1.1 This test method covers the testing apparatus, sampling, test specimen preparation, and testing procedures for determining the rebound hardness number of rock material using a spring-driven steel hammer, referred to variously as a rebound hammer, impact test hammer, or concrete test hammer. 1.2 This test method is best suited for rock material with uniaxial compressive strengths ranging between approximately 1 and 100 MPa. Test Method D7012 provides more information on compressive strength of rock. 1.3 The portable testing apparatus may be used in the laboratory or field to provide a means of rapid assessment of rock hardness or to serve as an indicator of rock hardness. 1.4 Rebound hammers are available from their original manufacturers in several different energy ranges. For a given plunger tip diameter and radius of curvature, the impact energy of the rebound hammer determines its range of applicability. Accordingly, this limitation should be kept in mind when selecting a hammer type. Earlier recommendations for rock mechanics applications were only for hammers with an impact energy of 0.735 Nm, especially on smaller core samples and weaker rocks (see also Brown 1981 2 ). Any rebound hammer may be used, however, this test method applies only to hammers with an impact energy not to exceed 0.735 Nm. Hammers with energies above 0.735 Nm tend to break the rock and are not recommended. 1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 . 1.6 This test method is used to test rock. For concrete testing, see Test Method C805/C805M . 1.7 The 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 and health practices and determine the applicability of regulatory limitations prior to use.