Lesson 5/Learning Event 2
that is 28 percent coarse, 50 percent fine, 19 percent FRB, and 3 percent LSD (mineral filler).
Total Mix Weight
The percentage of aggregates -28/58/19/3-that were determined by the trial and error method in
the example problem make up the total aggregate weight. Bituminous material (binder) must be
added to the aggregate to obtain the total mix weight. The binder material is listed as a
percentage of the total mix weight. Assume that the percent binder as determined by the design
procedure was 6 percent by weight of a total mix. The weight of the aggregate then becomes
100%-6 and/or 94% of the total mix weight.
It is necessary to adjust the percentages of the aggregate to a percentage by weight of the total
mix weight as follows:
The job mix formula is then 26.3 percent CA, 47.4 percent FA, 17.9 percent FRB, 2.8 percent
LSD, and 6 percent bituminous material.
It is now possible to advise the operator at the mixing plant of the percentages or actual weights
of each ingredient that is to be combined in the mix. This is the next step in mix design. It is
outlined in Learning Event 3.