# Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Raw Material and Proportioning

#### 2.2. Specimen Design and Fabrication

#### 2.3. Static Compressive Testing

#### 2.4. Digital Speckle Correlation Method

## 3. Results and Discussion

#### 3.1. Mechanical Property

#### 3.2. Deformability Analysis

_{0}, y

_{0}) on the surface of the concave hexagonal cell in an axial two-dimensional way, and the lateral displacement nephogram of the concave hexagonal cell during static compression was obtained. In this experiment, the deformation when the specimen was damaged was taken as the equivalent deformation, and the displacement nephogram of concave hexagonal cells with different fiber contents under peak stress was made, as shown in Figure 4.

_{y}can be directly obtained from the recorded data of the RMT system during the static compression of the specimen, so the Poisson’s ratio v of the concave hexagonal unit cell is calculated as follows:

_{y}is the longitudinal strain of the concave hexagonal unit cell. Table 4 shows the Poisson’s ratios of the samples of the concave hexagonal unit cell with different fiber contents, calculated from the strain data of the experimentally obtained specimens.

#### 3.3. Destruction Process

#### 3.4. Energy Absorption Capacity

_{a}, specific energy absorption E

_{sa}, etc.

_{a}is the strain value of the specimen at a certain moment, σ

_{a}is the stress value corresponding to it, and ε

_{D}is the compaction strain, i.e., the strain corresponding to the maximum value of energy absorption efficiency. In practical application, it is necessary to combine the actual foam concrete stress-strain curve to determine the compaction strain of the specimen. The energy absorption capacity w per unit volume of foam concrete is defined as:

_{a}absorbed by the foam concrete specimen was obtained by calculating the area enclosed by the load-displacement curve of the specimen, the significance of which is that the greater the total energy absorbed, the better the impact resistance of the material:

_{D}, and p is the magnitude of the load corresponding to the displacement of l. The ratio of the total energy absorbed by the test block to its mass, i.e., the specific absorbed energy E

_{sa}, is calculated by:

## 4. Conclusions

- The increase in polypropylene fiber volume content reduces the compressive strength of foam concrete under static compression, but the peak stress of the concave hexagonal unit cell decreases less rapidly than that of the cube specimen with the same size.
- Adding the proper amount of polypropylene fiber into the concave hexagonal cell structure of foam concrete can improve the toughness and reduce the Poisson’s ratio of concave hexagonal cells. The effect is best when the fiber content is 1.5%, the width of its transverse displacement interval is increased by 34.1% compared with that of the concave hexagonal unit cells with 0% fiber content, and it has the lowest Poisson’s ratio.
- In the process of static compression, the concave hexagonal unit cell is the first to crack at the concave portion of the cell wall of the specimens, and the damage is the most thorough there, indicating that the left and right concave surfaces of the cell wall play a major role in energy absorption during the process of ballasting. Additionally, the cracks are distributed in the form of “upper left and lower right” or “lower left and upper right”.
- Adding the proper amount of polypropylene fiber can significantly improve the energy absorption efficiency of concave hexagonal cells. When the content of polypropylene fiber is 0.5%, the total energy absorption of concave hexagonal cells increases by 12.98%. When the fiber content exceeds 0.5%, excessive polypropylene fiber reduces the strength and deformation of the specimen greatly, thus reducing the energy absorption efficiency.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 3.**Effect of different fiber content on the peak stress of the specimen: (

**a**) concave hexagonal unit cells; (

**b**) cubic specimens.

**Figure 4.**Cloud diagram of lateral displacement of the concave hexagonal unit cell: (

**a**) A-0; (

**b**) A-0.5; (

**c**) A-1.0; (

**d**) A-1.5; (

**e**) A-2.0; (

**f**) A-2.5.

**Figure 6.**Transverse deformation curve of the concave hexagonal unit cell (A-0-1): (

**a**) transverse deformation ΔX; (

**b**) longitudinal deformation ΔY.

**Figure 8.**Failure process of different concave hexagonal cell specimens: (

**a**) A-0; (

**b**) A-0.5; (

**c**) A-2.5.

**Figure 10.**Effect of fiber content on energy absorption capacity of the concave hexagonal unit cell.

**Figure 11.**Microscopic morphology of cracks in the concave hexagonal unit cell: (

**a**) low fiber content; (

**b**) high fiber content.

Fiber Content | Concrete/(kg·m^{−3}) | Coal Ash/(kg·m^{−3}) | Water/(kg·m^{−3}) | Foam/(kg·m^{−3}) | Polypropylene Fiber/(kg·m^{−3}) |
---|---|---|---|---|---|

0% | 600 | 400 | 400 | 7.293 | 0 |

0.50% | 600 | 400 | 400 | 7.293 | 4.550 |

1.00% | 600 | 400 | 400 | 7.293 | 9.100 |

1.50% | 600 | 400 | 400 | 7.293 | 13.650 |

2.00% | 600 | 400 | 400 | 7.293 | 18.200 |

2.50% | 600 | 400 | 400 | 7.293 | 22.750 |

Sample | Stress/MPa | Average/MPa | Strain/10^{−3} | Average/10^{−3} |
---|---|---|---|---|

