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Continuously Reinforced Concrete Pavement
June 5, 1990
- PURPOSE. To outline recommended practices for the design, construction,
and repair of continuously reinforced concrete pavement (CRCP).
- CANCELLATION. Technical Advisory T 5080. 5, Continuously Reinforced
Pavement, dated October 14, 1981, is cancelled.
- Continuously Reinforced Concrete Pavement is a Portland cement concrete
(PCC) pavement that has continuous longitudinal steel reinforcement and
no intermediate transverse expansion or contraction joints. The pavement
is allowed to crack in a random transversecracking pattern and the cracks
are held tightly together by the continuous steel reinforcement.
- During the 1970's and early 1980's, CRCP design thickness was approximately
80 percent of the thickness of conventional jointed concrete pavement.
A substantial number of the thinner pavements developed distress sooner
- Attention to design and construction quality control of CRCP is critical.
A lack of attention to design and construction details has caused premature
failures in some CRCPs. The causes of early distress have usually been
traced to: (1) construction practices which resulted in pavements which
did not meet design requirements; (2) designs which resulted in excessive
deflections under heavy loads; (3) bases of inferior quality, or; (4)
combinations of these or other undesirable factors.
- DESIGN RECOMMENDATIONS
- Concrete Thickness. Generally the slab thickness is the same
as the thickness of a jointed concrete pavement unless local performance
has shown thinner pavements designed with an accepted design process to
- Reinforcing Steel
- (1) Longitudinal Steel
- (2) Transverse Reinforcing and Tiebars
- (a) If transverse reinforcement is included, it should be #4, #5, or
#6 grade 60 deformed bars meeting the same specifications as mentioned
for the longitudinal reinforcement.
- (b) Although it can be omitted, transverse reinforcing reduces the risk
of random longitudinal cracks opening up and thus reduces the potential
of punch-outs. If transverse reinforcement is included, the following
equation can be used
to determine the amount of reinforcement required (see number 5 of Attachment
Pt = transverse steel, %
Ws = total pavement width, (ft)
F = subbase friction factor
fs = allowable working stress in steel, psi, (0. 75 yield strength)
- (c) The spacing between transverse reinforcing bars can be calculated
using the following equation (see numbers 1 and 5 of Attachment 2):
Y = transverse steel spacing (in)
As = cross-sectional area of steel, (in2) per bar
(#4, #5, or #6 bar)
Pt = percent transverse steel
D = slab thickness (in)
Note: The transverse bar spacing should be no closer than 36 inches
and no further than 60 inches.
- (d) In cases where transverse steel is omitted, tiebars should be placed
in longitudinal joints in accordance with the FHWA Technical Advisory,
Concrete Pavement Joints.
- (1) The base design should provide a stable foundation, which is critical
for CRCP construction operations and should not trap free moisture beneath
the pavement. Positive drainage is recommended. Free moisture in a base
or subgrade can lead to slab edge-pumping, which has been identified
as one of the major contributors to causing or accelerating pavement
distress. Bases that will resist erosion from high water pressures induced
from pavement deflections under traffic loads, or that are free draining
to prevent free moisture beneath the pavement will act to prevent pumping.
Stabilized permeable bases should be considered for heavily traveled
routes. Pavements constructed over stabilized or crushed stone bases
have generally resulted in better performing pavements than those constructed
on unstabilized gravel.
- (2) The friction between the pavement and base plays a role in the
development of crack spacing in CRCP. Most design methods for CRCP assume
a moderate level of pavement/base friction. Polyethylene sheeting should
not be used as a bond breaker unless the low pavement/base friction
is considered in design. Also, States have reported rideability and
construction problems when PCC was constructed on polyethylene sheeting.
- Subgrades. Continuously Reinforced Concrete Pavement is not recommended
in areas where subgrade distortion is expected because of known expansive
soils, frost heave, or settlement areas. Emphasis should be placed on obtaining
uniform and adequately compacted subgrades. Subgrade treatment may be warranted
for poor soil conditions.
