**4. Conclusions**

This study investigated a series of foamed geopolymer samples reinforced with fiberglass mesh. The precursors used in the synthesis of the geopolymer were fly ashes obtained from the combustion of two types of coal: anthracite and lignite. The effects of reinforcement with GFRP mesh and the type of fly ash on the strength properties of geopolymer were explored, and the results of this research and theoretical analyses give rise to the following conclusions:

(1) The origin of fly ash is of great importance for the mechanical properties of the geopolymer concrete. The compressive strengths of geopolymers based on anthracite coal fly ash are at least 73% higher than those based on lignite coal, which is rich in calcium. Similar differences were obtained in tests of the tensile strength and the modulus of elasticity. The worst mechanical properties were shown by geopolymer made from ashes from the Belchatow power plant.


Future research should focus on using reinforcing meshes that are more resistant to alkaline solutions, based on carbon or basalt fibers, and on developing a bonding model that is suitable for porous materials.

**Author Contributions:** Conceptualization, R.K. and S.D.; methodology, R.K. and S.D.; investigation, R.K. and S.D.; data curation, R.K.; writing—original draft preparation, R.K.; writing—review and editing, R.K. and S.D.; visualization, R.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the European Union for financing the project No 645696 RICON and the Silesian University of Technology (Grant no BK-296/RB6/2020).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

