ACI-214.3R-1988-R1997.pdf
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1、AC1 214.3R-88 (Reapproved 1997) Simplified Version of the Recommended Practice for Evaluation of Strength Test Results of Concrete Reported by AC1 Committee 214 Edward A. Abdun-Nur David F. Anderson John Bickley Stanley J. Blas, JI. Jerrold L. Brown Ronald L. Dilly Donald E. Dixon Richard D. Gaynor
2、V. Ramakrishnan Chairman Steven H. Gebler Eugen O. Goeb Gilbert J. Haddad David F. Harrald Peter A. Kopac Kenneth R. Lauer H. S. Lew V. M. Malhotra The purpose of this report is to introduce the use of a simplified ver- sion of the statistical concepts as outlined in ACI 214 for the specifi- cation,
3、 control, and evaluation of the production of concrete. For a more elaborate discussion of the concepts, see the ?Recommended Practice for the Evaluation of Strength Test Results o f Concrete? CI 214). Keywords: coefficient of variation; compression tests; compressive strength; concrete construction
4、; concretes; cylinders; evaluation; quality control; sam- pling; standard deviation; statistical analysis; variations. CONTENTS INTRODUCTION The strength test is widely used in specifying, con- trolling, and evaluating concrete quality. Quality con- crete must be able to: 1) carry loads imposed upon
5、 it; 2) resist deterioration; and 3) be dimensionally stable. AC1 Committee Reports, Guides, Standard Practices, and Commentanes are intended for guidance in designing, plan- ning, executing, or inspecting construction and in preparing specifications Reference to these documents shall not be made in
6、 the Project Documents If items found in these documents are desired to be part of the Project Documents they should be phrased in mandatory language and incorporated into the Project Documents P. N.Balagun Secretary Larry W. Matejcek Tann R. Naik Robert E. Neal Robert E. Philleo Francis J. Principe
7、 Owen Richards Orrin Riley Ephraim Senbetta S. N. Shanmughasundram Shyam N. Shukla Luke M. Snell Roger L. Sprouse Rodney J. Stebbins Michael A. Taylor J. Derle Thorpe* Don J. Wade T?here are several tests that can be made with plastic and hardened concrete, but the strength test is gener- ally accep
8、ted as a measure of the quality of concrete being placed on a project. Although the strength test is not a direct measure of concrete durability or dimensional stability, it provides an indication of the water-cement ratio of the concrete. The water-cement ratio, in turn, directly influences the str
9、ength; durability; wear resistance; dimensional sta- bility; and other desirable properties of concrete. The strength test is also used to measure the variability of concrete. By using statistical methods based on the strength test, realistic specifications can also be pre- pared. VARIABILITY OF CON
10、CRETE Portland cement concrete is subject to numerous factors that affect its strength and other properties. These may include variations in the manufacture of portland cement; preparation of aggregates; batching, mixing, and curing of concrete; and finally in the prep- aration, handling, and testin
11、g of the cylinders. The major variables are listed in ?.:N-: i. These variables must be considered when speciing, producing, or controlling the strength of concrete. NORMAL DISTRIBUTION Test data from large concrete projects with many tests show a grouping around the average strength. A *Principal a
12、uthor of this report. Copyright ?I? 1988, 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 photo process, or by any electronic or mechanical device, printed, written, or oral, or recording for
13、 sound or visual reproduction or for use in any knowledge or retrieval system or de- vice, unless permission in writing is obtained from the copyright proprietors. Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr No
14、t for Resale, 03/05/2007 00:54:41 MSTNo reproduction or networking permitted without license from IHS -,-,- 214.3R-2 AC1 COMMITTEE REPORT Variations in properties of concrete Changes in water-cement ratio Poor control of water Excessive variation of Retempering Aggregate grading, moisture in aggrega
15、te Variations in water requirement absorption, particle shape Cement and admixture properties Air content Delivery time and temperature Variations in characteristics and proportions of ingredients Aggregates Cement Pozzolans Admixtures Variations in batching, mixing, transporting, placing, and compa
16、ction curing Variations in temperature and Table 1 - Principal sources of variations in strength test results Discrepancies in testing methods Improper sampling procedures Variations due to fabrication techniques Cylinder molding Poor quality molds Handling and curing of newly made cylinders Changes
17、 in curing Temperature variation Variable moisture Delays in bringing cylin- ders to the laboratory Poor testing procedures Care of cylinders, transportation and cap- Ping Improper placement in testing machine Testing machine platens out of specifications Incorrect speed of testing 10 O O O0 o O0 O0
18、00 0000000 0000000 o o o o o o o o o 00000000000 10 m 3 z O I I I I I I i i 3 S i l psi C o o o o o o o o 2400 2300 3200 3600 4000 4400 4800 5200 COMPRESSIVE STRENGTH (psi) (Plotted In cells of 200 psi) Fig. 2-Strength tests plotted in Fig. I with normal dis- tribution curve superimposed on data n W
19、 m 3 z O 2400 2800 3200 3600 4000 4400 4800 5200 COMPRESSIVE STRENGTH (psi) (Plotted in cells of 200 psi) 2400 2300 3200 3600 4000 4400 4800 5200 COMPRESSIVE STRENGTH psi) (Plotted in cells of 200 psi) Fig. 3-Normal distribution curve represents variation of individual test results plotted in Fig. I
20、 and 2 distribution on the plot of individual strengths. As shown in Fig. 2, this curve smooths out the plot by re- Fig. I-Plot of 45 strength tests in cell width of 200 psi typical grouping is illustrated in Fi$; .!. To produce Fig. 1, the strength tests are divided into cells. The cell width for F
21、ig. 1 is 200 psi. For example, the seven tests that fall between 3900 and 4099 psi have been plotted in the cell listed as 4000 psi.* Similarly, all other strengths from the series of tests have been plotted in their re- spective cells. Since the grouping of tests on each side of the average is near
22、ly symmetrical, it is called a nor- mal distribution. It is possible to superimpose a normal *I psi = 6.895 kPa ducing the effect of individual differences through av- eraging. The center of the curve is located at the aver- age of all the tests. The area under the curve represents 100 percent of th
23、e tests. Fiq. I! shows the normal distri- bution curve used to represent all of the tests, rather than using the individual tests plotted in their respec- tive cells. This curve will be used to represent all of the strength tests without the individual plotted tests throughout the remainder of this
24、report. The example illustrated in this report is the compressive strength test, but the procedures outlined here may be used on test data from any test used to determine the strength of con Crete. Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/11
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