30 June 2001
From Figure 13-1, the thickness of reinforced concrete overlay using the thickness of plain
concrete of 470 millimeters (18.5 inches) and a percent steel of 0.20 is 380 millimeters
d. Continuously Reinforced Concrete Overlay. A continuously reinforced concrete overlay may
be used to strengthen either an existing plain concrete or reinforced concrete pavement. For both
conditions, a bond-breaking medium is required between the overlay and the existing pavement.
The required thickness of a continuously reinforced concrete pavement is determined in the same
manner and will be equal in thickness to a plain concrete overlay. Jointing and sealing of joints in a
continuously reinforced concrete pavement will be the same as for continuously reinforced concrete
pavements on grade.
e. Fibrous Concrete Overlay. A fibrous concrete overlay may be used to strengthen either an
existing plain or reinforced concrete pavement. The mix proportioning of the fibrous concrete
overlay will follow the considerations presented for fibrous concrete pavements on grade.
(1) Thickness determination. The required thickness of fibrous concrete overlay will be
determined using the partially bonded or nonbonded overlay equations. Normally, the partially
bonded equation will be used, but in cases of extremely faulted or uneven existing pavement
surfaces, a leveling course may be required and the design of the overlay will be made using the
nonbonded overlay equation. If the existing rigid pavement is plain concrete, then the equivalent
thickness is equal to the existing slab thickness. If the existing rigid pavement is reinforced
concrete, however, then the equivalent thickness must be determined from Figure 13-1 using the
thickness of the existing slab and the percent of reinforcing steel. The minimum thickness of
fibrous concrete overlay will be 100 millimeters (4 inches).
(2) Jointing. In general, the joint types, spacing, and designs discussed for plain concrete
pavements apply to fibrous concrete overlays, except that for thicknesses from 100 millimeters
(4 inches) to 150 millimeters (6 inches), the maximum spacing will be 3.8 meters (12.5 feet).
Joints in the fibrous overlay should coincide with joints in the existing rigid pavement. Longitudinal
construction joints will be the butt-doweled type, and dowels will be required in transverse
contraction joints exceeding 15-meter (50-foot) spacings. For pavement thickness less than
150 millimeters (6 inches), it will be necessary to obtain guidance on joint construction from
HQUSACE (CEMP-ET), the appropriate Air Force Major Command, or the Naval Facilities
Engineering Command. Sealing of joints in fibrous overlays will be in accordance with sealing of
joints in fibrous concrete pavements on grade.
(3) Example of fibrous concrete overlay design. An existing rigid pavement will be
strengthened to serve as a type B traffic area for an Air Force light-load pavement using a fibrous
concrete overlay. The pertinent physical properties of the existing rigid pavement are: existing
thickness is 150 millimeters (6 inches), R = 4.8 MPa (700 psi), and k = 27 MN/m3 (100 pci). The
design (90-day) flexural strength of the fibrous concrete overlay is 6.2 MPa (900 psi). The existing
rigid pavement is plain concrete with a structural condition, C, of 1.0. A leveling course will not be
required; therefore, the required thickness of fibrous concrete overlay will be determined using the