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.