UFC 3-260-03
15 Apr 01
The weighted average flexural strength is 4.13 MPa (600 psi), and the k value is 13.6 kPa/mm (50 pci).
Since the base pavement contains a few initial cracks, the C factor is 0.75. With these data, the evalu-
ation is made in the following manner.
(1)
Step 1. Calculate the equivalent thickness, hE ,using equation 6-3:
1.4
(152)1.4 % C (152)1.4 ' 225 millimeters, using SI units
hE '
1.4
(6)1.4 % C (6)1.4 ' 8.93 inches using English units
hE '
(2) Step 2. Enter figure 6-8 with the k = 13.6 kPa/mm (50 pci), R = 4.13 MPa (600 psi) and
equivalent thickness of 8.93 inches and determine the load factor of 57,600 kilograms (127 kips).
(3)
Step 3. Divide the load factor by 61,236 kilograms (135 kips) to obtain the design factor of
0.94.
(4) Step 4. Enter figure 6-44 with the design factor of 0.94 and the k = 13.6 kPa/mm (50 pci)
for type B traffic area and determine the allowable passes of 850.
8.
NONRIGID OVERLAY ON RIGID PAVEMENTS.
a. Data Required. The data required for the evaluation of a nonrigid overlay on rigid pavement are
presented in chapter 3. It is also necessary to determine the quality and strength of the nonrigid overlay
material.
(1) For bituminous concrete overlays which consist of bituminous concrete for full depth, the
data required will be the same as for the evaluation of the bituminous concrete portion of flexible
pavements.
(2) For flexible overlays consisting of a granular base and a bituminous surface, the data
required will be the same as for the evaluation of flexible pavements.
(3) The method of evaluation for nonrigid-type overlay pavements presented herein assumes
that the bituminous concrete meets the design requirements set forth in TI 825-01/AFM 32-1124
(I)/NAVFAC DM 21.10, and that the base-course material of the overlay, if any, has a CBR of 80 or
greater. Therefore, tests on the nonrigid overlay materials may be necessary to determine whether they
meet design requirements. These tests should be made in accordance with concepts and procedures set
forth in chapter 3. Often the quality of the overlay materials can be determined from a study of construc-
tion records. If it can be ascertained that the overlay materials met design requirements during construc-
tion and there has been no deterioration of the overlay under traffic, the overlay materials may be
assumed to be satisfactory, and no testing other than gradation of materials is required. When it is deter-
mined that the overlay materials (bituminous concrete or base-course materials) did not meet design
requirements, the narrative portion of the evaluation report should discuss the consequences, such as
rutting and raveling. Inadequacies of the nonrigid overlay can often be determined from surface condi-
tions. Rutting or surface cracking are sometimes signs of inadequate strengths of the bituminous con-
crete and base course and should be investigated. However, in the case of thin overlays, care must be
taken to determine whether surface cracking is the result of inadequate strength in the overlay or reflective
cracking from joints and structural defects in the rigid base pavement.
6-10
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