UFC 3-260-02
30 June 2001
(2) Any bond between the lean concrete base and the concrete slab to be placed on top must
be prevented to retard reflective cracking. A bond breaking material such as a wax-based curing
compound should be placed on top of all lean concrete base courses.
f. Recycled Concrete Bases. Recycled portland cement concrete can serve as an aggregate for
use in a granular base course or in recycled concrete base. The concrete must be properly crushed and
sized to meet gradation requirements.
g. Geotextile Fabrics. Geotextile fabrics may be considered for reinforcement of the subgrade to
provide a working platform for base course construction and to separate the subgrade and base course
to maintain the original base course gradation. See NAVFAC DM 7.01 and NAVFAC DM 21.06 for
design criteria on geotextile fabrics. The use of geotextile fabric is encouraged to prevent loss of fines
from the surrounding soil through subsurface utility lines.
5. STRENGTH OF AGGREGATE BASE COURSES FOR RIGID PAVEMENTS. The modulus of soil
reaction k of the unbound base courses will be determined by field plate bearing tests performed on the
surface of the compacted base course or by tests on the subgrade and from Figure 8-1. If both methods
are used, the lower value obtained by the two methods will be used for the pavement design. A
sufficient number of field plate bearing tests must be performed on the top of a finished base course to
determine a realistic design K value. Consideration should be given to the variations in base-course
thickness, types of materials, and the variation in subgrade strengths. Figure 8-1 yields an effective k
value at the surface of the base course as a function of the subgrade k value and base-course thickness.
These relationships have been generated by field testing. If the design k value is selected from
Figure 8-1, it should be verified in the field. The maximum value for the modulus of soil reaction to be
used in design is 135 KPa/mm (500 pci).
6. STRENGTH OF AGGREGATE BASE COURSES FOR FLEXIBLE PAVEMENTS. Because of the
effects of processing samples for the laboratory CBR tests and because of the effects of the test mold,
the laboratory CBR test will not be used in determining CBR values of base courses. Instead, selected
CBR ratings will be assigned as shown in the following tabulation. These ratings have been based on
service behavior records and, where pertinent, on in-place tests made on materials that have been
subjected to traffic. It is imperative that the materials conform to the quality requirements given in the
guide specifications so that they will develop the needed strengths.
Aggregate Base Course
Design CBR
1001
Graded Crushed Aggregate
Aggregate2
80
Limerock
80
Shell Sand
80
Coral
80
Shell Rock
80
Note: See Chapter 6 for open-graded and rapid-draining material requirements
1
Limited to 80 CBR for Navy and Marine Corps.
2
Formerly mechanically stabilized aggregate.
8-5
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