Report on Methods for Estimating In-Place Concrete Strength
Reported by ACI Committee 228
ACI 228.1R-19
ReportonMethodsforEstimatingIn-PlaceConcreteStrength
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ReportonMethodsforEstimatingIn-PlaceConcrete Strength
Todd AllenMuhammed P. A. Bagheer Michael D. BrounNicholas J. Carino Willam CiggelakisAldo B La Haza Ethan C. Dodge
Joha II. Bungey Honggang Cao1lemengldo CaratinNestor E. Chonillo
Andrew J. Boyd Chair
This repo prvides modsfo riting re in-plc streng ofconcrete in ew d exiting cotction These mehosile: rebou mmber peneration resistnce pullot pul-off -principle. inherenr limitotions omd repealabiliry of euch method sonic purlse vefociy. marurity. and casi-in-place cylinders Theare reviwed. Prceres are presemed for devlpig th rltioship meeded to estimre pressive stremgrh from in-place rests. Facors fo consider in plaing in-place lests are discussed ndsfaristical techsiqes lo inerpret fest reslts are presemed. The use of in-pface tests for acceplumce of concrele is inrosdced.The Appendix A provides information on the mmber of strength levels ht shomd be sed to deop he strgth reltiship explints α eression anass prcee h accoums for mr i both dependest and independent varibles.
intended for guidance in planning. designing excuting and ACI Commitee Reports Guides and Commentaries areinspecting construction This document iSintended for the use of individuals who are petent to evaluate the significanceand limitations of its content and remendations and who will accep responsibility for the application of the material iall resporsibility for the stated principles. The Institute shall contains. The American Concrete Institute disclaims any andnot be liable for any los or damage arising therefrom.
Reference to this document Shall not be made in contracldocuments. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents they shallbe restated in mandatory language forincorporation by the Architec/Engineer.
Cying gChristopher C. Ferraro Michael C. FordeMostafa Mohamed Gad Alla Eric R GuniniJuie Ann Ilartell Kerry S Ilall
Gerardo G. Clemena Neil A.CumngAkexander M. Leghchinsky A1 Ghorbanpoor
Reported byACI Committee228
Consulting Mlembers
Submittee Member
Bemard H. Hertlein Secretary
Frederick D. HeidbrinkMichael W. Hoag Rober S. JenkinsKeith E. Kesner Liying JiangMalcolm K. Lim 1lai S. Lew
Kenneth M. LozenClaus Germann PeletsenGeorge V. Teudunu
Keywords: coefficienl of variatisafety: in-place tls; nondestrutic tst: samling: stafistical analysis.
CONTENTS
CHAPTER1-INTRODUCTION p.2
1.1-Scope.p.2 1.2-Need for in-place tests during construction p. 21.3-Infuence ofAC1 318 p.3 1.4-Rcmendations in other AC1 documents p. 31.SExisting construction.p.41.6-Report objective p.4
CHAPTER2-NOTATIONANDDEFINITIONS p.4
2.1-Notation.p.42.2-Detinitions.p.5
CHAPTER3-REVIEWOFMETHODS p.5
3.1-Introduction p.5 3.2-Rcbound number (ASTM C805/C805M).p.63.3Penctration resistancc (ASTM C803/C803M). p. 7 3.4Pullout teSt (ASTM C900). p. 8
Lary D. OlsonJohn S. Popovics uasNathaniel Sheven Rende Patrice RivardPasrick J. E. Sullivan Paul L. Siwek
Ierbert Wiggenhauser
3.5-Pull-off test (ASTM C1583/C1583M). p. 113.7Maturity method (ASTM C1074）.p.14 3.6-UItrasonic pulse velocity (ASTM C597) p.123.9Strength limitations p.16 3.8Cast-in-place cylinders (ASTM C873.C873M).p.163.10Combined methods p.163.11Summary p.17
CHAPTER4-STATISTICALCHARACTERISTICS OFTESTRESULTS p.174.1-Need for statistical analysis p. 174.2-Repeatability of test results p. 18
RELATIONSHIP p.23 CHAPTER5-DEVELOPMENTOFSTRENGTH5.1-General p.23 5.2-New construction p.245.3Existingconstruction p.27
CHAPTER6-IMPLEMENTATIONOFIN-PLACETESTING p.28 6.1-New construction p. 286.2--Existing construction p.31
CHAPTER7-INTERPRETINGANDREPORTINGRESULTS p.32 7.1-General p.327.3Reporting restults.p.36 7.2-Statistical methods p.33
CHAPTER8-IN-PLACETESTSFOR ACCEPTANCEOFCONCRETEINNEWCONSTRUCTION p.38 8.1-General p.388.2--Acceptance criteria p. 388.3-Early-age testing p. 38
CHAPTER9-REFERENCES p.39 Authored documents p. 40
APPENDIX A p. 44
A.1Minimum number of strength levels p. 4A.2Regression analysis with.X-error (Mandel 1984) p. 44 A.3-Standard deviation of estimated Y-value Stone andReeve 1986).p.46 A.4--Example p. 46
CHAPTER1-INTRODUCTION
1.1-Scope
In-place tests are perfomed typically on concrete within astructure in contrast to tests performed on molded specimensmade from the concrete to be used in the structure. Histori- cally they have been called nondestructive tests becausesonic pulse velocity were noninvasive and did not damage some of the early tests such as rebound number and ultra-developed that result in superficial local damage. There- the concrete. Over the years however new methods have
