ISO 23945-3
(Main)Test methods for sprayed concrete — Part 3: Measurement of compressive strength
- Abstract
This document specifies the test methods for measurement and determination of the compressive strength of sprayed concrete at different age, from young hardened to long term hardened sprayed concrete. Initial and early compressive strength development of sprayed concrete up to 24h are measured using indirect methods, namely needle penetration and pin driving methods. Both methods correlate the impact of the compressive strength on the penetration of a needle. The test methods could be applied to measure compressive strength of sprayed concrete in the range of 0.5MPa to 100MPa. The specimens of hardened sprayed concrete are extracted from either an in situ element or a test panel.
- Status
- Not Published
- Technical Committee
- ISO/TC 71/SC 1 - Test methods for concrete
- Drafting Committee
- ISO/TC 71/SC 1 - Test methods for concrete
- Current Stage
- 6000 - International Standard under publication
- Start Date
- 10-Sep-2026
- Completion Date
- 10-Oct-2026
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ISO 23945-3 is an ISO standard for test methods for sprayed concrete, focused on measuring and determining compressive strength at different ages from young hardened to long-term hardened material. It gives three ways to do that: needle penetration, pin driving, and compression testing of extracted specimens. It is written for people who test sprayed concrete in the field or in the lab, and for anyone who needs a common method to report compressive strength results.
What does ISO 23945-3 specify?
ISO 23945-3 specifies how to measure compressive strength of sprayed concrete from hardened material taken from an in-situ element or a test panel. It covers indirect methods for early-age concrete and a direct compression method for stronger hardened material.
The document is organized into:
- Clause 1 Scope
- Clause 2 Normative references
- Clause 3 Terms and definitions
- Clause 4 Needle penetration method
- Clause 5 Pin driving method
- Clause 6 Determination of compressive strength by specimens
- Annex A and Annex B, both informative
- Bibliography
| Annex | What it covers |
|---|---|
| Annex A | Example calibration curves for a needle penetrometer |
| Annex B | Example calibration curves for the pin driving method |
What are the key requirements of ISO 23945-3?
ISO 23945-3 sets out three test routes, each aimed at a different strength range and stage of hardening. In practice, the user chooses the method that matches the age and expected strength of the sprayed concrete.
Needle penetration method
Clause 4 covers an indirect method for estimating the in-situ compressive strength of young hardened sprayed concrete. It is intended for the low-strength early period, where rapid site decisions often matter most.
The method uses a penetrometer to push a needle into the concrete to a fixed depth and measures the resistance force. That force is then converted to estimated compressive strength using a calibration curve supplied with the equipment. In practice, this means the operator must use the correct instrument and keep the calibration curve with the test record.
Clause 4 also sets specimen and apparatus expectations. The sprayed layer must be thick enough for the test, specimens are prepared according to ISO 23945-2, and no special specimen is needed for in-situ testing locations. The needle and penetrometer dimensions and force-reading performance are specified so the test remains comparable from one site to another.
The procedure requires repeated measurements in a representative area, recorded start and finish times, and a mean resistance force from 10 readings. The result is taken from the calibration curve, and extrapolation is not allowed. In practice, this keeps the result tied to the equipment’s validated range instead of guesswork.
Pin driving method
Clause 5 gives another indirect method for estimating in-situ compressive strength of young hardened sprayed concrete. It uses a driven pin and measures penetration depth rather than penetration force.
The method is intended for higher early strengths than the needle method, and the clause notes a recommended upper expected strength for its use. This matters because the result depends on the concrete being hard enough to resist the pin without over-penetration.
Clause 5 places detailed requirements on the equipment. The pin is single-use, the driver energy must be controlled, and the depth gauge must measure very small depth differences. The surface may need grinding if it is heavily textured, soft, or dusty with loose mortar. In practice, this means surface preparation and clean measurement holes are part of getting a usable reading.
Sampling rules also matter here. Penetrations must be spaced so they do not influence each other, and they must stay away from edges. Ten valid pin readings make one test, with outlier handling when a pin hits coarse aggregate or voids. The average penetration depth is converted to compressive strength using a calibration curve, and Annex B gives an example curve.
