**6. Conclusions**

The main findings of the study can be summarized as follows:


in negligible amounts). Regarding the aluminum sulfate solution, no resistance was observed in the case of all paste samples due to the acidic environment of the solution. - Lower resistance to MgSO4 was observed in CCS made of the cement containing more hydraulic calcium silicates (cement #3). In this case, the hydrated silica gel might be extensively modified with Ca. This can lead to a chemical reaction resulting in the formation of gypsum. Additionally, the consumption of magnesium ions and stabilization of silica indicate the interaction between hydrated silica gel and magnesium cations. This interaction, especially, might be due to cation exchange between calcium and magnesium ions. This, in turn, emphasizes the importance of the calcium ions and silica during the carbonation process and the level of pureness of the hydrated silica gel, with respect to sulfate resistance.


**Author Contributions:** Conceptualization, R.T. and J.O.; methodology, R.T.; formal analysis, R.T. and J.O.; investigation, R.T.; writing—original draft preparation, R.T., writing—review and editing, J.O. and S.S., funding acquisition, J.O. 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:** Not applicable.

**Acknowledgments:** SOLIDIA TECHNOLOGIES Inc. is acknowledged for providing the cement materials for the study. The publication cost of this paper was covered with funds from 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.
