TM 5-822-5/AFM 88-7, Chap. 1
CHAPTER 14
PAVEMENT OVERLAYS
repaired prior to the overlay. Such repair is
14-1. General.
especially needed in areas where excessive
Normally, overlays of existing pavements are used
pumping, bleeding of water at joints or cracks,
to increase the load-carrying capacity of an existing
excessive settlement in foundation, subgrade rut-
pavement or to correct a defective surface condition
ting, surface rutting, and slides have occurred. If
on the existing pavement. Of these reasons, the first
testing of the existing pavement indicates the pres-
requires a structural design procedure for
ence of voids beneath a rigid pavement, they should
determining the thickness of overlay; whereas the
be filled by grouting prior to the overlay. The
second requires only a thickness of overlay suffi-
properties of the existing pavement and foundation
cient to correct the surface condition, and no in-
such as the modulus of subgrade reaction, CBR,
crease in load-carrying capacity is considered. The
thickness, condition index, and flexural strength
design method for overlays included in this chap-
should be determined. The exact properties to be
ter determines the thickness required to increase
determined will depend upon the type of overlay to
load-carrying capacity. These methods have been
be used. The surface of the existing pavement
developed from a series of full-scale accelerated
should be conditioned for the various types of
traffic tests on various types of overlays and are,
overlays as follows.
therefore, empirical. These methods determine the
a. Rigid overlay. Overlay thickness criteria are
required thickness of overlay that, when placed on
presented for three conditions of bond between the
the existing pavement, will be equivalent in per-
rigid overlay and existing rigid pavement: fully
formance to the required design thickness of a new
bonded, partially bonded, and nonbonded. The fully
pavement placed on subgrade.
bonded condition is obtained when the concrete is
cast directly on concrete and special efforts are
14-2. Definitions and Symbols for Overlay
made to obtain bond. The partially bonded
Pavement Design.
condition is obtained when the concrete is cast
The following terms and symbols apply to the
directly on concrete with no special efforts to
design of overlay pavements.
achieve or destroy bond. The nonbonded condition
a. Rigid base pavement. An existing rigid pave-
is obtained when the bond is prevented by an in-
ment is one on which an overlay is to be placed.
tervening layer of material. When a fully bonded or
b. Flexibile base pavement. Existing pavement
partially bonded rigid overlay is to be used, the
to be overlaid is composed of bituminous concrete,
existing rigid pavement will be cleaned of all foreign
base, and subbase courses.
matter (such as oil and paint), spalled concrete,
c. Composite pavement. Existing pavement to be
extruded joint seal, bituminous patches, or anything
overlaid with rigid pavement is composed of an all-
else that would act as a bond-breaker be- tween the
bituminous or flexible overlay on a rigid base
overlay and existing rigid pavement. In addition, for
pavement.
the- fully bonded overlay, the surface of the existing
d. Overlay pavement A pavement constructed on
pavement must be prepared according to the
an existing base pavement to increase load-carrying
recommendation in TM 5-822-7. A sand-cement
capacity or correct a surface defect.
grout or an epoxy grout is applied to the cleaned
e. Rigid overlay. A rigid pavement used to
surface just prior to placement of the concrete
strengthen an existing flexible or rigid pavement.
overlay. When a nonbonded rigid overlay is being
f. Flexible overlay. A flexible pavement (either
used, the existing rigid pavement will be cleaned of
all-bituminous or bituminous with base course) used
all loose particles and covered with a leveling or
to strengthen an existing rigid or flexible pavement.
bond-breaking course of bituminous concrete, sand-
asphalt, heavy building paper, polyethylene, or other
14-3. Preparation of Existing Pavement.
similar stable material. The bond-breaking medium
Exploration and tests of the existing pavement
generally should not exceed a thickness of about 1
should be made to locate all areas of distress in the
inch except in the case of leveling courses where
existing pavement and to determine the cause of the
greater thicknesses may be necessary. When a rigid
distress. Areas showing extensive and progressive
overlay is being applied to an existing flexible
cracking, rutting, and foundation failures should be
pavement, the surface of the existing pavement will
14-1
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