ISO 1920-7:2004

INTERNATIONAL ISO
STANDARD 1920-7
First edition
2004-08-01
Testing of concrete —
Part 7:
Non-destructive tests on hardened
concrete
Essais du béton —
Partie 7: Essais non destructifs du béton durci

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
1 Scope. 1
2 Terms and definitions. 1
3 Determination of rebound number. 2
3.1 Principle . 2
3.2 Apparatus. 2
3.3 Test area. 2
3.4 Procedure. 3
3.5 Test results . 3
3.6 Test report. 4
4 Determination of ultrasonic pulse velocity . 4
4.1 Principle . 4
4.2 Apparatus. 4
4.3 Performance requirements of apparatus. 5
4.4 Procedure. 5
4.5 Expression of results. 6
4.6 Test report. 6
5 Determination of pull-out force . 6
5.1 Principle . 6
5.2 Apparatus. 6
5.3 Test area. 7
5.4 Procedure. 9
5.5 Expression of results. 9
5.6 Test report. 9
6 General requirements for test reports . 9
Annex A (informative) Method of obtaining a correlation between strength and rebound number . 11
Annex B (informative) Factors influencing the rebound of a concrete surface. 12
Annex C (informative) Example of a test report of the rebound number of hardened concrete. 14
Annex D (normative) Determination of pulse velocity — Indirect transmission . 15
Annex E (informative) Factors influencing pulse velocity measurements. 16
Annex F (informative) Correlation of pulse velocity and strength . 19
Annex G (informative) Example of a test report of the ultrasound pulse velocity of hardened
concrete . 21
Annex H (informative) Relationship between pull-out force and strength of concrete. 22
Annex I (informative) Example of a test report of the pull-out force of hardened concrete . 23
Bibliography . 24

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 1920-7 was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-
stressed concrete, Subcommittee SC 1, Test methods for concrete.
ISO 1920 consists of the following parts under the general title Testing of concrete:
 Part 1: Sampling of fresh concrete
 Part 2: Properties of fresh concrete
 Part 3: Making and curing test specimens
 Part 4: Strength of hardened concrete
 Part 5: Properties of hardened concrete other than strength
 Part 6: Sampling, preparing and testing concrete cores
 Part 7: Non-destructive tests on hardened concrete

iv © ISO 2004 – All rights reserved

INTERNATIONAL STANDARD ISO 1920-7:2004(E)

Testing of concrete —
Part 7:
Non-destructive tests on hardened concrete
1 Scope
This part of ISO 1920 specifies non-destructive test methods for use on hardened concrete.
The methods included are
a) determination of rebound number,
b) determination of ultrasonic pulse velocity, and
c) determination of pull-out force.
NOTE These test methods are not intended to be an alternative for the determination of compressive strength of
concrete, but with suitable correlations they can provide an estimate of in-situ strength.
2 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
NOTE Additional terms are defined in other parts of ISO 1920.
2.1
rebound number
〈rebound number test〉 reading on a rebound hammer, which is related to the proportion of the energy returned
to the hammer after striking the surface of the concrete
2.2
test area
〈rebound number test〉 region of concrete that is being assessed and which, for practical purposes, is
assumed to be of uniform quality
2.3
median
〈rebound number test〉 middle value of a set of numbers when arranged in size order
NOTE If the set has an even number of items, the median is taken as the mean of the middle two.
2.4
transit time
〈ultrasonic pulse velocity test〉 time taken for an ultrasonic pulse to travel from the transmitting transducer to
the receiving transducer, passing through the interposed concrete
2.5
onset
〈ultrasonic pulse velocity test〉 leading edge of the pulse detected by the measuring apparatus
2.6
rise time
〈ultrasonic pulse velocity test〉 time for the leading edge of the first pulse to rise from 10 % to 90 % of its
maximum amplitude
3 Determination of rebound number
3.1 Principle
A mass propelled by a spring strikes a plunger in contact with the surface. The test result is expressed in
terms of the rebound distance of the mass.
NOTE Annex A describes a method of obtaining a correlation between strength and rebound number.
3.2 Apparatus
3.2.1 Rebound hammer, hammer comprising a spring-loaded steel hammer that, when released, strikes a
steel plunger in contact with the concrete surface.
The spring-loaded hammer shall travel with a fixed and repeatable velocity. The rebound distance of the steel
hammer from the steel plunger shall be measured on a linear scale attached to the frame of the instrument.
The rebound hammer shall be calibrated twice a year to validate the calibration curve. It shall also be
calibrated whenever there is a reason to question its proper operation.
NOTE Several types and sizes of rebound hammers are commercially available for testing various strengths and
types of concrete. Each type and size of hammer should be used only with the strength and type of concrete for which it is
intended. For testing concretes with a low surface hardness, such as lightweight concrete, a pendulum-type rebound
hammer of low impact energy is suitable.
3.2.2 Steel reference anvil, for verification of the hammer, defined with a hardness of minimum 52 HRC
and a mass of 16 kg ± 1 kg and a diameter of approximately 150 mm, except where the annex in a national
standard defines a different mass.
NOTE Verification on an anvil will not guarantee that different hammers will yield the same results at other points on
the rebound scale.
3.2.3 Abrasive stone, medium-grain texture silicon carbide stone or equivalent material.
3.3 Test area
3.3.1 Selection
If the concrete elements to be tested are not at least 100 mm thick and fixed within a structure, they shall be
rigidly supported during testing. Areas exhibiting honeycombing, scaling, rough texture, or high porosity
should be avoided.
In selecting an area to be tested, the factors described in Annex B should be taken into account.
A test area shall be approximately 300 mm ¥ 300 mm.
NOTE It is normally better to confine the readings to a limited test area, rather than take random readings over the
whole structure or element.
2 © ISO 2004 – All rights reserved

3.3.2 Preparation
Heavily textured or soft surfaces and surfaces with loose mortar shall be ground smooth using the abrasive
stone (3.2.3).
Smooth-formed or trowelled surfaces may be tested without grinding.
Remove any water present on the surface of the concrete.
3.4 Procedure
3.4.1 Preliminaries
Use the rebound hammer (3.2.1) in accordance with the manufacturer’s instructions for its operation. Activate
it at least three times before taking any readings, to ensure that it is working correctly.
Before a sequence of tests on a concrete surface, take and record readings using the steel reference anvil
(3.2.2) and ensure that they are within the range recommended by the manufacturer. If they are not, then
clean and/or adjust the hammer.
The hammer should normally be operated at a temperature within the range of 10 °C to 35 °C.
3.4.2 Determination
Hold the hammer firmly in a position that allows the plunger to impact perpendicularly to the surface being
tested. Gradually increase the pressure on the plunger until the hammer impacts.
After impact, record the rebound number.
NOTE There are hammers with automatic writing equipment and, in these cases, the rebound number is recorded
automatically.
Use a minimum of nine readings to obtain a reliable estimate of the rebound number for a test area.
Record the position and orientation of the hammer for each set of readings.
No two impact points shall be closer together than 25 mm and none shall be within 50 mm from an ed
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