UFC 3-260-02
30 June 2001
7. REINFORCED CONCRETE PAVEMENTS IN FROST AREAS. Normally, plain concrete
pavements in frost areas will be designed in accordance with Chapter 22, and reinforcement will be
unnecessary. There may, however, be special instances when it will be directed that the pavement
thickness be less than required by frost design criteria. Two such instances are: the design of new
pavements to the strength of existing pavement when the existing pavement does not meet the frost
design requirements, and the design of an inlay section of adequate strength pavement in the center
portion of an existing runway when the existing pavement does not meet the frost design requirements.
In such instances, the new pavements will be reinforced with a minimum of 0.15 percent steel. The
minimum 0.15 percent steel will be placed in each of two directions (transverse and longitudinal) in the
slab. The reinforcing steel is required primarily to control cracking that may develop because of
differential heaving. The pavement thickness may be reduced, and the maximum slab length, consistent
with the percent steel, may be used. Longer slabs will help reduce roughness that may result from frost
action. Greater percentages of steel reinforcement may be used when it is desired to reduce the
pavement thickness more than is allowable for the required minimum percentage of steel.
8.
REINFORCING STEEL.
a. Type or Reinforcing Steel. The reinforcing steel may be either deformed bars or welded wire
fabric. Deformed bars should conform to the requirements of ASTM A 615, A 616, or A 617. In general,
grade 60 deformed bars should be specified, but other grades may be used if warranted. Fabricated
steel bar mats should conform to ASTM A 184. Cold drawn wire for fabric reinforcement should conform
to the requirements of ASTM A 82, and welded steel wire fabric to ASTM A 185.
b. Placement of Reinforcing Steel. The reinforcing steel will be placed at a depth of
hd/4 + 25 millimeters (hd/4 + 1 inch) from the surface of the reinforced slab. This will place the steel
above the neutral axis of the slab and will allow clearance for dowel bars. The wire or bar sizes and
spacing should be selected to give, as nearly as possible, the required percentage of steel per foot of
pavement width or length. In no case should the percent steel used be less than that required by
Figure 13-1. Two layers of wire fabric or bar mat, one placed directly on top of the other, may be used to
obtain the required percent of steel; however, this should only be done when it is impracticable to
provide the required steel in one layer. If two layers of steel are used, the layers must be fastened
together (either wired or clipped) to prevent excessive separation during concrete placement. When the
reinforcement is installed and concrete is to be placed through the mat or fabric, the minimum clear
spacing between bars or wires will be one and one-half times the maximum size of aggregate. If the
strike-off method is used to place the reinforcement (layer of concrete placed and struck off at the
desired depth, the reinforcement placed on the plastic concrete, and the remaining concrete placed on
top of the reinforcement), the minimum spacing of wires or bars will not be less than the maximum size
of aggregate. Maximum bar or wire spacing shall not exceed 305 millimeters (12 inches) nor the slab
thickness. Figure 13-3 shows the typical details of slab reinforcement with wire fabric or bar mats. The
bar mat or wire fabric will be securely anchored to prevent forward creep of the steel mats during
concrete placement and finishing operations. The reinforcement shall be fabricated and placed in such
a manner that the spacing between the longitudinal wire or bar and the longitudinal joint, or between the
transverse wire or bar and the transverse joint, will not exceed 76 millimeters (3 inches) or one-half of
the wire or bar spacing in the fabric or mat (Figure 13-3). The wires or bars will be lapped as follows.
(1) Deformed steel bars will be overlapped for a distance of at least 24 bar diameters,
measured from the tip of one bar to the tip of the other bar. The lapped bars will be wired or otherwise
securely fastened to prevent separation during concrete placement.
13-5
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