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 different power levels was followed by conventional mechanical strength and fragmentation effect tests in the laboratory. X-ray diffraction 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 reduction 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.
Abstract The mining and tunnelling industries are looking for solutions to increase the rates of advance of mechanical excavators in hard and abrasive rocks. Microwave assisted rock breakage has substantial advantages in the volumetric heating, selective heating, instantaneous control and energy savings, which is regarded as a promising technology. A 2 kW single-mode industrial microwave system was used to heat the Austral Black gabbro specimens at the frequency of 2.45 GHz. The temperature and ...
Abstract Mechanical comminution of rocks is an energy intensive process with energy efficiency around 1%. A possible way to enhance the efficiency is the prior application of high-power microwaves. Microwave irradiation of a heterogeneous material introduces inhomogeneous electromagnetic and thermal fields which result in stresses and potentially in damage. In order to assess the industrial applicability, various 3D numerical analyses with either constant microwave power or constant energy were ...
#1Gao-Ming Lu(MOE: Chinese Ministry of Education)H-Index: 4
Last. Xiwei Zhang(NU: Northeastern University)H-Index: 14
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Abstract The sample will burst into fragment when the thermal stress induced by thermal expansion greater than the ultimate strength of the rock after microwave irradiation. Microwave-assisted rock fragmentation has been illustrated to be potentially beneficial for mineral processing, mining and geotechnical engineering. In order to have a comprehensive understanding on the influence of microwave on thermo-mechanical properties of rocks, it is necessary to investigate the interaction effect betw...
#1Tamara Monti(University of Nottingham)H-Index: 7
#2Alexander Tselev(ORNL: Oak Ridge National Laboratory)H-Index: 34
Last. Sam Kingman(University of Nottingham)H-Index: 50
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Abstract Microwave energy was demonstrated to be potentially beneficial for reducing the cost of several steps of the mining process. Significant literature was developed about this topic but few studies are focused on understanding the interaction between microwaves and minerals at a fundamental level in order to elucidate the underlying physical processes that control the observed phenomena. This is ascribed to the complexity of such phenomena, related to chemical and physical transformations,...
Abstract This paper deals with experimental studies regarding the thermo-physical properties of granite, sandstone and basalt in the temperature range of 25–1000 °C. It is shown how phase transitions (e.g. α-β quartz phase transition) influence the texture and stability of these rock types. The results of these measurements and analyses are linked to microwave irradiation tests at 17.5 kW power. The measurements demonstrate the strong variation of effects depending on the parameter rock/mineralo...
Abstract The aim of this research is to present a novel 3D simulation procedure to assess microwave induced stresses in inhomogeneous hard rocks at a microstructure level. For a realistic rock model a two-component 3D microstructure is generated by a Voronoi tessellation algorithm. The two components are microwave absorbing (phase A) and transparent (phase T), respectively. In order to calculate the electric field inside the inhomogeneous rock, a 3D finite difference time domain (FDTD) simulatio...
Abstract Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of McGill University to make a real application of microwave-assisted mechanical rock breakage to full-face tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks (norit...
#1Yi-du Hong(CUMT: China University of Mining and Technology)H-Index: 7
#2Baiquan Lin(CUMT: China University of Mining and Technology)H-Index: 35
Last. Yao Hao(CUMT: China University of Mining and Technology)H-Index: 4
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Abstract This paper aims to predict the heating behaviors of coal sample by COMSOL Multiphysics software based on the finite element method. The effects of microwave frequency, microwave power and sample position on temperature profiles and electric field distributions are examined. The effect of microwave frequency on temperature is obvious. The maximum and minimum temperatures of the coal sample change with frequency in different laws respectively. There is just one optimal heating frequency t...
A numerical analysis in a two-component model rock is presented including the propagation and absorption of a microwave beam as well as the microwave-induced temperature and stress distributions in a consistent way. The analyses are two-dimensional and consider absorbing inclusions (discs) in a non-absorbing matrix representing the model of a heterogeneous rock. The microwave analysis (finite difference time domain — FDTD) is performed with values of the dielectric permittivity typical for hard ...
