1、Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) AASHTO Designation: T 97-17 Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) ASTM Designation: C78-15b American Association of State Highway and Transportation Officials 444 N
2、orth Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-3c T 97-1 AASHTO Standard Method of Test for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) AASHTO Designation: T 97-17 Technical Section: 3c, Hardened Concrete Release: Group 1 (April 2017) ASTM Designation: C
3、78-15b 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 loading. 1.2. The values stated in SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact eq
4、uivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with 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 conce
5、rns, if any, associated with 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 18, Establishing and Implementing
6、a Quality Management System for Construction Materials Testing Laboratories R 39, Making and Curing Concrete Test Specimens in the Laboratory T 23, Making and Curing Concrete Test Specimens in the Field T 24M/T 24, Obtaining and Testing Drilled Cores and Sawed Beams of Concrete T 231, Capping Cylind
7、rical Concrete Specimens 2.2. ASTM Standard: E4, Standard Practices for Force Verification of Testing Machines 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
8、 and reported as the modulus of rupture. The strength determined will vary where there are differences in specimen size, preparation, moisture condition, curing, or where the beam has been molded or sawed to size. 2017 by the American Association of State Highway and Transportation Officials.All rig
9、hts reserved. Duplication is a violation of applicable law.TS-3c T 97-2 AASHTO Note 2The measured modulus of rupture generally increases as the specimen size decreases.1,2,3Also, it has been shown that the variability of individual test results increases as the specimen size decreases.1,23.2. The re
10、sult of this test method may be used to determine compliance with specifications or as a basis for proportioning, mixing, and placement operations. It is used in testing concrete for construction of slabs and pavements. 4. APPARATUS 4.1. Testing MachineThe testing machine shall conform to the requir
11、ements of sections on Basis of Verifications, Corrections, and Time Interval Between Verification of ASTM E4. Hand-operated testing machines having pumps that do not provide a continuous loading in one stroke are not permitted. Motorized pumps or hand-operated positive displacement pumps having suff
12、icient 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. The testing machine shall be equipped with a means of recording or holding the peak value that will indicate
13、 the maximum load, to within 1 percent accuracy, applied to the specimen during a test. 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
14、 of the specimen and applied without eccentricity. A diagram of an apparatus that accomplishes this purpose is shown in Figure 1. Notes: 1 in. = 25.4 mm. 1.This apparatus may be used inverted. If the testing machine applies force through a spherically seated head, the center pivot may be 2.omitted,
15、provided one load-applying block pivots on a rod and the other 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
16、and distances between load-applying blocks and support blocks constant within 1.3 mm (0.05 in.). 4.2.2. The ratio of the horizontal distance between the point of application of the load and the point of application of the nearest reaction to the depth of the beam shall be 1.0 0.03. Head ofTesting Ma
17、chineSteel 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, LL/3 L/3 L/3Specimend=L/3 2017 by the American Assoc
18、iation of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-3 AASHTO 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.) hig
19、h, measured from the center or the axis of pivot, and should extend 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
20、 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 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 pos
21、ition 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. 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 use
22、d as pivots for the upper load-applying blocks. 5. TEST SPECIMENS 5.1. 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
23、with the top and bottom. All surfaces shall be smooth and free of scars, indentations, holes, or inscribed identification marks. 5.2. Provided the smaller cross-sectional dimension of the beam is at least three times the nominal maximum size of the coarse aggregate, the modulus of rupture can be det
24、ermined using different specimen sizes. However, measured modulus of rupture generally increases as the specimen size decreases1,2(Note 3). Note 3The strength ratio for beams of different sizes depends primarily on the maximum size of aggregate.3 Experimental data obtained in two different studies h
