TM 5-822-13/AFJMAN 32-1018
CHAPTER 8
OVERLAY PAVEMENTS
8-1. General.
Normally, overlays of existing pavements are used to increase the load-carrying capacity of an existing pave-
ment, or to correct a defective surface condition on the existing pavement. Of these reasons, the first requires a
structural design procedure for determining the thickness of overlay, whereas the second requires only a thick-
ness of overlay sufficient to correct the surface condition, and no increase in load-carrying capacity is considered.
The design method for overlays included in this chapter determines the thickness required to increase load-
carrying capacity. These methods have been developed from a series of full-scale accelerated traffic tests on
various types of overlays and is therefore empirical. These methods determine the required thickness of overlay
that, when placed on the existing pavement, will be equivalent in performance to the required design thickness
of a new plain concrete pavement placed on subgrade.
8-2. Definitions for Overlay Pavement Design.
The following terms and symbols apply to the design of overlay pavements and are defined for the purpose of
clarity.
a. Rigid base pavement. An existing rigid pavement on which an overlay is to be placed.
b. Flexible base pavement. Existing pavement to be overlaid is composed of bituminous concrete, base, and
subbase courses.
c. Composite pavement. Existing pavement to be overlaid with rigid pavement is composed of an all-bituminous
or flexible overlay on a rigid base pavement.
d. Overlay pavement. A pavement constructed on an existing base pavement to increase load-carrying capacity.
e. Rigid overlay. A rigid pavement used to strengthen an existing flexible or rigid pavement.
f. Flexible overlay. A flexible pavement (either all-bituminous or bituminous with base course> used to
strengthen an existing rigid or flexible pavement.
8-3. Preparation of Existing Pavement.
Existing pavement is prepared according to procedures in TM 5-822-5/AFM 88-7, Chap. 3.
8-4. Rigid Overlay of Existing Rigid Pavement.
The concrete overlay thickness for roads and streets can be determined using overlay equations 8-1 to 8-3. The
conditions for the use of the equations are described in TM 5-822-5/AFM 88-7, Chap. 3.
Fully bonded
ho = hd - hE
(eq 8-1)
Partially bonded
(eq 8-2)
Nonbonded
where
ho = required thickness of concrete overlay, inches
hE = thickness of existing concrete slab, or equivalent thickness of plain concrete pavement having the
same load-carrying capacity as the existing pavement, inches
8-1
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