Cerchar Abrasivity Index Test: a test to determine the abrasiveness of rocks
The test for determining the Cerchar Abrasiveness Index (CAI) is regulated by ASTM D7625: it consists in determining the abrasiveness of a rock starting from the degree of wear it induces on a steel tip. This test is widely used in the field of underground excavations, to evaluate the extent of wear of the cutting edges of the cutters. The Cerchar test consists in putting the rock specimen in contact with a metal tip and, thanks to a load applied to the latter, causing “incisions” (scratches) on the rock. From the measurement of the tip wear, a Cerchar Abrasivity Index value will subsequently be obtained, which will characterize the abrasiveness of the material. The name Cerchar is the acronym for Center d ‘Études et Recherches des Charbonnages, a French laboratory where this test technique was first developed. The execution of this type of test involves the use of an apparatus which can be the Original or the West Cerchar: LRRT is equipped with a West Cerchar apparatus, the diagram of which is shown in the following figure.
Other tools needed for the test are steel drills with a known aperture and a microscope to measure wear.
The Cerchar Abrasivity Index value is calculated differently if the test is performed on a surface cut with a diamond saw (CAIs) or on a fresh cut surface (CAI): the two values are linked by a linear relationship. This type of test – the Cerchar Abrasivity Index – finds wide applications in the design of tunnels: an assessment of the degree of abrasiveness of a rock allows us to make hypotheses on the timing of advancement and on the maintenance costs of excavation machinery.