**5. Conclusions**

From the above results and discussion, it is found that curing temperature and GGBFS replacement ratio have a significant effect on the development of concrete compressive strength. The addition of GGBFS also reduces the compressive strength of early age. As a result, the apparent activation energy and the compressive strength of concrete are affected by the GGBFS replacement ratio and curing temperature. Therefore, the existing compressive strength prediction model, i.e., Carino for OPC is not suitable for GGBFS concrete. The *Ea* of the proposed OPC, 10%, 30% and 50% of GGBFS are found to be 33.475 kJ/mol, 37.325 kJ/mol, 41.958 kJ/mol and 45.541 kJ/mol, respectively. Therefore, the equivalent age using *Ea* and a high level of accuracy (R2 = 0.91) is obtained.

**Author Contributions:** Data curation, H.-M.Y. and N.V.M.; Formal analysis, H.-M.Y. and S.-J.K.; Funding acquisition, H.-S.L.; Investigation, H.-M.Y., J.K.S. and S.M.; Methodology, H.-M.Y., H.-S.L.; Supervision, S.-J.K., N.V.M. and H.-S.L.; Writing—original draft, H.-M.Y., S.-J.K., N.V.M., J.K.S., H.-S.L. and S.M.; Writing—review and editing, H.-M.Y., S.-J.K., N.V.M., J.K.S., H.-S.L. and S.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** There is no external funding for this work.

**Acknowledgments:** This research was supported by a basic science research program through the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT and Future Planning (No. 2015R1A5A1037548).

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