1、:onal“ AC1 228.1 R-03 In-Place Methods to Estimate Concrete Strength Reported by AC1 Committee 228 american concrete institute PO, BOX 9094 FARMINGTON HILLS, MICHIGAN 48333-9094 First Printing, November 2003 In-Place Methods to Estimate Concrete Strength Most AC1 Standards and committee reports are
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7、sist in the effort for accuracy and clarity, the Technical Activities Committee solicits the help of indi- viduals using AC1 reports and standards in identifying and eliminating problems that may be associated with Concrete Strength Testing Technician Concrete Laboratory Testing Technician-Grade I t
8、heir use. Users who have suggestions for the improvement of AC1 documents are reauested to contact the AC1 Engi- Concrete Laboratory Testing Technician-Grade il Concrete Construction Inspector Concrete Transportation Construction Inspector-ln- Training neering Department in writing, with the followi
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11、to these AC1 certification programs, which can be incorporated into project specifications or quality control procedures. If not, suggested guide specifications are available on request from the AC1 Certification Department. ISBN 0-87031-132-8 AC1 228.1 R-03 In-Place Methods to Estimate Concrete Str
12、ength Reported by AC1 Committee 228 Stephen P. Pessiki* Chair Farhad Ansari Hermenegildo Caratin Nicholas J. Carino* K. Choi Neil A. Cumrning Allen G. Davis Aldo Delahaza Ronald L. Dilly Donald E. Dixon Boris Dragunsky AI Ghorbanpoor* Frederick D. Heidbrink Bernard H. Hertlein Ka1 R. Hindo Robert S.
13、 Jenkins Keith E. Kesnert H. S. Lew Kenneth M. Lozen* Larry D. Olson John S. Popovics* Sandor Popovics Randall W. Poston* Afshin Sadri Bryce P. Sirnons Patrick J. Sullivan George V. Teodoru Woodward L. Vogt Alexander B. Zoob *Members of the task force that prepared the revision +Task force Chair. Gu
14、idance is provided on the use of methods to estimate the in-place strength of concrete in new and existing construction. The methods include: rebound number; penetration resistance, pullout, break-o8 ultrasonic pulse velocity, maturity, and cast-in-place cylinders. The principle, inherent limi- tati
15、ons, and repeatability of each method are reviewed. Procedures are presented for developing the relationship needed to estimate compressive strength from in-place results. Factors to consider in planning in-place tests are discussed, and statistical techniques to interpret test results are presented
16、. The use of in-place tests for acceptance of concrete is intm- duced. The appendix provides information on the number of strength levels that should be used to develop the strength relationship and explains a AC1 Committee Reports, Guides, Standard Practices, and Commentaries are intended for guida
17、nce in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contain
18、s. The American Concrete Institute disclaims any and ali responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Archit
19、ecuEngineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the ArchitecuEngineer. It is the responsibility of the user of this document to establish health and safety practices appropriate to the specific circumstances involved with its use.
20、 AC1 does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applicable laws and regulations, including but not limited to, Un
21、ited States Occupational Safety and Health Administration (OSHA) health and safety standards. regression analysis procedure that accounts for error in both dependent and independent variables. Keywords: coefficient of variation; compressive strength; construction; in-place tests; nondestructive test
22、s; safety; sampling; statistical analysis. CONTENTS Chapter 1-Introduction, p. 228.1 R-2 1.1-Scope 1.2-Need for in-place tests during construction 1.3-Influence of AC1 3 18 1.4-Recommendations in other AC1 documents 1.5-Existing construction 1 .6-Objective of report Chapter 2-Review of methods, p. 2
23、28.1 R-4 2.1-Introduction 2.2-Rebound number (ASTM C 805) 2.3-Penetration resistance (ASTM C 803K 803M) 2.4-Pullout test (ASTM C 900) 2.5-Break-off number (ASTM C 1150) 2.6-Ultrasonic pulse velocity (ASTM C 597) 2.7-Maturity method (ASTM C 1074) 2.8-Cast-in-place cylinders (ASTM C 873) 2.9-Strength
24、limitations 2.1Wombined methods 2.1 1-Summary AC1 228.1R-O3 supersedes AC1 228.1R-95 and became effective September 16,2003. Copyright O 2003, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any
25、photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. 228.1 R-1 228.1 R-2 AC1 COMMITTEE REPORT
26、Chapter 3-Statistical characteristics of test results, p. 228.1 R-14 3.1-Need for statistical analysis 3.2-Repeatability of test results Chapter Bungey 1989; Malhotra and Carino 1991). No attempt is made to review all of these methods in this report; only those methods that have been standardized by
27、 ASTM are discussed. Teodoru (1989) prepared a compilation of national standards on in-place test methods. 1.2-Need for in-place tests during construction In North American practice, the most widely used test for concrete is the compressive strength test of the standard cylinder (ASTh4 C 3 1/C 3 1M)
28、. This test procedure is relatively easy to perform in terms of sampling, specimen preparation, and strength measurement. When properly performed, this test has low within-test variation and low interlaboratory variation and, therefore, readily lends itself to use as a stan- dard test method. The co
29、mpressive strength so obtained is used to calculate the nominal strengths of structural members. Therefore, this strength value is an essential parameter in design codes. When carried out according to standard procedures, however, the results of the cylinder compression test repre- sent the potentia
30、l strength of the concrete as delivered to a site. The test is used mainly as a basis for quality control of the concrete to ensure that contract requirements are met. It is not intended for determining the in-place strength of the concrete because it makes no allowance for the effects of placing, c
