# Investigation of the Porosity Distribution, Permeability, and Mechanical Performance of Pervious Concretes

^{*}

## Abstract

**:**

_{50}) approximately obey polynomial function. Based on the test results, the optimized parameters were suggested for practical engineering: W/C of 0.26–0.30; 0.5% SP content; 5% SF content; 15–21% design porosity; and aggregate sizes of 4.75–9.5 mm and 9.5–16 mm.

## 1. Introduction

## 2. Materials and Test Methods

#### 2.1. Materials

#### 2.2. Test Methods

#### 2.2.1. Fluidity

#### 2.2.2. Mix Proportions

_{c}), water (m

_{w}), and admixture (m

_{j}) were calculated as follows:

_{g}is the mass of the aggregate; ${\rho}_{g}$, ${\rho}_{c}$, ${\rho}_{w}$, ${\rho}_{j}$ are the apparent densities of aggregate, cement, water, and admixture, respectively; and P is the design porosity.

#### 2.2.3. Molding and Curing

#### 2.2.4. Segregation Index

_{t}) and the mass (m

_{b}) in the bottom section were measured after vibrating for 2 min on a vibration table. The segregation index (S) was calculated as follows:

#### 2.2.5. Porosity

_{d}) repelled by the specimen was acquired. The volume of open pores was calculated by subtracting V

_{d}from the sample bulk volume (V

_{b}) [21]. The volumetric porosity of the specimen was calculated as follows:

#### 2.2.6. Pore Structure Features

#### 2.2.7. Permeability Coefficient

^{2}).

#### 2.2.8. Mechanical Strength

## 3. Results, Analysis, and Discussion

#### 3.1. Fluidity Performance

#### 3.2. Porosity and Pore Distribution of Pervious Concrete

#### 3.2.1. Porosity of Pervious Concrete

#### 3.2.2. Pore Distribution of Pervious Concrete

#### 3.3. Permeability of Pervious Concrete

#### 3.3.1. Accurate Determination of Permeability Coefficient

#### 3.3.2. Influential Factors of the Permeability Coefficient

#### 3.4. Strength of Pervious Concrete

## 4. Conclusions

- The segregation index of pervious concrete increased with the increase of SP and the W/C ratio, and the decrease of SF. The use of SP could significantly increase the flow value, while the use of SF signally reduced the flow value. The flow values of pastes and the segregation index for pervious concretes were obtained and found to be very suitable when the W/C of 0.26–0.30, 0.5% SP, and 5% SF were used.
- In the paper, volume porosity, planar porosity, and pore sizes were obtained by the water displacement method and image processing technology. It was found that the planar porosity of pervious concrete was close to the volumetric porosity. There was little difference between the measured porosity (volumetric porosity and planar porosity) and the design porosity when a single-size aggregate was used. However, the difference was large when a blended aggregate was used. This may be due to the possible loosening effect of the blended aggregates. The aggregate size was the main influencing factor of the pore distribution of the pervious concrete, and the effective pore size increased with the increase of the aggregate size. The design porosity had little effect on the pore distribution. The dosage of cementitious material decreased when the design porosity increased; correspondingly, the number of open and connected pores increased and the connections became difficult.
- Based on Darcy’s law, the permeameter and the sealed sidewall method can effectively solve the problem of sidewall leakage and the permeability coefficient can be accurately determined. The standard deviation of the permeability coefficient was less than 0.03 under different hydraulic gradients. The permeability coefficient of the pervious concrete was determined by the porosity and aggregate size jointly, and the permeability coefficient increased with increase of the aggregate size and design porosity. It was found that the relationships between the permeability coefficient and the volumetric porosity (or effective pore size d
_{50}) approximately obey the polynomial function. - In the pervious concrete material system, the use of SF and SP improved the performance of pervious concrete, but the dosage of SF and SP should not be excessive. The strength of the concrete significantly increased with the increase of cementitious material and the decrease of aggregate size. When 15% design porosity and 4.75–9.5 mm aggregate size were used in concrete, the 28-day compressive strength was 27.2 MPa and the 28-day flexural strength was 4.1 MPa. Based on the performance of pervious concretes, the W/C of 0.26–0.30; 0.5% SP content; 5% SF content; 15–21% design porosity; and aggregate sizes of 4.75–9.5 mm and 9.5–16 mm are suggested.

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 3.**Flow values of pastes with different W/C (water cement ratio). Two to three pastes were prepared for each mix design and the figure shows an average of these together with the standard deviation.

**Figure 4.**Segregation index of pervious concretes. (Three concrete specimens were prepared for each mix design and the figure shows an average of these together with the standard deviation).

**Figure 5.**Porosity of pervious concrete. (

**a**) Planar porosity, the design porosity was 21%; (

**b**) volumetric porosity and average planar porosity, the design porosity was 15%, 21%, and 27%. The figure shows an average value and standard deviation of three to five specimens.

**Figure 6.**Effect of a single-size aggregate on the pore distribution of pervious concrete. (

**a**) Frequency distribution of pore sizes; (

**b**) cumulative frequency distribution of pore sizes. The design porosity was 15%. The figure shows the average value of three to five specimens.

**Figure 7.**Effect of a blended aggregate on the pore distribution of pervious concrete. (

**a**) Frequency distribution of pore sizes; (

**b**) cumulative frequency distribution of pore sizes. The design porosity was 15%. The figure shows the average value of three to five specimens.

