ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 390

9.30 The Marshall method of mix design has been widely used by many
highway agencies.
a. What are the steps of Marshall Mix Design?
b. What parameters are calculated?
c. Show the typical graphs that are plotted after tests are completed.
d. What is the purpose of plotting these graphs?
9.31 An asphalt concrete mixture is to be designed according to the
Marshall procedure. An AC-20 asphalt cement with a specific
gravity of 1.00 is to be used. A dense aggregate blend is to be used,
with a maximum size of 19 mm and bulk specific gravity of 2.696.
The theoretical maximum specific gravity of the mix is 2.470. Trial
mixes were made, with the average results shown in Table P9.31.
Using a spreadsheet program, plot the appropriate graphs necessary
for the Marshall procedure, and select the optimum asphalt content
using the Asphalt Institute design criteria for medium traffic. As-
sume a design air void content of 4% when using Table 9.14.

Table P9.31

Asphalt Content, Bulk Specific

% by Weight Gravity Stability, N Flow, 0.25 mm

4.0 2.303 7076 9

4.5 2.386 8411 10

5.0 2.412 7565 12

5.5 2.419 5963 15

6.0 2.421 4183 22

9.32 An asphalt concrete mixture is to be designed according to the Mar-
shall procedure. An AC-30 asphalt cement with a specific gravity
of 1.00 is to be used. A dense aggregate blend is to be used,
with a maximum aggregate size of 3/4 in. and a bulk specific gravity
of 2.786. The theoretical maximum specific gravity of the mix
at asphalt content of 5.0%, is 2.490. Trial mixes were made
with average results as shown in Table P9.32. Using a spreadsheet
program, plot the appropriate six graphs necessary for the Marshall
procedure and select the optimum asphalt content, using the As-
phalt Institute design criteria for medium traffic (see Table 9.13). As-
sume a design air void content of 4% when using Table 9.14.

1 G b 2

1 G sb 2

1 G mm 2 ,

Table P9.32

Asphalt Content ( P b ) Bulk Specific Stability, lb Flow, 0.01 in.

(% by Weight) Gravity ( G mb )

3.50 2.294 1600 8

4.00 2.396 1980 9

4.50 2.421 2130 11

5.00 2.416 1600 14

5.50 2.401 1280 20