1、Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) AASHTO Designation: T 97-14 ASTM Designation: C 78-08 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 97-1
2、 AASHTO Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) AASHTO Designation: T 97-14 ASTM Designation: C 78-08 1. SCOPE 1.1. This test method covers determination of the flexural strength of concrete by the use of a simple beam with third-point l
3、oading. 1.2. The values stated in SI units are to be regarded as the standard. Note 1For methods of molding concrete specimens, see T 23 and R 39. 1.3. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this
4、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 Laboratory T 23, Making and Curing Concrete Test Specimens in th
5、e Field T 24M/T 24, Obtaining and Testing Drilled Cores and Sawed Beams of Concrete 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 Field C 42/C 42M, Standard Test Method for Obtaining and Testing D
6、rilled Cores and Sawed Beams of Concrete C 192/C 192M, Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory C 617/C 617M, Standard Practice for Capping Cylindrical Concrete Specimens C 1077, Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use
7、in Construction and Criteria for Testing Agency Evaluation E 4, Standard Practices for Force Verification of Testing Machines 2.3. TRB Document: Tanesi, J., A. Ardani, and J. Leavitt. Reducing the Specimen Size of the AASHTO T 97 Concrete Flexural Strength Test for Safety and Ease of Handling. In Tr
8、ansportation Research Record 2342: Journal of the Transportation Research Board. Transportation Research Board of National Academies, Washington, DC, 2013, pp. 99105. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of app
9、licable law.TS-3c T 97-2 AASHTO 3. SIGNIFICANCE AND USE 3.1. This test method is used to determine the flexural strength of specimens prepared and cured in accordance with T 23, T 24M/T 24, or R 39. Results are calculated and reported as the modulus of rupture. The strength determined will vary wher
10、e there are differences in specimen size, preparation, moisture condition, curing, or where the beam has been molded or sawed to size. 3.2. The result of this test method may be used to determine compliance with specifications or as a basis for proportioning, mixing, and placement operations. It is
11、used in testing concrete for construction of slabs and pavements. 4. APPARATUS 4.1. The testing machine shall conform to the requirements of sections on Basis of Verifications, Corrections, and Time Interval Between Verification of ASTM E 4. Hand-operated testing machines having pumps that do not pr
12、ovide a continuous loading 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 loads at a uniform rate without
13、 shock or interruption. 4.2. Loading ApparatusThe third-point loading method shall be used in making flexure tests of concrete employing bearing blocks, which will ensure that forces applied to the beam will be perpendicular to the face of the specimen and applied without eccentricity. A diagram of
14、an apparatus that accomplishes this purpose is shown in Figure 1. Notes: 1. 1 in. = 25.4 mm. 2. This apparatus may be used inverted. If the testing machine applies force through a spherically seated head, the center pivot may be omitted, provided one load-applying block pivots on a rod and the other
15、 on a ball. Figure 1Diagrammatic View of a Suitable Apparatus for Flexure Test of Concrete by Third-Point Loading Method 4.2.1. All apparatus for making flexure tests of concrete should be capable of maintaining the specified span length and distances between load-applying blocks and support blocks
16、constant within 1.3 mm (0.05 in.). Head ofTesting MachineSteel Ball25 mm minSteel RodBed ofTesting Machine25 mm minOptional Positions forOne Steel Rod andOne Steel BallLoad-Applyingand Support BlocksSteel BallRigid Loading Structure or,if it is a loading accessory,Steel Plate or ChannelSpan Length,
17、LL/3 L/3 L/3Specimend=L/3 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-3 AASHTO 4.2.2. The ratio of the horizontal distance between the point of application of the load and the point of app
18、lication of the nearest reaction to the depth of the beam shall be 1.0 0.03. 4.2.3. If an apparatus similar to that illustrated in Figure 1 is used: 4.2.3.1. The load-applying and support blocks should not be more than 64 mm (21/2in.) high, measured from the center or the axis of pivot, and should e
19、xtend entirely across or beyond the full width of the specimen. Each case-hardened bearing surface in contact with the specimen shall not depart from a plane by more than 0.05 mm (0.002 in.) and should be a portion of a cylinder, the axis of which is coincidental with either the axis of the rod or c
20、enter of the ball, whichever the block is pivoted upon. The angle subtended by the curved surface of each block should be at least 45 degrees (0.79 rad). 4.2.3.2. 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-l
21、oaded screws that hold them in contact with the pivot rod or ball. 4.2.3.3. The uppermost bearing plate and centerpoint ball in Figure 1 may be omitted when a spherically seated bearing block is used, provided one rod and one ball are used as pivots for the upper load-applying blocks. 5. TESTING 5.1
22、. The test specimen shall conform to all requirements of T 23, T 24M/T 24, and R 39. The specimen 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 sca
