ISO 1920-4:2020

Testing of concrete — Part 4: Strength of hardened concrete

This document specifies procedures for testing the strength of hardened concrete.

Essais du béton — Partie 4: Résistance du béton durci

General Information

• Status: Published
• Publication Date: 06-Jan-2020
• 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: 6060 - International Standard published
• Start Date: 07-Jan-2020
• Due Date: 24-Aug-2019
• Completion Date: 07-Jan-2020

Relations

• Revises: ISO 1920-4:2005 - Testing of concrete — Part 4: Strength of hardened concrete
• Effective Date: 03-Sep-2016

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 1920-4
Second edition
2020-01
Testing of concrete —
Part 4:
Strength of hardened concrete
Essais du béton —
Partie 4: Résistance du béton durci
Reference number
ISO 1920-4:2020(E)
©
ISO 2020

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ISO 1920-4:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 1920-4:2020(E)

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Determination of compressive strength . 1
4.1 Test specimens . 1
4.2 Apparatus . 2
4.3 Age at test . 2
4.4 Number of specimens . 2
4.5 Procedure . 2
4.5.1 Preparation and positioning of specimens. 2
4.5.2 Loading . 3
4.5.3 Assessment of type of failure . 3
4.6 Test results. 6
4.7 Test report . 6
5 Determination of flexural strength . 6
5.1 Test specimens . 6
5.2 Age at test . 6
5.3 Number of specimens . 6
5.4 Apparatus . 7
5.5 Force application . 7
5.6 Procedures . 8
5.6.1 Preparation and positioning of specimens. 8
5.6.2 Loading . 9
5.6.3 Assessment of type of fracture . 9
5.7 Test results.10
5.8 Test report .11
6 Determination of tensile splitting strength .11
6.1 Specimens .11
6.2 Apparatus .11
6.3 Age at test .13
6.4 Number of specimens .13
6.5 Procedure .13
6.5.1 Condition of specimen at the time of testing: .13
6.5.2 Marking .13
6.5.3 Specimen positioning .14
6.5.4 Loading .14
6.5.5 Examination of specimen .14
6.6 Test results.15
6.7 Test report .15
7 Test report .15
Annex A (informative) Precision data for measurements of compressive strength .17
Annex B (normative) Adjustment of test specimens for the compressive strength test .18
Annex C (informative) Examples of test reports .27
Bibliography .30
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ISO 1920-4:2020(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 71, Concrete, reinforced concrete and pre-
stressed concrete, Subcommittee SC 1, Test methods for concrete.
This second edition cancels and replaces the first edition (ISO 1920-4:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the requirements for compressive testing machine have been included and defined;
— the testing age and number of specimens that need to be tested have been included and defined;
— the subclause on loading (see 5.6.2) has been updated.
A list of all parts in the ISO 1920 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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INTERNATIONAL STANDARD ISO 1920-4:2020(E)
Testing of concrete —
Part 4:
Strength of hardened concrete
1 Scope
This document specifies procedures for testing the strength of hardened concrete.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness — Part 2: Hardness between
10 IRHD and 100 IRHD
ISO 679, Cement — Test methods — Determination of strength
ISO 1920-3, Testing of concrete — Part 3: Making and curing test specimens
ISO 1920-6, Testing of concrete — Part 6: Sampling, preparing and testing of concrete cores
ISO 2781, Rubber, vulcanized or thermoplastic — Determination of density
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 4662, Rubber, vulcanized or thermoplastic — Determination of rebound resilience
EN 316, Wood fiberboards — Definition, classification and symbols
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Determination of compressive strength
4.1 Test specimens
The test specimen shall be:
— a cube or a cylinder in accordance with ISO 1920-3; or
— cores in accordance with ISO 1920-6.
Damaged specimens shall not be tested.
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ISO 1920-4:2020(E)

