GENERAL PROCEDURES AND GUIDELINES The objective of hot-mix design is to determine the most economical blend of components that will produce a final product that meets specified requirements. The following is a list of general procedures: 1.  Prepare  a  sieve  analysis  of  each  of  the aggregates  available. 2. Determine the aggregate blend that will achieve the  specified  gradation  (Paving   and   Surfacing Operations,   TM   5-337).   Plot   the   selected   blend proportions on a graph with the allowable limits to see that it conforms. 3.  Determine  the  specific  gravity  of  the components. 4.  Using  selected  percentages  of  bitumen  (TM 5-337), make trial mixes, and compute the design test properties of the mix. 5. Plot the test properties on individual graphs using  the  selected  bitumen  percentages.  Draw  smooth curves  through  the  plotted  points. 6. Select the optimum bitumen content (AC) for each test property from the curves of the Marshall test results. For a discussion of the Marshall stability test, you can refer to chapter 13 of this TRAMAN and to NAVFAC   MO-330. 7. Average the bitumen content values (from Step 6) and, from the graphs, read the test property value corresponding  to  this  average. 8. Check these read values with the satisfactoriness of mix criteria. The  selection  of  the  mix  ratios  of  materials  is tentative. The bitumen should be the same as the one to be used in construction. The aggregates and fillers must meet definite requirements. In general, several blends should be considered for laboratory mix-design tests. Gradation   specifications   are   based   on   limits   established by the U.S. Army Corps of Engineers as satisfactory.  Within  these  limits,  the  following  variables are considerations that will affect the final mix design: 1. Use of mix (surface course, binder course, or road mix) 2. Binder (asphalt, cement, or tar) 3.  Loading  (low  tire  pressure—100  psi  and  under, or high tire pressure—over 100 psi) 4.  Maximum  size  of  aggregate  (in  stockpile  or based on thickness of the pavement course) Once   the   gradation   specifications   have   been selected, you should check the available materials to determine how to proportion the blend to meet these specifications.  You  should  study  sieve  analyses  of  the available  aggregates  and  compute  a  series  of  trial blends. You may have to make adjustment of the blend after   testing   the   design   and   prepared   mix.   The considerations for establishing and adjusting the blend are explained in TM 5-337. The determination of optimum bitumen content is based on a definite design and testing procedure known as the Marshall method. This method is explained in chapter 13 of this TRAMAN and in NAVFAC MO-330. The  final  step  is  the  preparation  of  a  job-mix formula to be furnished to the construction unit. It is recognized that at times it will be necessary to shorten the design procedure as much as possible to expedite   military   construction.   For   additional information, refer to TM 5-337. EXAMPLE OF MARSHALL METHOD OF HOT-MIX  DESIGN A   typical   mix   design   is   illustrated   by   the calculations and graphs shown on figures 17-5 through 17-10. Aggregate Grading An aggregate grading chart is shown in figure 17-5 (DD Form 1207). This chart shows the gradation curves of the three aggregates that are available for the mix. The sieve analyses are run in the manner as described in the EA3 TRAMAN. Calculations may be made and data  recorded  on  standard  sieve  analysis  data  sheets before  the  curves  are  drawn.  A  gradation  curve  is  not shown for the mineral filler to be used. Aggregate  Blending The front and back sides of a data and computation sheet for aggregate blending is shown in figures 17-6A and  17-6B  (DD  Form  1217).  The  gradation  of  the available   aggregates   should   be   recorded   on   the upperpart (fig. 17-6A) of the form. The lower part (fig. 17-6A) may be used for the computation of the trial blend.  Several  attempts  may  be  required  before  a  blend meeting  specifications  is  obtained.  The  cold  feeds (quantities per batch) of aggregate to the asphalt plant 17-11