Design

Before installing precast pavement, the condition of the existing pavement should be assessed to determine the need for additional repairs or rehabilitation, such as drainage improvements and foundation repairs. Designers should determine the cause of distress to ensure the repair fixes the problem as well as prevents it from reoccurring. Precast concrete pavement systems are not a remedy for foundation problems, so the type, condition, and thickness of the existing base and subbase layers should be assessed.

In some cases, it is beneficial to design precast panels with increased structural capacity without increasing the panel thickness. This can be done by prestressing and/or post-tensioning the panels.

The presence of utilities—such as drainage structures, water and sewer pipes, natural gas and electrical pipes, and conduits—must be considered as well. Some of these utilities must be easily and regularly accessed, requiring penetration in the pavement surface in the form of manholes or inlet grates. Others don’t require access but must be reached through excavation for repair. There are precast concrete pavement systems features that exist to accommodate these utility needs, sometimes more easily than cast-in-place pavements can.

Using precast concrete pavement systems to replace flat, rectangular cast-in-place panels on straight pavement sections is straightforward. When placing precast panels in horizontal curves and transitions to elevated areas, nonplanar, trapezoidal and other-shaped panels may be needed. Those require special precasting forms and a need for them must be clearly specified.

Fabrication

Precast panels are fabricated at an established precast plant, preferably as close as possible to the installation site. For larger jobs, particularly in remote locations, it may be possible to set up a temporary precast bed near the jobsite. The concrete mixtures used are similar to those utilized for other precast prestressed elements and are not be restricted to “paving” mixtures. Steam curing, wet mat curing, or membrane curing are all options for precast pavement panels.

Panels are normally removed from the forms the day following casting and stored at the precast plant. Additional wet mat curing may be applied during the first few days of storage. Panels are handled and stored such that they will not be damaged prior to delivery to the jobsite.

Delivering straight from the precast plant to the jobsite, known as just-in-time delivery, is the most efficient way to deliver as there is no need for storage. It’s important to consider any limitations that may affect delivery, such as local, freight regulations, permits, limitations on turning movements, and overhead restrictions.

Construction

Using precast concrete pavement systems is most ideal for short work windows of 8 hours or less, such as repairing or reconstructing a highway overnight and reopening it before rush hour in the morning. If your project has a lengthy work window, precast concrete pavement systems may not be the most cost-efficient or productive option.

Other construction factors to consider include the available workspace on the jobsite for installing panels, vertical clearance space for the crane moving the panels, and access for large or heavy equipment and panel haul trucks—usually an issue only with urban applications. Precast concrete pavement systems are installed best when an adjacent lane is available for delivering the precast panels to the jobsite and for the panel lift equipment.

We help implement precast pavement design and construction methods around the globe.

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