**Figure 8.**Effect of the design porosity on the pore distribution of pervious concrete. (

**a**) Frequency distribution of pore sizes; (

**b**) cumulative frequency distribution of pore sizes. The aggregate size was 4.75–9.5 mm. The figure shows the average value of three to five specimens.

**Figure 9.**Standard deviation of the permeability coefficient of pervious concrete with different hydraulic gradients. The figure shows the average standard deviation values of three specimens.

**Figure 10.**The permeability coefficient of permeable concrete under different test methods. (

**a**) The design porosity of permeable concrete with 4.75–9.5 mm aggregate sizes; (

**b**) the aggregate size of permeable concrete with 21% design porosity. The figure shows the average value and standard deviation of three specimens.

**Figure 11.**Permeability coefficient of pervious concrete. (

**a**) The relationship between the permeability coefficient and volumetric porosity of pervious concrete with aggregate sizes of 4.75–9.5 mm; (

**b**) the relationship between the permeability coefficient and effective pore size of pervious concrete with 21% design porosity.

**Figure 12.**Effect of the design porosity on the strength of pervious concrete. (

**a**) Compressive strength; (

**b**) Flexural strength. The figure shows an average value and standard deviation of three specimens.

Name | Chemical Composition: % | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|

SiO_{2} | CaO | Al_{2}O_{3} | Fe_{2}O_{3} | MgO | K_{2}O | Na_{2}O | SO_{3} | TiO_{3} | LOI | Others | |

Cement | 23.52 | 61.47 | 7.59 | 2.42 | 1.70 | 0.57 | 0.27 | 0.65 | 0.11 | 0.84 | 0.86 |

Silica fume (SF) | 97.2 | 0.42 | 0.27 | 0.08 | 0.55 | 0.48 | 0.19 | 0.51 | - | - | 0.30 |

Solid Content: % Al_{2}O_{3} | pH | Density: g/mL Na_{2}O | Na_{2}SO_{4}: % TiO_{3} | Cl^{−}: % Others | Water Reducing Rate: % |
---|---|---|---|---|---|

30.25 0.42 0.27 | 5.01 | 1.095 | 0.67 - | 0.03 0.30 | 32.1 |

A | B | C | D | E | F | G | |
---|---|---|---|---|---|---|---|

Gravel sizes: mm | 4.75–9.5 | 9.5–16 | 16–19 | 75% 4.75–9.5 25% 9.5–16 | 50% 4.75–9.5 50% 9.5–16 | 50% 4.75–9.5 50% 16–19 | 50% 9.5–16 50% 16–19 |

Aggregate Size mm | Design Porosity % | Aggregate kg/m^{3} | Cement kg/m^{3} | SF (silica fume) kg/m^{3} | Water kg/m^{3} | SP(polycarboxylate superplasticizer) kg/m ^{3} |
---|---|---|---|---|---|---|

4.75–9.5 | 12 | 1489.0 | 546.1 | 28.7 | 161.0 | 2.87 |

15 | 1489.0 | 496.3 | 26.1 | 146.3 | 2.61 | |

18 | 1489.0 | 446.5 | 23.5 | 131.6 | 2.35 | |

21 | 1489.0 | 396.7 | 20.9 | 116.9 | 2.08 | |

24 | 1489.0 | 346.9 | 18.3 | 102.2 | 1.82 | |

27 | 1489.0 | 297.1 | 15.6 | 87.6 | 1.56 | |

9.5–16 | 12 | 1518.0 | 527.8 | 27.8 | 155.6 | 2.78 |

15 | 1518.0 | 478.0 | 25.2 | 140.9 | 2.51 | |

18 | 1518.0 | 428.2 | 22.5 | 126.2 | 2.25 | |

21 | 1518.0 | 378.4 | 19.9 | 111.5 | 1.99 | |

24 | 1518.0 | 328.7 | 17.3 | 96.9 | 1.73 | |

27 | 1518.0 | 289.4 | 15.2 | 85.3 | 1.52 | |

16–19 | 12 | 1529.0 | 519.5 | 27.3 | 153.1 | 2.73 |

15 | 1529.0 | 469.7 | 24.7 | 138.4 | 2.47 | |

18 | 1529.0 | 419.9 | 22.1 | 123.8 | 2.21 | |

21 | 1529.0 | 370.1 | 19.5 | 109.1 | 1.95 | |

24 | 1529.0 | 320.4 | 16.9 | 94.4 | 1.69 | |

27 | 1529.0 | 270.6 | 14.2 | 79.7 | 1.42 |

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**MDPI and ACS Style**

Liu, R.; Liu, H.; Sha, F.; Yang, H.; Zhang, Q.; Shi, S.; Zheng, Z.
Investigation of the Porosity Distribution, Permeability, and Mechanical Performance of Pervious Concretes. *Processes* **2018**, *6*, 78.
https://doi.org/10.3390/pr6070078

**AMA Style**

Liu R, Liu H, Sha F, Yang H, Zhang Q, Shi S, Zheng Z.
Investigation of the Porosity Distribution, Permeability, and Mechanical Performance of Pervious Concretes. *Processes*. 2018; 6(7):78.
https://doi.org/10.3390/pr6070078

**Chicago/Turabian Style**

Liu, Rentai, Haojie Liu, Fei Sha, Honglu Yang, Qingsong Zhang, Shaoshuai Shi, and Zhuo Zheng.
2018. "Investigation of the Porosity Distribution, Permeability, and Mechanical Performance of Pervious Concretes" *Processes* 6, no. 7: 78.
https://doi.org/10.3390/pr6070078