A-0-1 | 9.333 | 8.919 | 7.260 | 7.303 |

A-0-2 | 8.551 | 7.450 | ||

A-0-3 | 8.872 | 7.200 | ||

A-0.5-1 | 9.296 | 8.843 | 7.700 | 7.547 |

A-0.5-2 | 8.816 | 7.780 | ||

A-0.5-3 | 8.416 | 7.160 | ||

A-1.0-1 | 8.852 | 8.667 | 8.020 | 7.737 |

A-1.0-2 | 8.591 | 7.660 | ||

A-1.0-3 | 8.559 | 7.530 | ||

A-1.5-1 | 8.036 | 7.911 | 7.90 0 | 7.793 |

A-1.5-2 | 7.822 | 7.880 | ||

A-1.5-3 | 7.874 | 7.600 | ||

A-2.0-1 | 7.072 | 7.150 | 7.900 | 7.590 |

A-2.0-2 | 6.950 | 7.360 | ||

A-2.0-3 | 7.427 | 7.510 | ||

A-2.5-1 | 6.591 | 6.573 | 7.250 | 7.380 |

A-2.5-2 | 6.416 | 7.480 | ||

A-2.5-3 | 6.712 | 7.410 | ||

F-0-1 | 47.768 | 46.839 | 15.180 | 15.813 |

F-0-2 | 44.312 | 16.140 | ||

F-0-3 | 48.436 | 16.120 | ||

F-0.5-1 | 47.768 | 46.741 | 17.80 | 16.647 |

F-0.5-2 | 46.368 | 15.380 | ||

F-0.5-3 | 46.088 | 16.760 | ||

F-1.0-1 | 43.064 | 44.139 | 17.460 | 17.687 |

F-1.0-2 | 44.448 | 17.760 | ||

F-1.0-3 | 44.906 | 17.840 | ||

F-1.5-1 | 37.872 | 39.208 | 16.980 | 17.980 |

F-1.5-2 | 40.552 | 17.840 | ||

F-1.5-3 | 39.200 | 19.120 | ||

F-2.0-1 | 37.744 | 34.448 | 16.060 | 17.287 |

F-2.0-2 | 33.808 | 16.900 | ||

F-2.0-3 | 31.792 | 18.900 | ||

F-2.5-1 | 28.160 | 27.525 | 16.460 | 16.240 |

F-2.5-2 | 27.728 | 16.700 | ||

F-2.5-3 | 26.688 | 15.560 |

Source | Class III Sum of Squares | Freedom | Mean Square | F | p-Value |
---|---|---|---|---|---|

Revised Model | 3222.721a | 6 | 537.120 | 23.732 | 0.002 |

Intercept | 6862.314 | 1 | 6862.314 | 303.208 | 0.000 |

Fiber content | 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 | - | - | - |

Sample | A-0 | A-0.5 | A-1.0 | A-1.5 | A-2.0 | A-2.5 |
---|---|---|---|---|---|---|

1 | −0.072 | −0.101 | −0.131 | −0.149 | −0.132 | −0.105 |

2 | −0.068 | −0.095 | −0.138 | −0.142 | −0.129 | −0.109 |

3 | −0.076 | −0.099 | −0.136 | −0.140 | −0.130 | −0.106 |

Sample | Quality/g | Average/g | Ea/J | Average/J | Esa/J·kg^{−1} | Average/J·kg^{−1} |
---|---|---|---|---|---|---|

A-0-1 | 133.6 | 135.1 | 3.599 | 3.736 | 26.943 | 27.644 |

A-0-2 | 135.4 | 3.664 | 27.060 | |||

A-0-3 | 136.4 | 3.946 | 28.930 | |||

A-0.5-1 | 135.3 | 134.3 | 4.414 | 4.221 | 32.623 | 31.431 |

A-0.5-2 | 133.2 | 4.226 | 31.727 | |||

A-0.5-3 | 134.4 | 4.024 | 29.943 | |||

A-1.0-1 | 132.2 | 131.8 | 4.313 | 3.881 | 32.625 | 29.440 |

A-1.0-2 | 132.6 | 3.743 | 28.230 | |||

A-1.0-3 | 130.6 | 3.587 | 27.464 | |||

A-1.5-1 | 131.6 | 130.4 | 3.323 | 3.580 | 25.253 | 27.471 |

A-1.5-2 | 130.2 | 3.731 | 28.654 | |||

A-1.5-3 | 129.3 | 3.686 | 28.504 | |||

A-2.0-1 | 126.3 | 124.5 | 3.283 | 3.191 | 25.994 | 25.629 |

A-2.0-2 | 124.5 | 2.992 | 24.0330 | |||

A-2.0-3 | 122.8 | 3.298 | 26.860 | |||

A-2.5-1 | 121.5 | 120.8 | 2.961 | 2.937 | 24.374 | 24.307 |

A-2.5-2 | 120.7 | 3.105 | 25.723 | |||

A-2.5-3 | 120.3 | 2.746 | 22.826 |

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## Share and Cite

**MDPI and ACS Style**

Yin, Z.; Shao, Z.; Qi, C.; Wu, H.; Wang, J.; Gao, L.
Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell. *Appl. Sci.* **2023**, *13*, 132.
https://doi.org/10.3390/app13010132

**AMA Style**

Yin Z, Shao Z, Qi C, Wu H, Wang J, Gao L.
Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell. *Applied Sciences*. 2023; 13(1):132.
https://doi.org/10.3390/app13010132

**Chicago/Turabian Style**

Yin, Zhiqiang, Zhenguo Shao, Chao Qi, Haoyuan Wu, Jianen Wang, and Lulu Gao.
2023. "Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell" *Applied Sciences* 13, no. 1: 132.
https://doi.org/10.3390/app13010132