# Preliminary Study of New Sustainable, Alkali-Activated
## 4 Conclusions  
To develop new, sustainable materials and to reuse the CSP fraction generated during glass cullet recycling, different AAC formulations have been developed. These newly formulated sustainable binders contained the CSP as a sole precursor, while the different concentrations of NaOH was used as activator solutions. Glass is the main component of the CSP fraction, with a high level of amorphization degree and SiO\({}_{2}\), Na\({}_{2}\)O, CaO, and Al\({}_{2}\)O\({}_{3}\) as the main components; these are all key components for alkali-activated cement (AAC) development. The XRD pattern of the AAC, formulated using CSP as a sole precursor, showed a displacement of the amorphous halo when increasing the alkali concentration of the activator, due to the potential formation of NASH gel. Likewise, the FTIR results also indicated a displacement in the peak around 1000 cm\({}^{-1}\) (Si-O-Si) from CSP concerning the different AAC formulations, regarding again the formation of N-A-S-H gel. After the SEM observation, it was concluded that the AAC formulated with the NaOH 4 M and L/S = 0.5 were the specimens with proper cohesion and integrity of the matrix binder. This result was in accordance with the apparent density and compressive strength. On the one hand, a decrease was observed in the apparent density when increasing the L/S ratio from 0.5 to 0.6, and higher values were obtained in the 4 M NaOH formulations. On the other hand, a decrease in the compressive strength was tested when increasing the L/S ratio from 0.5 to 0.6, and an important increase was achieved in the 4 M NaOH formulations. Accordingly, it was demonstrated that CSP can be employed as a precursor for alkaline cement formulation for constructive purposes, considering as key parameters the activator concentration and L/S ratios, as these affect the physical and mechanical properties of the AAC obtained.  
This research sheds light on the potential use of the CSP as a precursor for AAC. It should be emphasized that CSP is a residue in Spain and is disposed of in landfills because it is not useful for the recycling glass cullet industry. Therefore, the present research is a relevant solution for enhancing sustainable and environmental criteria, as well as following a circular economy strategy.  
Figure 8: SEM micrographs of the AAC formulations with an L/S ratio of 0.5 (i.e., 1 M = 05 LS1M, 4 M = 05 LS4M, 8 M = 05 LS8M).  
**Author Contributions:** Conceptualization, A.M.-A., [PERSON] and J.F.; methodology, A.M.-A., [PERSON]-P., J.M.C. and J.F.; software, A.A.-R., J.M., [PERSON] and J.F.; formal analysis, A.M.-A., [PERSON]P. and J.F.; investigation, A.M.-A., [PERSON]-P., [PERSON]-A.-R. and J.M.; writing--original draft preparation, [PERSON]-P. and J.F.; writing--review and editing, A.M.-A. and J.M.C.; supervision, [PERSON]-P. and J.F.; funding acquisition, J.M.C. and J.F. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was partially funded by the Spanish Government (BIA2017-83912-C2-1-R). Mr. [PERSON] and Mr. [PERSON] are grateful to the Catalan Government for their research Grants, FI-DGR 2017 and FI 2020, respectively.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Acknowledgments:** The authors would like to thank the Catalan Government for the quality accreditation given to their research group DIOPMA (2017 SGR 118). The authors also want to thank Daniel Rosas S.A. company for supplying the CSP sample. [PERSON] is a Serra Hunter Fellow.  
**Conflicts of Interest:** The authors declare no conflict of interest.