UFC 3-260-02
30 June 2001
b. The criteria contained herein are based upon fibrous concrete containing 1 to 2 percent by
volume 45 to 113 kilograms (100 to 250 pounds) of steel fibers per cubic yard of concrete, and fiber
contents within this range are recommended.
c. Most experience to date has been with fibers 25 to 38 millimeters (1 to 1- inches) long, and for
use of the criteria contained herein, fiber lengths within this range are recommended.
d. For proper mixing, the maximum aspect ratio (length to diameter or equivalent diameter) of the
fibers should be about 100.
e. The large surface-area-to-volume ratio of the steel fibers requires an increase in the paste
necessary to ensure that the fibers and aggregates are coated. To accomplish this, cement contents of
445 to 535 kg/m3 (750 to 900 lb/yd3) of concrete are common. The cement content may be all portland
cement or a combination of portland cement and up to 25 percent by volume of fly ash or other
pozzolans.
f. Maximum size coarse aggregates should fall between 9.5 and 19 millimeters (3/8 and
3/4 inches). The percent of fine to coarse aggregate has been between 45 and 60 percent on typical
projects using fibrous concrete.
4. THICKNESS DETERMINATION. The required thickness of fibrous concrete will be a function of
the design concrete flexural strength, the modulus of soil reaction, the thickness and flexural modulus of
elasticity of stabilized material if used, the aircraft gross weight, the volume of traffic, the type of traffic
area, and the allowable vertical deflection. When stabilized material is not used, the required thickness
of fibrous concrete is determined directly from the appropriate chart (Figures 14-1 through 14-9). If the
base or subgrade is stabilized and meets the minimum strength requirements of TM 5-822-14/
AFJMAN 32-1019, the stabilized layer will be treated as a low-strength base and the design will be made
using Equation 12-1. The resulting thickness must then be checked for allowable deflection. The
minimum thickness for fibrous concrete pavements will be 102 millimeters (4 inches).
5. ALLOWABLE DEFLECTION FOR FIBROUS CONCRETE PAVEMENT. The elastic deflection that
fibrous concrete pavements experience must be limited to prevent overstressing of the foundation
material and thus premature failure of the pavement. Curves are provided (Figures 14-10 through
14-18) for the determination of the vertical elastic deflection that a pavement will experience when
loaded and must be checked for all design aircraft. Use of the curves requires three different inputs:
slab thickness, subgrade modulus, and gross weight of the design aircraft. The modulus value to use for
stabilized layers is determined from Figure 9-1. The slab thickness is that which is determined from
Figures 14-1 to 14-19. The computed vertical elastic deflection is then compared with appropriate
allowable deflections determined from Figure 14-19 or, in the case of shoulder design, with an allowable
deflection value of 0.15 millimeters (0.06 inches). If the computed deflection is less than the allowable
deflection, the thickness meets allowable deflection criteria and is acceptable. If the computed deflection
is larger than the allowable deflection, the thickness must be increased or a new design initiated with a
modified value for either concrete flexural strength or subgrade modulus. The process must be repeated
until a thickness based upon the limiting stress criterion will also have a computed deflection equal to or
less than the allowable value. Should the vertical deflection criteria indicate the need for a thickness
increase greater than that required by the limiting stress criteria, the thickness increase should be limited
to that thickness required for plain concrete with a flexural strength of 6.2 MPa (900 psi).
6. JOINTING. The jointing types and designs discussed for plain concrete pavements generally apply
to fibrous concrete pavement. For the mix proportioning in Table 14-1, the maximum spacing of
14-2
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