## 5 Conclusions  
* When the steel fibre content in steel fibre-doped steel slag micronized ultra-high-performance concrete (UHPC) is 1%, the axial compressive strength shows an increasing trend with an increase in coarse aggregate content, followed by a decrease. When the steel fibre content is 2%, the axial compressive strength exhibits a slight decrease with an increase in coarse aggregate content. The optimal combination of steel fibre content and coarse aggregate content for achieving the maximum axial compressive strength and peak strain is 1% and 20%, respectively.
* With a constant steel fibre content, the peak strain of each group of specimens shows an initial increase followed by a decrease as the coarse aggregate content increases. Overall, the peak strain ranges from 2985 \(\mu\epsilon\) to 3435 \(\mu\epsilon\). Based on the experimental variations in the peak strain and axial compressive strength of steel fibre-doped steel slag micronized UHPC, a relationship equation for peak strain strength is obtained through fitting.
* By analysing the measured experimental data, a uniaxial compressive constitutive relation equation is proposed for steel fibre-doped steel slag micronized UHPC, and the calculation formulae for the related parameter values of the constitutive relation equation are provided. The established constitutive relation curve fits well with the experimental curve, and the calculated values have a deviation within 10% of the measured values. This indicates that the selected constitutive relation equation and parameter calculation formulae are reasonably accurate, providing a reference for strength prediction and practical applications of steel fibre-doped steel slag micronized UHPC.
* Finite element software was used to perform a nonlinear analysis of the entire axial compressive process of prism specimens based on the proposed constitutive relation equation in this study, providing effective supplementary information for the measured values. The calculations show that the finite element simulation curve exhibits a  
Figure 10: Comparison of stress–strain curves between simulation and experiment.  
similar trend to the experimental curve, and the deviation in the peak load is within 10%. This further verifies the reliability of the proposed constitutive relation equation.  
Conceptualization, X.T. and B.H.; methodology, B.H.; software, B.H.; validation, X.T., B.H. and J.C.; formal analysis, B.H.; investigation, B.H.; resources, X.T and B.Y.; data curation, B.H.; writing--original draft preparation, B.H.; writing--review and editing, B.H., X.T. and J.C.; visualization, X.T.; supervision, B.Y. and J.C.; project administration, B.Y.; funding acquisition, B.Y. and X.T. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Natural Science Foundation of China (No. 42067044) and the Guangxi Graduate Education Innovation Program (YCSW2021171).  
Not applicable.  
The data used to support the findings of this study are available from the corresponding author upon request.  
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.