1. Scope 1.1 This test method covers the testing apparatus, sampling, test specimen preparation, and testing procedures for determinng the rebound hardness number of rock material using a spring-driven steel hammer, or concrete test hammer. 1.2 This test method is best suited for rock material with uniaxial compressive strengths (see Test Method D 2938) ranging between approximately 1 and 100 MPa. 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 The values stated in SI units are to be regarded as the standard. 1.5 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.