Progressive Weakening of Granite by Piezoelectric Excitation of Quartz with Alternating Current

• Published in: Rock mechanics and rock engineering 2024-10, Vol.57 (10), p.7963-7973
• Main Authors: Rubio Ruiz, Rafael Arturo, Pournoori, Nazanin, Isakov, Matti, Saksala, Timo, Bjørge, Ruben, Rack, Alexander, Lukic, Bratislav, Cohen, Amitay, Levi-Hevroni, David, Kane, Pascal-Alexandre, Hokka, Mikko
• Format: Article
• Language: English
• Subjects: Alternating current; Bend strength; Civil Engineering; Deformation; Drilling; Dynamic loads; Earth and Environmental Science; Earth Sciences; Energy absorption; Energy consumption; Energy usage; Excitation; Fragmentation; Geophysics/Geodesy; Granite; Image contrast; Image enhancement; Mechanical loading; Original Paper; Phase contrast; Piezoelectricity; Rock; Rocks; Static tests; Synchrotron radiation; Tensile strength; Vibrations; Water hardness; X ray imagery; X rays
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-024-03948-w

A promising solution to reduce energy usage and mitigate the wear of drilling and comminution tools during mining operations involves inducing vibrations within the piezoelectric phases dispersed in the structure of rocks using alternating current (AC). This paper presents experimental evidence of AC-induced weakening of Kuru granite, manifested as improvements in rock drillability and reductions of strength. Sievers’ J-miniature drill tests were used to assess surface drillability. The impact of AC treatment on the quasi-static strength of granite was assessed via three-point bending and indirect tension Brazilian disk tests. The influence of AC treatment on the dynamic tensile strength of the rock was determined using split Hopkinson bar tests, with the fragmentation process captured using in situ ultra-fast synchrotron X-ray phase contrast imaging. The quasi-static tests revealed no reduction in rock strength after the AC treatment. In contrast, reductions of 25% in hardness and 18% in dynamic tensile strength were observed. Fragmentation patterns differed between treated and non-treated rocks, with treated specimens exhibiting reduced macrocrack formation during loading. Highlights Diverse experiments confirm that alternating current excitations weaken Granite. Sievers’ J-tests evidenced enhanced drillability of Granite after the alternating current treatment. Exposure to alternating currents decreased the tensile strength of Granite in dynamic Brazilian disc experiments. Treated Brazilian disc specimens showed lower energy absorption during dynamic loading. Synchrotron X-ray phase contrast images revealed reduced crack branching of treated granite specimens during dynamic loading.