Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method

SIGNIFICANCE AND USE
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' Études et Recherches des Charbonnages de France (CERCHAR) (5). CAI is used to assess the abrasiveness of rock for mechanical excavation. Rock abrasiveness governs the performance of disc cutters, the rate of its replacement and therefore subsequent tunnel costs. Advances in methods of underground excavation, in particular the use of the tunnel boring machine (TBM), necessitates knowledge of rock abrasiveness. Abrasiveness expresses a behavioral characteristic of rock rather than a fundamental physical or mechanical property.  
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.  
Note 1: The quality of the result produced by these practices is dependent upon the competence of the personnel performing it and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing and sampling. Users of these practices are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
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, 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.  
1.3.1 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 (2).  
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 scratch’s length. The remaining 15 % of the stylus wear occurs during the last 8 mm of the scratch’s length. Therefore,...

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30-Sep-2022
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ASTM D7625-22 - Standard Test Method for Laboratory Determination of Abrasiveness of Rock Using the CERCHAR Abrasiveness Index Method
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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.
Designation: D7625 − 22
Standard Test Method for
Laboratory Determination of Abrasiveness of Rock Using
1
the CERCHAR Abrasiveness Index Method
This standard is issued under the fixed designation D7625; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* typestylusbutwithdifferenthardnessneedtobenormalizedto
standard stylus hardness (2).
1.1 This test method covers the determination of the abra-
siveness of rock by the CERCHARAbrasiveness Index (CAI) 1.5 The scratch distance shall be limited to 10 mm. In
method.Thetestmethodconsistsofmeasuringthewearonthe
general, 85% of the stylus wear occurs during the first 2 mm
tip of steel stylus with a cone shape and known Rockwell of scratch’s length. The remaining 15% of the stylus wear
Hardness,causedbyscratchingagainstafreshlybrokenorsaw
occurs during the last 8 mm of the scratch’s length. Therefore,
cut rock surface for a prescribed 10 mm distance using one of minor variation in the scratch’s length from test to test doesn’t
the two test apparatus. significantly affect the total stylus wear and the resulting CAI
when variation in scratch length is kept between 60.5mm in
1.2 This test method is intended for freshly broken rock
length (3).
surfaces; however, saw cut surfaces are covered for when a
satisfactory rock surface cannot be obtained. 1.6 All observed and calculated values shall conform to the
guidelines for significant digits and rounding established in
1.3 The Rockwell Hardness (HR) of the stylus can have a
Practice D6026.
profound effect on the results. The focus of this test method is
2
1.6.1 Theproceduresusedtospecifyhowdataarecollected/
an HRC value of 55 for every test (1, 2). However, there are
recorded or calculated, in this standard are regarded as the
situations where styli with different Rockwell Hardness can be
industry standard. In addition, they are representative of the
used.Therefore,thistestmethodincludesdiscussionsonstylus
significant digits that generally should be retained. The proce-
with different Rockwell Hardness.
dures used do not consider material variation, purpose for
1.3.1 The Rockwell hardness (HR) value is based on the
obtaining the data, special purpose studies, or any consider-
indentation hardness of a material. The Rockwell test, E18,
ations for the user’s objectives; and it is common practice to
measures the depth of penetration of an indenter under a large
increase or reduce significant digits of reported data to be
load (major load) compared to the penetration made by a
commensuratewiththeseconsiderations.Itisbeyondthescope
preload(minorload). (3)Therearedifferentscales,denotedby
of this standard to consider significant digits used in analysis
asingleletter(AtoF),thatusedifferentloadsorindenters.The
methods for engineering design.
result is a dimensionless number noted as HRA, HRB, HRC,
etc.,wherethelastletteristherespectiveRockwellscalewhich
1.7 Units—The values stated in SI units are to be regarded
in this test method is the scale C, which is for harden{steel.
asstandard.Nootherunitsofmeasurementareincludedinthis
standard.
1.4 Basically, the CERCHAR test is a measurement of the
relative different hardness of stylus tip and rock specimen 1.8 This standard does not purport to address all of the
surface. The stylus tip is made of steel having a known safety concerns, if any, associated with its use. It is the
Rockwell Hardness. Experiments have shown that CAI varies responsibility of the user of this standard to establish appro-
inversely with stylus hardness. Test results with the same steel priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1 1.9 This international standard was developed in accor-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
dance with internationally recognized principles on standard-
Rock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics.
Current edition approved Oct. 1, 2022. Published October 2022. Originally
ization established in the Decision on Principles for the
approved in 2010. Last previous edition approved in 2010 as D7625–10, which
Development of International Standards, Guides and Recom-
waswithdrawnJune2019andreinstatedinOctober2022.DOI:10.1520/D7625-22.
2
mendations issued by the World Trade Organization Technical
The bold numbers in parenthesis refer to a list of references at the end of this
standard. Barrier
...

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