ASTM D7625-22

5.1?The CERCHAR test and associated CAI were developed at a time of more demand for application of mechanical excavation machines at the Laboratoire du Center d' ?tudes et Recherches des Charbonnages de France (CERCHAR) 5.2?CAI tests were originally carried out on natural broken surfaces. In heterogeneous rock types such as conglomerates, coarse grained granite or schistose rock, suitable fresh test surfaces are not achieved by mechanical breakage using a hammer. In these cases CAI values for smooth surfaces cut with a diamond saw are acceptable for use but shall be normalized by Eq 2 or Eq 3 before they can be reported (4).

5.3?The test velocity for the Original CERCHAR apparatus is approximately 10 mm/s and 1 mm/s for the West CERCHAR apparatus. The CAI values obtained for both testing velocities (4) are estimated to be equal.

1.1?This 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.

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

1.3?The 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 1.3.1?The Rockwell hardness (HR) value is based on the indentation hardness of a material. The Rockwell test, E18, measures the depth of penetration of an indenter under a large load (major load) compared to the penetration made by a preload (minor load). (3) There are different scales, denoted by a single letter (A to F), that use different loads or indenters. The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last letter is the respective Rockwell scale which in this test method is the scale C, which is for harden-steel.

1.4?Basically, 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 1.5?The scratch distance shall be limited to 10 mm. In general, 85 % of the stylus wear occurs during the first 2 mm of scratchs length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratchs length. Therefore, minor variation in the scratchs length from test to test doesnt significantly affect the total stylus wear and the resulting CAI when variation in scratch length is kept between ?0.5 mm in length 1.6?All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.7?UnitsThe values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8?This 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.

1.9?This 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.