TM 5-822-5/AFM 88-7, Chap. 1
base pavement with 4 inches or more of either all-
from figure 13-2. The minimum thickness of
bituminous or bituminous with base course overlay,
reinforced concrete overlay will be 4 inches.
the required thickness of overlay should be de-
(2) Jointing. Whenever possible, the
termined by paragraph 14-6a. The same limitations
longitudinal construction joints in the overlay
for maximum k value and temperature of pavement
should match the longitudinal joints in the existing
at the time of test should apply.
pavement. All longitudinal joints will be doweled
with dowel size and spacing designated in chapter
14-7. Flexible Overlay of Flexible Pavement.
15 using the thickness of reinforced concrete
overlay. It is not necessary for transverse joints in
Overlays are used for strengthening or rehabilitation
the overlay to match joints in the existing pavement;
of an existing pavement. Strengthening is required
however, when practical, the joints should be
when heavier loads are introduced or when a
matched. The maximum spacing of transverse con-
pavement is no longer capable of supporting the
traction joints will be determined in accordance with
loads for which it was designed. Rehabilitation may
equation 16-1, but it will not exceed 75 feet
include sealing or resealing of cracks, patching,
regardless of the thickness of the pavement or the
limited reconstruction prior to an overlay, res-
percent steel used. Joint sealing for reinforced con-
toration of the surface profile, improvement of skid
crete pavements will conform to the requirements
resistance by a friction course, or improvement of
for plain concrete pavements.
the surface quality. When it has been determined
that strengthening is required, the design of an
14-6. Rigid Overlay of Existing Flexible or
overlay will be accomplished by initially designing
Composite Pavements.
a new pavement and comparing its thickness with
the thickness of the existing pavement. The
a. Flexible pavements. A rigid overlay of an ex-
difference between these two pavements is the
isting flexible pavement should be designed in the
thickness of overlay required to satisfy design
same manner as a rigid pavement on grade. A
requirements. Overlays may be all-bituminous
modulus of subgrade reaction k should be deter-
concrete or AC and base course. The flexible
mined by a plate-bearing test made on the surface of
pavement after being overlaid shall meet all
the existing flexible pavement. If not practicable to
compaction requirements of a new pavement.
determine k from a plate-bearing test, an
Where the existing construction is complex, con-
approximate value may be determined using figure
sisting of several layers, and especially where there
9-1. Figure 9-1 yields an effective k value at the
are semirigid layers, such as soil cement, cement-
surface of the flexible pavement as a function of the
stabilized soils, or badly cracked portland cement
subgrade k and thickness of base and sub- base
concrete, careful exercise of judgment will be
above the subgrade. When using figure 9-1, the
necessary to evaluate the existing materials.
bituminous concrete is considered to be unbound
Guidance for evaluating existing construction is
base course material. Using this k value and the
given in TM 5-826-2/AFM 88-24, Chap 2.
concrete flexural strength, the required thickness of
plain concrete overlay is determined from figure 12-
14-8. Flexible Overlay of Rigid Base Pavement.
1 or 12-2. However, the following limitations
should apply:
a. Design procedure. The design procedure pre-
(1) In no case should a k value greater than
sented determines the thickness of flexible overlay
500 pci be used.
necessary to increase the load-carrying capacity of
(2) The plate-bearing test to determine the k
existing rigid pavement. This method is limited to
value should be performed on the flexible pavement
the design of the two types of flexible overlay, the
at a time when the temperature of the bituminous
all-bituminous and the bituminous with base course.
concrete is of the same order as the ambient
The selection of the type of flexible overlay to be
temperature of the hottest period of the year in the
used for a given condition is dependent only on the
locality of the proposed construction.
required thickness of the overlay. Normally, the
b. Composite base pavements. Two conditions
bituminous with base course overlay should be used
of composite pavement can be encountered when
when the required thickness of overlay is sufficient
to incorporate a minimum 4-inch compacted layer
considering a rigid overlay. When the composite
of high-quality base-course material plus the
pavement is composed of a rigid base pavement
required thickness of bituminous concrete surface
with less than 4 inches of all-bituminous overlay,
courses. For lesser thicknesses of flexible overlay,
the required thickness of rigid overlay should be
the all-bituminous overlay should be used. The
determined using the nonbonded overlay equation.
method of design is referenced to the deficiency in
If the composite pavement is composed of a rigid
14-4
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