#1Yicai Wang(UQ: University of Queensland)H-Index: 3
#2N. Djordjevic(UQ: University of Queensland)H-Index: 10
This paper presents a study of a thermal breakage process used to analyse the thermal stress and crack development that occur when rock is exposed to short-pulse microwave energy. A two-dimensional circular plate, containing two-phase minerals, was used in finite element simulation to calculate thermal stress for the purpose of better understanding thermal fracture behaviour in comminution. It is found that the thermal mismatch between a microwave-absorbing inclusion and a low-absorbing matrix m...
#1Chen Wenwen(Xi'an University of Architecture and Technology)H-Index: 2
#2Shao Zhushan(Xi'an University of Architecture and Technology)H-Index: 9
Last. Yong Hong(Xi'an University of Architecture and Technology)
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Abstract Using microwave heating technology to assist concrete recycling have great potential for improve the quality of recycled concrete aggregate. Unfortunately, there are few studies explored on the properties of concrete incorporating microwave treated coarse aggregates. This study aims to investigate the performance of coarse aggregate after microwave treatment and to evaluate the properties of the resulting concrete incorporated microwave treatment aggregate. The water absorption and crus...
#1Qiang Li(CSU: Central South University)H-Index: 3
#2Xibing Li(CSU: Central South University)H-Index: 44
Last. Tubing Yin(CSU: Central South University)H-Index: 14
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Abstract Hard rock breaking is a great challenge for deep drilling and mining engineering, and the microwave-assisted rock breaking technique offers a promising solution. However, the lack of knowledge of the effects of microwave irradiation on hard rocks limits the further development of this technology. Laboratory tests have been conducted to investigate the variations of fracture properties of granite subjected to microwave heating. The semi-circular bend (SCB) specimens were prepared, and mo...
Abstract Microwave assisted mechanical rock breaking is a hybrid rock breaking method that combines microwave heating and mechanical rock breaking technologies and is proven to have potential applications in mineral processing, mining, and geotechnical engineering. It is, thus, important to understand the effect of microwave-induced damage on rock fracture characteristics. In this study, granite specimens of the Cracked Straight Through Brazilian Disc (CSTBD) were used to carry out the mode I fr...
Last. Su Xiangxin(MOE: Chinese Ministry of Education)
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Abstract This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress. The test system comprises a true triaxial stress loading system, an open-ended microwave-induced fracturing system, a data acquisition system, an acoustic emission (AE) monitoring system, and an auxiliary specimen loading system. Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time, which overcomes the problem of m...
#1Wei Wei(Xi'an University of Architecture and Technology)H-Index: 2
#2Shao Zhushan(Xi'an University of Architecture and Technology)H-Index: 9
Last. Junxi Cheng(Xi'an University of Architecture and Technology)H-Index: 2
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Abstract Microwave assisted concrete recycling is highlighted by a large number of research groups all over the world due to its potential for significant process benefit. In this paper, systematic experiments are established to investigate the heating process of mortar-aggregate under microwave irradiation. Four different aggregate types are selected that widely used as aggregates in concrete to represent different kinds of aggregates. The temperature field of both mortar and aggregate under di...
#2Ming Tao(CSU: Central South University)H-Index: 21
Last. Wang Yiqing(CSU: Central South University)H-Index: 1
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Abstract Weakening rocks using microwave irradiation has been a major topic in research for the past 50 years. However, the thermal effect of microwaves on rocks is mostly studied with a multi-mode metal cavity, in which rocks absorb microwaves reflected from all directions, and this method cannot represent how the microwave pre-treatment affects the rock mass in the rock excavation process. To simulate microwave treatment before an excavation, we wrapped a sample of red sandstone in a copper fo...
Understanding the dynamic tensile response of microwave damaged rock is of great significance to promote the development of microwave-assisted hard rock breakage technology. However, most of the current research on this issue is limited to static loading conditions, which is inconsistent with the dynamic stress circumstances encountered in real rock-breaking operations. The objective of this work is to investigate the effects of microwave irradiation on the dynamic tensile strength, full-field d...
Microwave heating and grinding experiments were conducted on samples of Hongtoushan copper ore and Dandong gold ore with different particle sizes and forms. The differences between the heating effects observed were then investigated using the electromagnetic characteristics of the bulk and powdered ore samples. The results show that the bulk copper ore experiences a high shielding effect as the microwaves are strongly reflected. The dielectric constant and reflection from a powdered sample are s...
Microwave technology is increasingly used in laboratory tests and field applications as an effective rock breaking technique. The underlying mechanism of rock fracturing induced by microwave energy...