4. After soaking the sample, place it in the bucket, which is filled with water. Then turn the bucket and aggregate sharply back and forth to help remove any air. 5.  Suspend  the  bucket  from  the  brass  hanger  and bring the water level up to the overflow pipe. 6. Determine the submerged weight using weights placed  in  the  scoop  on  the  right-hand  pan.  Record  the weights in the appropriate spaces on the data sheet. The calculations  required  for  the  determination  of  the apparent  specific  gravity  of  coarse  aggregate  are  shown on the data sheet and are self-explanatory. MIX DESIGN TESTS Mixture design tests for bituminous pavement are carried out on samples mixed and compacted in the laboratory to determine the optimum bitumen content, the  optimum  aggregate  content,  and  gradation  required to produce a pavement that will meet given quality specifications.  Mixes  with  various  bitumen  and aggregate  contents  and  gradations  are  prepared, compacted to specified density, and tested. From the test results,  design  engineers  determine  optimum  values. Mix design test procedures vary considerably. this course can give only a general description of typical procedures.  Mixture  design  is  more  fully  discussed  in NAVFAC MO-330 and at the EA1 level in Part 2 of this TRAMAN. Selection of Sample Bitumen Contents Bitumen content for laboratory test mixes must be estimated to get the tests started. Tests are made with a minimum of five contents: two above, two below, and one at a content estimated to be about right. Bitumen content is expressed in terms of percentage of bitumen by weight to the total weight of the mix. Percentages commonly run from 3 to 7, depending upon the type of binder  used  and  the  specification  requirements. Preparation of Aggregate A  quantity  of  aggregate  of  the  selected  blend sufficient to make the required number of test samples is dried at 230°F. The dry aggregate is separated into several  size  ranges  by  sieving,  and  a  sieve  analysis  is then made of each range. From   this   procedure,   design   engineers   can determine  trial  percentages  for  test  blends.  Test  blends are then made with these trial percentages. Again, a sieve analysis is made, this time to determine a blending gradation, such as shown in figure 13-36. The  explanation  of  figure  13-36  is  as  follows.  The aggregate here was first sifted into four categories: coarse, fine, fine river bar sand (FRBS), and limestone dust (LSD)-the last being a commonly used mineral filler. All of the coarse aggregate consisted of material that would not pass the No. 8 sieve; 89.5 percent of fine aggregate consisted of material that would not pass the No. 80 sieve; and 90 percent of the FRBS consisted of material that would not pass the No. 200 sieve. These three sieves, then, were the ones used to make the original  broad  separation.  Limestone  dust  was  added  to the extent of 2 percent. After  the  sample  was  broadly  divided,  a  sieve analysis was made of each broad division category, as shown.  This  analysis  was  studied  by  experts,  who estimated,  among  other  things,  the  probable  void percentages that would exist in pavements made with the   aggregate   used   in   various   combinations. Percentages that would minimize void percentages were estimated. For trial blend No. 1, these percentages are listed under “percent used.” The percentages are 27 coarse, 63 fine,  8  FRD,  and  2  LSD.  A  blend  containing  these percentages was made, and again the material in each category was sieve-analyzed, as shown. From these individual analyses, the blend analysis (that is, the sieve analysis for the mixed blend) was determined by adding together  the  percentages  in  each  column. Thus an aggregate gradation for the blend was obtained.  If  tests  showed  that  this  particular  gradation produced  a  mix  that  met  the  specifications  for  the pavement, this gradation would be specified for the aggregate used in the highway. Specimen Mixing and Compacting for Testing To  prepare  an  aggregate  blend  for  testing, thoroughly   mix   and   heat   enough   blend   for   two specimens  (about  3,000  grams)  to  the  desired  mixing temperature. Trough the aggregate blend; then heat the test amount of bitumen to mixing temperature and pour it  into  the  trough.  Mix  the  aggregate  and  bitumen together thoroughly with a mechanical mixer if one is available. Then place the mix in a compaction mold and compact it with a tamper. Give the number of blows required to produce the density that will be attained under  the  traffic  for  which  the  pavement  is  being designed.  NAVFAC  DM-5.4,   Civil   Engineering, specifies 50 blows for secondary roads and 75 blows for 13-48