UFC 3-260-03
15 Apr 01
be in the form of chunks of about 254-millimeter (10-inch) maximum dimension so that the various layers
or course can be identified. If the pavement consists of more than one course, the courses should be
separated and treated individually. The courses may be separated by heating the pieces of pavement
and driving a hot knife between the layers or by other similar methods. After a course has been sepa-
rated, it should be broken into small pieces and heated to a temperature of 115E to 127EC (240E to
260EF). The material should be thoroughly mixed during heating. Heating should be accomplished as
rapidly as possible and should be performed in an oven or on a hotplate with constant stirring to ensure
uniform heating. The hot mixture should be compacted in accordance with the standard procedures for
the Marshall method. Compaction efforts of 50 and 75 blows on each side of the specimen should be
used for comparison with criteria for tire pressures of 0.7 MPa and 1.4 MPa (100 and 200 pounds per
square inch), respectively. Six or eight specimens should be compacted with each effort and tested in
accordance with standard procedures for the Marshall method. In analyzing the test data, it should be
recognized that reheating produces a hardening of the asphalt cement. This hardening causes some-
what higher stability values but has little effect on the other test values.
B-3. SOILS SAMPLING.
a. Disturbed Sampling. Two types of disturbed sampling will normally be required during an airfield
pavement evaluation.
(1) Samples of the foundation materials will be needed for developing soil profiles, and the
most suitable method of obtaining these samples is by auger borings. These borings can be made into
the foundation materials to the desired depth either in test pits or through small 102-millimeter or
152-millimeter- (4- or 6-inch-) diameter holes cored through the pavement. Samples of the foundation
materials should be taken for each 152-millimeter (6-inch) vertical increment to a depth of 610 millimeter
(2 feet) and for each 305-millimeter (12-inch) increment thereafter to the desired depth. Additional sam-
ples should be taken whenever there is a change in materials or moisture conditions. The samples
should be sealed in jars and clearly marked before transportation to the laboratory, where they will be
subjected to classification tests and moisture-content determinations.
(2) Samples of the foundation materials will also be required for compaction tests. Normally,
these will be bag samples obtained from test pits. Samples of each type of material encountered should
be obtained. The size of the bag samples required will depend on the type of material and the type of
test to be performed. Generally, if the material is fine-grained, a 45-kilogram (100-pound) sample will be
sufficient for the moisture-density determination; when the moisture-density-CBR relations are to be
developed, a 204-kilogram (450-pound) sample should be obtained. If the material is granular, the size
of the sample should be increased to 90 kilograms (200 pounds) for the moisture-density tests and
272 kilograms (600 pounds) for the moisture-density-CBR tests.
b. Undisturbed Sampling. If the subgrade is composed of a fine-grained cohesive material, undis-
turbed samples may be required for laboratory California Bearing Ratio (CBR) tests to evaluate a non-
rigid overlay on rigid pavement. When laboratory CBR tests are required, an additional undisturbed
sample will be needed. There is no prescribed method for obtaining undisturbed samples of the sub-
grade material. Any method that will provide enough material and maintain it in its existing condition is
satisfactory. The method most widely used for undisturbed sampling is to trim a sample by hand to fit
into a split cylinder of galvanized metal approximately 203 millimeters (8 inches) in diameter and at least
305 millimeters (12 inches) high. The sample should then be sealed at the sides and ends with paraffin
to prevent moisture loss.
B-4. PLATE-BEARING TESTS. When the plate-bearing test is used to determine the k value on the
surface of a pavement, such as required for the evaluation of a composite pavement or a rigid overlay
on flexible pavement, the load reaction must be placed far enough away from the plates so that the
B-2
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