**4. Conclusions**

This study found that ternary cementless composites can be formed using ggbs, cofired fly ash and ultrafine fly ash. The highest compressive strength was 17.5 MPa for two raw materials and 16.4 MPa for three raw materials. The average 28-day compressive strength ranged from 13 to 18 MPa, making it an innovative cementless material that meets net-zero carbon emissions. The cementless materials had better hydration and crystallization reactions when they were maintained in water, and the main products were C-S-H, C-A-S-H colloids and calcium alumina. These crystalline reactants can be verified using XRF, SEM and EDX analysis. The results also suggest that the novel ternary cementless composites developed in this study are worthy of further investigation into their engineering properties for future applications in construction materials.

**Author Contributions:** Conceptualization, W.-T.L. and Y.-H.C.; methodology, Y.-H.C.; validation, W.-T.L., Y.-H.C., M.Z. and D.K.; investigation, L.F.; resources, A.C.; data curation, M.Z. and D.K.; writing—original draft preparation, W.-T.L. and Y.-H.C.; writing—review and editing, W.-T.L. and L.F.; visualization, A.C.; supervision, W.-T.L. and L.F.; project administration, W.-T.L. and L.F.; funding acquisition, A.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** The National Science and Technology Council (NSTC) in Taiwan supported this research with grant NSTC 111-2923-E-197-001-MY3 and the Czech Science Foundation in Czech Republic with project GACR 22-00987J. ˇ

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Publication cost of this paper was covered with founds of the Polish National Agency for Academic Exchange (NAWA): "MATBUD'2023-Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023.

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