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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