Clause 5 also addresses precision. That is useful for quality control because it tells the user how much spread to expect when comparing repeated tests or different test areas.
Determination by specimens
Clause 6 covers compressive strength measured directly on hardened sprayed concrete specimens. This is the route for stronger material and for results based on extracted samples rather than indirect penetration.
The clause applies to specimens cut or drilled from sprayed concrete panels or in-situ structures prepared according to ISO 23945-2. Specimens must meet minimum size and geometry rules, and damaged or honeycombed specimens are not suitable unless their condition is clearly stated in the report. For a user, that means specimen quality and geometry are part of the validity of the result.
The test is carried out in a compression testing machine conforming to ISO 1920-4. Strength is calculated from the maximum load at failure and the loaded area of the specimen. If a core has a height/diameter ratio outside the reference condition, the result is converted using the conversion factors in Table 2. That helps make results from different core shapes comparable.
Clause 6 also provides precision data and detailed reporting items. In practice, this supports laboratory traceability and lets users compare results from different operators and test conditions with more confidence.
What terms does ISO 23945-3 define?
ISO 23945-3 uses these key terms and abbreviations in its test methods:
- Sprayed concrete - concrete applied by spraying rather than placing in moulds, used here as the material being tested.
- In-situ element - sprayed concrete that is tested in the structure where it was placed, rather than as a removed sample.
- Test panel - a prepared sprayed concrete panel used to make specimens or carry out tests under controlled conditions.
- Needle penetration method - the early-age indirect method that estimates strength from the force needed to push a needle to a fixed depth.
- Pin driving method - the indirect method that estimates strength from the depth reached by a driven pin.
- Calibration curve - the relationship used to convert penetration force or depth into estimated compressive strength.
- Compressive strength - the strength value determined from resistance to crushing or from the penetration test calibration.
- MPa - megapascal, the unit used for compressive strength values in this document.
Who uses ISO 23945-3?
ISO 23945-3 is used by testing laboratories, site engineers, concrete technologists, quality managers, and contractors working with sprayed concrete. It is relevant in tunnelling, mining, ground support, repairs, restoration, and new construction.
People use it when they need to check whether sprayed concrete has gained enough strength for the next step in the job, or when they need a documented test result for quality control, acceptance, or troubleshooting. Buyers and specifiers use it to name a repeatable method in project requirements.
Which standards are used with ISO 23945-3?
ISO 23945-3 refers to several other standards that support sampling, testing, and reporting:
- ISO 23945-2 - gives the sampling requirements for fresh and hardened sprayed concrete and is used for preparing specimens.
- ASTM C803/C803M - is referenced for penetration resistance of hardened concrete and for the pin method precision note.
- ISO 1920-3 - supports making and curing test specimens and is used when actual specimen dimensions need to be determined.
- ISO 1920-4 - provides the compression testing machine and strength testing basis for the specimen method in Clause 6.
- EN 12390-3 - is used for precision data associated with compressive strength testing of hardened concrete specimens.
What does the ISO 23945-3 document contain?
ISO 23945-3 contains three test method clauses, each with principle, specimens, apparatus, procedure, result expression, and test report requirements. It also includes precision information where relevant.
Clause 4 gives the needle penetration test, including the penetrometer, needle requirements, test sequence, and reporting items. Clause 5 gives the pin driving method, including pin use, surface preparation, penetration spacing, reading depth, and precision. Clause 6 gives the specimen compression method, including specimen suitability, strength calculation, conversion for non-standard core shapes, and report content.
Annex A and Annex B provide example calibration curves, which are the practical link between test readings and estimated compressive strength. Table 1 supports the pin method precision discussion, Table 2 gives conversion factors for core shapes, and Tables 3 and 4 give precision data for the specimen method. Figure 1 shows the spacing arrangement for pin penetrations.
