Standard Test Method for Determining Rock Hardness by ASTM D5873 Knockback Hammer Method

Developed by the American Association of Testing and Materials (ASTM), the ASTM D5873 standard uses the test apparatus to determine the rebound hardness number of rock material using a spring-operated steel hammer, variously called the rebound hammer, impact tester, or concrete tester. It includes sample preparation and testing procedures. This test method is best suited for rock material with uniaxial compressive strength ranging from approximately 1 to 100 MPa. The portable test apparatus can be used in the laboratory or in the field for rapid assessment of rock hardness or to serve as an indicator of rock hardness. The full name of this standard is as follows: ASTM D5873-14 Standard test method for determining rock hardness by the kickback hammer method.

Recoil hammers are available in several different energy ranges depending on the manufacturer. For a given piston tip diameter and radius of curvature, the impact energy of the concrete hammer determines the range of applicability. Accordingly, this limitation should be taken into account when choosing a hammer type. Previous recommendations for rock mechanics applications are for hammers with an impact energy of only 0.735 nanometers, especially on smaller core samples and weaker rocks. This test method is only valid for hammers whose impact energy does not exceed 0,735 nanometers. Hammers with energies above 0,735 nanometers tend to break through the rock and are not recommended.

Rocks exhibiting bubbly texture are beyond the scope of this test. Care should be taken when testing such rocks as rebound values ​​vary between testing a large piece of aggregate versus a softer conglomerate matrix. All observed and calculated values ​​must comply with the essential digits and rounding guidelines specified in the ASTM D6026 standard (ASTM D6026-13 Standard practice for the use of key digits in geotechnical data).

The procedures used to determine how data are collected and recorded or calculated are considered the industry standard in this standard. It also often represents important numbers that should be kept. The procedures used do not take into account the significant differences, the purpose of obtaining the data, special purpose work or any consideration of the user's goals. It is beyond the scope of this standard to consider the important steps used in analytical methods for engineering design.

In short, the rebound hardness method provides a tool for rapid classification of rock hardness during field characterization for engineering, design and construction purposes, geotechnical mapping of large underground openings in rock, or reporting the physical description of the rock core.

The rebound hardness number serves a variety of engineering applications requiring characterization of rock material. These applications include, for example, estimating penetration rates for tunneling machines, determining rock quality for construction purposes, batching test samples, and estimating the hydraulic erodibility of the rock. This test method has limited use in very soft rock or very hard rock defined as having a uniaxial compressive strength of less than about 1 Mpa or more than 100 Mpa.

The results of this test method are not intended to be converted into strength data suitable for design.

Various types of backfire hammers are commercially available to accommodate various sizes and types of rock tests. The rebound numbers obtained from different hammers for the same rock or material cannot be compared.

Our organization provides standard testing services for the determination of rock hardness with the backlash hammer method within the scope of ASTM D5873 standard, within the framework of national and international standards, with a trained and expert staff and advanced technological equipment, among numerous testing, measurement, analysis and evaluation studies. .