1、ACI 214.4R-10Reported by ACI Committee 214Guide for Obtaining Coresand InterpretingCompressive Strength ResultsGuide for Obtaining Cores and Interpreting Compressive Strength ResultsFirst PrintingJune 2010ISBN 978-0-87031-254-0American Concrete InstituteAdvancing concrete knowledgeCopyright by the A
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10、CI.Most ACI standards and committee reports are gathered together in the annually revised ACI Manual ofConcrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgACI 214.4R-10 supersedes ACI 214.4R-03
11、 and was adopted and published June 2010.Copyright 2010, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, or recor
12、ding for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors.214.4R-1ACI Committee Reports, Guides, Manuals, and Commentariesare intended for guidance in planning, designing, executing,and ins
13、pecting construction. This document is intended for theuse of individuals who are competent to evaluate thesignificance and limitations of its content and recommendationsand who will accept responsibility for the application of thematerial it contains. The American Concrete Institute disclaimsany an
14、d all responsibility for the stated principles. The Instituteshall not be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, th
15、eyshall be restated in mandatory language for incorporation bythe Architect/Engineer.Guide for Obtaining Cores and Interpreting Compressive Strength ResultsReported by ACI Committee 214ACI 214.4R-10Core testing is the most direct method to determine the compressivestrength of concrete in a structure
16、. Generally, cores may be obtained toassess whether concrete in a new structure complies with strength-basedacceptance criteria or to evaluate the structural capacity of an existing struc-ture based on the in-place concrete strength. In either case, the process ofobtaining core specimens and interpr
17、eting strength test results is oftenconfounded by various factors affecting in-place concrete strength ormeasured strength of test specimens. The scatter in strength test data,which is unavoidable given the inherent randomness of in-place concretestrengths and the uncertainty attributable to prepara
18、tion and testing of thespecimens, may further complicate compliance and evaluation decisions.This guide summarizes practices for obtaining cores and interpretingcore compressive strength test results. Factors that affect in-place concretestrength are reviewed so sampling locations that are consisten
19、t with objectivesof the investigation can be selected. Strength correction factors arepresented for converting the measured strength of non-standard core-testspecimens to the strength of equivalent specimens with standard diameters,length-to-diameter ratios, and moisture conditioning. This guide pro
20、videsdirection for checking strength compliance of concrete in a structure underconstruction and methods for determining equivalent specified strength toassess capacity of an existing structure. The materials, processes, qualitycontrol measures, and inspections described in this document should bete
21、sted, monitored, or performed as applicable only by individuals holdingthe appropriate ACI Certifications or equivalent.Keywords: compressive strength; core; hardened concrete; sampling; test.CONTENTSChapter 1Introduction, p. 214.4R-21.1Introduction1.2Background1.3ScopeChapter 2Notation and definiti
22、ons, p. 214.4R-32.1Notation2.2DefinitionsChapter 3Variation of in-place concrete strength in structures, p. 214.4R-33.1Bleeding3.2Consolidation3.3Curing3.4Microcracking3.5Overall variability of in-place strengthsDavid J. Akers Alejandro Graf John J. Luciano Bryce P. SimonsMadasamy Arockiasamy Thomas
23、 M. Greene Allyn C. Luke Luke M. SnellWilliam L. Barringer Gilbert J. Haddad Stephen Marchese Patrick J. E. SullivanF. Michael Bartlett*Kal R. Hindo Richard E. Miller Eugene TakhtovichJerrold L. Brown Robert S. Jenkins Venkataswamy Ramakrishnan Michael A. TaylorJames E. Cook Alfred L. Kaufman, Jr.*D
24、. V. Reddy Roger E. VaughanRonald L. Dilly*William F. Kepler David N. Richardson*Woodward L. Vogt*Donald E. Dixon Michael L. Leming James M. Shilstone, Jr. Orville R. Werner IIRichard D. Gaynor Colin L. Lobo*Subcommittee members who prepared this document.Casimir BognackiChairJerry ParnesSecretary21
25、4.4R-2 ACI COMMITTEE REPORTChapter 4Planning the testing program,p. 214.4R-54.1Investigating concrete in a new structure usingstrength-based acceptance criteria4.2Evaluating existing structure capacity using in-placestrengthsChapter 5Obtaining test specimens, p. 214.4R-6Chapter 6Core testing, p. 214
26、.4R-6Chapter 7Analyzing strength test data,p. 214.4R-77.1ASTM C42/C42M precision statements7.2Review of core strength correction factors7.3Statistical analysis techniquesChapter 8Investigation of low-strength test results in new construction using ACI 318,p. 214.4R-10Chapter 9Determining an equivale
27、nt fc value for evaluating structural capacity of an existing structure, p. 214.4R-109.1Conversion of core strengths to equivalent in-placestrengths9.2Uncertainty of estimated in-place strengths9.3Percentage of in-place strengths less than fc9.4Methods to estimate the equivalent specified strengthCh
28、apter 10References, p. 214.4R-1310.1Referenced standards and reports10.2Cited referencesAppendixExample calculations, p. 214.4R-15A.1Outlier identification in accordance with ASTME178 criteriaA.2Students t test for significance of differencebetween observed average valuesA.3Equivalent specified stre
29、ngth by tolerance factorapproachA.4Equivalent specified strength by alternate approachCHAPTER 1INTRODUCTION1.1IntroductionCore testing is the most direct method to determine the in-place compressive strength of concrete in a structure.Generally, cores are obtained to:Assess, if required, whether con
30、crete in a new structurecomplies with strength-based acceptance criteria; orDetermine in-place concrete strengths in an existingstructure for evaluation of structural capacity.In new construction, cylinder strength tests failing to meetstrength-based acceptance criteria can be investigated usingprov
