Effect of scratch length on the Cerchar abrasivity index

Cerchar Abrasivity Index test (CAI) is widely used for determining the abrasiveness of rocks. This test provides an index value that can be used as a gauge for the abrasiveness of rocks in order to estimation of bit life and wear in various mining and tunneling applications. In this study, changes in CAI with the changes in scratch length were investigated by the use of West apparatus to determine the effects of length on CAI. The tests were carried out on 6 different rock types (3 types of sandstone, limestone, granite and quartzite) where on rough and saw cut surfaces with a scratch length between 2 mm to 20 mm with an increment of 2 mm. It has been found that about 60% of the final Cerchar index (at a 20 mm sliding) was observed at the first 2 mm scratch and continued at a constant rate up to 16-18 mm, then rests around 20 mm sliding distance. This initial high tip wears may partly depend on the deformation and shear failure at the tip of pins. It has been also observed that 87% of the final Cerchar index was reached at 10 mm sliding distance while 97% of the final Cerchar index at the 15 mm sliding distance. Since initial wear at the 2 mm sliding distance is not dependent on the amount of abrasive material in the host rock. Approximately 35% of the Cerchar index can be attributed to the abrasion effect which corresponds to the final 8 mm of sliding distance. However if the sliding distance is increased to 15 mm then 45% of the Cerchar index can be attributed to the rock abrasion effects. This is very important for the tool life estimation in tunneling applications.