## 3 Results and Analysis  
### Static Test Results and Analysis  
After standard curing, the specimens were removed and compressive and splitting tensile tests were carried out according to the GB/T50080-2016 Standard Test Method for Performance of Ordinary Concrete Mix and JGJ55-2011 Code for Design of Ordinary Concrete Mix. In the statics test, cubes with dimensions of 100 \(\times\) 100 \(\times\) 100 mm were selected, with six in each group for the compressive strength test and splitting tensile test, respectively. Additionally, the compressive and tensile strength calculation results had to be multiplied by conversion coefficients of 0.95 and 0.85, respectively. The orthogonaltest results of each group of specimens are shown in Figures 4 and 5. As can be seen from Figure 4, the compressive strength of the concrete in each fiber group was slightly increased by 14.6-25% compared to that of the base group. At the same volume content, the compressive strength of the concrete first increased and then decreased with the increasing length-diameter ratio of the polypropylene fiber. The compressive strength followed the same trend when the length-diameter ratio of the polypropylene fiber was constant. By comparing the test results of each group, it can be seen that the compressive strength of the SPB2 group was the highest, that is, when the volume content of steel fiber was 2%, the volume content of polypropylene was 0.1%, the length-diameter ratio was 6000, and the compressive strength of the hybrid fiber concrete was the highest.  
As can be seen from Figure 5, the splitting tensile strength of concrete in each fiber group was significantly increased by 13.8-60.4% compared to that of the base group. At the same volume content of polypropylene fiber, the splitting tensile strength of concrete first increased and then decreased with the increasing length-diameter ratio. This was due to the fact that when the polypropylene length-diameter ratio was 3000 and 6000, its dispersibility in the concrete was sufficient enough for the concrete to have a large contact area, enhanced cohesion, enhanced friction, and (therefore) increased concrete splitting tensile strength. However, as the length-diameter ratio of the polypropylene fibers increased, the fibers could not be effectively dispersed and a weak surface was formed where the fibers gathered, thus reducing the split tensile strength of the concrete. When the length-diameter ratio of the polypropylene fiber was constant, the splitting tensile strength of the concrete first increased and then decreased with the increase in its  
Figure 4: Compressive strength of concrete specimens in each group.  
Figure 5: Splitting tensile strength of concrete specimens in each group.  
volume content, which was due to the fact that when the volume of the polypropylene fiber was 0.05% and 0.1%, it was able to bridge cracks and enhance the bonding effects of the cement, thus effectively improving the splitting tensile strength of the concrete. However, as the volume of polypropylene increased, lumps easily formed during mixing, resulting in decreases in concrete compactness and increases in internal voids, thus reducing the splitting tensile strength of the concrete.  
The combined analysis of the compressive and splitting tensile strength results showed that SPB2 is the optimal group, that is, the static properties of the concrete specimen mixed with 2% steel fiber and 0.1% polypropylene fiber at a length-diameter ratio of 6000 are the best.