UFC 3-260-02
30 June 2001
(a) The existing rigid pavement is plain concrete with a structural condition C of 0.35;
however, there is no significant faulting of the slabs and a leveling course is not needed. The
required thickness of plain concrete overlay is determined using the partially bonded overlay
equation (Equation 17-2). The required thickness hd of plain concrete pavement for the overlay
design flexural strength of 5.17 MPa (750 psi) and the k value of 54 MN/m3 (200 pci) for the
foundation under the existing pavement determined from Figure 12-8 (heavy-load design curve)
type B traffic area is 521 millimeters (20.5 inches). The design thickness he of plain concrete
pavement for the flexural strength of 4.48 MPa (650 psi) of the existing pavement and the k value
of 54 MN/m3 (200 pci) from Figure 12-8 is 574 millimeters (22.6 inches). Since the existing
pavement is plain concrete, the equivalent thickness hE is equal to the 250-millimeter (10-inch)
thickness of the existing slab. Substituting these values in Equation 17-2,
&
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This is the thickness of the plain concrete overlay required to strengthen the existing plain concrete
pavement for the design loading condition. The thickness of reinforced concrete overlay is then
dependent upon the percent of reinforcing steel S that will be used. Let it be assumed that
because of grade problems, the overlay thickness must be limited to 380 millimeters (15 inches).
Then, the value of S required, determined from Figure 13-1 using the plain concrete overlay
thickness of 478 millimeters (19.0 inches) and the reinforced concrete overlay thickness of
380 millimeters (15 inches), is 0.25 percent. It is also noted from Figure 13-1 that a maximum
joint spacing of 30 meters (100 feet) may be used with a reinforcing steel having a yield strength
ys of 413 MPa (60,000 psi).
(b) The existing pavement in the example above consists of 250 millimeters
(10 inches) of reinforced concrete with 0.10 percent of reinforcing steel and all other properties
and design requirements remain the same. The thickness of plain concrete pavement hE equivalent
to the 250 millimeters (10 inches) of existing reinforced concrete pavement, determined from
Figure 13-1 using the existing thickness of 250 millimeters (10 inches) and S = 0.10, is
287 millimeters (11.3 inches). Substituting these values in the partially bonded overlay equation
yields a required overlay thickness ho of plain concrete equal to:
&
17-9
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