UFC 3-260-03
15 Apr 01
3.1416(9.5)2 (2)
' 142 square millimeters, using SI units
As '
4
(3.1416) (0.375)2 (2)
' 0.221 square inches using IP units
As '
4
Ap ' 305 305 ' 93,025 square millimeters, using SI units
Ap ' 12 12 ' 144 square inches, using IP units
Since hr = 305 millimeters (12 inches) and S = 0.153 percent, figure 6-55 shows the corresponding hE
value to be 366 millimeters (14.4 inches). This hE value is then used to determine the evaluation in the
same manner as a plain concrete pavement.
7.
RIGID OVERLAY ON RIGID PAVEMENT.
a. Data Required. The data required for the evaluation of a rigid overlay on rigid pavement do not
differ greatly from those required for plain concrete pavements. The data needed for use with the eval-
uation curves are presented in chapter 3. A study of the overlay design, construction records, and pre-
vious condition surveys must be made to determine the condition of the base pavement prior to the over-
lay. If the overlay pavement contains only a minimum of structural defects, then it can be assumed that
very little "breakup" of the base pavement has occurred since it was overlaid, and the condition of the
base pavement can be rated the same as it was immediately prior to the overlay. Methods for conducting
the necessary tests are outlined or referenced in appendix B.
b. Method of Evaluation. The first step in the evaluation of a rigid overlay on a rigid pavement is the
determination of the equivalent thickness of the combined section of the rigid overlay and the rigid base
pavement. The equivalent thickness, which is defined as a single thickness of plain concrete pavement
having the same load-carrying capacity as the combined thickness of the rigid overlay and the rigid base
pavement, can be determined as follows:
(1) If the overlay slab was cast directly on the base slab and no effort was made to break the
bond between the overlay and the base pavement by means of a tack coat, sand, paper, bituminous
concrete, or other materials placed between the overlay and the base pavement, then the equivalent
thickness hE of the combined overlay section can be computed from the following equation for partial
bond between the overlay and the base pavement:
1.4
(ho )1.4 % C (hb)1.4
hE '
(eq 6-3)
where
6-8
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