Specimens that are badly honeycombed and cracked shall not be regarded as being representative of
the quality of concrete supplied. In general, standard cube and cylinder specimens should not be tested
if they are badly honeycombed as this is an indication of poor specimen making. When such specimens
are tested, the test report shall include the fact that the specimen was honeycombed.
Where the designated size, l or l , of the cross-section is outside the tolerances, the specimens may be
1 2
used for testing by using the actual dimensions; see 4.6.
Where the dimensions or shape of a test specimen exceed the respective tolerances given in ISO 1920-3,
the specimen shall be rejected or adjusted (if feasible) by one or more of the following methods:
— uneven surfaces levelled by grinding or by capping;
— the deviation of angles corrected by cutting and/or grinding.
The procedures given in Annex B shall be used to adjust the specimen.
Adjustment by grinding shall be the reference method.
4.2 Apparatus
The test shall be carried out using the following:
4.2.1 A compression-testing machine, robust, related to the size of specimen and capable of
providing the rate of loading with minimum desired specifications as mentioned in 4.5.1 and 4.5.2. It
shall be in calibration at the time of test. The calibration shall be carried out at least once per year.
Accuracy of the test machine shall be such that the percentage error for the loads within proposed
range of use of the machine and shall not exceed ±1,0 % of the indicated load.
The compression testing machine shall be provided with a control system. The control system may
be operated either by manual or automatic means. If the machine is not equipped with automatic
application of force, a pacer shall be fitted to enable the operator to maintain the specified rate. The
pacer shall indicate a rate within ±5,0 % of the specified rate.
4.2.2 Machine platens and auxiliary platens, with a hardness value at least 550 HV (Vickers
Hardness).
The thickness of the auxiliary platens shall be at least 23 mm. The roughness value, Ra, for the surface
texture of the contact faces of the auxiliary platen shall be between 0,4 µm and 3,2 µm.
4.3 Age at test
Tests shall be made at recognized ages of the test specimens, the most usual being 7 days and 28 days.
Test at other ages can be performed as per the requirement. The ages shall be calculated from the time
water is added to the dry ingredients.
4.4 Number of specimens
At least three specimens, preferably from different batches, shall be made for testing at each selected age.
4.5 Procedure
4.5.1 Preparation and positioning of specimens
For specimens stored in water, excess moisture shall be wiped from the surface of the specimen before
placing them in the testing machine. The dimensions of the specimens shall be measured to the nearest
0,2 mm and their weight shall be noted before testing.
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ISO 1920-4:2020(E)

The time between the extraction of the specimen from the humidity chamber or the water tank until
the test shall be as short as possible and no more than 2 h. The specimen shall be protected from drying
while it is outside the humidity chamber or water tank (e.g. by covering with wet burlap).
All testing-machine bearing surfaces shall be wiped clean and any loose grit or other extraneous
material shall be removed from the surfaces of the specimen that will be in contact with the platens.
Do not use packing, other than auxiliary platens or spacing blocks, between the specimen and the
platens of the testing machine.
Cube specimens shall be compressed perpendicularly to the direction of casting.
The specimen shall be centred on the lower platen to an accuracy of 1 % of the designated size of cubic
or diameter of cylindrical specimens.
Where physical means of ensuring centring are provided on the testing machine, and they are in
calibration, they shall be deemed to satisfy the requirements for accuracy of centring.
If auxiliary platens are used, the top auxiliary platen shall be aligned with the top of the specimen.
With two-column testing machines, cubic specimens should be placed with the trowelled surface facing
a column.
4.5.2 Loading
The load shall be applied without shock and shall be increased continuously at a constant rate until no
greater load can be sustained. Select a constant rate of loading within the range 0,6 MPa/s ± 0,2 MPa/s,
After the application of the initial load, which does not exceed approximately 30 % of the failure load,
apply the load to the specimen without shock and increase continuously at the selected constant rate
±10 %, until no greater load can be sustained.
When using manually controlled testing machines, any tendency for the selected rate of loading
to decrease as specimen failure is approached shall be corrected by appropriate adjustment of the
controls.
When using automatically controlled testing machines, the rate of loading while testing concrete
specimens in compression shall be periodically checked to ensure that it is constant.
The maximum load indicated shall be recorded.
4.5.3 Assessment of type of failure
For cubic specimens, if the failure is satisfactory (see Figure 1), this fact shall be recorded. If the failure
pattern is unsatisfactory, this fact shall also be recorded, as well as the type of failure recorded with
reference to pattern number according to Figure 2 closest to that observed.
For cylindrical specimens, if the failure is satisfactory (see Figure 3), this fact shall be recorded. If the
failure pattern is unsatisfactory, this fact shall also be recorded, as well as the type of failure recorded
with reference pattern letter in Figure 4 closest to that observed.
NOTE Unsatisfactory failures can be caused by insufficient attention to the detailed procedures for making,
capping and testing specimens or by a machine fault.
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ISO 1920-4:2020(E)

