## 4 Conclusions  
This study investigated the performance of one-part MK-based geopolymer concrete and the effects of RESIN8 and FWG as partial replacements of natural sand (5% and 10% by volume) on its properties. The following conclusions are drawn from the investigation:  
1. The inclusion of R5%, R10%, G5%, and G10% improved the workability of OMGPC by 5.3%, 13.7%, 15.8%, and 26.3%, respectively. However, replacing natural sand with RESIN8 reduced the fresh density of OMGPC; on the other hand, the addition of FWG led to improved fresh density. In addition, 2-3% trisodium phosphate by wt. of the binder effectively retard the early setting time of OMGPB by 238.3% (initial setting time) and 133.9% (final setting time) compared to the control.
2. The hardened density of OMGPC at all replacements for RESIN8 and FWG ranges from 2232 to 2324 kg/m\({}^{3}\), classifying them as normal-weight concrete. However, the inclusion of R5% and R10% reduced the hardened density by 1.1% and 1.4%, respectively, while G5% and G10% improved the density by 1.6% and 0.6%, respectively, for 28 days of cured specimens.
3. A 28.6 MPa OMGPC (at 28 days curing) is obtained in this study, which could be used for structural concrete. The inclusion of R5% and R10% decreased the 28-day strength by 15.7% and 24.1%, respectively. While G5% improved the 28-day strength by 3.5%, and G10% had similar strength to the control.
4. The flexural and splitting tensile strengths decreased with an increase in RESIN8 but increased with the inclusion of FWG.
5. The Young's modulus of elasticity of OMGPC was drastically reduced with the incorporation of RESIN8 and FWG. The addition of R5% and R10% decreased the Young's modulus by 60.6% and 78.8%, respectively, while G5% and G10% contents in OMGPC led to 9.1% and 30.3% decrease in the Young's modulus of the matrices, respectively.
6. The RESIN8 and FWG induced porous structure and weak ITZ in the concrete matrix.  
It is recommended that the incorporation of RESIN8 as a substitute for sand in OMGPC be optimised. This should focus on developing strategies to reduce the porosity induced by plastic and improving the ITZ between the plastic aggregates and OMGPC. In addition, the durability properties of OMGPC should be investigated to better understand its resistance to environmental factors, such as freeze-thaw cycles, chemical exposure, and long-term exposure to moisture.  
Conceptualization, B.L.A. and A.J.B.; methodology, B.L.A.; validation, B.L.A.; formal analysis, B.L.A.; investigation, B.L.A.; resources, A.J.B.; data curation, B.L.A.; writing--original draft preparation, B.L.A.; writing--review and editing, A.J.B.; visualisation, B.L.A.; supervision, A.J.B.; project administration, A.J.B.; funding acquisition, A.J.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. Data Availability Statement: The raw data supporting the conclusions of this article will be made available by the authors on request. The data are not publicly available due to privacy.  
**Acknowledgments:** The authors are grateful to the Postgraduate Scholarship Programme Committee, Stellenbosch University, South Africa. The authors' appreciation also goes to the Kaolin Group (Pty) Ltd., CRDC, and Adargh packaging Company, all in Cape Town, South Africa, for donating Metakacolin (MK\({}_{60}\)), RESIN8, and fine waste glass, respectively, for this study. [PERSON] of the Chemistry Department, Obafemi Awolowo University, Nigeria, is also appreciated for his valuable comments during the preparation of this manuscript.  
**Conflicts of Interest:** The authors declare no conflicts of interest.