Abstract
Ideally, an abrasivity test should be physically similar to the real cutting process of a drag bit or roller cutter and should generate a force of a few tonnes. The note describes how an m-type Schmidt hammer was modified and used as a portable in-situ tester. The indentation tool is a replaceable hardened steel cylinder, inclined at 45 degrees giving a typical penetration in hard rock of 2 to 3 mm. The test consists of between 20 and 50 separate impacts in the rock formation and measurement of total weight loss of the tool. Abrasivity is measured as the weight loss for a given total impact energy in mg/kj. Typical readings of weight loss are 15 mg after 20 impacts on granite or 7 mg after 40 impacts on hard sandstone. Because of the difficulty of comparing Schmidt data with actual readings from tunnels, Schmidt abrasivity data have been compared to laboratory tests with a miniature disc cutter on samples of the same rock. Reasonable correlation was obtained between the wear of the miniature disc cutter and the wear of the indentation of the Schmidt hammer. (TRRL)
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