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Paving the Way

Paving the Way

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    Transtec Group Inc.

    General precast panel layout for PPCP

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    Pomeroy Corp. manufactures a wide range of precast products, including bridge girders, crossties, parking structures, piles, segmental bridges, and prison cells.

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    The first precast-prestressed concrete pavement project in the U.S. was near George-town, Texas, in 2001-02. The panels were fabricated on a 400-foot-long casting bed.

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    Each precast panel for the I-10 project in El Monte, Calif., was 37 feet long and 8 feet wide.

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    The panels for the I-57 project near Sikeston, Mo., were post-tensioned onsite.

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As with many precast applications, acceptance is on a national basis. While the projects completed to date have already shown the adaptability of precast concrete products, they truly only scratch the surface of what precast concrete pavement can accomplish.

Unbonded pavement overlays, weigh-in-motion installations, and temporary pavements are some of the other applications to consider. The precast/prestressed concrete industry has openly embraced this new technology.

The Precast/Prestressed Concrete Institute and American Concrete Institute have both recently established committees to further the market for PPCP. Through the continued support of FHWA, state departments of transportation and the precast concrete and concrete paving industries, precast concrete pavement will provide transportation agencies and contractors with another tool to help them “get in, get out, and stay out.” Here is a closer look at the five projects:

Texas

The first PCPP project was near Georgetown, Texas, in 2001–02. In all, 2300 feet of frontage road pavement was constructed using PPCP spanning the full width of the frontage road, including two traffic lanes and inside and outside shoulders.

A total of 339 precast panels were fabricated and installed. The 8-inch-thick panels were pretensioned in the transverse direction (long axis of the panel) during fabrication with six ½-inch strands, and post-tensioned together onsite in 250-foot, 225-foot, and 325-foot sections with mono-strand 0.6-inch tendons spaced at 2 feet on center across the width of the roadway.

Texas Concrete Co. of Victoria, Texas, was the precast supplier. Half of the project consisted of “full-width” precast panels, 36 feet long and 10 feet wide. The other half of the project consisted of 20-foot and 16-foot panels (10 feet wide), tied together with transverse post-tensioning to achieve the full 36-foot roadway width.

The panels were fabricated on a 400-foot-long line casting bed, with up to 10 of the 36-foot-long panels produced at a time. Armored expansion joints and blockouts for the post-tensioning tendons were cast into several of the panels, increasing the complexity of the fabrication process. The finished pavement has been open to traffic for almost six years and is performing very well.

California

The second project was constructed in El Monte in 2004. In all, 248 feet of mainline pavement on I-10 was constructed with PPCP, adding 27 feet of traffic lanes and a 10-foot shoulder to the existing pavement. Thirty-one precast panels were fabricated and installed, and post-tensioned onsite in two 124-foot sections.

The panels were pretensioned during fabrication in the transverse direction with six ½-inch strands, and were post-tensioned onsite in the longitudinal direction with 0.6-inch, grit-impregnated, epoxy-coated monostrand tendons. These were spaced at 3 feet on center across the width of the road.

Pomeroy Corp. of Perris, Calif., produced the panels. Varying the thickness of the precast panels to achieve a change in finished pavement cross-slope increased the complexity of the fabrication process. The panels varied in thickness from 10 inches at the ends to just more than 13 inches at the “peak.” This formed the transition in cross-slope between the traffic lanes and shoulder of the finished pavement.

The panels were fabricated on a self-stressing bed large enough for two panels to be cast and steam-cured at a time. Each pre-cast panel was 37 feet long and 8 feet wide. The panels were installed during two consecutive overnight operations, minimizing disruption to traffic on the busy interstate.

For more, Web exclusive project photos, click here