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Heating-Dominated Fracturing of Granite by Open-Ended Microwave: Insights from Acoustic Emission Measurement

Abstract

Microwave fracturing of hard rocks holds great promise in the civil, mining and tunnelling industries. The role of heating and cooling in the fracturing of rocks and when and where cracks initiate from and propagate to remain unclear and need to be addressed for future field applications of the technology. This study treated an alkali feldspar granite using a 6 kW industrial microwave source and a customised open-ended dielectric-loaded converging waveguide antenna. The real-time acoustic emission (AE) characteristics in the microwave heating and natural cooling phases were recorded and investigated. The surface temperature and P-wave velocity reduction of the specimens were also measured to quantify the thermal damage. The fracturing of granite is found to be tensile failure and is heating-dominated. Although a considerable amount of AE hits and events was detected in the cooling phase, they were of low energy, and therefore, the role of cooling in rock fracturing by open-ended microwave can be neglected. Fractures initiated from the exterior of the antenna and propagated towards the edges and the interior of the specimens. The cracks obtained from the AE localisation were in good agreement with those observed. With the increase of power level, the time for crack initiation was shortened, confirming the high-power effect.

Highlights

  • Acoustic emission activities were measured in the microwave heating and cooling phases on granite blocks.

  • Microwave fracturing of the granite is found to be heating-dominated.

  • The microwave-induced rock fracturing is primarily tensile failure.

  • The test results confirm the high-power effect in microwave fracturing of rocks.

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Acknowledgements

The authors would like to acknowledge the financial support from the National Natural Science Foundation of China (Nos. 52104121 and 41831281), the Entrepreneurial Team Program and the of Jiangsu Province, China (JSSCTD202140), the Innovative and Entrepreneurial Doctor Program of Jiangsu Province, China as well as the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (No. KYCX20_0114).

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Correspondence to Yanlong Zheng or Jianchun Li.

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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Zheng, Y., Ma, Z., Gong, Q. et al. Heating-Dominated Fracturing of Granite by Open-Ended Microwave: Insights from Acoustic Emission Measurement. Rock Mech Rock Eng (2022). https://doi.org/10.1007/s00603-022-02887-8

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  • DOI: https://doi.org/10.1007/s00603-022-02887-8

Keywords

  • Microwave fracturing
  • Heating and cooling
  • Acoustic emission
  • Crack initiation and propagation
  • Fracture mode