ISO 1920-7:2004

Testing of concrete — Part 7: Non-destructive tests on hardened concrete

ISO 1920-7:2004 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.

Essais du béton — Partie 7: Essais non destructifs du béton durci

General Information

• Status: Published
• Publication Date: 15-Jul-2004
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: ISO/TC 71/SC 1 - Test methods for concrete
• Drafting Committee: ISO/TC 71/SC 1 - Test methods for concrete
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 29-Oct-2019

Standards Content (Sample)

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 1920-7:2004(E)
©
ISO 2004

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ISO 1920-7:2004(E)
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ISO 1920-7:2004(E)
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

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ISO 1920-7:2004(E)
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

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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
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ISO 1920-7:2004(E)
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.
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ISO 1920-7:2004(E)
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 edge.
NOTE It is preferable to draw a regular grid of lines 25 mm to 50 mm apart and take the intersections of the lines as
the test points.
Examine each impression made on the surface after impact. If the impact has crushed or broken through a
near-to-surface void, the result shall be discounted.
3.4.3 Reference checking
After testing the concrete, take readings using the steel anvil (3.2.2). Record and compare these with those
taken prior to the test (see 3.4.1). If the results differ, clean and/or adjust the hammer and repeat the test.
3.5 Test results
The result for the test area shall be taken as the mean of all the readings, adjusted if necessary to take into
account the orientation of the hammer in accordance with the manufacturer’s instructions, and expressed as a
whole number.
If more than one hammer is to be used, a sufficient number of tests should be made on similar concrete
surfaces so as to determine the magnitude of the differences to be expected.
NOTE 1 A method for obtaining a correlation between strength and rebound number is given in Annex A.
NOTE 2 For factors influencing the rebound number, see Annex B.
If more than 20 % of all the readings differ from the mean value by more than 6 units, the entire set of
readings shall be discarded.
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ISO 1920-7:2004(E)
3.6 Test report
An example of a test report is given in Annex C.
In addition to the details required by Clause 6, the report shall include the following:
a) identification of the rebound hammer;
b) reference anvil readings, before and after tests;
c) test result (mean value) and hammer orientation for each test area;
d) individual rebound hammer readings (when specified);
e) test result adjusted for hammer orientation (if appropriate).
4 Determination of ultrasonic pulse velocity
4.1 Principle
A pulse of longitudinal vibrations is produced by an electro-acoustical transducer held in contact with one
surface of the concrete under test. After traversing a known path length in the concrete, the pulse of vibrations
is converted into an electrical signal by a second transducer and electronic timing circuits enable the transit
time of the pulse to be measured.
4.2 Apparatus
The apparatus comprises the following.
4.2.1 Electrical pulse generator
The pulse velocity of the apparatus should be calibrated against a standard calibration bar, generally supplied
by the manufacturer of the apparatus.
4.2.2 Pair of transducers
The natural frequency of the transducers should normally be within the range 20 kHz to 150 kHz.
NOTE Frequencies as low as 10 kHz and as high as 200 kHz can sometimes be used. High-frequency pulses have a
well-defined onset but, as they pass through the concrete, they become attenuated more rapidly than pulses of lower
frequency. It is therefore preferable to use high-frequency transducers (60 kHz to 200 kHz) for short path lengths (down to
50 mm) and low frequency transducers (10 kHz to 40 kHz) for long path lengths (up to a maximum of 15 m). Transducers
with a frequency of 40 kHz to 60 kHz are found to be useful for most applications.
4.2.3 Amplifier
4.2.4 Electronic timing device, for measuring the time interval elapsing between the onset of a pulse
generated at the transmitting transducer and the onset of its arrival at the receiving transducer.
Two forms of the electronic timing apparatus are available:
 an oscilloscope on which the first front of the pulse is displayed in relation to a suitable time scale;
 an interval timer with a direct reading digital display.
NOTE An oscilloscope provides the facility for examining the wave form, which can be advantageous in complex
situations.
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ISO 1920-7:2004(E)
4.2.5 Apparatus for determination of arrival time of the pulse
The apparatus shall be capable of determining, in microseconds, the time of arrival of the first front of the
pulse, even though this may be of small amplitude compared with that of the first half wave of the pulse.
4.3 Performance requirements of apparatus
The apparatus shall conform to the following performance requirements:
a) it shall be capable of measuring transit times in the calibration bar to an accuracy of ± 0,1 µs;
b) the electronic excitation pulse applied to the transmitting transducer shall have a rise time of not greater
than one-quarter of its natural period; this is to ensure a sharp pulse onset;
c) the pulse repetition frequency shall be low enough to ensure that the onset of the received signal is free
from interference by reverberations;
d) the apparatus shall be used within the operating conditions stated by the manufacturer;
e) the apparatus shall be in calibration at the time of the test.
4.4 Procedure
4.4.1 Factors influencing pulse velocity measurements
In order to provide a measurement of pulse velocity that is repeatable, it is necessary to take into account the
various factors that influence the measurements. These are set out in Annex E.
4.4.2 Transducer arrangement
Place the two transducers on opposite faces (direct transmission), or on adjacent faces (semi-direct
transmission), or on the same face (indirect or surface transmission) (see Figure 1). Although the direction in
which the maximum energy is propagated is at right angles to the face of the transmitting transducer, it is
possible to detect pulses that have travelled through the concrete in some other direction.
It may be necessary to place the transducers on opposite faces but not directly opposite each other. Such
arrangements shall be regarded as a semi-direct transmission [see Figure 1 b)].
The indirect transmission arrangement is the least sensitive and should be used when only one face of the
concrete is accessible, or when the quality of the surface concrete relative to the overall quality is of interest.
See Annex D for the method of determining the ultrasonic pulse velocity by indirect transmission.
The semi-direct transmission arrangement has a sensitivity intermediate between the other two arrangements
and should only be used when the direct arrangement cannot be used.

