Vol.:(0123456789) 1 3 Rock Mechanics and Rock Engineering https://doi.org/10.1007/s00603-019-1743-y ORIGINAL PAPER Experimental Investigation on the Efects of Microwave Treatment on Basalt Heating, Mechanical Strength, and Fragmentation Gao‑Ming Lu 1  · Xia‑Ting Feng 1,2  · Yuan‑Hui Li 2  · Ferri Hassani 3  · Xiwei Zhang 2 Received: 7 May 2018 / Accepted: 29 January 2019 © Springer-Verlag GmbH Austria, part of Springer Nature 2019 Abstract Microwave energy can be used to assist mechanical rock breakage for civil and mining engineering operations. To assess the industrial applicability of this technology, microwave heating of basalt specimens in a multi-mode cavity (a microwave chamber) at diferent power levels was followed by conventional mechanical strength and fragmentation efect tests in the laboratory. X-ray difraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy were used to determine the mineral composition and distribution of the basalt, to aid interpretation of crack propagation patterns and the associated strength reduction mechanism. These analyses demonstrated that cracks mainly occurred around olivine grains, primarily as intergranular cracks between olivine and plagioclase grains and intragranular cracks within olivine grains. Strength reduc- tion during microwave fracturing of basalt is driven by heat from enstatite (a microwave-sensitive mineral) and volumetric expansion of olivine (a thermally expansive mineral). Uniaxial compressive, Brazilian tensile, and point load strengths all decreased with increasing microwave irradiation time at rates that were positively related to the power level. For a given power level, mechanical strength reduction can be estimated from linear relationships with irradiation time. On the other hand, a power function best described burst time (the irradiation time at which the specimen burst into fragments) vs. power level (for a given specimen size) and burst time vs. specimen size (for a given power level) relationships. Microwave-induced hard rock fracturing can be an integral part of new methods for rock breakage and tunnel excavation. Keywords Microwave-assisted rock fragmentation · SEM-EDX elemental analysis · Crack propagation mechanism · Strength reduction · Fragmentation efects List of Symbols δ Dielectric loss angle tanδ Loss tangent ε Absolute permittivity ε r Dielectric constant (also known as relative permittivity) ε 0 Permittivity of free space, 8.854 × 10 −12 F/m ε’ Real part of the plural dielectric constant ε" Imaginary part of the plural dielectric constant θ Difraction angle λ 0 Resonant wavelength of the rectangular cavity f Microwave frequency a, b, l Wide side, narrow side and length of the rectan- gular cavity, respectively m, n, p Number of semi-standing waves distributed on rectangular cavity a, b and l, respectively D Electric displacement feld E : Electric feld P Free charge density Pʹ Loss power density deposited within the specimen 1 Introduction Microwave preconditioning damages (via cracks and spal- lation) and weakens rock (Hassani et al. 2016; Lu 2018), thus it has the potential to enhance mechanical rock break- age for civil and mining engineering applications. Several * Xia-Ting Feng xia.ting.feng@gmail.com; xtfeng@whrsm.ac.cn 1 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China 2 Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110819, China 3 Department of Mining and Materials Engineering, Mc Gill University, H3A 2A7 Montreal, Canada