25、ave shown that for maximum aggregate size between 19.0 and 25.0 mm (3/4and 1 in.), the ratio between the modulus of rupture determined with a 152 by 152 mm (6 by 6 in.) and a 100 by 100 mm (4 by 4 in.) may vary from 0.90 to 1.071for maximum aggregate size between 9.5 and 37.5 mm (3/8and 11/2in.), th
26、e ratio between the modulus of rupture determined with a 152 by 152 mm (6 by 6 in.) and a 115 by 115 mm (4.5 by 4.5 in.) may vary from 0.86 to 1.00.2 5.3. The specifier of tests shall specify the specimen size and number of specimens to be tested to obtain an average test result (Note 4). The same s
27、pecimen size shall be used for qualification and acceptance testing. Note 4It has been shown that the variability of individual test results increases as the specimen size decreases.1,26. PROCEDURE 6.1. Flexural tests of moist-cured specimens shall be made as soon as practical after removal from moi
28、st storage. Surface drying of the specimen results in a reduction in the measured flexural strength. 6.2. When using molded specimens, 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 t
29、hat the tension face corresponds to the top or bottom of the specimen as cut from the parent material. 2017 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 6.2.1. Center the loading system
30、 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. 6.2.2. Using 0.10-mm (0.004-in.) and 0.38-mm (0.015-in.) leaf-type feeler gauges, determine wh
31、ether 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. Leather shi
32、ms 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 grinding m
33、ay 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 to the breaking point. Apply a load at a rate that constantly increases the maximum stress on the te
34、nsion face between 0.9 and 1.2 MPa/min (125 and 175 psi), until rupture occurs. The loading rate is calculated using the following 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.)
35、; d = average depth of specimen mm (in.); and L = span length, mm (in.). 7. MEASUREMENT OF SPECIMENS AFTER TEST 7.1. To determine 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 d
36、epth are measured with the specimen as oriented for testing. For each dimension, take one measurement at each edge 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 nearest 1.3
37、mm (0.05 in.). If the fracture occurs at a capped section, include the cap thickness in the measurement. 8. CALCULATIONS 8.1. If 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 r
38、upture, kPa (psi); P = maximum applied load indicated by the testing machine, N (lbf); l = span length, mm (in.); b = average width of specimen mm (in.); and d = average depth of specimen mm (in.). 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Du
39、plication is a violation of applicable law.TS-3c T 97-5 AASHTO Note 5The 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 modulus
40、 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 5. 8.3. If the fracture occurs in the tension surface outside of the middle third of the span length by more than 5 perce
41、nt of the span length, discard the results of the test. 9. REPORT 9.1. The report shall include the following: 9.1.1. 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. Ma
42、ximum applied load in newtons (pounds-force); 9.1.6. Modulus of rupture calculated to the nearest 0.05 MPa (5 psi); 9.1.7. 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
43、were sawed or molded and any defects in the specimens; and 9.1.10. Age of specimens. 10. PRECISION AND BIAS 10.1. Precision4The 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 t
44、o be 5.7 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 16 percent. The multilaboratory coefficient of variation has been found to be 7.0 percent. Therefore, results of two diffe
45、rent 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 meth od, no statement on bias is made. 2017 by the American Association of State Highway and Transpo
46、rtation Officials.All rights reserved. Duplication is a violation of applicable law.TS-3c T 97-6 AASHTO 11. KEYWORDS 11.1. Concrete; flexure strength; third-point loading. 1Tanesi, J., A. Ardani, and J. Leavitt. Reducing the Specimen Size of Concrete Flexural Strength Test (AASHTO T 97) for Safety a
47、nd Ease of Handling. In Transportation Research Record No. 2342. TRB, National Research Council, Washington, DC, 2013, pp. 99105. 2Carrasquillo, P. M. and R. L. Carrasquillo. Improved Concrete Quality Control Procedures Using Third Point Loading. Research Report 119-1F, Project 3-9-87-1119. Center f
48、or Transportation Research, The University of Texas at Austin, November 1987. 3Bazant, Z. and D. Novak. Proposal for Standard Test of Modulus of Rupture of Concrete with its Size Dependence. In ACI Materials Journal, Vol. 98, No. 1, JanuaryFebruary 2001. American Concrete Institute, Farmington Hills
49、, MI, pp. 7987. 4See 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 possible guidance as to the relationship of strength and variability. 2017 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.