a)  Direct transmission b)  Semi-direct transmission c)  Indirect transmission
Key
T is the transmitter
R is the receiver
Figure 1 — Positioning of transducers
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ISO 1920-7:2004(E)
4.5 Expression of results
For direct and semi-direct transmissions the pulse velocity shall be calculated from the formula:
L
V =
T
where
V is the pulse velocity, in kilometres per second;
L is the path length, in millimetres;
T is the time taken by the pulse to traverse the length, in microseconds.
For indirect transmission, the pulse velocity shall be calculated in accordance with Annex D.
The resultant determination of the pulse velocity shall be expressed to the nearest 0,01 km/s or to three
significant figures.
NOTE For a method of determining a correlation between pulse velocity and strength, see Annex F.
4.6 Test report
An example of a test report is given in Annex G.
In addition to the details required by Clause 6, the report shall include the following:
a) type and make of apparatus used, including: dimensions of contact area transducers, natural pulse
frequency of transducers, and any special characteristics;
b) arrangements of transducers and transmission method (including a sketch, where appropriate);
c) details of reinforcing steel or ducts in the vicinity of the test areas (if known);
d) surface conditions and preparation at test points;
e) measured values of path length (for direct and semi-direct transmission), including method of
measurement and accuracy of measurement;
f) pulse velocity.
5 Determination of pull-out force
5.1 Principle
The force required to pull out a disc installed a fixed distance below the surface of the concrete is measured.
5.2 Apparatus
The apparatus shall be as follows [see Figure 2 c)].
5.2.1 Insert, made of metal not readily attacked by fresh concrete, of sufficient thickness and strength to
avoid deformation during the test.
The diameter of the head of the pull-out insert shall be 25 mm ± 0,1 mm. The sides of the insert shall be
smooth.
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ISO 1920-7:2004(E)
The shaft, which may be removable, should have a diameter not more than 0,6 of the diameter of the head
and a length such that the outer surface of the head is the same depth below the concrete surface as its
diameter.
The insert may be cast into the concrete or positioned in hardened concrete in an under-reamed groove from
a drilled hole. Inserts for casting-in should have a circular head and tapered shaft to minimize side friction
during subsequent testing [see Figure 2 a) and b)].
The inserts may be coated with a release agent to prevent bonding to the concrete and may be notched to
prevent their rotation in the concrete if the shafts are to be unscrewed.
Inserts for use in drilled holes should have means for expanding to 25 mm ± 0,1 mm.
5.2.2 Drilling and under-reaming equipment
Specialized equipment shall be used for drilling and then enlarging the base of the hole, when the insert is not
cast into the concrete.
5.2.3 Bearing ring, that can be placed on the concrete surface symmetrically around the insert axis, having
an inside diameter of 55 mm ± 0,1 mm and an outside diameter of 70 mm ± 1 mm.
The width of the bearing ring shall not be less than 0,4 of the diameter of the head of the pull-out insert.
5.2.4 Loading system, capable of applying a tensile force to the insert with the reaction being transmitted
to the concrete surface through the bearing ring.
The loading system should ensure that the bearing ring is concentric with the insert shaft and that the load is
applied perpendicular to the plane of the insert.
The loading system should include a means of indicating the maximum applied force to an accuracy of 2 % in
the anticipated working range. The dial, scale or display shall have a resettable device that records the
maximum applied force.
The loading system shall be calibrated twice a year and whenever there is a reason to question its proper
operation.
5.3 Test area
5.3.1 Specimen location
The centres of test positions shall be at least 200 mm apart.
The centres shall be at least 100 mm from the edge of the concrete.
The inserts shall be placed so that all reinforcement is outside the expected conic failure surface by at least
one bar diameter, or the maximum aggregate size, whichever is the greater.
The minimum thickness of the concrete to be tested shall be 100 mm.
5.3.2 Number of tests
The number of tests required to represent an area or part of a structure shall be specified and will depend
upon
a) the variability of the concrete, and
b) the purpose of the test and the accuracy required.
Care should be exercised to avoid averaging individual results if the differences between them reflect real
differences in strength due to factors such as variations in curing conditions or batches of concrete.
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ISO 1920-7:2004(E)
Dimensions in millimetres


