TM 5-809-12/AFM 88-3, Chap. 15
c. Mix proportioning considerations. The design
(5) Maximum size coarse aggregates should
mix proportioning of fibrous concrete will be deter-
fall between 3/8 and 3/4 inch. The percent of coarse
mined by a laboratory study. The following are
aggregate (of the total aggregate content) can vary
offered as guides and to establish limits where
between 25 and 60 percent.
d. Thickness determination. The required thick-
necessary for the use of the design criteria included
herein.
ness of FJC floor slabs will be a function of the
(1) The criteria contained herein are based
design concrete flexural strength R, modulus of soil
upon fibrous concrete containing 1 to 2 percent by
reaction k, the thickness hb and flexural modulus of
volume (100 to 250 pounds) of steel fibers per cubic
yard of concrete, and fiber contents within this
vehicle or axle gross load, the volume of traffic, the
range are recommended.
type of traffic area, and the allowable vertical
(2) Most experience to date has been with
deflection. When stabilized material is not used, the
fibers from 1 to 1-1/2 inches long, and for use of the
required thickness hdf of JFC is determined directly
criteria contained herein, fiber lengths within this
from the appropriate chart (figs 5-15 and 5-16). If
range are recommended.
the base or subgrade is stabilized meets the
(3) For proper mixing, the maximum aspect
minimum strength requirements of TM 5-822-
ratio (length to diameter or equivalent diameter) of
4/AFM 88-7, Chap. 4, the stabilized layer will be
the fibers should be about 100.
treated as a low-strength base and the design will be
(4) The large surface area to volume ratio of
made using the equation given in paragraph 5-2d(3)
the steel fibers requires an increase in the paste
above. The resulting thickness, h or hdof , will be
necessary to ensure that the fibers and aggregates
rounded up to the nearest half or full inch. The
are coated. To accomplish this, cement contents of
rounded thickness, hdf or hdof will then be checked
750 to 900 pounds per cubic yard of concrete are
for allowable deflection in accordance with
paragraph 5-9e. The minimum thickness for JFC
recommended. The cement content may be all
portland cement or a combination of portland
floor slabs will be 4 inches.
cement and up to 25 percent fly ash or other
pozzolans.
5-26
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