**5. Conclusions Remarks and Research Perspective**

The conducted review provides clear evidence of how urgent the problem of C&D waste is and confirms the interest of researchers in the development of various building materials using such widespread wastes as CBW and AAC waste. Although, during the planning of the review, the possibility of using both AAC waste and CBW for the production of geopolymers was foreseen, a thorough analysis of the literature allowed CBW to be prioritized.

Even though scientists have studied geopolymers for more than two decades, many factors must be evaluated and analyzed when designing geopolymer compositions. It is necessary to choose suitable curing conditions, precursor materials and activators, and an alkaline solution concentration when trying to reduce the necessary resources and environmental impact.

Particular attention should be paid to the effect of CBW particle size, as the results widely vary. Some articles provide information that the compressive strength of geopolymers, produced using only CBW or CBW in combination with fly ash, is only slightly affected by the particle size change. At the same time, other studies indicate more than a 70% increase in compressive strength after decreasing CBW particle size. In contrast, while using CBW with slag, CBW particle size significantly affected the properties of the geopolymers.

Future research will focus on developing geopolymers using CBW and slag and on providing ambient curing conditions. This direction seems promising and not so resource intensive. This is not only an opportunity to develop geopolymers and reduce the C&D waste simultaneously, it is also a way to reduce the necessary amount of high amorphous precursors such as fly ash, silica fume, and ground granulated blast-furnace slag that are unavailable locally in Latvia.

**Author Contributions:** L.R.: methodology, conceptualization, formal analysis, and writing—original draft preparation. A.S.: validation, conceptualization, methodology, validation, formal analysis, writing—review and editing, and supervision. L.P.: writing—review and editing, supervision, project administration, and funding acquisition. R.G.: validation, writing—review and editing G.S.: validation, writing—review and editing, and supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This publication was supported by Riga Technical University's Doctoral Grant program.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** This research was supported by the Latvian Council of Science within the scope of the project "Foamed Geopolymer Made by Additive Manufacturing for the Construction Technology Applications (3D-FOAM)" No. project9608. This research was supported by the European Social Fund within Project No 8.2.2.0/20/I/008 "Strengthening of PhD students and academic personnel of Riga Technical University and BA School of Business and Finance in the strategic fields of specialization" of the Specific Objective 8.2.2. "To Strengthen Academic Staff of Higher Education Institutions in Strategic Specialization Areas" of the Operational Programme "Growth and Employment. 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.