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Frequently Asked Questions
ISO 23945-3 is a draft published by the International Organization for Standardization (ISO). Its full title is "Test methods for sprayed concrete — Part 3: Measurement of compressive strength". This standard covers: This document specifies the test methods for measurement and determination of the compressive strength of sprayed concrete at different age, from young hardened to long term hardened sprayed concrete. Initial and early compressive strength development of sprayed concrete up to 24h are measured using indirect methods, namely needle penetration and pin driving methods. Both methods correlate the impact of the compressive strength on the penetration of a needle. The test methods could be applied to measure compressive strength of sprayed concrete in the range of 0.5MPa to 100MPa. The specimens of hardened sprayed concrete are extracted from either an in situ element or a test panel.
This document specifies the test methods for measurement and determination of the compressive strength of sprayed concrete at different age, from young hardened to long term hardened sprayed concrete. Initial and early compressive strength development of sprayed concrete up to 24h are measured using indirect methods, namely needle penetration and pin driving methods. Both methods correlate the impact of the compressive strength on the penetration of a needle. The test methods could be applied to measure compressive strength of sprayed concrete in the range of 0.5MPa to 100MPa. The specimens of hardened sprayed concrete are extracted from either an in situ element or a test panel.
ISO 23945-3 is classified under the following ICS (International Classification for Standards) categories: 91.100.30 - Concrete and concrete products. The ICS classification helps identify the subject area and facilitates finding related standards.
ISO 23945-3 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
International
Standard
First edition
Test methods for sprayed
concrete —
Part 3:
Measurement of compressive
strength
PROOF/ÉPREUVE
Reference number
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Needle penetration method . 1
4.1 General .1
4.2 Principle .1
4.3 Specimens .2
4.4 Apparatus .2
4.4.1 Penetrometer .2
4.4.2 Needle .2
4.5 Procedures .2
4.6 Expression of results . .2
4.7 Test report .2
5 Pin driving method . 3
5.1 General .3
5.2 Principles .3
5.3 Specimens .3
5.4 Apparatus .3
5.4.1 Pin driving equipment . .3
5.4.2 Spring-actuated driver .4
5.4.3 Pin .4
5.4.4 Measuring Instrument .4
5.5 Sampling .4
5.6 Procedures .6
5.7 Expression of results .6
5.8 Test report .6
5.9 Precision . . .7
6 Determination of compressive strength by specimens . 7
6.1 General .7
6.2 Principle .7
6.3 Specimens .7
6.4 Expression of results . .7
6.5 Precision . . .8
6.6 Test report .9
Annex A (informative) Example of calibration curves for needle penetrometer .10
Annex B (informative) Example of calibration curves for pin driving method .11
Bibliography .12
PROOF/ÉPREUVE
iii
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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.
A list of all parts in the ISO 23945 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.
PROOF/ÉPREUVE
iv
Introduction
Sprayed concrete is widely used for the stabilization of structures in a very short time and for concrete
applications without using moulds. In addition to being ideal for ground support in tunnelling and mining,
sprayed concrete is also used in repairs, restoration, new constructions and many other fields.
The requirements for properties, test methods, standards and specifications for the spray forming process
of concrete are different from those of cast forming concrete. This document is intended to provide a
normative test method for sprayed concrete.
This document is applied under various climatic and geographical conditions, various levels of protection
and under different established regional traditions and experiences. Consequently, this document includes
conditions for tests covering standard, tropical and subtropical region environments.
This document is intended for use with other parts of the ISO 23945 series which provide requirements
associated with the level of quality specified and the methods to be employed for the execution of sprayed
concrete.
PROOF/ÉPREUVE
v
International Standard ISO 23945-3:2026(en)
Test methods for sprayed concrete —
Part 3:
Measurement of compressive strength
1 Scope
This document specifies the test methods for measurement and determination of the compressive strength
of sprayed concrete at different age, from young hardened to long term hardened sprayed concrete. The test
methods could be applied to measure compressive strength of sprayed concrete in the range of 0,2 MPa to
100 MPa. The specimens of hardened sprayed concrete are extracted from either an in-situ element or a test
panel.
