ASTM D 7625 : 2022

1.1This test method covers the determination of the abrasiveness of rock by the CERCHAR Abrasiveness Index (CAI) method. The test method consists of measuring the wear on the tip of steel stylus with a cone shape and known Rockwell Hardness, caused by scratching against a freshly broken or saw cut rock surface for a prescribed 10 mm distance using one of the two test apparatus.

1.2This test method is intended for freshly broken rock surfaces; however, saw cut surfaces are covered for when a satisfactory rock surface cannot be obtained.

1.3The Rockwell Hardness (HR) of the stylus can have a profound effect on the results. The focus of this test method is an HRC value of 55 for every test (1, 2).2 However, there are situations where styli with different Rockwell Hardness can be used. Therefore, this test method includes discussions on stylus with different Rockwell Hardness.

1.4Basically, the CERCHAR test is a measurement of the relative different hardness of stylus tip and rock specimen surface. The stylus tip is made of steel having a known Rockwell Hardness. Experiments have shown that CAI varies inversely with stylus hardness. Test results with the same steel type stylus but with different hardness need to be normalized to standard stylus hardness (2).

1.5The scratch distance shall be limited to 10 mm. In general, 85 % of the stylus wear occurs during the first 2 mm of scratch’s length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratch’s length. Therefore, minor variation in the scratch’s length from test to test doesn’t significantly affect the total stylus wear and the resulting CAI when variation in scratch length is kept between ±0.5 mm in length (3).

1.6All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.7Units—The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.9This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.