## 4 Conclusions  
In the present study, an experimental investigation was carried out to explore the effect of various fibers on the spalling resistance, residual mechanical properties, and physical properties of self-compacting concrete (SCC) after heating to an elevated temperatures. The following conclusions can be drawn:  
1. Steel fiber affects the workability of the concrete marginally up to a fiber dosage of 50 kg/m\({}^{3}\). However, the polypropylene fiber used in the present study has a negative impact on workability, and a large volume of superplasticizer should be utilized to preserve the same water-to-binder ratio and a proper slump flow for SCC.
2. At ambient temperature, steel fiber with dosages ranging from 20 kg/m\({}^{3}\) to 50 kg/m\({}^{3}\) had little effect on the compressive strength, while a great increase of up to 47% was observed for the flexural tensile strength of SCC. Moreover, for polypropylene fiber with dosages of 1 kg/m\({}^{3}\) and 2 kg/m\({}^{3}\), there was no clear impact on the flexural tensile strength of SCC, while a negative effect (15% reduction) on the compressive strength of SCC was obtained.
3. The inclusion of polypropylene fiber can effectively reduce the spalling of concrete even with a low dosage of 1 kg/m\({}^{3}\). Referring to steel fiber specimens, the spalling resistance of concrete can be improved, while relatively high fiber content (e.g., 50 kg/m\({}^{3}\)) is recommended. A temperature of 400 \({}^{\circ}\)C was found to be a key heating level for the residual compressive strength of SCC without and with fibers.
4. Elevated temperatures were found to be more detrimental to the flexural tensile strength of all mixtures. When the target temperature was above 200 \({}^{\circ}\)C, a significant decrease in the residual flexural tensile strength of the plain and fiber-reinforced SCC was observed. Moreover, steel fiber was found to be more effective than polypropylene fiber in enhancing the residual flexural tensile strength of concrete.
5. The incorporation of cocktail fibers blended with 20 kg/m\({}^{3}\) steel fiber and 1 kg/m\({}^{3}\) polypropylene fiber in SCC well satisfies the workability requirements of the fresh SCC. No explosive spalling and less degradation of mechanical properties were observed in specimen SPF201 after exposure to various high temperatures. The mixed fibers exhibit a promising way to improve the fire resistance feature of SCC.
6. Based on the regression analysis, correlations between residual strength and elevated temperature are proposed. A comparison of the equations of reduction coefficient in the literature and the present study illustrates that the proposed equation  
Figure 15: Mass loss of specimens after heating to various high temperatures: (**a**) compression specimens and (**b**) bending specimens.  
is more suitable for predicting the residual strength of the fiber-reinforced SCC at elevated temperatures.  
Conceptualization, X.N. and Y.L.; methodology, X.N. and J.L.; software, X.N. and J.L.; validation, X.N., J.L. and Y.L.; formal analysis, X.N.; investigation, X.N. and J.L.; resources, X.N.; data curation, J.L. and Y.L.; writing--original draft preparation, X.N., J.L. and Y.L.; writing--review and editing, X.N. and J.L.; visualization, X.N. and Y.L.; supervision, X.N., J.L. and Y.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Project No. 51608100) and Science and Technology Project of Jilin Province Education Department (Project No. JJKH20220121 KJ).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available as the data also form part of an ongoing study.  
The authors declare no conflict of interest.