This document does not purport to address all of the safety concerns, if any, associated with its use.
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 23945-2, Test Methods for Sprayed Concrete —Part 2: Sampling fresh and hardened concrete
ISO 1920-3, Testing of concrete — Part 3: Making and curing test specimens
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Needle penetration method
4.1 General
This part specifies the method from which an estimate of the in-situ compressive strength of young hardened
sprayed concrete can be made in the range of 0,2 MPa to 1,5 MPa.
4.2 Principle
Needle penetration method is used to measure the force required to push a needle of specified dimensions
to penetrate into the sprayed concrete to a depth of 15 mm +/- 2 mm. A penetrometer indicates the resisting
force, through compression of a calibrated spring from which an estimated compressive strength can be
derived from a calibration curve provided by the producer of the test equipment.
PROOF/ÉPREUVE
4.3 Specimens
The thickness of the sprayed concrete layer shall be not less than 100 mm for testing.
The specimens for test shall be prepared according to ISO 23945-2.
No special test specimen is required for test of in-situ structures. The testing procedure can be used for
measurements at any location without advance preparation.
4.4 Apparatus
4.4.1 Penetrometer
The penetrometer shall be capable of driving the needle into the surface and recording the force required to
an accuracy of 10 N. The penetrometer shall be provided with a certified calibration curve, able to correlate
readings to estimated compressive strength. An example of calibration curves is shown in Annex A.
4.4.2 Needle
The needle shall be with a diameter of 3 mm ± 0,1 mm and a tip with a taper angle of 60° ± 5°, the needle
length shall be more than 15 mm.
4.5 Procedures
4.5.1 Record time and place of completion of spraying and start of testing.
4.5.2 Ensure the force indicator is set to zero.
4.5.3 Apply the device perpendicularly to the surface of the sprayed concrete layer and steadily push in
the needle to a depth of 15 mm in a single continuous movement. If this is prevented, for instance because of
a large aggregate particle or reinforcement, then discontinue the test and repeat in an adjacent location.
4.5.4 Read the resistance force from the scale, record the value on the protocol form and return indicator
to original position.
4.5.5 Clean the needle if necessary.
4.5.6 Repeat the test ten times as quickly as possible (and within 1 min for strengths below 0,5 MPa) in an
area representative of the sprayed region.
4.5.7 Record the time at which the testing is finished (on protocol form).
4.6 Expression of results
Calculate the mean resistance force from the 10 measurements.
The estimated compressive strength is derived from the man
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ISO/TC 71/SC 1/WG 7
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Date: 2026-04-16.08-12
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Test methods for sprayed concrete —
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or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO Before: 0 pt, No page break before, Adjust space
at the address below or ISO’s member body in the country of the requester. between Latin and Asian text, Adjust space between
Asian text and numbers
ISO copyright office
Formatted: Left: 1.5 cm, Right: 1.5 cm, Bottom: 1 cm,
CP 401 • Ch. de Blandonnet 8
Header distance from edge: 1.27 cm, Footer distance
CH-1214 Vernier, Geneva
from edge: 0.5 cm
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
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ii © ISO #### 2026 – All rights reserved
ii
ISO/DISPRF 23945-3:2026(en)
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Contents
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Foreword . v
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Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Needle penetration method . 1
4.1 General . 1
4.2 Principle . 2
4.3 Specimens . 2
4.4 Apparatus . 2
4.5 Procedures . 2
4.6 Expression of results . 2
4.7 Test report . 3
5 Pin driving method . 3
5.1 General . 3
5.2 Principles . 3
5.3 Specimens . 3
5.4 Apparatus . 4
5.5 Sampling . 4
5.6 Procedures . 6
5.7 Expression of results . 6
5.8 Test report . 6
5.9 Precision . 7
6 Determination of compressive strength by specimens . 7
6.1 General . 7
6.2 Principle . 7
6.3 Specimens . 7
6.4 Expression of results . 8
6.5 Precision . 8
6.6 Test report . 9
Annex A (informative) Example of calibration curves for needle penetrometer . 11
Annex B (informative) Example of calibration curves for pin driving method . 13
Bibliography . 15
Foreword . v
Introduction . vi
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1 Scope . 1
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2 Normative references . 1
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3 Terms and definitions . 1
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4 Needle penetration method . 1
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iii
