Estimating rock strength with the equotip hardness tester

Abstract

This technical note reports the preliminary results of the investigation of the Equotip Hardness Tester by the Section of Engineering Geology of Delft University of Technology. The tester is a relatively new product in the field of hardness testing, and was developed to measure the hardness of nonmetallic materials. It is a small battery-operated electronic spring-loaded device, in which a 3mm diameter spherical tungsten carbide test tip is mounted in an impact body, which bounces under spring force against a test surface from which it rebounds. A digital display shows the measured values of the impact and rebound velocities. The device was used in experiments on a series of rock samples, mostly limestone, prepared for the unconfined compressive strength test. During testing, rock samples were placed on a table with a 10cm thick rock top. For example, tests were performed on three types of limestone, each with four different surface treatments giving different grades of roughness. No major difference was found between the measurements taken on the different surface treatments. The authors conclude that the Equotip seems to be a convenient portable tool for estimating the unconfined compressive strength of rock material. The Equotip's ability to make diametral measurements on rock cores makes it very useful for core logging.