UFC 3-260-03
15 Apr 01
requirements. The 50 millimeters (2 inches) is converted to subbase by multiplying the equivalency
factor of 2.0 times the excessive thickness of 50 millimeters (2.0 inches) and then added to the subbase
thickness. Therefore, the thicknesses to use for evaluation are 76 millimeters (3.0 inches) for asphaltic
concrete, 152 millimeters (6.0 inches) for base, and 330 millimeters (13 inches) for subbase. All equiva-
lency factors used by the Army, Navy, Marine Corps, and Air Force are shown in paragraph titled
"Evaluations for Stabilized Layers."
6.
QUALITY OF BITUMINOUS PAVEMENT.
a. Ability to Support Traffic. The ability of a mix to support traffic of a given load depends on the
type and gradation of the aggregate, the amount of bitumen in the mix, and the compaction of the mix.
Mixes with rounded aggregates are less stable than those with crushed-face aggregates; mixes with
aggregates of irregular gradings are less stable than those with well-graded aggregates. A deficiency in
bitumen produces a pavement that may ravel, but too much bitumen produces a pavement that may rut
and shove. The condition of bituminous pavement, either surface or binder course, at the time of sam-
pling is evaluated by comparing the test data from the core samples with the design criteria given in
TI 825-01/AFM 32-1124 (I)/NAVFAC DM 21.10. Future behavior of the pavement under additional traffic
is predicted by comparing the test data from the laboratory recompacted specimens with the design
criteria. The following example shows the prediction of behavior from tests on cores and on laboratory
recompacted surface course specimens. Assume that the thickness and aggregate gradation are satis-
factory. The other test data are as follows:
Recompacted Samples
Field
Cores
50-blows
75-blows
Unit weight (density), kilograms/cubic meter (pounds
2,308
2,396
2,415
per cubic foot)
(144.2)
(149.7)
(150.9)
Unit weight, percent of 50-blow laboratory compaction
96
---
---
Unit weight, percent of 75-blow laboratory compaction
95
---
---
Stability, Newtons (pounds)
8,375
13,028
14,571
(1,883)
(2,929)
(3,276)
Flow, in millimeters (1/100 inch)
3.81
4.06
4.06
(15)
(16)
(16)
Voids total mix, percent
8.5
4.5
3.7
Voids filled, percent
57.2
72.1
75.8
According to the test data above, the current density (field cores) is relatively low, the flow is approach-
ing the upper limit, and the void relations are outside the acceptable ranges, but the stability is
satisfactory. The data from the recompacted specimens indicate that additional compaction from traffic
will increase the stability but also cause some rutting of the pavement. Thus, the pavement will probably
be able to withstand heavier loads than it has sustained in the past and will be satisfactory under traffic
having up to 1.38 MPa (200 psi) tire pressure. It should be noted that at 75-blow laboratory compaction,
the voids total mix value is below the midpoint of the acceptable range and the flow is at the upper limit,
indicating a mix slightly rich of optimum. However, no danger from flushing would be expected.
b. Ability to Withstand Fuel Spillage.
5-4
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