Key
1 explosive failure
NOTE All four exposed faces are cracked approximately equally, generally with little damage to faces in
contact with the platens.
Figure 1 — Satisfactory failures of cube specimens
Key
T tensile crack
Figure 2 — Some unsatisfactory failures due to unequal cracking of the exposed faces of cube
specimens
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ISO 1920-4:2020(E)

Figure 3 — Satisfactory failure of cylinder specimen
Figure 4 — Unsatisfactory failures of cylinder specimens
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ISO 1920-4:2020(E)

4.6 Test results
The compressive strength is given by Formula (1):
F
f = (1)
c
A
c
where
f is the compressive strength, expressed in megapascals;
c
F is the maximum load, expressed in newtons;
A is the cross-sectional area, expressed in square millimetres, of the specimen on which the
c
compressive force acts.
If the actual dimensions of the test specimen are within ±0,5 % of the designated size, the strength may
be calculated on the basis of the designated size. If the actual dimensions are outside this tolerance,
the strength calculation shall be based on the actual dimensions of the test specimen, determined in
accordance with ISO 1920-3.
The compressive strength shall be expressed to the nearest 0,1 MPa.
NOTE Refer to informative Annex A, for precision data for measurements of compressive strength.
4.7 Test report
In addition to the requirements in Clause 7, the test report shall include the following:
— type of specimen: cube, cylinder or core;
— method of adjustment, if relevant;
— compressive strength of specimen (to the nearest 0,1 MPa);
— type of failure (satisfactory or unsatisfactory, and, if unsatisfactory, the nearest type).
5 Determination of flexural strength
5.1 Test specimens
The test specimen shall be a prism conforming to ISO 1920-3.
Sawn specimens of nominal size, l, of 100 mm or 150 mm with a square cross-section and overall length,
L, of between 4l and 5l may also be tested as presented in this document. The ratio of l to the maximum
size of aggregate shall be no less than four, except for specimens with a nominal width of 150 mm and a
maximum size of aggregate of 40 mm, which may also be tested.
The direction of casting shall be identified on the specimen.
5.2 Age at test
Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. Test
at other ages can be performed as per requirement. The ages shall be calculated from the time of the
addition of water to the dry ingredients.
5.3 Number of specimens
At least three specimens, preferably from different batches, shall be made for testing at each selected age.
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ISO 1920-4:2020(E)

5.4 Apparatus
The test shall be carried out using the following:
5.4.1 Compression-testing machine, robust, related to the size of specimen and capable of providing
the rate of loading with minimum desired specifications in 5.4 and 5.5. It shall be in calibration at the
time of test. The calibration shall be carried out at least once per year.
Accuracy of the test machine shall be such that the percentage error for the loads within proposed
range of use of the machine and shall not exceed ±1,0 % of the indicated load.
The compression testing machine shall be provided with a control system. The control system may
be operated either by manual or automatic means. If the machine is not equipped with automatic
application of force, a pacer shall be fitted to enable the operator to maintain the specified rate. The
pacer shall indicate a rate within ±5,0 % of the specified rate.
5.4.2 Machine platens and auxiliary platens, with a hardness value of at least 550 HV (Vickers
Hardness).
The thickness of the auxiliary platens shall be at least 23 mm. The roughness value, Ra, for the surface
texture of the contact faces of the auxiliary platen shall be between 0,4 µm and 3,2 µm.
5.5 Force application
The device for applying loads shall consist of two upper rollers and two lower rollers (see Figure 5).
All rollers shall be manufactured from steel and shall have a circular cross-section with a diameter
between 20 mm and 40 mm and shall be at least 10 mm longer than the width of the test specimen.
Each roller, except one of the lower ones, shall be capable of rotating around its axis and of being inclined
in a plane normal to the longitudinal axis of the test specimen.
The distance, L , between the lower (outer) rollers (i.e. the span) shall be equal to 3l, where l is the
rol
width of the specimen. The distance between the upper (inner) rollers shall be equal to l. The inner
rollers shall be equally spaced between the outer rollers as shown in Figure 5. All rollers shall be
adjusted in the positions illustrated in Figure 5 to an accuracy of ±2 mm.
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ISO 1920-4:2020(E)

