AASHTO T 177-2017 Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading).pdf

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1、Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading) AASHTO Designation: T 177-17 Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) ASTM Designation: C293-16 American Association of State Highway and Transportation Officials 444

2、 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 177-1 AASHTO Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading) AASHTO Designation: T 177-17 Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) ASTM Designati

3、on: C293-16 1. SCOPE 1.1. This method covers the determination of the flexural strength of concrete specimens by the use of a simple beam with center-point loading. It is not an alternative to T 97. 1.2. The values stated in SI units or inch-pound units are to be regarded separately as standard. The

4、 values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 1.3. This standard does not purport to address all of the safety concerns associated with

5、 its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: R 39, Making and Curing Concrete Test Specimens in the Laborator

6、y T 23, Making and Curing Concrete Test Specimens in the Field T 97, Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) T 231, Capping Cylindrical Concrete Specimens 2.2. ASTM Standard: E4, Standard Practices for Force Verification of Testing Machines 3. SIGNIFICANCE AND USE

7、3.1. This test method is used to determine the modulus of rupture of specimens prepared and cured in accordance with R 39 or T 23. The strength determined will vary where there are differences in specimen size, preparation, moisture, condition, or curing. 3.2. The results of this test method may be

8、used to determine compliance with specifications or as a basis for proportioning mixing and placement operations. This test method produces values of flexural strength significantly higher than T 97. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved.

9、Duplication is a violation of applicable law.TS-3c T 177-2 AASHTO 4. APPARATUS 4.1. Testing MachineThe testing machine shall conform to the requirements of the sections on Basis of Verification, Corrections, and Time Interval Between Verifications of ASTM E4. Hand-operated testing machines having pu

10、mps that do not provide a continuous loading to failure in one stroke are not permitted. Motorized pumps or hand-operated positive displacement pumps having sufficient volume in one continuous stroke to complete a test without requiring replenishment are permitted and shall be capable of applying lo

11、ads at a uniform rate without shock or interruption. The testing machine shall be equipped with a means of recording or holding the peak value that will indicate the maximum load applied to the specimen during a test, to within 1 percent accuracy of the load being applied. 4.2. Loading ApparatusThe

12、mechanism by which forces are applied to the specimen shall employ a load-applying block and two specimen support blocks. It shall ensure that all forces are applied perpendicular to the face of the specimen without eccentricity. A diagram of an apparatus that accomplishes this purpose is shown in F

13、igure 1. Note: Apparatus may be used inverted. Figure 1Diagrammatic View of a Suitable Apparatus for Flexure Test of Concrete by Center-Point Loading Method 4.2.1. All apparatus for making center-point loading flexural tests shall be similar to Figure 1 and maintain the span length and central posit

14、ion of the load-applying block with respect to the support blocks constant within 1.3 mm (0.05 in.). 4.2.2. Reactions shall be parallel to the direction of the applied load at all times during the test and the ratio of the horizontal distance between the point of load application and nearest reactio

15、n to the depth of the beam shall be 1.5 2 percent. 4.2.3. The load-applying and support blocks shall not be more than 64 mm (2.50 in.) high, measured from the center or the axis of pivot, and shall extend at least across the full width of the specimen. Each hardened bearing surface in contact with t

16、he specimen shall not depart from a plane by more than 0.051 mm (0.002 in.) and shall be a portion of a cylinder, the axis of which is coincidental with either the axis of the rod or center of the ball, whichever the block is pivoted upon. The angle subtended by the curved surface of each block shal

17、l be at least 0.79 rad (45 degrees). The load-applying and support blocks should be maintained in a vertical position and in contact with the rod or ball by means of spring-loaded screws that hold them in contact with the pivot rod or ball. The rod in the center load-applying block in Figure 1 may b

18、e omitted when a spherically seated bearing block is used. D=L 3L2L2Head of Testing Machine25 mm(1 in.) minSteel RodBed ofTesting MachineSpecimenSpan Length, LLoad Applying andSupport BlocksSteel BallRigid Loading Structureor, if it is a loadingaccessory, Steel Plateor ChannelSteel Rod (may be omitt

19、edwhen spherically seatedBearing Block is used)25 mm(1 in.) min 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 177-3 AASHTO 5. TESTING 5.1. The test specimen shall conform to all requirements of

20、 R 39 or T 23 applicable to beam specimens and shall have a test span within 2 percent of being three times its depth as tested. The sides of the specimen shall be at right angles with the top and bottom. All surfaces shall be smooth and free of scars, indentations, holes, or inscribed identificatio

21、n marks. 6. PROCEDURE 6.1. Flexural tests of moist-cured specimens shall be made as soon as practical after removal from moist storage. Surface drying of the specimen results in a reduction in the measured modulus of rupture. 6.2. Turn the test specimen on its side with respect to its position as mo

22、lded and center it on the support blocks. Center the loading system in relation to the applied force. Bring the load-applying block in contact with the surface of the specimen at the center and apply a load of between 3 and 6 percent of the estimated ultimate load. Using 0.10-mm (0.004-in.) and 0.38