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4.1 Scope . 1
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4.2 Principle . 1
4.3 Specimens . 2
4.4 Apparatus . 2
4.4.1 Penetrometer . 2
4.4.2 Needle . 2
4.4.3 Test protocol form . 2
4.5 Procedures . 2
4.6 Expression of results. 2
4.7 Test report . 2
5 Pin driving method . 3
5.1 Scope . 3
5.2 Principles . 3
5.3 Specimens . 3
5.4 Apparatus . 3
5.4.1 Pin driving equipment . 3
5.4.2 Spring-actuated driver . 3
5.4.3 Pin . 3
5.4.4 Measuring Instrument . 4
5.5 Sampling . 4
5.6 Procedures . 5
5.7 Expression of results. 5
5.8 Test report . 5
5.9 Precision . 5
6 Determination of compressive strength by specimens . 6
6.1 Scope . 6
6.2 Principle . 6
6.3 Specimens . 6
6.4 Expression of results. 6
6.5 Precision . 8
6.6 Test report . 8
Annex A (informative) Example of calibration curves for needle penetrometer . 10
Annex B (informative) Example of calibration curves for pin driving method . 11
Example of calibration curves for penetration pneumatic pin method
Annex C (informative) . 11
Bibliography . 12
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ISO/DISPRF 23945-3:2026(en)
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Foreword
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ISO (the International Organization for Standardization) is a worldwide federation of national standards
Adjust space between Asian text and numbers
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/directiveswww.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
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.htmlwww.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.
A list of all parts in the ISO 23945 series can be found on the ISO website.
Formatted: English (United Kingdom)
Formatted: Font: Cambria
Any feedback or questions on this document should be directed to the user’s national standards body. A
Formatted: Adjust space between Latin and Asian text,
complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
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v
ISO #####-#:####(X/PRF 23945-3:2026(en)
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Introduction
Line spacing: single
Sprayed concrete is widely used for the stabilization of structures in a very short time and for concrete
applications without using moulds. In addition to being ideal for ground support in tunnelling and mining,
sprayed concrete is also used in repairs, restoration, new constructions and many other fields.
The requirements for properties, test methods, standards and specifications for the spray forming process of
concrete are different from those of cast forming concrete. This document is intended to provide a normative
test method for sprayed concrete.
This document is applied under various climatic and geographical conditions, various levels of protection and
under different established regional traditions and experiences. Consequently, this document includes
conditions for tests covering standard, tropical and subtropical region environments.
Formatted: English (United Kingdom)
Formatted: English (United Kingdom)
This document is intended for use with other parts of the ISO 23945 series which provide requirements
Formatted: Default Paragraph Font
associated with the level of quality specified and the methods to be employed for the execution of sprayed
concrete.
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DRAFT International Standard ISO/DIS 23945-3:2026(en)
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Test methods for sprayed concrete — —
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Part 3:
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Measurement of compressive strength
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1 Scope
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This document specifies the test methods for measurement and determination of the compressive strength of
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sprayed concrete at different age, from young hardened to long term hardened sprayed concrete. The test New page, Header distance from edge: 1.27 cm, Footer
methods could be applied to measure compressive strength of sprayed concrete in the range of 0,2 MPa to distance from edge: 0.5 cm
100 MPa. The specimens of hardened sprayed concrete are extracted from either an in-situ element or a test
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panel.
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This document does not purport to address all of the safety concerns, if any, associated with its use.
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2 Normative references
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The following documents are referred to in the text in such a way that some or all of their content constitutes
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requirements of this document. For dated references, only the edition cited applies. For undated references,
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the latest edition of the referenced document (including any amendments) applies.
