TM 5-822-5/AFM 88-7, Chap. 1
thickness of the existing rigid base pavement and
overlay used for strengthening purposes will be 4
assumes that a controlled degree of cracking will
inches. No limitation is placed on the minimum
take place in the rigid base pavement during the
thickness of an all-bituminous overlay when used
design life of the pavement.
for maintenance or to improve pavement surface
b. Thickness determination. Regardless of the
smoothness. In certain instances, the flexible
type of nonrigid overlay, the required thickness to
overlay design equation will indicate thickness
will be determined by
requirements less (sometimes negative values) than
the minimum values. In such cases the minimum
thickness requirement will be used. When
where hd is the design thickness of plain concrete
strengthening existing rigid pavements that exhibit
pavement from figure 12-1 or 12-2 using the flex-
low flexural strength (less than 500 psi) or that are
ural strength R of the concrete in the existing rigid
constructed on high-strength foundation (k
pavement, the modulus of soil reaction k of the
exceeding 200 pci), it may be found that the flexible
existing pavement, and the appropriate design
pavement design procedure in this manual indicates
index. The factor he represents the thickness of plain
a lesser required overlay thickness than the overlay
concrete pavement equivalent in load-carrying
design formula. For these conditions, the overlay
ability to the thickness of existing rigid pavement. If
thickness will be determined by both methods, and
the existing rigid pavement is plain concrete, then
the lesser thickness will be used for design. For the
the equivalent thickness equals the existing
flexible pavement design procedure, the existing
thickness; however, if the existing rigid pavement is
rigid pavement will be considered an equivalent
reinforced concrete, the equivalent thickness must
thickness of high-quality crushed aggregate base
be determined from figure 13-2. F is a factor,
(CBR=100), and the total pavement thickness
determined from figure 14-1, that projects the
determined based upon the subgrade CBR. Any
cracking expected to occur in the base pavement
existing base or subbase layers will be considered as
during the design life of the overlay. C is a
corresponding layers in the flexible pavement. The
coefficient from paragraph 14-4 based upon the
thickness of required overlay will then be the
structural condition of the existing rigid pavement.
difference between the required flexible pavement
The computed thickness of overlay will be rounded
thickness and the combined thicknesses of existing
to the nearest whole or inch. To reduce reflective
rigid pavement and any base or subbase layers
cracking, the minimum thickness of all-bituminous
above the subgrade.
14-5
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