This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles

for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Designation: C805/C805M − 18

Standard Test Method for

Rebound Number of Hardened Concrete1
This standard is issued under the fixed designation C805/C805M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

1. Scope* 2.2 Other Standard:3

BS EN 13791 Assessment of In-Situ Compressive Strength
1.1 This test method covers the determination of a rebound
in Structures and Pre-Cast Concrete Components
number of hardened concrete using a spring-driven steel
hammer. 3. Terminology
1.2 The values stated in either SI units or inch-pound units 3.1 Definitions:
are to be regarded separately as standard. The values stated in 3.1.1 For definitions of terms used in this test method, refer
each system may not be exact equivalents; therefore, each to Terminology C125.
system shall be used independently of the other. Combining
values from the two systems may result in non-conformance 4. Summary of Test Method
with the standard. 4.1 A steel hammer impacts, with a predetermined amount
1.3 This standard does not purport to address all of the of energy, a metal plunger in contact with a concrete surface.
safety concerns, if any, associated with its use. It is the Either the distance that the hammer rebounds is measured or

iTeh Standards
responsibility of the user of this standard to establish appro- the hammer speeds before and after impact are measured. The
priate safety, health, and environmental practices and deter- test result is reported as a dimensionless rebound number.
mine the applicability of regulatory limitations prior to use.
(https://standards.iteh.ai)
5. Significance and Use
1.4 This international standard was developed in accor-
5.1 This test method is applicable to assess the in-place
dance with internationally recognized principles on standard-
Document Preview
uniformity of concrete, to delineate variations in concrete
ization established in the Decision on Principles for the
quality throughout a structure, and to estimate in-place strength
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical if a correlation is developed in accordance with 5.4.
Barriers to Trade (TBT) Committee. 5.2 For a given concrete mixture, the rebound number is
ASTM C805/C805M-18
affected by factors such as moisture content of the test surface,
https://standards.iteh.ai/catalog/standards/sist/8a231707-ea64-4f05-bac5-efe085333cf5/astm-c805-c805m-18
2. Referenced Documents the type of form material or type of finishing used in construc-
2.1 ASTM Standards:2 tion of the surface to be tested, vertical distance from the
C42/C42M Test Method for Obtaining and Testing Drilled bottom of a concrete placement, and the depth of carbonation.
Cores and Sawed Beams of Concrete These factors need to be considered in interpreting rebound
C125 Terminology Relating to Concrete and Concrete Ag- numbers.
gregates 5.3 Different instruments of the same nominal design may
C670 Practice for Preparing Precision and Bias Statements give rebound numbers differing from 1 to 3 units. Therefore,
for Test Methods for Construction Materials tests should be made with the same instrument in order to
E18 Test Methods for Rockwell Hardness of Metallic Ma- compare results. If more than one instrument is to be used,
terials perform comparative tests on a range of typical concrete
surfaces so as to determine the magnitude of the differences to
be expected in the readings of different instruments.
1
This test method is under the jurisdiction of ASTM Committee C09 on 5.4 Relationships between rebound number and concrete
Concrete and Concrete Aggregates and is the direct responsibility of Subcommittee strength that are provided by instrument manufacturers shall be
C09.64 on Nondestructive and In-Place Testing.
used only to provide indications of relative concrete strength at
Current edition approved Dec. 15, 2018. Published February 2019. Originally
approved in 1975. Last previous edition approved in 2013 as C805/C805M – 13a. different locations in a structure. To use this test method to
DOI: 10.1520/C0805_C0805M-18. estimate strength, it is necessary to establish a relationship
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3
Standards volume information, refer to the standard’s Document Summary page on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.

