## 5 Conclusions  
Based on the studies of this paper, conclusions can be drawn as follows:  
1. Based on the multi-index synthetical evaluation of pull-out behaviors of hooked-end steel fiber embedded in mortars, the indices for evaluating the synergistic bond properties of different deformed steel fibers are proposed by using the concept of per unit weight of steel fibers. The bond strength indices of the loads of per unit weight steel fibers and the load on per embedded length of per unit weight steel fibers, the expended energy indices of the work of per unit weight steel fibers and the toughness indices of energy ratios are proposed to comprehensively express the bond properties, considering the geometry and numbers of different deformed steel fibers. 2. Hooked-end steel fibers with a tensile strength higher than 1150 MPa are strength and toughness enhanced type fibers with different degrees of enhancement. HFb, HF2, and HF3 with tensile strengths between 1150-1500 MPa have excellent strengthening, energy dissipation effect, and toughening capacity in the normal serviceability and ultimate bearing capacity of concrete. Their strength use efficiency \(u_{\text{sf}}\) was close to the limit of 71.4% for high-strength steel bar. However, HF5 with a tensile strength of 1150 MPa could develop a higher strength use efficiency \(u_{\text{sf}}\) that reached about 100%, which led the broken steel fiber due to the strong anchorage of a 4-D type hooked-end. HF6 with a tensile strength of 2200 MPa had a large affluence with a smaller strength use efficiency \(u_{\text{sf}}\) of 37.1%. Although they all match the self-compacting SFRC with cubic compressive strength of 60 MPa, it is better to produce steel fiber with appropriate geometry and tensile strength for the economical application with the premise of reliability. Hooked-end steel fiber HF4 with a tensile strength of 600 MPa was broken during the pull-out process, which can be used mainly for the improvement of the strength of concrete. 3. Crimped steel fiber CF2 with a tensile strength of 2000 MPa had excellent bond strength and toughness, which provides the strengthening and energy dissipation effect and the toughening capacity in the cracking resistance, normal serviceability, and ultimate bearing capacity of concrete, due to matching with the self-compacting SFRC with a cubic compressive strength of 60 MPa. The rectangular sectional crimped steel fiber CF with a tensile strength of 800 MPa had a poor bond behavior in this test. 4. The indentation, milled, and large-end steel fibers are strength enhanced type fibers with a certain energy dissipation ability and toughening capacity, before the bond \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No.** & **HFb** & **HF2** & **HF3** & **HF4** & **HF5** & **HF6** & **CF** \\ \hline \(UW_{\text{de}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & 0.268 & 0.282 & 0.321 & 0.139 & 0.173 & 0.137 & 0.067 \\ \(UW_{\text{max}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & 2.193 & 3.971 & 3.412 & 1.203 & 1.238 & 1.514 & 1.338 \\ \(UW_{\text{res}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & 6.727 & 8.238 & 7.588 & - & - & 3.788 & 2.236 \\ \hline
**No.** & **IF1** & **IF2** & **IF3** & **IF4** & **MF** & **LF** & **CF2** \\ \hline \(UW_{\text{de}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & 0.184 & 0.343 & 0.095 & 0.553 & 0.219 & 0.063 & 0.399 \\ \(UW_{\text{max}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & 0.599 & 0.733 & 0.283 & 0.553 & 0.555 & 0.131 & 2.582 \\ \(UW_{\text{res}}\) (\(\times 10^{6}\) N\(\cdot\)mm/kg) & - & 0.972 & - & - & - & - & 6.673 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The pull-out works of per unit weight steel fibers. strength reached the maximum. The bond relies mainly on the geometry of steel fiber with different tensile strength. 5. To realize the expected properties of concrete reinforced by steel fibers, the bond property of steel fiber in mortar can be used for the fiber selection. Not all kinds of steel fiber can simultaneously improve the strength and toughness of concrete.