# Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell
## 3 Results and Discussion  
### Mechanical Property  
By static compression test, the peak stress and peak strain of the specimens were obtained and the average value of each group of samples was taken, and the data parameters were obtained, as shown in Table 2.  
Figure 3 shows the trend of the effect of different fiber contents on the peak stress of cubic specimens and the concave hexagonal unit cells. It can be seen that the variation of mechanical parameters in static compression for foam concrete with different fiber contents in the concave hexagonal unit cells has similar characteristics to that of the cubic specimens. \begin{table}
\begin{tabular}{c c c c c} \hline
**Sample** & **Stress/MPa** & **Average/MPa** & **Strain/10\({}^{-3}\)** & **Average/10\({}^{-3}\)** \\ \hline A-0-1 & 9.333 & & 7.260 & \\ A-0-2 & 8.551 & 8.919 & 7.450 & 7.303 \\ A-0-3  
As seen in Figure 3, with the increase in polypropylene fiber content, the peak stress of concave hexagonal cells and cubics decreases gradually. When the volume fraction of polypropylene fiber increased from 0% to 0.5%, the average peak stress of the concave hexagonal unit cell decreased by 0.85%, and the average peak stress of the cube decreased by 0.21%. When the volume fraction of polypropylene fiber increased from 0.5% to 1.0%, the average peak stress of concave hexagonal unit cell decreased by 1.99%, and the average peak stress of cube decreased by 5.57%. With the further increase in polypropylene fiber, the peak stress of foam concrete weakened by polypropylene fiber was more significant. When the volume fraction of polypropylene fiber increased from 1.0% to 1.5%, the average peak stress of the concave hexagonal unit cell decreased by 8.72%, and the average peak stress of the cube decreased by 11.17%. When the volume fraction of polypropylene fiber increased from 1.5% to 2.0%, the average peak stress of concave hexagonal unit cell decreased by 9.61%, and the average peak stress of the cube decreased by 12.14%. When the volume fraction of polypropylene fiber increased from 1.5% to 2.0%, the average peak stress of concave hexagonal unit cell structure decreased by 8.07%, and the average peak stress of cube decreased by 20.10%. It can be seen that the reduction in peak stress of the concave hexagonal unit cell by polypropylene fiber content is smaller than that of the cube. In order to explore the influence of cell structures on their pick stress, a two-way ANOVA was conducted on the peak stress of two kinds of specimens. The processing results are shown in Table 3. The \(p\)-value of the structure is less than 0.050, and it more clearly verifies that there are differences in the change in peak stress of cells with different structures. A small amount of polypropylene fiber added to the foam concrete, uniformly dispersed inside the foam concrete, and this did not significantly change the compressive strength of the foam concrete. The deformation capacity of the concrete was enhanced under the action of the binding force of the fiber. When the amount of polypropylene fiber added reached more than 1.5% during the concrete mixing and casting process, the  
Figure 3: Effect of different fiber content on the peak stress of the specimen: (**a**) concave hexagonal unit cells; (**b**) cubic specimens. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Class III Sum of Squares** & **Freedom** & **Mean Square** & **F** & \(p\)**-Value** \\ \hline Revised & 3222.721a & 6 & 537.120 & 23.732 & 0.002 \\ Model & 6862.314 & 1 & 6862.314 & 303.208 & 0.000 \\ Intercept & 187.825 & 5 & 37.565 & 1.660 & 0.296 \\ Structure & 3034.897 & 1 & 3034.897 & 134.096 & 0.000 \\ Deviation & 113.162 & 5 & 22.632 & - & - \\ Total & 10,198.197 & 12 & - & - & - \\ Correction & 3335.883 & 11 & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the two-way ANOVA.