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Figure   13-22.Compression-testing   machine. - 14070_297
Flexural-Strength Test (ASTM C 78) - CONTINUED - 14070_299

Engineering Aid 1 - Advanced Structural engineering guide book
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Figure  13-24.—Flexural-strength  testing  assembly  for  6-inch by 6-inch by 21-inch concrete beam. For  each  tested  specimen,  your  test  report  should include  the  identification,  diameter,  length,  maximum load, compressive strength, irregular fracture or defect in caps or specimen, and age of specimen at test. Report the average compressive strength of all cylinders from the  same  concrete  sample. Flexural-Strength Test (ASTM C 78) Flexural strength is the ability to resist an applied bending  force  such  as  encountered  by  concrete pavements or other slabs on ground. A determination of the flexural strength is frequently necessary as part of the design of concrete mixtures to check compliance with  established  specifications  or  to  provide  informa- tion necessary to the design of an engineering structure. In the flexural-strength test, a test load is applied to the  sides  of  a  test  beam.  Although  the  test  can  be performed upon beams sawed from existing concrete structures, it is more commonly performed upon beams Figure 13-25.—Alternate testing assembly using CBR test equipment. that are cast for testing purposes. The standard test beam measures 6 inches by 6 inches by 21 inches. When performing  the  test  for  mix-design  purposes,  you  will need at least five beam specimens for each mixture design  being  evaluated.  Two  of  the  specimens  are broken at 7 days to permit an early evaluation of the mix. The  remaining  beams  are  broken  at  28  days.  The procedures  for  preparing  test  beams  is  discussed  in  the EA3  TRAMAN.  If  necessary,  you  should  review  those procedures. The following paragraphs discuss only the procedures used to perform the test. When performing the flexural-strength test, you use a concrete beam tester with third-point loading. An example of that equipment is illustrated in figure 13-24. An alternate testing assembly can be made from the loading frame and certain attachments provided with the California bearing ratio (CBR) test set, the breaker (third-point loading), and the 10,000-pound capacity proving ring. That alternate assembly is shown in figure 13-25. 13-32







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