Process

Fabrication

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Delivery

Delivery of the precast panels to the site is a critical aspect of the installation process.  Enough delivery trucks must be available to meet the required installation rate.  Care must be taken during the delivery process to ensure that the panels are not damaged in any way during shipment.

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Installation

The installation process will vary with each job.  Temporary post-tensioning can be used to “snug” the panels together as they are installed.  Both “full width” and “partial width” construction have been utilized to date.  Full width panels span the width of the roadway and may include integral shoulders.  Partial width or lane-by-lane construction may require additional transverse post-tensioning to tie the two halves of the pavement together.

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Post-Tensioning

After the panels are installed, the post-tensioning strands are threaded through the panels, anchored at the ends and tensioned.  The post-tensioning tendons utilized to date have been 0.6-inch diameter 7-wire monostrand tendons.  Generally, the strands are tensioned to 75% of their guaranteed ultimate tensile strength.  After the tendons are tensioned, the stressing pockets or blockouts are patched.  A fast-setting patch material can be used if necessary.

It should be emphasized that post-tensioning does not need to be completed prior to opening to traffic.  While it is desirable to complete post-tensioning as soon as possible, time constraints on construction may not permit it.

 

Grouting

The post-tensioning system used for precast prestressed pavement is a bonded post-tensioning system.  Grouting not only provides an additional layer of corrosion protection for the post-tensioning strands, but also bonds the tendons to the pavement so that if it is necessary to remove a precast panel at a later time, the post-tensioning system will remain intact.

In addition to tendon grouting, underslab grouting may also be required to fill any voids beneath the pavement.  Grout ports can either be cast into the panels or drilled on site.  Underslab grouting is essentially a “gravity” fed process as applying pressure can actually lift the pavement.

Open to Traffic

Precast pavement can be opened to traffic as soon as the panels are installed.  Post-tensioning and grouting operations can be completed during a subsequent operation if necessary.  The surface will be smooth enough to open to traffic and can be diamond ground during a subsequent operation if necessary.

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