23、rs, indentations, holes, or inscribed identification 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 flexural strength. 6.2. When using molded s
24、pecimens, turn the test specimen on its side with respect to its position as molded and center it on the support blocks. When using sawed specimens, position the specimen so that the tension face corresponds to the top or bottom of the specimen as cut from the parent material. 6.3. Center the loadin
25、g system in relation to the applied force. Bring the load-applying blocks in contact with the surface of the specimen at the third points and apply a load of between 3 and 6 percent of the estimated ultimate load. 6.4. Using 0.10-mm (0.004-in.) and 0.38-mm (0.015-in.) leaf-type feeler gauges, determ
26、ine whether any gap between the specimen and the load-applying or support blocks is greater or lesser 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.) in width. Leath
27、er shims shall be of uniform 6.4 mm (0.25 in.) thickness, 25 to 50 mm (1 to 2 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 should be minimized in as much as grin
28、ding may change the physical characteristics of the specimens. Capping shall be in accordance with T 231. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-4 AASHTO 6.5. Load the specimen contin
29、uously and without shock. The load shall be applied at a constant rate to the breaking point. Apply a load at a rate that constantly increases the maximum stress on the tension face between 0.9 and 1.2 MPa/min (125 and 175 psi), until rupture occurs. The loading rate is calculated using the followin
30、g equation: r = Sbd2/L (1) where: r = loading rate, N/min (lb/min); S = rate of increase in extreme fiber stress, MPa/min (psi/min); b = average width of specimen mm (in.); d = average depth of specimen mm (in.); and L = span length, mm (in.). 7. MEASUREMENT OF SPECIMENS AFTER TEST 7.1. To determine
31、 the dimensions of the specimen cross 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 edge and one at the
32、 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 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. If
33、the fracture initiates in the tension surface within the middle third of the span length, calculate the modulus of rupture as follows: 2R Pl bd (2) where: R = modulus of rupture, kPa (psi); P = maximum applied load indicated by the testing machine, N (lbf); l = span length, mm (in.); b = average wid
34、th of specimen mm (in.); and d = average depth of specimen mm (in.). Note 2The weight of the beam is not included in the above calculation. 8.2. If the fracture occurs in the tension surface outside of the middle third of the span length by not more than 5 percent of the span length, calculate the m
35、odulus of rupture as follows: 23R Pa bd (3) where: a = average distance between line of fracture and the nearest support measured on the tension surface of the beam, mm (in.). See Note 2. 8.3. If the fracture occurs in the tension surface outside of the middle third of the span length by more than 5
36、 percent of the span length, discard the results of the test. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-5 AASHTO 8.4. Since the modulus of rupture of a 100-by-100-by-355-mm (4-by-4-by-14
37、-in.) specimen is not equivalent to the modulus of rupture of a 152-by-152-by-533 mm (6-by-6-by-21 in.) specimen, the modulus of rupture obtained from a 100-by-100-by-355-mm (4-by-4-by-14-in.) specimen shall be converted to the modulus of rupture of a 152-by-152-by-533-mm (6-by-6-by-21 in.) specimen
38、. See Note 3. Note 3The conversion can be done either by using Equation 4 or 5 or by establishing a relationship between the flexural strength of the two different specimen sizes for the specific mixture design. 100 1001.11 0.76stRR= (4) where: Rst= modulus of rupture of 152-by-152-by-533-mm specime
39、n size, MPa; and R100100= modulus of rupture of 100-by-100-by-355-mm specimen, MPa. 441.11 110stRR= (5) where: Rst= modulus of rupture of 6-by-6-by-21-in. specimen size, psi; and R44= modulus of rupture of 4-by-4-by-14-in. specimen, psi. 9. REPORT 9.1. The report shall include the following: 9.1.1.
40、Identification number; 9.1.2. Average width to the nearest 1 mm (0.05 in.); 9.1.3. Average depth to the nearest 1 mm (0.05 in.); 9.1.4. Span length in millimeters (inches); 9.1.5. Maximum applied load in newtons (pounds-force); 9.1.6. Modulus of rupture calculated to the nearest 0.05 MPa (5 psi); 9.
41、1.7. Curing history 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. If specimens were sawed or molded and any defects in the specimens; 9.1.10. Age of specimens; and 9.1.11. Specimen size. 10. PRECIS
42、ION AND BIAS 10.1. PrecisionThe coefficient of variation of test results ha s been observed to be dependent on the strength level of the beams. The single operator coefficient of variation has been found to be 5.7 percent. Therefore, results of two properly conducted tests by the same operator on be
43、ams made from the same batch sample should not differ from each other by more than 16 percent. The 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-6 AASHTO multilaboratory coefficient of varia
44、tion has been found to be 7.0 percent. Therefore, results of two different laboratories on beams made from the same batch sample should not differ from each other by more than 19 percent. 10.2. BiasBecause there is no accepted standard for determining bias in this test method, no statement on bias is made. 2014 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
