Civil Engineering Reference
In-Depth Information
10.0
16.0
8.0
15.0
6.0
14.0
4.0
13.0
2.0
0.0
12.0
3.5
4.0
4.5
5.0
5.5
3.5
4.0
4.5
5.0
5.5
Asphalt content, percent
Asphalt content, percent
100.0
153.0
2452
80.0
60.0
40.0
20.0
0.0
152.0
151.0
2432
2412
150.0
149.0
148.0
2392
2372
3.5
4.0
4.5
5.0
5.5
3.5
4.0
4.5
5.0
5.5
Asphalt content, percent
Asphalt content, percent
2800
12
11
10
9
8
7
6
5
12
12
11
10
9
8
7
6
5
2600
11
2400
10
2200
9
2000
1800
8
3.5
4.0
4.5
5.0
5.5
3.5
4.0
4.5
5.0
5.5
Asphalt content, percent
Asphalt content, percent
FIGURE 9.33
Graphs used for Marshall mix design analysis. (See Table 9.12)
(The Asphalt Institute 1995).
The design asphalt content is usually the most economical one that will
satisfactorily meet all of the established criteria. Different criteria are used
by different agencies. Table 9.13 and 9.14 depict the mix design criteria rec-
ommended by The Asphalt Institute. Figure 9.34 shows an example of the
narrow range of acceptable asphalt contents. The asphalt content selection
can be adjusted within this narrow range to achieve a mix that satisfies the
requirements of a specific project. Other agencies, such as the National As-
phalt Paving Association, use the asphalt cement content at 4% air voids as
the design value, and then check that the other factors meet the criteria. If
the Marshall stability, Marshall flow, VMA, or VFA fall outside the allow-
able range, the mix must be redesigned using an adjusted aggregate grada-
tion or new material sources.
The laboratory-developed mixture design forms the basis for the initial
job mix formula (JMF). The initial JMF should be adjusted to reflect the
slight differences between the laboratory-supplied aggregates and those
used in the field.
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