SIST EN 13791:2007

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Assessment of in-situ compressive strength in structures and precast concrete componentsEvaluation de la résistance a la compression du béton en place dans les structures et les éléments préfabriquésBewertung der Druckfestigkeit von Beton in Bauwerken oder in BauwerksteilenTa slovenski standard je istoveten z:EN 13791:2007SIST EN 13791:2007en91.100.30Beton in betonski izdelkiConcrete and concrete products91.080.40Betonske konstrukcijeConcrete structuresICS:SLOVENSKI
STANDARDSIST EN 13791:200701-april-2007







EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13791January 2007ICS 91.080.40 English VersionAssessment of in-situ compressive strength in structures andprecast concrete componentsEvaluation de la résistance à la compression du béton enplace dans les structures et les éléments préfabriquésBewertung der Druckfestigkeit von Beton in Bauwerkenoder in BauwerksteilenThis European Standard was approved by CEN on 10 November 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2007 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13791:2007: E



EN 13791:2007 (E) 2 Contents Page Foreword.4 Introduction.5 1 Scope.7 2 Normative references.7 3 Terms and definitions.8 4 Symbols and abbreviations.9 5 Principles.10 6 Characteristic in-situ compressive strength in relation to compressive strength class.10 7 Assessment of characteristic in-situ compressive strength by testing of cores.11 7.1 Specimens.11 7.2 Number of test specimens.11 7.3 Assessment.11 7.3.1 General.11 7.3.2 Approach A.12 7.3.3 Approach B.12 8 Assessment of characteristic in-situ compressive strength by indirect methods.13 8.1 General.13 8.1.1 Methods.13 8.1.2 Alternative 1 – Direct correlation with cores.13 8.1.3 Alternative 2 – Calibration with cores for a limited strength range using an established relationship.14 8.2 Indirect tests correlated with in-situ compressive strength, (Alternative 1).14 8.2.1 Application.14 8.2.2 Testing procedure.14 8.2.3 Establishing the relationship between test result and in-situ compressive strength.14 8.2.4 Assessment of in-situ compressive strength.14 8.3 Use of a relationship determined from a limited number of cores and a basic curve, (Alter-native 2).15 8.3.1 General.15 8.3.2 Testing.15 8.3.3 Procedure.15 8.3.4 Validity of relationships.19 8.3.5 Estimation of in-situ compressive strength.19 8.4 Combination of in-situ strength test results by various test methods.19 9 Assessment where conformity of concrete based on standard tests is in doubt:.20 10 Assessment report.21 Annex A (informative) Factors influencing core strength.22 A.1 General.22 A.2 Concrete characteristics.22 A.2.1 Moisture content.22 A.2.2 Voidage.22 A.2.3 Direction relative to the casting.22 A.2.4 Imperfections.22 A.3 Testing variables.22 A.3.1 Diameter of core.22 A.3.2 Length/diameter ratio.23



EN 13791:2007 (E) 3 A.3.3 Flatness of end surfaces.23 A.3.4 Capping of end surfaces.23 A.3.5 Effect of drilling.23 A.3.6 Reinforcement.23 Annex B (informative) Factors influencing results by indirect test methods.24 B.1 Rebound hammer tests.24 B.2 Ultrasonic pulse velocity measurements.24 B.3 Pull-out tests.24 Annex C (informative)
Concepts concerning the relationship between in-situ strength and strength from standard test specimens.25 Annex D (informative) Guidelines for planning, sampling and evaluation of test results when assessing in-situ strength.26 D.1 Planning.26 D.2 Sampling.26 D.3 Testing programme.26 D.4 Assessment.27 Bibliography.28



EN 13791:2007 (E) 4 Foreword This document (EN 13791:2007) has been prepared by Technical Committee CEN/TC 104 “Concrete and related products”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by July 2007, and conflicting national standards shall be withdrawn at the latest by July 2007. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.



EN 13791:2007 (E) 5 Introduction This European Standard provides techniques for estimating in-situ compressive strength in concrete structures and precast concrete components. Testing in-situ strength takes into account the effects of both the materials and execution (compaction, curing, etc.). These tests do not replace concrete testing according to EN 206-1. EN 206-1 refers to the guidance of this standard for assessing the strength in structures and precast concrete components. The following examples illustrate where this estimate of in-situ strength of concrete may be required:  when an existing structure is to be modified or redesigned;  to assess structural adequacy when doubt arises about the compressive strength in the structure due to defective workmanship, deterioration of concrete due to fire or other causes;  when an assessment of the in-situ concrete strength is needed during construction;  to assess structural adequacy in the case of non-conformity of the compressive strength obtained from standard test specimens;  assessment of conformity of the in-situ concrete compressive strength when specified in a specification or product standard. Where identified in this standard, national provisions are permitted or required. An outline of the procedures for these different uses of this standard is given in Flowchart 1. For specific production conditions and constituent materials, development of economic design where permitted by national provisions may be possible through the assessing the partial safety factor, γc from knowledge of the in-situ compressive strength and the strength of standard test specimens. When assessing compressive strengths in cases other than checking the quality of the concrete or the workmanship during execution or before accepting the structure for use, the appropriate reduction in the partial safety factor should be determined on a case-by-case basis according to national provisions.



