UFC 3-260-03
15 Apr 01
slightly different than that for plain concrete. The flexural strength value is normally higher on the stress-
strain curve than the value selected for plain concrete specimens.
b. Method of Evaluation. Fibrous concrete slabs on grade will be evaluated in the same manner
as plain concrete slabs. A load factor is determined from figures 6-1 to 6-18. The load factor is then
divided by the aircraft weight in kips to determine a design factor. The design factor is then used with
figures 6-81 to 6-90 to determine the allowable number of passes. The allowable gross weight in kips is
determined by dividing the load factor from figures 6-1 to 6-18 by the design factor from figures 6-81 to
6-90. A fibrous concrete overlay pavement will be evaluated by determining an equivalent thickness of
concrete pavement according to equation 6-3 or 6-4 and then evaluating as a slab on grade.
12. PAVEMENT CLASSIFICATION NUMBER. In addition to evaluating airfield pavements for allow-
able load, it is necessary to report weight-bearing capacity of pavements in terms of the pavement
classification number. The PCN can then be compared with an ACN to determine if a pavement can
support a particular pavement. Values of ACN for given aircraft can be calculated from the computer
program ACN that can be obtained from the Army Corps of Engineers Transportation System Center, as
discussed in chapter 9. The PCN is presented in chapter 8.
13. EVALUATIONS FOR FROST CONDITIONS. If the existing soil, water, and temperature conditions
are conducive to detrimental frost effects in the base or subgrade materials, the pavement evaluation
will be based on frost area index of reaction as given in chapter 7 of this manual.
6-15
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