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ISO 23945--2, Test Methods for Sprayed Concrete —Part 2: Sampling fresh and hardened concrete Adjust space between Asian text and numbers, Tab
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
ASTM C803/C803M, Standard Test Method for Penetration Resistance of Hardened Concrete
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ISO 1920-3, Testing of concrete — Part 3: Making and curing test specimens
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ISO 1920-4, Testing of concrete —Strength of hardened concrete Formatted: Default Paragraph Font, English (United
Kingdom)
EN 12390-3, Testing hardened concrete—Part 3: Compressive strength of test specimens
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3 Terms and definitions
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numbers, Tab stops: Not at 0.7 cm + 1.4 cm + 2.1 cm
No terms and definitions are listed in this document.
+ 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
cm + 7 cm
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
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— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
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stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
4 Needle penetration method 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
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4.1 General
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This part specifies the method from which an estimate of the in-situ compressive strength of young hardened
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sprayed concrete can be made in the range of 0,2 MPa to 1,5 MPa.
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ISO #####-#:####(X/PRF 23945-3:2026(en)
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4.2 Principle
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Needle penetration method is used to measure the force required to push a needle of specified dimensions to
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penetrate into the sprayed concrete to a depth of 15 mm +/- 2 mm. A penetrometer indicates the resisting
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force, through compression of a calibrated spring from which an estimated compressive strength can be
derived from a calibration curve provided by the producer of the test equipment. Formatted: English (United Kingdom)
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4.3 Specimens
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The thickness of the sprayed concrete layer shall be not less than 100 mm for testing.
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The specimens for test shall be prepared according to ISO 23945-2.
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No special test specimen is required for test of in-situ structures. The testing procedure can be used for
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measurements at any location without advance preparation.
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4.4 Apparatus
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4.4.1 Penetrometer
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The penetrometer shall be capable of driving the needle into the surface and recording the force required to
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an accuracy of 10 N. The penetrometer shall be provided with a certified calibration curve, able to correlate
readings to estimated compressive strength. An example of calibration curves is shown in Annex A.Annex A. Formatted
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4.4.2 Needle
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The needle shall be with a diameter of 3 mm ± 0,1 mm and a tip with a taper angle of 60° ± 5°, the needle length
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shall be more than 15 mm.
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4.5 Procedures Formatted
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4.5.1 4.5.1 Record time and place of completion of spraying and start of testing.
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4.5.2 4.5.2 Ensure the force indicator is set to zero.
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4.5.3 4.5.3 Apply the device perpendicularly to the surface of the sprayed concrete layer and steadily push
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in the needle to a depth of 15 mm in a single continuous movement. If this is prevented, for instance
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because of a large aggregate particle or reinforcement, then discontinue the test and repeat in an
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4.5.4 4.5.4 Read the resistance force from the scale, record the value on the protocol form and return
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indicator to original position.
4.5.5 4.5.5 Clean the needle if necessary.
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4.5.6 4.5.6 Repeat the test ten times as quickly as possible (and within 1 min for strengths below 0,5 MPa)
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in an area representative of the sprayed region.
4.5.7 4.5.7 Record the time at which the testing is finished (on protocol form).
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4.6 Expression of results Formatted
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Calculate the mean resistance force from the 10 measurements.
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The estimated compressive strength is derived from the manufacturer's calibration curve. Extrapolation is not
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permitted.
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2 © ISO #### 2026 – All rights reserved
ISO/DISPRF 23945-3:2026(en)
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4.7 Test report
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The test report shall include the following information:
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a) a) the identification of the test sample;
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b) b) the International Standard used (including its year of publication);
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c) c) the method used;
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d) d) type and serial number of the test equipment;
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e) e) the location where the test was performed;
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f) f) the date and time of test, age of specimen at time of test (if known);
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g) g) time of completing spraying and start and finish of testing, to the nearest minute;
h) h) ten measurements of resistance force and the mean value to nearest 10 N;
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i) i) the result (compressive strength);
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j) j) the ambient temperature and humidity;
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k) k) any deviations from the procedure; Formatted: English (United Kingdom)
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l) l) any unusual features observed;
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