Credit: TRANSTEC GROUP INC.
The first precast-prestressed concrete pavement project in the U.S. was near Georgetown, Texas, in 2001 – 2002. The panels were fabricated on a 400-foot-long casting bed.
Highway departments are always looking for ways to repair damaged pavement quickly and in ways that will keep the roadway performing is growing in popularity is precast concrete pavement systems (PCPS). The U.S. Federal Highway Administration ( FHWA ) has adopted this as one of its Highways for Life programs, and there are several demonstration projects under way — as well as many successfully completed projects.
According to the FHWA, the advantages are “improved user satisfaction and positive economic impact due to shorter construction time, off-peak working hours, longer pavement life, and fewer repairs required in the future also resulting in reduced user impact.”
There are several approaches to the technique, including some precasters who have made very large sections — up to 36x10 feet — that are post-tensioned onsite.
Others make smaller panels for pavement repair that have embedded dowels or that are tied to the existing pavement using the dowel-bar retrofit method . And one FHWA-funded project used ultra-high-performance concrete (UHPC) for bridge panels.
The objective for all these approaches is the same: to produce a high-quality repair that can be accomplished quickly, so traffic disruption is as brief as possible. And because the panels are cast already when they arrive at the repair site, work can be scheduled during nighttime off-hours and be completed by the next morning's rush hour.
What's needed is a slab panel, usually cast a full 12-foot lane width and 8 or 12 feet longitudinally. Then some technique needs to accomplish load transfer across the joints to tie the new panel into the existing pavement. There are various ways to do this, including tongue-and-groove, casting dowel bars into the pre-cast panel, and drilling into the existing pavement and affixing dowels that key into the precast panel. Some systems use corrosion-free fiberglass dowels.
Repairs are started by cutting out a damaged section of pavement. “We provide a template the exact size and shape of the precast panel,” says Adam Brodal, PE, chief engineer for Roman Stone Construction, Bayshore, N.Y. This allows the contractor to make the cut to precisely match the precast panel.
Then subgrade is removed or graded. Trying to get the exact elevation using compacted fines has met with mixed success. The most elegant approach seems to be setting the precast panel so the top traffic surface is about 1 inch below the existing pavement. An expanding polyurethane is injected beneath the panel through cast-in ports to bring the panel up to existing grade and provide a solid noncompressible base. “We work with Uretek,” says Brodal. “I was a little surprised how well it worked, but they really have it nailed down.”
Brodal's company has installed more than 800 precast panels for repairs on the Long Island Expressway — one of the busiest highways in the United States. Although the New York DOT is enthusiastic about this method, it's not sold on any of the typical load-transfer devices, but prefers the dowel-bar replacement method of cutting in slots for dowels across the joints after installation of the panels. “We've proposed other connectors, but they want to stick with the tried and true,” says Brodal.
— Palmer is editor in chief of PUBLIC WORKS' sister publication, CONCRETE CONSTRUCTION, and editorial director of Hanley Wood's Commercial Construction Group.