Longitudinal Reinforcement Construction
See FHWA’s CRCP Design and Construction Guidelines for the references included in this page. A new, more comprehensive FHWA CRCP Design, Construction, Maintenance and Rehabilitation manual is currently under development and this page will be updated upon its release in the spring of 2016.
As stated previously, the design basis of CRCP allows the pavement to crack at approximate intervals in the transverse direction, but includes a sufficient amount of longitudinal steel reinforcement to keep cracks closed very tight over the design life. Longitudinal steel placed on grade prior to concrete placement is illustrated in the figure to the right.
Bar Size and Quantity
The amount of longitudinal steel is commonly expressed as a percentage of the total slab cross-sectional area. Lon- gitudinal steel is normally delivered in 40 or 60 ft (12 or 18 m) lengths. It should be noted that the required bar size and percentage of steel should be determined by the design process.
When epoxy-coated steel is specified, ensure that the coating is not damaged during shipping, handling, or installation. For example, epoxy-coated bars should not be dropped or dragged and should be stored on wooden or padded steel cribbing.
Bar Spacing and Depth
A minimum steel depth of 3.5 in. (90 mm) to a maximum of mid-depth of the slab are recommended, as measured from top of slab to top of reinforcement bars.(85) Spacing of longitudinal reinforcement should allow for easy placement of the bars and consolidation of the concrete. The spacing should be no less than 4 in. (102 mm) or 2.5 times the maximum size of the aggregate, whichever is greater.(85) To achieve proper load transfer and bond strength, experi- ence indicates that the spacing of longitudinal bars should not exceed 9 in. (230 mm). In two-lane construction, an even number of longitudinal bars should be used to avoid locating a bar under a longitudinal joint, where it would interface with sawing.
A placing tolerance of ± 0.5 in. (13 mm) vertically and ± 1.0 in. (25 mm) horizontally is normally permitted for longitudinal bars. However, this vertical tolerance has often been difficult to achieve and a ±1.0 in. (25 mm) may be a more practical vertical tolerance.
Longitudinal steel must be adequately lapped at splices. Splices should also be staggered in arrangements that do not cause localized strains in the pavement or a nearby construction joint. Inadequate laps resulting from faulty construction have been direct causes of structural failures in CRCP. The length of splices is related to embed- ment length and the bond strength developed between the deformities on the bar and the concrete matrix.
Bond strength at early ages is critical to the development of desirable random cracking in CRCP, requiring splices to keep stresses and strains relatively uniform within the slab. Unless adequate bond strength is achieved at lap splices, the continuity of the CRCP slab may be lost and wide cracks that lead to structural failures can occur.
Lap splices must be tied or secured in such a manner that the two bars are held firmly in contact. However, the lap requirements and arrangements differ somewhat among the States to meet this requirement. The recommended minimum lap length of longitudinal steel splices is 25 times the bar diameter.(85) A minimum of two ties per lap is recommended.
These lap treatments apply to all manual and mechanical steel placement methods. If a staggered splice pattern is used, not more than one-third of the bars should termi- nate in the same transverse line, and the minimum distance between staggers should be 4 ft (1.2 m). If a skewed arrangement is used, the minimum skew should be 12 ft (3.7 m) in a 24 ft (7.3 m) wide pavement, or a 1:2 ratio. Typical lap patterns are shown in Figure 35.