EN 13791:2007 (E) 6
Flowchart 1



EN 13791:2007 (E) 7
1 Scope This European Standard:  gives methods and procedures for the assessment of the in-situ compressive strength of concrete in structures and precast concrete components;  provides principles and guidance for establishing the relationships between test results from indirect test methods and the in-situ core strength;
 provides guidance for the assessment of the in-situ concrete compressive strength in structures or precast concrete components by indirect or combined methods. This European Standard does not include the following cases:  where indirect methods are used without correlation to core strength;  assessment based on cores less than 50 mm in diameter;  assessment based on less than 3 cores;  use of microcores. NOTE In these cases provisions valid in place of use apply. This European Standard is not for the assessment of conformity of concrete compressive strength in accordance with EN 206-1 or EN 13369 except as indicated in EN 206-1:2000, 5.5.1.2 or 8.4. 2 Normative references The following referenced documents are indispensable for the application 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. EN 206-1:2000, Concrete – Part 1: Specification, performance, production and conformity EN 12350-1,Testing fresh concrete – Part 1: Sampling EN 12390-1, Testing hardened concrete - Part 1: Shape, dimensions and other requirements for specimens and moulds EN 12390-2, Testing hardened concrete – Part 2: Making and curing specimens for strength tests EN 12390-3, Testing hardened concrete – Part 3: Compressive strength of test specimens EN 12504-1, Testing concrete in structures – Part 1: Cored specimens – Taking, examining and testing in compression EN 12504-2, Testing concrete in structures – Part 2: Non-destructive testing – Determination of rebound number EN 12504-3, Testing concrete in structures – Part 3: Determination of pull-out force



EN 13791:2007 (E) 8 EN 12504-4, Testing concrete in structures – Part 4: Determination of ultrasonic pulse velocity 3 Terms and definitions For the purposes of this European Standard, the terms and definitions given in EN 206-1:2000 and the following apply. 3.1 standard compressive strength compressive strength determined on standard test specimens (cubes or cylinders) which are sampled, made, cured and tested in accordance with EN 12350-1, EN 12390-2 and EN 12390-3 3.2 core compressive strength compressive strength of a core determined in accordance with EN 12504-1 3.3 in-situ compressive strength strength in a structural element or precast concrete components expressed in terms of the equivalent strength of a standard cube or cylinder specimen 3.4 characteristic in-situ compressive strength value of in-situ compressive strength below which 5 % of the population of all possible strength determinations of the volume of concrete under consideration are expected to fall NOTE This population is unlikely to be the same population used to determine the conformity of the fresh concrete in EN 206-1. 3.5 test location limited area selected for measurements used to estimate one test result, which is to be used in the estimation of in-situ compressive strength 3.6 test region one or several structural elements, or precast concrete components assumed or known to be from the same population. A test region contains several test locations



EN 13791:2007 (E) 9 4 Symbols and abbreviations ûf shift of the basic curve /f difference between the core strength and the strength value according to the basic relationship /fm(n) mean of n, values of /f F
pull-out force test result fis in-situ compressive strength test result fis, lowest lowest in-situ compressive strength test result fm(n), is mean in-situ compressive strength of n test results fck characteristic compressive strength of standard specimens fck, is characteristic in-situ compressive strength
fck, is, cube characteristic in-situ compressive strength expressed in equivalent strength of a 150 mm cube, see 7.1 fck, is, cyl characteristic in-situ compressive strength expressed in equivalent strength of a 150 mm × 300 mm cylinder, see 7.1 fis, l estimated in-situ compressive strength test result by indirect test methods when a specificrelationship is established by core tests, (Alternative 1) fis, F estimated in-situ compressive strength test result by pull-out tests calibrated by core tests, (Alternative 2) fis, R estimated in-situ compressive strength test result by rebound hammer tests calibrated by coretests, (Alternative 2) fis, v estimated in-situ compressive strength test result by ultrasonic pulse velocity tests calibrated bycore tests, (Alternative 2) fF initial
value of in-situ strength obtained from the basic curve for a pull-out force, Figure 4, test result F used in the determination of the shift fR initial value of in-situ strength obtained from the basic curve for a rebound hammer, Figure 2, testresult R
used in the determination of the shift fv initial value of in-situ strength obtained from the basic curve for a pulse-velocity, Figure 3 test result v used in the determination of the shift γc partial safety factor for concrete k margin associated with small numbers of test results k1 coefficient that depends on the number of paired tests k2 coefficient that depends upon provisions valid in the place of use or, if none are given, acoefficient with a value of 1,48 n number of test results R rebound hammer test result s standard deviation v ultrasonic pulse velocity test result



