Figure 13-5.—Sample data sheet, calibration of sand-cone density apparatus.will also need a baking pan, moisture content canisters,a paintbrush with moderately long bristles, and somemodeling clay.CALIBRATION.— The sand-displacement methodincludes three calibration procedures that must becompleted before you conduct the test.The first of the calibration procedures is theapparatus calibrationthat determines the volume ofthe jar and connecting cone (up through the cone valve).To perform the calibration, you first weigh theassembled apparatus (jar and cone) when it is empty,clean, and dry. Record this weight on a data sheet similarto figure 13-5. Then you weigh the apparatus when thejar and the smaller end of the cone is filled with water(making sure that no air is entrapped in the water).Record this weight on the data sheet and then empty thewater from the apparatus. After repeating these steps atleast three times, you can then determine the averageweight of the water and compute the volume of theapparatus, using the formulas shown in figure 13-5.The second calibration that you must make beforeperforming the sand-cone test is sand calibration.The sand that you use in the sand-cone test must beclean, dry, and free-flowing with a constant moisturecontent while the test is performed. Uniformly gradedand well-rounded sand passing the No. 20 sieve andretained on the No. 40 sieve is most suitable for the test.Almost no material finer than the No. 200 sieve shouldbe in the sand. This sand is usually purchased in bulkquantities that can be used for many sand-cone testsperformed over extended lengths of time. The densityof the sand may be determined soon after the sand isreceived; however, since the bulk density of the sand isaffected by changes in temperature and humidity, youmust recalibrate the sand before each test.To calibrate (or recalibrate) the sand, you first weighthe assembled apparatus when it is empty, clean, and dry.This weight is recorded on line 2 of DD Form 1215 (fig.13-6A). Next, the apparatus is filled with air-dried sandby pouring the sand into the apparatus through the largeend of the cone. When the jar and lower end of the coneis filled and all excess sand is removed, weigh thesand-filled apparatus. Record that weight on line 1. Thenby subtracting these weights, you can determine theweight of the sand (in grams). Finally, to determine thecalibrated density of the sand, you convert the weight ofthe sand to pounds and divide by the volume of theapparatus.13-6
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