AASHTO-T-97-2003.pdf

standard method of test for flexural strength of concrete (using simple beam wtth thirdpoint loading) aashto designation: t 97-03 astm designation: c 78-02 1. scope 1.1. this test method covers determination of the flexural strength of concrete by the use of a simple beam w i t h third-point loading. 1.2. the values stated in s i units are to be regarded a s the standard. note i-for methods of molding concrete specimens, see t 23 and t 126. 1.3. this standard may involve hazardous niarerials, operaiions, and equipment. this standard does not purport to address all o f the safety problems associafed with its we. if i s the responsibility o f the user ofthis standard to consirlt and establish appropriate safev and health practices and detennne the applicabiis o f regularoty litniraiions prior to use. 2. referenced documents 2.1. aashto standards: t 23, making and curing concrete test specimens in the field t 24, obtaining and testing drilled cores and sawed beams of concrete b t 67, standard practices for force verification of testing machines r t 126, making and curing concrete test specimens in the laboratory m t 23 1, capping cylindrical concrete specimens 3 . summary of method 3.1. sigiiificance and use: 3.1.1. this test method is used to detcnnine the flexural strength of specimens prepared and cured in accordance with t 23, t 24, or t 126. results are calculated and repored 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. 4. apparatus 4.1. the testing machine shall conform to the requirements of sections 16, 17, and 18 of t 67. hand- operated testing machines having pumps that do not provide a continuous loading in one stroke shall not be permitted. motorized pumps or hand-operaied positive displacement pumps having 4 aashto ts-3 t 97-1 copyright american association of state highway and transportation officials provided by ihs under license with aashto licensee=university of texas revised sub account/5620001114 not for resale, 01/11/2009 02:20:21 mstno reproduction or networking permitted without license from ihs -,-,- suficient volume in one continuous stroke to complete a test without requiring replenishment are permitted and shall be capable of applying loads at a uniform mte without shock or interruption. thethird-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 an apparatus that accomplishes this purpose is shown in figure 1. head of optional positions for one steel rod and one steel bail rigid loading structure or, if it is a loading accessoty, steel plate or channel i l span length, l , - a noles i. i n . = 25.4 mm 2. k appamius may be used invmed. ifihe miing machinc applies forcc through a spherically sentcd head. ihe center pivot may be omined, pmvide one-load applying block pivots on a rod and othe other on a ball. figure 1-diagrammatic view of a suitable apparatus for flexure test of concrete by third-point method 4.2. 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 constant within i1.3 mm (i0.05 in.). 4.3. reactions should be parallel to the direction of the applied forces at all times during the test and the ratio of distance between the point of load application and nearest reaction to the depth of the beam should not be less than 1 .o *0.03. note 2 - i f an apparatus similar to that illustrated in figure 1 is used the load-applying and support blocks should not be more than 64 mm (2/2 in.) high, measured from the center or 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 mrn (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 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). 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 which hold them in contact w i t h the pivot rod or ball. the uppermost bearing place 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. * w 3 c t 97-2 aashto copyright american association of state highway and transportation officials provided by ihs under license with aashto licensee=university of texas revised sub account/5620001114 not for resale, 01/11/2009 02:20:21 mstno reproduction or networking permitted without license from ihs -,-,- 5. test specimen 5.1. the test specimen shall confom-i to all applicable requirements of t 23, t 24, and t 126. the specimen shall have a test span within 2 percent of being three times its depth as tested. the sides of che specimen shall be at right angles with the top and bottom. all surfaces in contact with load- applying and support blocks shall be smooth and free of scars, indentations, holes, or inscribed identifications. 6. procedure 6 . 1 . turn che test specimen on its side with respect ta its position as molded and center on the bearing blocks. center the loading system in relation to the applied force. bring the load-applying blocks in contact with the surface of the specimen at the third points between the supports and apply a load of between 3 and 6 percent of the estimated ultimate load. using standard o. 10 mm (0.004 in.) and 0.38 mm (0.01 5 in.) leaf-type feeler gages, determine whether any gap between the specimen and the load-applying or support blocks is grcater or lesser than each of the gages over a length of 25 nim (i in.) or more. grind, cap, or use leather shims on the specimen contact surface to eliminate any gap in excess of o. 10 mm (0.004 in.). leather shims shall be uniform 6.4 mm (0.25 in.) thickness, 25 to 50 nun (1 to 2 in.) width, and shall extend across the full width of the specimen. gaps in excess of 0.38 mm (0.01 5 in.) shall be eliminated only by capping or grinding. grinding of lateral surfaces should be minimized in as much as grinding may change the physical characteristics of the specitnens. capping sliall be in accordance with t 23 1. 6.2. load the specimen continuously and without shock. the load shall be applied at a rate which constantly increases the extreme fiber stress between 0.9 and 1.2 mpdmin (125 and 175 psi), until rupture occurs. the loading rate is computed using the following equation: r = sbd/l 0) where: i= s= b= d= l= loading rate, mn/min (ib/min), rate of increase in extreme fiber stress, mpa/min (psilmin), average width of specimen min (in.), average depth of specimen nun (in.), and span length, mm (in.), 7. measurement of specimens after test 7.1. after testing, at one of the fractured faces, take three measuremeiits across each dimension (one at each edge and at the center) to the nearest 1.3 mm (0.05 in.) to determine the average width, average depth, and line of fracture iocatioii of the specimen at the section of failure. 7.1.1. if fracture occurs at a capped section, include the cap thickness in the measurement. 8. calculations 8.1. if the fiacturc initiates in the tension surface within the middle third of thc span length, calculate c h e modulus of rupture as follows: r = pl/bd (2) ts-3 t 97-3 aashto copyright american association of state highway and transportation officials provided by ihs under license with aashto licensee=university of texas revised sub account/5620001114 not for resale, 01/11/2009 02:20:21 mstno reproduction or networking permitted without license from ihs -,-,- 8.2. where: r= p= i= b= d= modulus of rupture, kpa (psi), maximum applied load indicated by the testing machine, n (ibf), span length, mm (in.), average width of specimen mm (in.), and average depth of specimen mrn (in.). 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 of rupture as follows: r = 3pa/bd (3) where: a = average distance between line of fracture and the nearest support measured on the tension surface of the beam, mm (in.). note 3-the weight of the beam is not included in the above calculations. 8.3. if the fracture occurs in the tension surface outside of the middle third of tbe span length by more than 5 percent 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. maximum 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. defects in specimens; and 9.1.10. age of specimens. 1 o. precision and bias 10.1, precision-the 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 5.7 percent. therefore, results of two properly conducted tes