30 June 2001
contraction joints will be the same as for plain concrete, except that for thicknesses of 102 to
152 millimeters (4 to 6 inches), the maximum spacing will be 3.8 meters (12.5 feet). Joints in pavements
152 millimeters (6 inches) or greater in thickness will be cut one-third of the depth of the pavement and
joints less than 152 millimeters (6 inches) long will be cut one-half the depth of the pavement.
Longitudinal construction joints may be either doweled, keyed, keyed and tied, or thickened-edge with a
key, in which case the key dimensions will be based upon the thickened-edge thickness. The keyed and
tied construction joint will be limited to a width of 30.5 meters (100 feet). For widths greater than
30.5 meters (100 feet), combinations of keyed and tied, doweled, or thickened-edge-type joints may be
used. Sealing of joints in fibrous concrete will follow the criteria presented in Chapter 12.
EXAMPLE OF FIBROUS CONCRETE PAVEMENT DESIGN.
a. General. An Air Force medium-load airfield is to be designed using fibrous concrete. On-site
and laboratory investigations have yielded the following data required for design: (a) subgrade material
is a silty sand; (b) modulus of subgrade reaction is 54 kPa/mm (200 pci); (c) an available source of
crushed gravel meets the base course requirements; (d) frost does not enter subgrade; and (e) 90-day
flexural strength is 6.9 MPa (1,000 psi) with 0.15 percent steel fibers.
b. Example Design--Slab On Grade. Figure 14-5 is entered with the subgrade k, concrete flexural
strength, and the pavement thickness determined for the various traffic areas as follows:
Thickness mm (in.)
215 ( 8.5)
152 ( 6.0)
Since the medium-load pavement is designed for the F-15, C-141, and B-52, deflections must be
determined for each aircraft. Therefore, by entering Figures 14-13, 14-14, and 14-15 with these
thicknesses, the computed deflections for all aircraft may be determined and the controlling value is
shown in the tabulation. It should be noted that a comparison of the computed deflections with the
allowable deflections from Figure 14-19 reveals that the thicknesses determined by the allowable stress
criterion are satisfactory, since the allowable deflections are equal to or greater than the computed
deflections for all traffic areas.