31、isions given in ACI 318. These criteria specify thecircumstances when core tests are permitted, the number ofcores to be tested, the conditioning of the cores before testing,the limits on the time interval between coring and testing, andthe basis for determining whether the concrete in the arearepre
32、sented by the core strengths is structurally adequate. Thisguide presents procedures for obtaining and testing cores andinterpreting results in accordance with ACI 318.If strength records are unavailable, the in-place strength ofconcrete in an existing structure can be evaluated usingcores. This in-
33、place strength determination is simplifiedwhen in-place strength data are converted into an equivalentspecified compressive strength fc value that can be directlysubstituted into conventional strength equations withcustomary strength reduction factors. This guide presentsprocedures for performing th
34、is conversion in a mannerconsistent with the assumptions used to derive strengthreduction factors for structural design.1.2BackgroundAnalysis of core test data can be difficult and can subsequentlylead to uncertain interpretations and conclusions. Basedon 10 hypothetical core test results, 23 practi
35、tionersresponding to a survey in 2000 estimated the compressivestrength of in-place concrete between 3000 and 5000 psi (21and 35 MPa) (Hanson 2007). Strength interpretations shouldalways be made by, or with the assistance of, an investigatorexperienced in concrete technology. Factors contributing to
36、the scatter of core strength test results include:Systematic variation of in-place strength along amember or throughout the structure;Random variation of concrete strength, both within onebatch and among batches;Low test results attributable to flawed test specimens orimproper test procedures;Effect
37、s of the size, aspect ratio, and moisture conditionof the test specimen on the measured strengths; andAdditional uncertainty attributable to testing that ispresent even for tests performed in strict accordancewith standardized testing procedures.1.3ScopeThis guide summarizes current practices for ob
38、tainingcores and interpreting core compressive strength test resultsin light of past and current research findings. Many of thesefindings are based on older references as the research hasreached a mature state. Parallel procedures are presented forcases where cores are obtained to assess whether con
39、cretestrength in a new structure complies with strength-basedacceptance criteria, and to determine a value based on theactual in-place concrete strength equivalent to the specifiedcompressive strength fc. The latter can be directly substitutedinto conventional strength equations with customarystreng
40、th reduction factors for strength evaluation of anexisting structure. It is inappropriate to use procedures fordetermining the equivalent specified concrete strength toassess whether concrete strength in a new structure complieswith strength-based acceptance criteria.The order of contents parallels
41、the logical sequence ofactivities in a typical core-test investigation. Chapter 3describes how bleeding, consolidation, curing, and micro-cracking affect in-place concrete strength in structures so theinvestigator can account for this strength variation whenplanning the testing program. Chapter 4 id
42、entifies preferredOBTAINING CORES AND INTERPRETING COMPRESSIVE STRENGTH RESULTS 214.4R-3sample locations and provides guidance on the number ofspecimens that should be obtained. Chapter 5 summarizescoring techniques that should result in undamaged, repre-sentative test specimens. Chapter 6 describes
43、 procedures fortesting cores and detecting “outliers” by inspection of load-machine displacement curves or using statistical tests fromASTM E178. Chapter 7 summarizes the subsequent analysisof strength test data including use of ASTM C42/42M precisionstatements that quantify expected variability of
44、properlyconducted tests for a sample of homogeneous material,research findings concerning accuracy of empiricallyderived core strength correction factors, and statistical anal-ysis techniques that can determine if the data can be groupedinto unique categories. Chapter 8 briefly elaborates on criteri
45、apresented in ACI 318 for using core test results to investigatelow-strength cylinder test results in new construction.Chapter 9 presents two methods for estimating the lowertenth-percentile value of in-place concrete strength usingcore test data to quantify in-place strength. This value isequivalen
46、t to the specified compressive strength fc and canbe directly substituted into conventional strength equationswith customary strength reduction factors for strengthevaluation of an existing structure.Example calculations are presented in an appendix for:Outlier identification in accordance with ASTM
47、 E178criteria;Determining whether a difference in mean strengths ofcores from beams and columns is statistically signifi-cant; andComputing the equivalent specified strength using thetwo approaches presented in Chapter 9.CHAPTER 2NOTATION AND DEFINITIONS2.1NotationC = a constant related to the numbe
48、r of batches, numberof members, and type of construction, AlternateMethodd = diameter of core, in. (mm)e = predetermined maximum error expressed as apercentage of the population averageFd= correction factor for core damageFdia= correction factor for core diameterFl/d= correction factor for length-to
49、-diameter ratio ofcoreFmc= correction factor for moisture content of coref0.10= compressive strength of concrete at 10% fractile,psi (MPa)fc= equivalent in-place compressive strength ofconcrete, psi (MPa)fc= sample mean of equivalent in-place compressivestrength of concrete, psi (MPa)fc = specified compressive strength of concrete, psi(MPa)(fc)CL= lower bound estimate of the sample mean equivalentin-place compressive strength of concrete atconfidence limit CL, Alternate Method, psi (MPa)f c,eq= equivalent design compressive strength ofconcre