23、-mm (0.015-in.) leaf-type feeler gauges, determine whether any gap between the specimen and the load-applying or support blocks is greater or less than each of the gauges over a length of 25 mm (1 in.) or more. Grind, cap, or use leather shims on the specimen contact surface to eliminate any gap in

24、excess of 0.10 mm (0.004 in.). Leather shims shall be of uniform 6.4 mm (0.25 in.) thickness, 25 to 50 mm (1 to 2 in.) in width, and shall extend across the full width of the specimen. Gaps in excess of 0.38 mm (0.015 in.) shall be eliminated only by capping or grinding. Grinding of lateral surfaces

25、 shall be minimized inasmuch as grinding may change the physical characteristics of the specimens. Capping shall be in accordance with T 231. 6.3. Load the specimen continuously and without shock. The load shall be applied at a constant rate for the duration of the test. Apply the load so the maximu

26、m stress on the tension face increases at a rate between 0.9 and 1.2 MPa/min (125 and 175 psi). The loading rate is computed using: r = 2Sbd2/3L (1) where: r = loading rate, mN/min (lb/min); S = rate of increase in extreme fiber stress, MPa/min (psi/min); b = average width of the specimen, mm (in.);

27、 d = average depth of the specimen, mm (in.); and L = span length, mm (in.). 7. MEASUREMENT OF SPECIMENS AFTER TEST 7.1. To determine the dimensions of the specimen section for use in calculating modulus of rupture, take measurements across one of the fractured faces after testing. The width and dep

28、th are measured with the specimen as oriented for testing. For each dimension, take one measurement at each end of the specimen and one at the center of the cross section. Use the three measurements for each direction to determine the average width and the average depth. Take all measurements to the

29、 nearest 1.3 mm (0.05 in.). If the fracture occurs at a capped section, include the cap thickness in the measurement. 8. CALCULATIONS 8.1. Calculate the modulus of rupture as follows: 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a

30、 violation of applicable law.TS-3c T 177-4 AASHTO 232PlRbd (2) where: R = modulus of rupture, MPa (psi); P = maximum applied load indicated by the testing machine, (N or lbf); l = span length, mm (in.); b = average width of specimen, at the point of fracture, mm (in.); and d = average depth of speci

31、men, at the point of fracture, mm (in.). Note 1The weight of the beam is not included in the above calculation. 9. REPORT 9.1. Report the following information: 9.1.1. Identification number; 9.1.2. Average width to the nearest 1.3 mm (0.05 in.), at the fracture; 9.1.3. Average depth to the nearest 1

32、.3 mm (0.05 in.), at the fracture; 9.1.4. Span length in millimeters (or inches); 9.1.5. Maximum applied load in newtons (or pounds-force); 9.1.6. Modulus of rupture calculated to the nearest 0.05 MPa (5 psi); 9.1.7. Record of curing and apparent moisture condition of the specimens at the time of te

33、st; 9.1.8. If specimens were capped, ground, or if leather shims were used; 9.1.9. Defects in specimens; and 9.1.10. Age of specimens. 10. PRECISION AND BIAS 10.1. PrecisionThe coefficient of variation of test results has been observed to be dependent on the strength level of the beams. The single o

34、perator coefficient of variation has been found to be 4.4 percent. Therefore, results of two properly conducted tests by the same operator on beams made from the same batch sample should not differ from each other by more than 12 percent. The multilaboratory coefficient of variation has been found t

35、o be 5.3 percent. Therefore, results of two different laboratories on beams made from the same batch sample should not differ from each other by more than 15 percent (Notes 24). Note 2This precision statement was determined using 150 by 150 by 510 mm (6 by 6 by 20 in.) specimens.1The variability of

36、test results changes with specimen size 1 and should not be extrapolated to other sizes. Note 3This precision statement was determined using a single brand and model testing machine (Rainhart Series 416, Recording Beam Tester).1 2017 by the American Association of State Highway and Transportation Of

37、ficials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 177-5 AASHTO Note 4This precision statement was obtained by measuring the flexural strength of two concrete mixtures with an average modulus of rupture of 5.10 and 6.45 MPa (740 and 940 psi). This modulus of rupture wa

38、s determined in accordance with TEX-420-A.1The version of TEX- 420-A used in the study (1986) may differ from the current test method. 10.2. BiasBecause there is no accepted standard for determining bias in this test method, no statement on bias is made. 11. KEYWORDS 11.1. Center-point loading; conc

39、rete flexural strength; concrete simple beam. 1See “Improved Concrete Quality Control Procedures Using Third Point Loading,” by P. M. Carrasquillo and R. L. Carrasquillo. Research Report 119-1F, Project 3-9-87-1119. Center for Transportation Research, The University of Texas at Austin, November 1987 for information as to the relationship of strength and variability under center-point loading. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.