EN 13791:2007 (E) 10 5 Principles Assessment of in-situ compressive strength directly from core tests constitutes the reference method, see 7. The assessment of in-situ compressive strength may also be done indirectly by other tests, see 8.2 and 8.3, or by a combination of various test methods, see 8.4. Where indirect tests are used, the uncertainty associated with the relationship between the test and core test is taken into account. The test data may be used to estimate the in-situ characteristic strength and the corresponding strength class according to EN 206-1. 6 Characteristic in-situ compressive strength in relation to compressive strength class Table 1 gives requirements for the minimum characteristic in-situ compressive strength with respect to the compressive strength classes according to EN 206-1.
Table 1 — Minimum characteristic in-situ compressive strength for the EN 206-1 compressive strength classes Minimum characteristic in-situ strength N/mm2
Compressive
strength class
according to EN 206-1 Ratio of in-situ characteristic strength to characteristic strength of standard specimens fck, is, cyl fck, is, cube C8/10 0,85 7 9 C12/15 0,85 10 13 C16/20 0,85 14 17 C20/25 0,85 17 21 C25/30 0,85 21 26 C30/37 0,85 26 31 C35/45 0,85 30 38 C40/50 0,85 34 43 C45/55 0,85 38 47 C50/60 0,85 43 51 C55/67 0,85 47 57 C60/75 0,85 51 64 C70/85 0,85 60 72 C80/95 0,85 68 81 C90/105 0,85 77 89 C100/115 0,85 85 98 NOTE 1 The in-situ compressive strength may be less than that measured on standard test specimens taken from the same batch ofconcrete.
NOTE 2 The ratio 0,85 is part of
γc in EN 1992-1-1: 2004.



EN 13791:2007 (E) 11 7 Assessment of characteristic in-situ compressive strength by testing of cores 7.1 Specimens Cores shall be taken, examined and prepared in accordance with EN 12504-1 and tested in accordance with EN 12390-3. Except for where it is not feasible, cores shall be exposed to a laboratory atmosphere for at least 3 days prior to testing.
NOTE 1 For factors influencing the core strength, see Annex A. NOTE 2 If for practical reasons 3 days of exposure is not feasible, record the period of exposure, if any. The influence of this deviation from standard procedure should be evaluated. Where the in-situ strength is determined from cores:
 testing a core with equal length and a nominal diameter of 100 mm gives a strength value equivalent to the strength value of a 150 mm cube manufactured and cured under the same conditions;  testing a core with a nominal diameter at least 100 mm and not larger than 150 mm and with a length to diameter ratio equal to 2,0 gives a strength value equivalent to the strength value of a 150 mm by 300 mm cylinder manufactured and cured under the same conditions;  the transposition of the test results from cores with diameters from 50 mm up to 150 mm and other length to diameter ratios shall be based on conversion factors of established suitability. NOTE 3 Conversion factors of established suitability for other specimen sizes and length to diameter ratios may be given in provisions valid in the place of use. Normally the core result should not be modified to take account of the direction of drilling unless required by provisions valid in pace of use or required by the project specification. 7.2 Number of test specimens The number of cores to be taken from one test region shall be determined by the volume of concrete involved and the purpose for the testing of cores. Each test location comprises one core. For assessment of in-situ compressive strength for statistical and safety reasons, as many cores as are practicable should be used. An assessment of in-situ compressive strength for a particular test region shall be based on at least 3 cores. Consideration shall be given to any structural implications resulting from taking cores, see EN 12504-1. NOTE The number of specimens identified above relates to cores with a nominal diameter of at least 100 mm. The number of cores should be increased when the nominal diameter is less than 100 mm, see A.3.1. 7.3 Assessment 7.3.1 General In-situ characteristic compressive strength is assessed using either approach A in 7.3.2 or approach B in 7.3.3. Approach A applies where at least 15 cores are available. Approach B applies where 3 to 14 cores are available. The applicability of the two approaches to the assessment of the strength of concrete in existing structures, about which there is no prior knowledge, may be defined in the place of use.



