# Mechanical Characteristics and Acoustic Emission Characteristics of Mortar-Rock Binary Medium

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## Abstract

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## 1. Introduction

## 2. Materials and Methods

## 3. Test Results and Analysis

#### 3.1. Shear Mechanics Characteristics of Mortar-Rock Binary Medium

#### 3.2. Analysis of Acoustic Emission Characteristic Parameters

#### 3.2.1. AE Counts

#### 3.2.2. b Value

#### 3.2.3. Crack Identification Analysis

_{max}is the maximum voltage value in μV, and A is the amplitude in dB.

#### 3.2.4. Peak Frequency Analysis

## 4. Conclusions

- The direct shear process of the mortar-rock binary medium is divided into five stages. There is a linear relationship between the shear strength of the binary medium and the normal stress, and the relationship between the sawtooth angle and the shear strength of the binary medium, cohesive force, internal friction angle, and residual in-ternal friction angle is established.
- The AE count and cumulative count of the binary medium direct shear test are both affected by the interface roughness. The greater the sawtooth angle, the greater the AE count and cumulative count.
- In the plastic failure stage, the AE b value will decrease suddenly, and the proportion of shear cracks in the specimen will increase suddenly. The sudden drop of the AE b value and the sudden increase of the shear crack signal ratio can be used as reference indicators for predicting the macroscopic damage of mor-tar-rock binary medium.
- The shear and tensile cracks are distinguished and their proportion is statistically analyzed. With the increase of shear stress, the number of shear cracks increases suddenly, but the change of tensile cracks is little. The development of shear cracks plays a decisive role in the failure of specimens in the shear failure stage. The variation of AE shear crack number can play a role in the early warning and prediction of structural failure. In the practice of monitoring practical engineering, this parameter can be used as one of the parameters to predict structural failure.
- The peak frequency of shear acoustic emission in the mortar-rock binary medium is distributed in high and low-frequency bands. The effective peak frequency of acoustic emission signal in the direct shear process of binary medium structure is mainly concentrated in 120–340 kHz, and the sudden increase of high-frequency signal (220–320 kHz) has an efficient prediction effect on structural surface damage.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**Specimen preparation before direct shear test. (

**a**) Schematic diagram of specimens with different sawtooth angles. (

**b**) Specimens after pouring.

**Figure 6.**Relationship between shear stress and shear displacement of mortar-rock binary medium. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

**Figure 14.**Relationship between AE counts, AE cumulative counts and time. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

**Figure 15.**Relationship between AE b value and time in the whole shearing process. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

**Figure 17.**Relation between the RA value and the average frequency in direct shear test of binary medium. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

**Figure 18.**Relation between the RA value and the time in direct shear test of binary medium. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

**Figure 19.**Relation between the crack ratio and the time in direct shear test of binary medium. (

**a**) 8° (

**b**) 30° (

**c**) 45° (

**d**) 55°.

Normal Stress | The Value of k | ||||
---|---|---|---|---|---|

Sawtooth Angle of 8° | Sawtooth Angle of 30° | Sawtooth Angle of 45° | Sawtooth Angle of 55° | Intact Rock | |

1 MPa | 1.74 | 3.46 | 5.72 | 5.61 | 12.01 |

2 MPa | 1.75 | 4.83 | 6.07 | 7.21 | 13.23 |

3 MPa | 5.85 | 8.06 | 5.79 | 8.03 | 15.58 |

4 MPa | 6.45 | 5.67 | 6.26 | 8.82 | 16.21 |

5 MPa | 6.92 | 9.29 | 8.02 | 11.59 | 18.56 |

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**MDPI and ACS Style**

Tang, W.; Lin, H.; Chen, Y.; Feng, J.; Hu, H.
Mechanical Characteristics and Acoustic Emission Characteristics of Mortar-Rock Binary Medium. *Buildings* **2022**, *12*, 665.
https://doi.org/10.3390/buildings12050665

**AMA Style**

Tang W, Lin H, Chen Y, Feng J, Hu H.
Mechanical Characteristics and Acoustic Emission Characteristics of Mortar-Rock Binary Medium. *Buildings*. 2022; 12(5):665.
https://doi.org/10.3390/buildings12050665

**Chicago/Turabian Style**

Tang, Wenyu, Hang Lin, Yifan Chen, Jingjing Feng, and Huihua Hu.
2022. "Mechanical Characteristics and Acoustic Emission Characteristics of Mortar-Rock Binary Medium" *Buildings* 12, no. 5: 665.
https://doi.org/10.3390/buildings12050665