**9. Recommendations**

Waste wood ash has the possibility of being a substitute construction material for sustainability purposes, as a fractional substitute of binder and aggregates. The usage of waste wood ash in large volumes is conceivable. Some research has been conducted on this and some hopeful outcomes have been observed, as WWA can be utilized as an eco-efficient material with little to no compromise on the properties of geopolymer concrete samples. However, for now, WWA has been utilized in a limited amount in the development of samples. This extensive review study of WWA on geopolymer concrete as a fractional substitute of binder showed that the shape, size, source, method of making WWA, and chemical and physical composition of WWA have a significant impact on the strength and durability properties of the sample in which WWA is utilized. Thus, waste wood ash is suitable as a binder replacement, and if it is used in construction as a building material, it will reduce the demand for cement, which will reduce the outflow of greenhouse gases from the production of cement and also preserve the natural reserves of limestone used in the making of cement, thus helping the environment and assisting the construction industry by increasing its sustainability.

**Author Contributions:** Conceptualization, R.M.-G. and P.J.; methodology, R.M.-G. and O.Z.; software, P.J. and S.M.A.Q.; validation, C.M.G., J.d.P.-G. and A.A.S, .; formal analysis, F.J.F.-F.; investigation, A.A.S, .; resources, F.J.F.-F.; data curation, C.M.G.; writing—original draft preparation, R.M.-G. and O.Z.; writing—review and editing, O.Z.; visualization, S.M.A.Q.; supervision, R.M.-G.; project administration, A.A.S, .; funding acquisition, J.d.P.-G. 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:** Data can be provided upon request from the corresponding author.

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