**4. Conclusions**

Despite the significant changes in the technological properties of SSA-containing binders, mainly concerning their setting time and water demand, this additive does not preclude its use in cement composites. SSA content is possible even at the level of 30% by the weight of cement causing an acceptable level of reduction of the performance of binders. Due to their high water demand, it becomes necessary to use superplasticizers

during the preparation of mortars or concretes. The results of chemical shrinkage tests confirmed that the addition of SSA has a positive effect on this characteristic, reducing its value by up to approx. 30%. This is due to its rather low pozzolanic reactivity and relatively small specific surface area. Reducing the amount of cement in the paste further increases the reduction of chemical shrinkage. The effect of hydration of hematite grains in SSA, with simultaneous inhibition of the cement hydration process by the activity of phosphate ions in the initial phase of binder hydration, entails the occurrence of an expansion effect, facilitated by increasing amounts of added SSA.

**Author Contributions:** Conceptualization, M.A. and T.Z.; methodology, M.A.; validation, T.Z. and T.T.; investigation, M.A.; resources M.A and T.Z.; writing—original draft preparation, M.A.; writing review and editing, T.Z. and T.T. 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:** 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.
