## 3 Experimental Results and Analysis
### Analysis of Compressive Peak Strain in Prismatic Specimens  
A stress-strain curve test was conducted on prismatic specimens of UHPC mixed with varying amounts of steel fibre and steel slag micro-powder. Compressive strength and peak strain values were measured for each group of UHPC specimens containing steel fibre and steel slag micro-powder. The numerical values for each group are presented in Table 4.  
In Table 4, it is evident that the average peak stress of the steel slag micro-powder UHPC prismatic specimens is 105.1 MPa, with an average peak strain of 3277 \(\mu\)c. When the steel fibre content is 1% and 1.5%, the axial compressive strength shows a trend of first increasing and then decreasing with the increase in coarse aggregate content; when the steel fibre content is 2%, the axial compressive strength shows a slight decreasing trend with the increase in coarse aggregate content. When the steel fibre content is 1.5% and the coarse aggregate content is 20%, both the axial compressive strength and peak strain reach their maximum values, indicating the optimal content at this time. The strength is increased by 20% compared to without adding coarse aggregate and by 14.6% compared to adding 40% coarse aggregate. When the amount of steel fibre added is constant, the peak strain of each group of specimens shows a trend of first increasing and then decreasing with the increase in coarse aggregate content. When the amount of coarse aggregate added is constant, an increase in steel fibre content generally leads to an increase in peak strain. Compared with the non-steel fibre group, the nine experimental groups mixed with steel fibre showed higher strength and peak strain. The experimental groups mixed with 1%, 1.5%, and 2% steel fibre increased the peak strain by about 20.3%, 25.3%, and 26.2%, respectively, compared to the non-steel fibre specimens. It can be seen that the toughening effect of UHPC with steel fibre and slag micro powder is good, and it can also be seen that the peak strain effect of UHPC with 2% steel fibre content is no longer significant compared to 1.5% content, and the compressive strength is still reduced. The optimal economic and mechanical properties are achieved when the 1.5% steel fibre content is added. To investigate the relationship between the peak strain \(\varepsilon_{c}\) and the compressive strength \(\mathrm{f_{c}}\) of steel slag micro-powder UHPC, three formulae presented in Table 5 were compared with the experimental results. The peak strain of the UHPC specimens mixed with steel fibre and steel slag micro-powder ranged from 2985 \(\mu\)c to 3435 \(\mu\)c. To determine the variation relationship between the peak strain \(\varepsilon_{c}\) and the axial compressive strength fc \begin{table}
\begin{tabular}{c c c c c} \hline
**Group** & **Steel Fibre Content\%** & \
\begin{tabular}{c} **Coarse Aggregate** \\ **Content /\%** \\ \end{tabular} &
\begin{tabular}{c} **Compressive Strength** \\ _f/MPa_ \\ \end{tabular} & **Peak Strain \(\varepsilon_{c}\)/10\({}^{-6}\)** \\ \hline SSP1 & 1 & 0 & 95.1 & 2985 \\ SSP2 & 1 & 20 & 111.5 & 3370 \\ SSP3 & 1 & 40 & 98.3 & 3071 \\ SSP4 & 1.5 & 0 & 100.6 & 3112 \\ SSP5 & 1.5 & 20 & 120.6 & 3435 \\ SSP6 & 1.5 & 40 & 105.2 & 3275 \\ SSP7 & 2 & 0 & 106 & 3285 \\ SSP8 & 2 & 20 & 105.3 & 3310 \\ SSP9 & 2 & 40 & 103.7 & 3227 \\ Average & & & 105.1 & 3277 \\ P10(No Steel Fibre) & / & / & 90.5 & 2611 \\ \hline \end{tabular}
\end{table} 
Table 4: UHPC compressive strength and peak strain of steel slag micro-powder mixed with steel fibre. of steel slag micro-powder UHPC, a statistical analysis of \(\epsilon_{c}\) and \(\ell_{c}\) of the nine groups of specimens was performed.