*A Summary of Changes section appears at the end of this standard

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1
 C805/C805M − 18
between strength and rebound number for a given concrete and 6.2 Abrasive Stone, consisting of medium-grain texture
given apparatus (see Note 1). Establish the relationship by silicon carbide or equivalent material.
correlating rebound numbers measured on the structure with
the measured strengths of cores taken from corresponding 6.3 Verification Anvil, used to check the operation of the
locations (see Note 2). At least two replicate cores shall be rebound hammer. An instrument guide is provided to center the
taken from at least six locations with different rebound rebound hammer over the impact area and keep the instrument
numbers. Select test locations so that a wide range of rebound perpendicular to the anvil surface. The anvil shall be con-
numbers in the structure is obtained. Obtain, prepare, and test structed so that it will result in a rebound number of at least 75
cores in accordance with Test Method C42/C42M. If the for a properly operating instrument (see Note 6). The manu-
rebound number is affected by the orientation of the instrument facturer of the rebound hammer shall stipulate the type of
during testing, the strength relationship is applicable for the verification anvil to be used and shall provide the acceptable
same orientation as used to obtain the correlation date (see range of rebound numbers for a properly operating instrument.
Note 3). Locations where strengths are to be estimated using The anvil manufacturer shall indicate how the anvil is to be
the developed correlation shall have similar surface texture and supported for verification tests of the instrument, and shall
shall have been exposed to similar conditions as the locations provide instructions for visual inspection of the anvil surface
where correlation cores were taken. The functionality of the for surface wear.
rebound hammer shall have been verified in accordance with
6.4 before making the correlation measurements. NOTE 6—A suitable anvil has included an approximately 150 mm [6 in.]
NOTE 1—See ACI 228.1R4 or BS EN 13791 for additional information diameter by 150 mm [6 in.] tall steel cylinder with an impact area
on developing the relationship and on using the relationship to estimate hardened to an HRC hardness value of 64 to 68 as measured by Test
in-place strength. Methods E18.
NOTE 2—The use of molded test specimens to develop a correlation
may not provide a reliable relationship because the surface texture and 6.4 Verification—Rebound hammers shall be serviced and
depth of carbonation of molded specimens are not usually representative verified annually and whenever there is reason to question their
of the in-place concrete. proper operation. Verify the functional operation of a rebound
NOTE 3—The use of correction factors to account for instrument hammer using the verification anvil described in 6.3. During
iTeh Standards
orientation may reduce the reliability of strength estimates if the correla-
tion is developed for a different orientation than used for testing. verification, support the anvil as instructed by the anvil
manufacturer.
5.5 This test method is not suitable as the basis for accep-
(https://standards.iteh.ai)
tance or rejection of concrete. NOTE 7—Typically, a properly operating rebound hammer and a
properly designed anvil should result in a rebound number of about 80.

6.1 Rebound Hammer, consisting Document

of a spring-loaded steel Preview
6. Apparatus The anvil needs to be supported as stated by the anvil manufacturer to
obtain reliable rebound numbers. Verification on the anvil does not
hammer that, when released, strikes a metal plunger in contact guarantee that the hammer will yield repeatable rebound numbers at other
points on the scale. At the user’s option, the rebound hammer can be
with the concrete surface. The spring-loaded hammer must
ASTM
travel with a consistent and reproducible speed. The reboundC805/C805M-18
verified at lower rebound numbers by using blocks of polished stone
having uniform hardness. Some users compare several hammers on
https://standards.iteh.ai/catalog/standards/sist/8a231707-ea64-4f05-bac5-efe085333cf5/astm-c805-c805m-18
number is based on the rebound distance of the hammer after concrete or stone surfaces encompassing the usual range of rebound
it impacts the plunger, or it is based on the ratio of the hammer numbers encountered in the field.
speed after impact to the speed before impact. Rebound
numbers based on these two measurement principles are not 7. Test Area and Interferences
comparable.
7.1 Selection of Test Surface—Concrete members to be
NOTE 4—Several types and sizes of rebound hammers are commercially tested shall be at least 100 mm [4 in.] thick and fixed within a
available to accommodate testing of various sizes and types of concrete
construction.
structure. Smaller specimens must be rigidly supported. Avoid
areas exhibiting honeycombing, scaling, or high porosity. Do
6.1.1 A means shall be provided to display the rebound not compare test results if the form material against which the
number after each test.
concrete was placed is not similar (see Note 8). Troweled
NOTE 5—Methods of displaying rebound numbers include mechanical surfaces generally exhibit higher rebound numbers than
sliders and electronic displays. Instruments are available that will store the screeded or formed finishes. If possible, test structural slabs
rebound numbers, which can then be transferred to a computer for
analysis. from the underside to avoid finished surfaces.
6.1.2 The manufacturer shall supply rebound number cor- 7.2 Preparation of Test Surface—A test area shall be at least
rection factors for instruments that require such a factor to 150 mm [6 in.] in diameter. Heavily textured, soft, or surfaces
account for the orientation of the instrument during a test. The with loose mortar shall be ground flat with the abrasive stone
correction factor is permitted to be applied automatically by the described in 6.2. Smooth-formed or troweled surfaces do not
instrument. The manufacturer shall keep a record of test data have to be ground prior to testing (see Note 8). Do not compare
used as the basis for applicable correction factors. results from ground and unground surfaces. Remove free
surface water, if present, before testing.
4
ACI 228.1R, “In-Place Methods to Estimate Concrete Strength,” American
Concrete Institute (ACI), P.O. Box 9094, Farmington Hills, MI 48333-9094, NOTE 8—Where formed surfaces were ground, increases in rebound
http://www.concrete.org. number of 2.1 for plywood formed surfaces and 0.4 for high-density