fore the tenminology “in-place tests" is used as a generalname for these test methods which includes those that do not damage the concrete and those that result in some near-surface damage. In this report the principal application ofin-place tests is to estimate the pressive strength of the concrete. The pull-off test can be used to estimate the tensilestrength of concrete or evaluate bond Strength between layers. The significant characteristic of most of these tests isthat they do not directly measure the pressive strengthof the concrete in a structure. InStead they measure some other property that can be correlated to pressive strengthpreviously established relationship between the measured (Popovics 1998). The strength is then estimated from aproperty and concrete strength. The uncertainty of the esti- mated pressive strength depends on the variability ofin-place test results and the uncertainty of the relationshipbetween these two parameters. These sources of uncer- tainty are discussed in this report An altemative approachpresented in EN 13791 (2007) and BS 6089 (2010). for correlation between teSts reSults and concrete Strength is
In-place tests can be used to estimate concrete strengthstrength can be performed saf ely or curing procedures termi-nated They can also be used to estimate concrete strength during the evaluation of existing structures. These twoapplications require slightly different approaches so parts of this report are separated into sections dealing with new andexisting construction.
A variety of techniques are available for estimating thein-place strength of concrete (Malhotra 1976; Bungey etto review all methods in this report only those methods al. 2006; Malhotra and Carino 2004). No attempt is madethat have been standardized by ASTM Intemational are discussed. Examples of methods not covered include intermalfracture tess (Chabowski and Bryden-Smith 1980; Domoneand Castro 1987) and torque tests (Stoll 1985).
1.2-Need for in-place tests during construction
In North American practice the most widely used test forconcrete is the pressive strength test of standard cylin-ders (ASTM C39/39M). This test procedure is relatively easy to perfom in terms of sampling. specimen preparation(ASTM C31/C31M) andstrengthmeasurement. When prop- erly performed this test has low single-operator variationlends itself to use as a standardized testing procedure. The and low interlaboratory variation and therefore the methodpressive strength so obtained is used to verify that thespecified strength (/') used to calculate the nominal strengths of structural members has been achieved. Therefore thepresSive strength of standard cylinders is an e5sential parameter in design codes and project specifications.
however the results of the cylinder pression test repre- When carried out according to standard procedures sent the potential strength of the concrete as delivered to aof the concrete to ensure that contract requirements are met. site. The test is uSed mainly as a basis for quality assuranceIt is not intended for determining the in-place strength of the concrete because it makes no allowance for the effects
of placing consolidation or curing. lt is unusual for theconcrete in a structure to have the same properties as a standardcured cylinder at the same test age. Also standardcured cylinders are usually tested for acceptance purpoSes atan age of 28 days; therefore the results of these tests cannot be used to determine whether adequate Sirength exists atearlier ages for safe removal of formwork or the application of post-tensioning. The concrete in some parts of a struc-ture such as columns may develop strength equal to the standard 28-day cylinder Strength by the time it is sub jectedto design loads. Concrete in flexural members especiallypretensioned members can be required to support a large percentage of the design load before an age of 28 days. Forthese reasors in-place tests are used to estimate the concrete strength at critical locations in a structure and at times whencrucial construction operations are scheduled.
structural capacity under construction loading it is neces-sary to have an estimate of the equivalent cylinder strength of the concrete as it exists in the structure. If in-place testsare used a valid relationShip between the reSults of in-placeAt present there are no standard practices for developing the tests and the pressive strength of cylinders is required.required relationShip.