EN 13791:2007 (E) 12 7.3.2 Approach A The estimated in-situ characteristic strength of the test region is the lower value of: skff2m(n),isck,is×−=
(1) or 4+=lowestis,isck,ff (2)
where s is the standard deviation of the test results or 2,0 N/mm2, whichever is the higher value;
k2 is given in national provisions or, if no value is given, taken as 1,48. The strength class is obtained from Table 1 using the estimated in-situ characteristic strength. NOTE 1 The estimate of characteristic strength using the lowest core result should reflect the confidence that the lowest core result represents the lowest strength in the structure or component under consideration. NOTE 2 Where the distribution of the core strength appears to come from two populations, the region may be split into two test regions. 7.3.3 Approach B The estimated in-situ characteristic strength of the test region is the lower value of: kff−=ism(n),isck, (3) or 4+=lowestis,isck,ff (4) The margin k depends on the number n of test results and the appropriate value is selected from Table 2.



EN 13791:2007 (E) 13 Table 2 – Margin k associated with small numbers of test results n k 10 to14
7 to 9
3 to 6 5 6 7
NOTE Because of the uncertainty associated with small numbers of test results and the need to provide the same level of reliability, this approach gives estimates of characteristic strengths that are generally lower than those obtained with more test results. Where these estimates of in-situ characteristic strength are judged to be too conservative, it is recommended that more cores are taken or a combined technique approach, see 8.4, is used to obtain more test results. For this reason, this approach should not be used in cases of dispute over the quality of concrete based on standard test data, see clause 9 for details of a suitable approach. 8 Assessment of characteristic in-situ compressive strength by indirect methods
8.1 General 8.1.1 Methods This clause applies to methods other than core tests, which are used for strength assessment in-situ. The indirect tests provide alternatives to core tests for assessing the in-situ compressive strength of concrete in a structure or they may supplement data obtained from a limited number of cores. The indirect methods are semi-destructive or non-destructive in nature. Indirect methods may be used after calibration with core tests in the following ways: - singly; - in a combination of indirect methods; - in a combination of indirect methods and direct method (cores). When testing with an indirect method a property other than strength is measured. It is thus necessary to use a relationship between the results of indirect tests and the compressive strength of cores.
Two alternative methods for assessment of in-situ compressive strength are provided, see 8.1.2 and 8.1.3.
When an indirect technique is combined with only one or two core test results, interpretation shall be based on provisions valid in place of use. 8.1.2 Alternative 1 – Direct correlation with cores Sub-clause 8.2 describes procedures applicable on a general basis for assessment of in-situ compressive strength, when a specific relationship between the in-situ compressive strength and the test result by the indirect method is established for the concrete under consideration.
Alternative 1 requires at least 18 core test results to establish the relationship between the in-situ compressive strength and the test result by the indirect method



EN 13791:2007 (E) 14 8.1.3 Alternative 2 – Calibration with cores for a limited strength range using an established relationship Sub-clause 8.3 describes procedures for assessment of in-situ strength within a limited range of strengths, based on an established relationship, i.e. a basic curve, together with a shift of the basic curve, established by means of core tests. Procedures are described for rebound hammer tests, ultrasonic pulse velocity tests and pull-out tests.
NOTE Test results assessed by indirect test methods can be influenced by various factors other than concrete strength, see Annex B. 8.2 Indirect tests correlated with in-situ compressive strength, (Alternative 1) 8.2.1
Application Sub-clause 8.2 is applicable to indirect test methods for assessment of in-situ compressive strength when a specific relationship for the in-situ concrete is established by means of core tests.
8.2.2
Testing procedure The apparatus, the test procedure and the expression of test results shall be in accordance with EN 12504-1 for the core tests and EN 12504-2, EN 12504-3 and EN 12504-4 when rebound number, pull-out force or ultrasonic pulse velocity is measured.
8.2.3 Establishing the relationship between test result and in-situ compressive strength To establish a specific relationship between the in-situ compressive strength and the test result by the indirect method, a comprehensive testing programme shall be carried out.
The relationship shall be based on at least 18 pairs of results, 18 core test results and 18 indirect test results, covering the range of interest. NOTE 1 A pair of test results is a core test result and an indirect test result from the same test location. NOTE 2 These numbers are a minimum but in many cases it is advantageous to have a considerably higher number of observations in the data set to establish a relationship.
Establishing the relationship comprises the following steps:
 best fit line or curve is determined by regression analysis on the data pairs that are obtained in the testing programme. The indirect test result is viewe
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