AASHTO T 177-2010 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 177-10 ASTM Designation: C 293-08 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 1

2、77-1 AASHTO Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading) AASHTO Designation: T 177-10 ASTM Designation: C 293-08 1. SCOPE 1.1. This method covers the determination of the flexural strength of concrete specimens by the use of a simple beam wi

3、th center-point loading. It is not an alternative to T 97. 1.2. The values stated in SI units are to be regarded as the standard. 1.3. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appr

4、opriate 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 Laboratory T 23, Making and Curing Concrete Test Specimens in the Field T 97, Flexural Str

5、ength of Concrete (Using Simple Beam with Third-Point Loading) T 177, Flexural Strength of Concrete (Using Simple Beam with Center-Point Loading) T 231, Capping Cylindrical Concrete Specimens 2.2. ASTM Standards: C 31/C 31M, Standard Practice for Making and Curing Concrete Test Specimens in the Fiel

6、d C 78/C 78M, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) C 192/C 192M, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory C 617, Standard Practice for Capping Cylindrical Concrete Specimens C 1077, Standard Pract

7、ice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation E 4, Standard Practices for Force Verification of Testing Machines 3. SIGNIFICANCE AND USE 3.1. This test method is used to determine the modulus of rupture of specimens prepa

8、red 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. 2011 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation o

9、f applicable law.TS-3c T 177-2 AASHTO 3.2. The results of this test method may be 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. 4. APPARATUS 4.1.

10、Testing MachineThe testing machine shall conform to the requirements of the sections on Basis of Verification, Corrections, and Time Interval Between Verifications of ASTM E 4. Hand-operated testing machines having pumps that do not provide a continuous loading to failure in one stroke are not permi

11、tted. 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 loads at a uniform rate without shock or interruption. 4.2. Loading ApparatusThe mech

12、anism 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 Figur

13、e 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 position

14、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 reaction to

15、 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 (21/2in.) 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 the sp

16、ecimen 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 shall be

17、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 2011 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

18、AASHTO 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 be omitted when a spherically seated bearing block is used. 5. TESTING 5.1. The test specimen shall conform to all requirements of R 39 or T

19、 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 identification marks. 5

20、.2. The individual who tests concrete beams for acceptance testing shall meet the concrete laboratory requirements of ASTM C 1077, including T 177 as a relevant test. 6. PROCEDURE 6.1. Flexural tests of moist-cured specimens shall be made as soon as practical after removal from moist storage. Surfac

21、e 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 molded and center it on the support blocks. Center the loading system in relation to the applied force. Bring the load-applying block in contact

22、 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 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

23、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 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 ext

24、end 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 shall be minimized in as much as grinding may change the physical characteristics of the specimens. Capping shall be in accordance with T 231

25、. 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 maximum 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 = 2Sbd

26、2/3L (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.); 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 di

27、mensions of the specimen section for use in calculating modulus of rupture, take measurements across one of the fractured faces after testing. The width and depth are measured with the specimen as oriented for testing. For each dimension, take one measurement at each end of the specimen and one at t

28、he center of the cross section. Use the three measurements 2011 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 177-4 AASHTO for each direction to determine the average width and the average depth. Ta

29、ke all measurements to the 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: 232PlRbd= (2) where: R = modulus of rupture, MPa (psi); P = maximum applied load indicated

30、 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 specimen, 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 f

31、ollowing 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 1.3 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);

32、 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 test; 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.

33、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 operator coefficient of variation has been found to be 4.4 percent. Therefore, results of two properly conducted tests by the same operator

34、on beams made from the same batch sample should not differ from each other by more than 12 percent. The 2011 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 177-5 AASHTO multilaboratory coefficient of

35、 variation has been found to 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. 10.2. BiasBecause there is no accepted standard for determining bias in this test method, no statement on bias is made. 2011 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.