1.4-Remendations in otherACIdocuments
Afer the 1995 verion of this report waS published otherACI documents incorporated in-place tests as alternativeprocedures for estimating in-place strength. One of these docu- ments is ACI 301 a specification for new concrete construc-in-place testing of hardened concrete includes the following: tion. In the 2016 version of ACI 301 Section 1.6.4.2 on
Use of the rebound hammer in accordance with ASTM C805/C805M or the pulse-velocity methodfied by Architect/Engineer to evaluate unifor- in accordance with ASTM C597 may be speci-mity of in-place concrete or to select areas to be cored. These methodS shall not be used to evaluatein-place strength.
the structure has been obtained by using field-cured cylinders Traditionally a measure of the strength of the concrete inprepared and cured in accordance with ASTM C31/C31M. These cylinders are cured on or in the structure under asnearly as possible the same conditions as the concrete in the structure. Measured strengths of field-cured cylinders maybe significantly different from in-place strengths because itis difficult and often impossible to have identical bleeding consolidation and curing conditions for concrete in cylin-ders and concrete in structures (Soutsos et al. 2000). Field- cured specimens should be handled with care and storedproperly to avoid misleading test results.
Regarding the validity of in-place strength tests ACI301-16 states in Section 1.6.5.3(a):
Results of in-place strength tests will be evaluatedcondugted using properly calibrated equipment in by Architect/Engineer and are valid only if tests areaccordance with recognized standard procedures and an acceptable correlation between test resultsand concrete pressive strength is established and submitted.
as form removal post-tensioning termination of curing and Constnuction schedules often require that operations suchremoval of reshores be carried out as early as possible to keep the project on schedule. To enable these operations toproceed safely at the earliest possible time requires the use of reliable in-place tests to estimate the in-place strength.q pzis si u uns s u prevented had in-place testing been used (Lew 1980; Carino Several construction failures that possibly could have beenet al. 1983a). In-place testing not only increases safety but can result in substantial cogt savings by permitting acceler-ated construction schedules (Bickley 1982a).
use of these tests in acceptance of concrete by stating Section 1.6.6.4 of ACI 301-16 however restricts thethat “In-place tests shall not be used as the sole basis for psn aq eu a q a uaa o aespecified to *evaluate” concrete if standard-cured cylinderstrengths fail to meet the specified strength criteria.
1.3-Influence of ACI318
AC1 301-16 also mentions in-place tests in Section 2.3.4dealing with required strength for removal of formwork. Specifically it is stated that if specified in Contract Docu-ments the following methods may be used to estimate in-place strength:
ders to demonstrate the adequacy of concrete strength bef ore Before 1983 AC1 318 required testing of field-cured cylin-allowed the use of other procedures instead of tess forfield removal of formwork or reshoring. In 1983 AC1 318 firstcured cylinders if approved by the building official (ACIComitee3181983）Theesignprofessinal whenrequst by the building official however was required to approve tealtemative procedure before its use. Since 1983 AC1 3 18 has permitted the uge of in-place testing as an altemative to testingfield-cured cylindersifapprovedby thlicense design profes sional and ifrequted appovedby the building official. Tmentary to AC1 318-14 (Section R26.11.2.1(e) lists fourprovided there are sufficient correlation data. procedures which are covered in this repor that may be used
(a) ASTM C873/C873M (cast-in-place cylinders)(b) ASTM CR03/C803M (penetration resistance) (c)ASTM C900 (pullout)(d) ASTM C 1074 (maturity method)
These same methods may be used if specified as alterna-tives to testing field-cured cylinders for estimating in-place strength for the purpoe of terminating curing procedures.
AC1 562-16 the repair code for existing concrete build-ings allowed the use of in-place test methods for assement of concrete strength. Section 6.4.3.2 states
pressivestrengthofstandardcylinders. Thus to evaluate Most design provisions in AC1 318 are based on the
