UFC 3-260-03

15 Apr 01

accomplished for 100,000 passes of the F-14 aircraft. The pavement consists of a 102-millimeter (4-inch)

bituminous overlay, a 152-millimeter (6-inch) plain concrete base pavement with a 4.5-MPa (650-psi)

flexural strength, and a subgrade with a modulus of subgrade reaction of 81 kPa/mm (300 pci) and a CBR

of 20. The pavement will be evaluated using both the flexible and rigid evaluation methods.

(1)

Rigid pavement evaluation. The following steps are followed:

(a)

From figure 6-79, determine F to be 0.793.

(b)

Calculate the equivalent thickness by substituting in equation 6-6:

1

[ 0.33 (101) % 152 ] ' 234 *millimeter*, *using SI units*

0.793

1

[ 0.33 (4) % 6 ] ' 9.2 *inches*, *using IP units*

0.793

(c) Having determined the equivalent pavement thickness, the remainder of the evaluation

will be accomplished in the same manner as a plain concrete thickness using the equivalent thickness as

the existing thickness. Therefore, using the k on the subgrade and figure 6-55, the allowable load would

be 26,400 kilograms (58.2 kips).

(2) Flexible pavement evaluation. The flexible pavement evaluation is conducted by consider-

ing the concrete pavement as a high-quality base course. It is then evaluated by considering the pave-

ment as 102 millimeters (4 inches) of asphalt concrete, 152 millimeters (6 inches) of 100 CBR base

course, and a 20 CBR subgrade. Using figure 5-35, the allowable load for the subgrade is 22,200 kilo-

grams (49 kips) and for the base course is 40,800 kilograms (90 kips). The controlling load for the flexible

pavement is therefore 22,200 kilograms (49 kips).

(3) Controlling evaluation. In evaluating flexible overlays on rigid pavements, the larger of the

controlling loads for the flexible and rigid evaluation controls the overall pavement evaluation and is there-

fore 26,400 kilograms (58.2 kips).

9.

RIGID OVERLAY OF FLEXIBLE PAVEMENT.

a. Data Required. When evaluating rigid overlay on flexible pavement, the flexible pavement

(bituminous concrete, base course, and subbase course) is considered to be a base course for the rigid

overlay. The data needed for use with the evaluation curves are presented in chapter 3. In the deter-

mination of the k value on the surface of the flexible pavement with the plate-bearing test, the following

limitations are imposed:

In no case will a k value greater than 135 kPa/mm (500 pci) be used.

(1)

(2) When the temperature of the existing bituminous pavement surface is above 24 degrees

Centigrade (75 degrees Fahrenheit), the asphaltic concrete pavement should be cut out and the test run

on the base. When the temperature of the existing bituminous pavement surface is below 24 degrees

centigrade (75 degrees Fahrenheit), run the tests on the asphaltic concrete pavement. Compare the

value from the test with the value from figure 3-6, then select the smallest value to use. Figure 3-6 may

also be used as an alternative method for determining the k value on the flexible pavement.

b. Method of Evaluation. Representative values must be selected for thickness of the rigid over-

lay, flexural strength of the rigid overlay, and modulus of reaction on the surface of the existing flexible

6-13