31、ompaction, or curing. It is unusual for the concrete in a structure to have the same properties as a standard-cured cylinder at the same test age. Also, standard-cured cylinders are usually tested for acceptance purposes at an age of 28 days; therefore, the results of these tests cannot be used to d
32、etermine whether adequate strength exists at earlier ages for safe removal of formwork or the application of post-tensioning. The concrete in some parts of a structure, such as columns, may develop strength equal to the standard 28-day cylinder strength by the time it is subjected to design loads. C
33、oncrete in most flexural members (especially pretensioned flexural members) does not develop its 28-day strength before the members are required to support large percentages of their design loads. For these reasons, in-place tests are used to estimate the concrete strength at critical locations in a
34、 structure and at times when crucial construction operations are scheduled. Traditionally, some measure of the strength of the concrete in the structure has been obtained by using field- cured cylinders prepared and cured in accordance with ASTM C 3 1/C 3 1M. These cylinders are cured on or in the I
35、N-PLACE METHODS TO ESTIMATE CONCRETE STRENGTH 228.1 R-3 structure under, as nearly as possible, the same conditions as the concrete in the structure. Measured strengths of field- cured cylinders may be significantly different from in-place strengths because it is difficult, and often impossible, to
36、have identical bleeding, consolidation, and curing conditions for concrete in cylinders and concrete in structures (Soutsos et al. 2000). Field-cured specimens need to be handled with care and stored properly to avoid misleading test results. Construction schedules often require that operations such
37、 as form removal, post-tensioning, termination of curing, and removal of reshores be carried out as early as possible. To enable these operations to proceed safely at the earliest possible time requires the use of reliable in-place tests to estimate the in-place strength. The need for such strength
38、information is emphasized by several construction failures that possibly could have been prevented had in-place testing been used (Lew 1980; Carino et al. 1983). In-place testing not only increases safety but can result in substantial cost savings by permitting accelerated construction schedules (Bi
39、ckley 1982a). 1.3-Influence of AC1 31 8 Before 1983, AC1 318 required testing of field-cured cylinders to demonstrate the adequacy of concrete strength before removal of formwork or reshoring. Section 6.2.2.1 of AC1 318-83 allowed the use of alternative procedures to test field-cured cylinders. The
40、building official, however, must approve the alternative procedure before its use. Since 1983, AC1 3 18 has permitted the use of in-place testing as an alter- native to testing field-cured cylinders. The commentary to AC1 318-02 (Section R6.2) lists four procedures, which are covered in this Report,
41、 that may be used, provided there are sufficient correlation data (AC1 3 18R). Most design provisions in AC1 318 are based on the compressive strength of standard cylinders. Thus, to evaluate structural capacity under construction loading, it is necessary to have an estimate of the equivalent cylind
42、er strength of the concrete as it exists in the structure. If in-place tests are used, a valid relationship between the results of in-place tests and the compressive strength of cylinders must be established. At present, there are no standard practices for developing the required relationship. There
43、 are also no generally accepted guidelines for interpretation of in-place test results. These deficiencies have been impediments to widespread adoption of in-place tests. One of the objectives of this Report is to eliminate some of these deficiencies. 1.4-Recommendations in other AC1 documents After
44、 the 1995 version of this Report was published, other AC1 documents incorporated in-place tests as alternative procedures for estimating in-place strength. One of these documents is AC1 301. In the 1999 version of AC1 301, Paragraph 1.6.5.2 on in-place testing of hardened concrete includes the follo
45、wing: “Use of the rebound hammer in accordance with ASTM C 805, pulse-velocity method in accordance with ASTM C 597, or other nondestructive tests may be permitted by the Architecmngineer in evaluating the uniformity and relative concrete strength in-place, or for selecting areas to be cored.” AC1 3
46、01-99 states in Paragraph 1.6.6.1 that the results of in-place tests “will be valid only if the tests have been conducted using properly calibrated equipment in accor- dance with recognized standard procedures and acceptable correlation between test results and concrete compressive strength has been
47、 established and is submitted.” Paragraph 1.6.7.2 of AC1 301-99, however, restricts the use of these tests in acceptance of concrete by stating that: “Nondestructive tests shall not be used as the sole basis for accepting or rejecting concrete,” but they may be used to “evaluate” concrete when the s
48、tandard-cured cylinder strengths fail to meet the specified strength criteria. AC1 301-99 also mentions in-place tests in Article 2.3.4 dealing with required strength for removal of formwork. Specifically, it is stated that the following methods may be used when permitted or specified, provided suff
49、icient correlation data are submitted: ASTM C 900 (pullout); ASTM C 1150 (break-off). These same methods are also recommended as alternatives to testing field-cured cylinders for estimating in-place strength for the purpose of terminating curing procedures. AC1 308.1 also mentions in-place tests as acceptable methods for estimating in-place strength for the purpose of terminating curing procedures (see Paragraph 1.6.4 of AC1 308.1-98). Thus, project specifications can reference standard specifications that allow in-place testing as an alter- native to testing field-cured cylinde
