UFC 3-260-03
15 Apr 01
(3) The size of the test pits for rigid pavements will, in part, depend on the thickness of the
pavement. Inasmuch as beams for flexural strength tests must be cut from the concrete specimen and
removed from the slab, the length of the specimen must be greater than three times the pavement thick-
ness, except when 152 by 152 millimeters (6- by 6-inch) beams are cut from the top and bottom of the
slab for a three-point beam test. Since plate-bearing tests on the foundation materials will require the use
of a 762-millimeter- (30-inch-) diameter plate, test pits should be 1.22 by 1.52 meters (4 by 5 feet) to allow
access to the foundation materials for testing and sampling. Tensile splitting tests are acceptable for
computing flexural strengths and will require 152-millimeter- (6-inch-) diameter core samples. An
equation for calculating flexural strength from tensile splitting strength is presented in appendix B.
(4) Test pits for flexible pavements (approximately 1.22 meters (4 feet) wide by 1.52 meters
(5 feet) long) or core holes (up to 200 millimeters (8 inches) in diameter) are dug through the pavement to
permit the performance of in-place tests and to obtain samples for laboratory tests. Tests conducted in a
core hole are referred to as small aperture testing. Core holes up to 200 millimeters (8 inches) in diame-
ter do not create an operational problem for most aircraft but a 1.22- by 1.52-meter (4- by 5-foot) test pit
does. The same data are required for evaluation whether they are obtained from a test pit or from a core
hole. A description of the general condition and a visual classification of materials from each test pit or
core hole should be recorded. The thickness of the pavement should be measured to the nearest
6 millimeters (1/4 inch) and the total thickness of base and pavement to the nearest 13 millimeters
(1/2 inch). Several measurements should be made around the sides of the test pit or core hole to obtain
representative thickness values. Each soil course should be described, giving color, in situ conditions,
texture, and visual classification. References for testing and sampling procedures are given in
appendix B.
c.
In-Place Tests for Rigid Pavements.
(1) Thickness Measurements. The thickness of all layers above the subgrade in all types of
rigid pavements should be measured including base course, concrete slab, and all overlays. Thickness of
the layers should be measured to the nearest 6 millimeters (1/4 inch).
(2)
Modulus of Soil Reaction.
(a) All Rigid Pavements. The modulus of soil reaction on the subgrade or base course
should be determined by the plate-bearing test as discussed in appendix B. In those instances when the
plate-bearing test cannot be conducted, an approximate value of k can be determined by taking Cali-
fornia Bearing Ratio (CBR) readings on the subgrade in 152-millimeter (6-inch) core holes (small aperture
procedure) and determining the k value from the curve in figure 3-5. The plate-bearing test should
normally be conducted on the surface of the material immediately beneath the pavement, that is, on the
base course or on the subgrade if there is no base course. The relationship between the thickness of
base or subbase and the effective k of the base or subbase may be determined using figure 3-6. With
subgrades or base courses that have been modified, the k value will be determined from figure 3-5 as
previously noted. Subgrade or base-course materials that have been stabilized to the extent that they
qualify as stabilized layers as outlined in TM 5-822-14/AFJMAN 32-1019 require tests other than plate-
bearing to determine their effect on the supporting value of the pavement structure. Plate-bearing tests
are also required in other areas as indicated in the following paragraphs.
(b) Rigid Overlay on a Flexible Pavement. When an evaluation is being made of a rigid
overlay on a flexible pavement, the plate-bearing test will be performed on the surface of the flexible pave-
ment, since the flexible pavement is considered to be a base course.
(c) Composite Pavements. When a composite pavement is being evaluated, the plate-
bearing test will be performed on the surface of the nonrigid portion (bituminous concrete or flexible
overlay) of the pavement provided the nonrigid portion of the pavement is 102 millimeters (4 inches) or
3-5
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