**5. Conclusions**

tively.

It should be noted that FA has a significant impact on the resistance to chloride ion penetration of SCC. Gnanaraj et al. [93] discovered that FA could greatly enhance its resistance to chloride ion penetration. The studies of Mahalingam et al. [21] and Esquinas et The application techniques and hydration mechanisms of SCMs in SCC were discussed, and the impacts of FA, SF, GBFS, and LP on the microstructure and performance of SCC were reviewed. The major conclusions are as follows:

	- proportion of aluminum phase and predominantly spherical particles; SF primarily contains SiO2 and has a high specific surface area. GBFS mainly contains SiO2 and CaO; LP chiefly consists of CaCO3, and both of them show obvious irregular and angular shapes due to mechanical grinding. The hydration mechanisms of these SCMs in SCC include pozzolanic reaction, alkaline activation, and adsorption effect. Moreover, the filling effect and dilution effect of some SCMs on the paste will con-• The pozzolanic reaction and filling effect of SCMs reduce the porosity of the hardened paste, resulting in a denser microstructure in the interfacial transition zone, thus increasing the durability of SCC. Furthermore, because of the high aluminum phase composition, FA and GBFS are typically capable of improving the resistance to chloride ion penetration and sulfate attack of SCC.

tribute to reducing the porosity and limiting the temperature rise of concrete, respec-

It is worth mentioning that although the employment of multiple SCMs in a composite system may provide a superposition effect, the chemical composition of different SCMs varies widely, and the issues of compatibility may rise. The rules governing the influence of composite SCMs added to SCC are not consistent and require additional investigation.

**Author Contributions:** Conceptualization, Z.L. and D.W.; validation, Z.L., M.A. and D.W.; investigation, L.P.; resources, Z.L.; writing—original draft preparation, L.P.; writing—review and editing, D.W.; visualization, L.P.; supervision, D.W.; project administration, D.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by Natural Science Foundation of China [No. 51478248].

**Acknowledgments:** The authors would like to acknowledge the National Natural Science Foundation of China (No. 51478248).

**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
