UFC 3-260-03
15 Apr 01
more in thickness. In this case, the rigid base pavement and the nonrigid overlay pavement are con-
sidered to be base-course materials. When the plate-bearing test is performed on the surface of a flexible
pavement or nonrigid-type overlay, both the test and k values are subject to certain limitations as
discussed in the paragraph titled Rigid Overlays of Flexible Pavements in chapter 6.
(3) Percent Steel. For reinforced concrete pavements, the diameter and spacing of the steel in
both the longitudinal and transverse directions should be measured.
(4) Field In-place CBR Tests. To evaluate a nonrigid overlay on rigid pavement, field in-place
CBR tests may be required on the foundation materials in addition to plate-bearing tests. When the k
value of the foundation material is greater than 54 MN/cubic meter (200 pci) or the concrete flexural
strength is less than 2.758 MPa (400 psi), a higher load-carrying capacity may be obtained for the nonrigid
overlay or rigid pavement by using the flexible pavement evaluation procedure and assuming the rigid
pavement to be a high-quality base-course material. When either of these conditions prevail, in-place
CBR tests should be conducted on the foundation materials in addition to the plate-bearing tests. The
in-place CBR tests must be conducted on both the base-course materials (if any) and on the subgrade in
the same manner as in tests for the evaluation of flexible pavements.
(5) Penetrometer Tests. Penetrometer tests can be used to determine the load-bearing capac-
ity of subsurface pavement layers. There are two basic types of penetrometers that can be used to
evaluate pavements: the Electric Cone Penetrometer (ECP) and the Dynamic Cone Penetrometer (DCP).
The ECP is mounted in a C-130 transportable vehicle and measures the shear strengths of the various
subsurface material layers. The ECP uses a standard 35.8-millimeter (1.41-inch)-diameter cone with a
60-degree conical tip. The cone point is hydraulicly pushed through the pavement structure typically to a
depth of 1.52 meters (5 feet) at a rate of 20.3 millimeters (0.8 inches)/second. The ECP can provide
valuable information pertaining to the pavement structure including bearing strength (correlated to CBR),
layer thicknesses, and material classification. The DCP is a hand-held portable penetrometer device
designed to penetrate soils to depth of 0.99 meters (39 inches). The 20.3-millimeter (0.79-inch)-diameter
60-degree cone is driven into the ground by raising and dropping a 7.97-kilogram (17.6-lb) hammer. Data
is collected in terms of penetration per hammer blow, termed the DCP index value (mm/blow). The index
can then be correlated to CBR using derived relationships. For testing rigid pavements, a 50.8-millimeter
(2-inch) (ECP) or 25.4-millimeter (1-inch) (DCP)-diameter hole is drilled through the portland cement
concrete (PCC) until the top of the base subgrade is encountered. The test device is then lowered to this
point to begin the test sequence. Detailed test procedures and correlations for using the ECP and DCP
are provided in Appendix B. The ECP is typically used for tests requiring greater penetration depths. The
DCP is adequate for most pavement structures and is considered easier to deploy and implement.
(6) Field Density Tests. Density tests must be made on the base-course and subgrade mate-
rials. If the base course or subgrade is composed of granular materials, the most satisfactory methods
of obtaining the density are by the sand-displacement or balloon methods, which are described in
ASTM D 1556 and ASTM D 2167, respectively. If the subgrade is composed of a fine-grained cohesive
material, the density can be best obtained either by drive-sampling (ASTM D 2937) or balloon methods
(ASTM D 2167) or by the undisturbed sampling that may be required in connection with the plate-bearing
test. The nuclear density meter may also be used to determine densities, but special care must be taken
because of the influence of the sides of the test pits on test results. All field density tests should be con-
ducted adjacent to the area that was loaded during the plate-bearing test. When the overlay portion of a
nonrigid overlay on rigid pavement is composed of a bituminous concrete and base course, density tests
should be made on the base-course portion of the overlay.
d. In-place Tests for Flexible Pavements.
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