- (1) Longitudinal Joints. Longitudinal joints are necessary to
relieve stresses caused by concrete shrinkage and temperature differentials
in a controlled manner and should be included when pavement widths are
greater than 14 feet. Pavements greater than 14 feet wide are susceptible
to longitudinal cracking. The joint should be constructed by sawing
to a depth of one-third the pavement thickness. Adjacent slabs should
be tied together by tiebars or transverse steel to prevent lane separation.
Tiebar design is discussed in the FHWA Technical Advisory entitled "Concrete
Pavement Joints. "
- (2) Terminal Joints. The most commonly used terminal treatments
are the wide-flange (WF) steel beam which accommodates movement, and
the lug anchor which restricts movement.
- (3) Transverse Construction Joints
- (a) A construction joint is formed by placing a slotted headerboard
across the pavement to allow the longitudinal steel to pass through
the joint. The longitudinal steel through the construction joint is
increased a minimum of one-third by placing 3-foot long shear bars
of the same nominal size between every other pair of longitudinal
bars. No longitudinal steel splice should fall within 3 feet of the
stopping side nor closer than 8 feet from the starting side of a construction
joint. Refer to paragraph 4b(1) (e) for recommended splicing patterns.
If it becomes necessary to splice within the above limits, each splice
should be reinforced with a 6-foot bar of equal size. Extra care is
needed to ensure both concrete quality and consolidation at these
joints. If more than 5 days elapse between concrete pours, theadjacent
pavement temperature should be stabilized by placing insulation material
on it for a distance of 200 feet from the free end at least 72 hours
prior to placing new concrete. This procedure should reduce potentially
high tensile stresses in the longitudinal steel.
- (b) Special provisions for the protection of the headerboard and
adjacent rebar during construction may be necessary.
- Leave-Outs. Temporary gaps in CRCPs should be avoided. The necessity
for leave-outs is minimized by giving proper consideration to the paving
schedule during project design. The following precautions can be specified
to reduce distress in the leave-out portion of the slab in the event a leave-out
does become necessary.
- Ramps Auxiliary Lanes, and Shoulders. PCC pavement for ramps, auxiliary
lanes, and shoulders adjacent to CRCP is recommended because of the possible
reduction in pavement edge deflections and the tighter longitudinal joints
adjacent to the mainline pavement. Ramps should be constructed using jointed
concrete pavement. The use of jointed pavement in the ramps will accommodate
movement and reduce the potential for distress in the CRCP at the ramp terminal.
When PCC pavement is used for ramps, auxiliary lanes, or shoulders, the
joint should be designed as any other longitudinal joint. Refer to the FHWA
Technical Advisory T 5040. 29, Paved Shoulders, for further information
on proper joint design.
- Widened Lanes. Widened right lane slabs should be considered to
reduce or eliminate pavement edge loadings. This is discussed in the FHWA
Technical Advisory T 5040. 29, Paved Shoulders.
- CONSTRUCTION CONSIDERATIONS
- Many CRCP performance problems have been traced to construction practices
which resulted in a pavement that did not meet the previously described
design recommendations. Because CRCP is less forgiving and more difficult
to rehabilitate than jointed pavements, greater care during construction
is extremely important. Both the contractor and the inspectors should
be made aware of this need and the supervision of CRCP construction should
be more stringent.
- Steel placement has a direct effect on the performance of CRCP. A number
of States have found longitudinal steel placement deviations of ±3
inches in the vertical plane when tube feeders were used to position the
steel. The use of chairs is recommended to hold the steel in its proper
location. The chairs should be spaced such that the steel will not permanently
deflect or displace to a depth of more than 1/2 the slab thickness. An
example chair device is shown in Figure 3, Combination Chair and Transverse
Figure 3: Combination Chair and Transverse Steel
- Procedures should be implemented to ensure a uniform base and subgrade.
