Internal Fractures After Blasting Confined Rock and Mortar Cylinders

Abstract

Blast-induced fines in rock negatively influence multiple aspects of raw-mineral sustainability. The Austrian Science Fund (FWF) sponsored a project to investigate the cause of the fines by studying blast fragmentation through small-scale blast tests and numerical simulations. The paper covers the experimental part of the project focusing on internal blast-induced fracturing and related mechanisms. The blast tests were done by blast-loading confined granite and mortar cylinders. The blast-driven dynamic cracking at the end face of the cylinder opposite to the initiation point was filmed with a high-speed camera. Following analyses covered internal crack patterns, fracture surfaces, and sieving of the blasted cylinders to quantify the amount of fine material created. The internal crack patterns and fracture surfaces were analysed by means of computer tomography (CT) and scanning-electron microscopy (SEM). The CT scans show that the amount of explosive charge affects the changing of the topological features of the crack patterns along the cylinder. They also depict different deformation zones around the blast-hole wall with respect to the blasted material and the amount of charge. Although fracture surfaces of larger fragments do not clearly differ in measured roughness and curvature, the SEM scans of smaller fragments show clear difference in fracture surfaces with respect to the blasted material and the amount of charge. SEM scans of thin sections extracted from the blasted cylinders show different fracture features that could be related to the branching/merging mechanism.

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…The failure pattern in Specimen No. 3 was similar to those observed in rocks such as granite [14,15,21], sandstone [59,60], and concrete [10,12].…”

“…Nevertheless, for the tested configurations, four main radial cracks were observed in the top and bottom surfaces of all specimens, supporting the assumption of quasi-plane strain conditions. • Due to its heterogeneity and numerous imperfections, inclusions, pores, and initial cracks, the observed cracking characteristics of dolomite differed slightly from those of other rocks, such as granite [14,15,21], sandstone [59,60], and concrete [10,12]. Nevertheless, typical radial cracks were observed in the bottom and top surfaces of the specimens in the tests using the blasting cap.…”

“…However, large-scale and field tests are relatively costly and difficult to conduct. Consequently, small-scale laboratory experiments are often used to study the failure of various materials subjected to strongly dynamic loading resulting from HE detonation [10][11][12][13][14][15][16][17][18]. Most recent laboratory-scale blasting studies have focused on fracture patterns and crack propagation in granite rock [14][15][16][19][20][21][22] or concrete [10,12,23,24], although a recent paper by Jeong H. et al [25] presented experimental and numerical tests of cylindrical specimens of polymethyl methacrylate (PMMA).…”

JH-2 constitutive model of sandstone for dynamic problems

“…The implemented small-scale blast setup was previously adopted for testing a dolomite rock 56,87 and generated similar failure patterns and cracking www.nature.com/scientificreports/ characteristics, with certain differences resulting from the different properties of dolomite and sandstone. Similar failure patterns were observed in concrete 89,90 , sandstone 91,92 and granite 19,93,94 .…”