a)  Insert installed before casting b)  Insert installed after casting

c)  Apparatus
Key
1 bearing ring
F is the pull-out force
2 assured conic fracture d is the diameter of the insert head
3 removable pull-out insert shaft
h is the distance from the pull-out insert head to the
concrete surface
4 pull-out insert head
Figure 2 — Schematic representation of pull-out test arrangement
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ISO 1920-7:2004(E)
5.4 Procedure
5.4.1 Installation of inserts
Securely fix the cast-in inserts to the formwork or locating device at the required test positions.
NOTE A small separately removable panel may be incorporated in the formwork when the test is being used to
determine the formwork stripping time. It is important to ensure that the shafts are disconnected from the formwork before
its removal.
Drill holes for other types of inserts, under-reamed, and assemble the inserts according to the manufacturer’s
instructions.
5.4.2 Loading
Do not apply the test to frozen concrete.
First remove the tapered shaft of a cast-in insert and then connect the loading system to the insert in
accordance with the manufacturer’s instructions.
Apply the load and increase at a steady rate of 0,5 kN/s ± 0,2 kN/s, without shock, until either the concrete is
fractured (if the strength is to be estimated) or to the specified proof load (if the purpose of the test is to verify
that the concrete has achieved a required minimum strength).
Record the maximum indicated force.
5.5 Expression of results
The maximum indicated force shall be expressed to the nearest 0,05 kN or to three significant figures.
If there is a requirement to determine the pull-out strength, then the procedures given in Annex H should be
followed.
5.6 Test report
An example of a test report is given in Annex I.
In addition to the details required by Clause 6, the report shall include the following:
a) type of apparatus (inserted or drilled);
b) whether the concrete was loaded to rupture or proof loaded;
c) individual force measurement(s).
6 General requirements for test reports
Test reports shall include the following:
a) identification of the concrete structure/element;
b) location of the test area;
c) date of the test;
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ISO 1920-7:2004(E)
d) description of the concrete tested; where known, include mix design, age of concrete, details of curing of
the concrete, temperature of the concrete at time of the test, surface moisture condition of the concrete at
the time of the test, description of the preparation of the test area;
e) any deviation from the methods set out in this International Standard;
f) declaration by the person technically responsible for the test, that the test was carried out according to
this International Standard, except as detailed in e).
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ISO 1920-7:2004(E)
Annex A
(informative)

Method of obtaining a correlation between strength and rebound number
A.1 The most convenient method of producing a correlation between strength and rebound number is by
tests in which both measurements are made on cast specimens. However, it is difficult to ensure that cast
specimens represent in-situ concrete in all respects. More reliable results may be obtained, either by using
cores taken from
...