Soft spots or gradeline variations should be repaired and corrected prior
to concrete placement. Emphasis should be placed on batching, mixing,
and placing concrete to obtain uniformity and quality. Strict inspection
of batching and mixing procedures is extremely important and mayrequire
rejection of batches because of deviations that may have been considered
minor under previously existing practices. When placing concrete, adequate
vibration and consolidation must be achieved. This is especially critical
in areas of pavement discontinuity such as construction or terminal joints.
Automatic vibrators should be checked regularly to ensure operation at
the specified frequency and amplitude and at the proper location in the
plastic concrete. Hand-held vibrators should be used adjacent to transverse
joints. Any concrete which exhibits signs of aggregate segregation should
be replaced immediately.
- Inspection procedures are needed to ensure that final reinforcing splice
lengths and patterns, as well as bar placement, are consistent with the
design requirements. Special precautions should be taken to prevent rebar
bending and displacement at construction joints. When leave-outs are necessary,
they should be constructed in absolute conformity to the design requirements.
Longitudinal joints should be sawed as early as possible to prevent random
cracking. This is especially true in multi-lane construction. Sawing should
not begin until the concrete is strong enough to prevent raveling.
- Asphalt concrete patches are not recommended as a temporary or a permanent
repair technique because they break the continuity of the CRCP and provide
no load transfer across the joint.
Anthony R. Kane
for Engineering and
The design engineer should perform the following calculations to ensure that
the bond between the reinforcing steel and the concrete and the longitudinal
steel spacing meet the criteria in paragraph 4c. The equation to determine the
ratio of bond area to cubic inches of concrete is as follows and the equation
to determine the minimum longitudinal steel spacing follows it:
||n x Ps x L|
|W x t x L|
- Ps = Perimeter of Bar (in.)
- L = Length of slab = 1"
- W = Width of slab (in.)
- t = Slab thickness (in.)
- n = Number of Longitudinal Bars
Given: #6 reinforcing bars, therefore Ps = 2. 356" and Bar Area
= 0. 44 in. 2
||W = 12'
t = 10"
||0. 6% steel
||The required minimum area of steel and the required minimum number of bars
Area of Conc. = 10 x 144 = 1440 in. 2
Required steel = 0. 006 x 1440 = 8. 64 in. 2
Minimum number if bars required (n) = 8. 64 / 0. 44 = 19. 6 bars, say
||The minimum ratio of bond area to cubic inches of concrete.
||20 x 2.356 x 1"
|1440 x 1"|
the minimum ratio of bond area to cubic inches of concrete is met so the
minimum spacing should be checked.
||Longitudinal steel spacing should be checked as follows:
||= 7.2 in., say 7 in.,
| || |
therefore the minimum bar spacing is also met.
1. "AASHTO GUIDE FOR DESIGN OF PAVEMENT STRUCTURES," 1986.
2. "FHWA Pavement Rehabilitation Manual," FHWA-ED-88-025, September
1985 as supplemented.
3. Mooncheol Won, B. Frank McCullough, W. R. Hudson, Evaluation of Proposed
Design Standards for CRCP, Research Report 472-1, April 1988.
4. "Techniques For Pavement Rehabilitation - A Training Course,"
FHWA, October 1987.
5. "Design of Continuously Reinforced Concrete for Highways," Associated
Reinforcing Bar Producers - CRSI, 1981.
6. "CRCP - Design and Construction Practices of Various States,"
Associated Reinforcing Bar Producers - CRSI, 1981.
7. "Design, Performance, and Rehabilitation of Wide Flange Beam Terminal
Joints," FHWA, Pavement Branch, February 1986.
8. Darter, Michael I., Barnett, Terry L., Morrill, David J., "Repair and
Preventative Maintenance Procedures for Continuously Reinforced Concrete Pavement,"
FHWA/IL/UI-191, June 1981.
9. "Failure and Repair of CRCP," NCHRP, Synthesis 60, 1979.
10. Snyder, M. B., Reiter, M. J., Hall, K. T., Darter, M. I., "Rehabilitation
of Concrete Pavements, Volume I - Repair Rehabilitation Techniques, Volume III
- Concrete Pavement Evaluation and Rehabilitation System," FHWA-RD-88-071,