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CURING  AND  STORING  CYLINDERS
CHAPTER 16 ADMINISTRATION

Engineering Aid 3 - Beginning Structural engineering guide book
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Table 15-6.-Number of Roddings to be Used in Molding Cylinder  Specimens Diameter  of  Cylinder, Number  of in.  (mm) Strokes/Layer 6 (152) 25 8 (200) 50 10  (250) 75 plates and squeezing out excess material to pro- vide a cap that is as thin as possible. Sulfur caps may be applied in time to harden for at least 2 hr before testing. Plaster caps cannot be stored over 4 hr in a moist room. Neat cement caps must be aged 6 days or more in a moist room (2 days when Type II cement is used). During capping, protect moist, cured specimens against drying by cover- ing  them  with  wet  burlap. Beam  Specimens Tests   are   performed   on   concrete   beam specimens  to  evaluate  the  flexural  strength  of  the concrete. The standard beam specimen is 6 in. by 6 in. by 21 in. (152 mm by 152 mm by 532 mm) for  concrete  in  which  the  maximum  size  of  the coarse aggregate is 2 in. (50 mm). When the max- imum size of the coarse aggregate exceeds 2 in. (50 mm), the smaller cross-sectional dimension is to be increased to at least three times the nominal maximum size of the coarse aggregate. All beam specimens prepared in the field are to be at least 6 in. wide and 6 in. deep unless required other- wise  by  project  specifications. STANDARDS FOR BEAM MOLDS.—  The beam molds are to be smooth on all interior sur- faces  and  free  from  warpage.  The  molds  are  to produce  specimens  that  do  not  exceed  the  required cross-sectional dimensions by 1/8 in. The length of the specimens is not to be more than 1/16 in. shorter  than  the  specified  length,  but  it  may exceed that length. RODDING.— Place the concrete in the mold in  the  required  number  of  layers.  (See  table  15-5.) Rod  the  bottom  layer  throughout,  distributing  the strokes  uniformly  over  the  cross  section  of  the mold. When rodding the upper layers, allow the rod  to  penetrate  the  previous  layer  1/2  in., providing the previous layer is 4 in. or less and 1 in. if the previous layer is greater than 4 in. The number of strokes’ per layer is one for each 2 in.2 (13 cm2) of the top surface area of the specimen. After each layer is rodded, spade the concrete with a  trowel  along  the  sides  of  the  mold  to  help  in the  removal  of  surface  voids.  Strike  off  the  top surface with a straightedge, and finish it with a wooden   float. CURING.—   YOU  should  cure  the  beam specimens  in  the  same  manner  as  the  cylinder specimens  with  the  following  exceptions:  (1)  ex- tend the initial curing period to 48 hr ± 4 hr and (2) do not allow the surface of the beam specimen to become dry between the time of removal from curing  and  the  completion  of  testing. When  transporting  specimens  from  the  field to  the  laboratory,  be  sure  they  are  sufficiently cushioned   to   protect   them   from   damage   by jarring.   Additional   measures   are   required   to prevent  damage  by  freezing  temperatures  and moisture loss. You can prevent moisture loss by covering the specimens with plastic or surround- ing  them  by  wet  sand  or  wet  sawdust. 15-39







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