Key
1 loading roller (capable of rotation and of being inclined)
2 supporting roller
3 supporting roller (capable of rotation and of being inclined)
F maximum load
Figure 5 — Arrangement for loading a test specimen (two‑point loading)
5.6 Procedures
5.6.1 Preparation and positioning of specimens
The specimen shall be examined and any abnormalities shall be reported.
For specimens stored in water, excess moisture shall be wiped from the surface of the specimen before
placing in the testing machine.
The time between the extraction of the specimen from the humidity chamber or the water tank until
the test shall be as short as possible and no more than 2 h. The specimen shall be protected from drying
while it is outside the humidity chamber or water tank (e.g. by covering with wet burlap).
All testing-machine bearing surfaces shall be wiped clean and any loose grit or other extraneous
material shall be removed from the surfaces of the specimen that will be in contact with the rollers.
The test specimen shall be placed in the machine, correctly centred with the longitudinal axis of the
specimen at right angles to the longitudinal axis of the upper and lower rollers.
The reference direction of loading shall be perpendicular to the direction of casting of the specimen.
The test result may be affected by the direction of loading with respect to the direction of casting.
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ISO 1920-4:2020(E)

5.6.2 Loading
Do not apply the load until all loading and supporting rollers are resting evenly against the test
specimen.
The load shall be applied without shock and shall be increased continuously at a constant rate until
no greater load can be sustained. Select a constant rate of stress of no less than 0,04 MPa/sec and not
greater than 0,06 MPa/sec. After the application of the initial load, which does not exceed approximately
20 % of the failure load, apply the load without shock and increase continuously, at the selected constant
rate ±1 %, until no greater load can be sustained.
NOTE The required loading rate on the testing machine is given by Formula (2):
2
sl××l
bh
F = (2)
R
l
rol
where
F is the required loading rate, expressed in newtons per second;
R
s is the stress rate, expressed in megapascals per second;
l , l are the lateral dimensions (respectively, breadth and height) of the specimen, expressed in
b h
millimetres;
l is the spacing of the lower rollers, expressed in millimetres.
rol
When using manually controlled testing machines, any tendency for the selected rate of loading
to decrease, as specimen failure is approached, shall be corrected by appropriate adjustment of the
controls.
When using automatically controlled testing machines, the rate of loading shall be periodically checked
to ensure that the rate is constant.
The maximum load indicated shall be recorded.
5.6.3 Assessment of type of fracture
The fractured specimen shall be examined and the appearance of the concrete and the type of fracture
shall be recorded (see Figure 6).
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ISO 1920-4:2020(E)

a) Satisfactory failure b) Unsatisfactory failure
Key
1 loading points
2 fracture
3 supporting roller
Figure 6 — Types of fracture
A fracture outside the loading rollers (see Figure 6) shall be reported as unsatisfactory.
5.7 Test results
The flexural strength is given by Formula (3):
Fl×
rol
f = (3)
cf
2
ll×
b h
where
f is the flexural strength, expressed in megapascals;
cf
F is the maximum load, expressed in newtons;
l , l are the lateral dimensions (respectively, breadth and height) of the specimen, expressed in
b h
millimetres;
l is the spacing of the lower rollers, expressed in millimetres.
rol
The flexural strength shall be expressed to the nearest 0,1 MPa.
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ISO 1920-4:2020(E)

5.8 Test report
In addition to the requirements in Clause 7, the test report shall include the f
...