GENERAL PROCEDURES ANDGUIDELINESThe objective of hot-mix design is to determine themost economical blend of components that will producea final product that meets specified requirements. Thefollowing is a list of general procedures:1. Prepare a sieve analysis of each of theaggregates available.2. Determine the aggregate blend that will achievethe specified gradation(Paving and SurfacingOperations, TM 5-337). Plot the selected blendproportions on a graph with the allowable limits to seethat it conforms.3. Determine the specific gravity of thecomponents.4. Using selected percentages of bitumen (TM5-337), make trial mixes, and compute the design testproperties of the mix.5. Plot the test properties on individual graphsusing the selected bitumen percentages. Draw smoothcurves through the plotted points.6. Select the optimum bitumen content (AC) foreach test property from the curves of the Marshall testresults. For a discussion of the Marshall stability test,you can refer to chapter 13 of this TRAMAN and toNAVFAC MO-330.7. Average the bitumen content values (from Step6) and, from the graphs, read the test property valuecorresponding to this average.8. Check these read values with the satisfactorinessof mix criteria.The selection of the mix ratios of materials istentative. The bitumen should be the same as the one tobe used in construction. The aggregates and fillers mustmeet definite requirements. In general, several blendsshould be considered for laboratory mix-design tests.Gradation specifications are based on limitsestablished by the U.S. Army Corps of Engineers assatisfactory. Within these limits, the following variablesare considerations that will affect the final mix design:1. Use of mix (surface course, binder course, orroad 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 orbased on thickness of the pavement course)Once the gradation specifications have beenselected, you should check the available materials todetermine how to proportion the blend to meet thesespecifications. You should study sieve analyses of theavailable aggregates and compute a series of trialblends. You may have to make adjustment of the blendafter testing the design and prepared mix. Theconsiderations for establishing and adjusting the blendare explained in TM 5-337.The determination of optimum bitumen content isbased on a definite design and testing procedure knownas the Marshall method. This method is explained inchapter 13 of this TRAMAN and in NAVFAC MO-330.The final step is the preparation of a job-mixformula to be furnished to the construction unit.It is recognized that at times it will be necessary toshorten the design procedure as much as possible toexpedite military construction. For additionalinformation, refer to TM 5-337.EXAMPLE OF MARSHALL METHOD OFHOT-MIX DESIGNA typical mix design is illustrated by thecalculations and graphs shown on figures 17-5 through17-10.Aggregate GradingAn aggregate grading chart is shown in figure 17-5(DD Form 1207). This chart shows the gradation curvesof the three aggregates that are available for the mix.The sieve analyses are run in the manner as describedin the EA3 TRAMAN. Calculations may be made anddata recorded on standard sieve analysis data sheetsbefore the curves are drawn. A gradation curve is notshown for the mineral filler to be used.Aggregate BlendingThe front and back sides of a data and computationsheet for aggregate blending is shown in figures 17-6Aand 17-6B (DD Form 1217). The gradation of theavailable aggregates should be recorded on theupperpart (fig. 17-6A) of the form. The lower part (fig.17-6A) may be used for the computation of the trialblend. Several attempts may be required before a blendmeeting specifications is obtained. The cold feeds(quantities per batch) of aggregate to the asphalt plant17-11