## 4 Conclusions  
The following conclusions were drawn from the presented results:  
1. The difference between the microhydration heat of the three mixes was not large. Note that the microhydration heat of the FA20 FN00 mix was slightly higher than that of the FA00 FN20 mix. It is supposed that the use of the ferronickel-slag powder can reduce the hydration heat of mortar and concrete. In addition, the flow of the samples containing at least 10% of ferronickel-slag powder ranged approximately from 117 to 124 mm. The mortar flow increased as the amount of ferronickel-slag powder increased.
2. The compressive strength of the FA15 FN05 and FA20 FN00 mixes using more than 15% of fly ash was relatively high, reaching approximately 35.8 MPa after 7 days. After 28 days, the compressive strength of the FA20 FN00 mix was approximately 39.6 MPa, that is, higher than that of other samples, and the compressive strength of the FA05 FN15 mix using 15% of ferronickel-slag powder was 35.0 MPa, that is, approximately 11.6% lower than the FA20 FN00 mix including only fly ash.
3. The drying shrinkage of the FA20 FN00 sample containing only fly ash was the highest, whereas the FA00 FN20 sample without fly ash presented the lowest shrinkage compared to the other mixes. Therefore, if ferronickel-slag powder is used as a cement substitute, it is likely to be effective in controlling the drying shrinkage of cement mortar and concrete.
4. The carbonation depths of the FA20 FN00 and FA15 FN05 samples including more than 15% of fly ash ranged approximately from 6.85 to 6.92 mm, that is, larger than that of the other samples. The carbonation depth of the FA00 FN20 sample without fly ash was lower than the carbonation depth of the sample containing more than 15% of fly ash, but it was higher than the carbonation depth of the FA10 FN10 and FA05 FN15 samples containing both fly ash and ferronickel-slag powder. In general, the carbonation resistance of the sample with FA and FN was better than that of the sample using FA or FN alone.  
Further studies are needed to confirm the effects of the chemical components of the materials on the strength and durability of cement mortar and the pozzolanic activity index (PAI), etc.  
Figure 7: Accelerated carbonation depth.  
**Author Contributions:** [PERSON] conducted all of the experimental studies and analyzed the test data. [PERSON] and [PERSON] conducted some experiments and wrote the manuscript. [PERSON] advised the experimental work and revised the manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R11A3A01049510). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No.2020R1A4A3079595).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors gratefully acknowledge the National Research Foundation of Korea and Ministry of Education for the financial support of this work. The authors would like to thank Editage for English language editing.  
**Conflicts of Interest:** The authors declare no conflict of interest.