In the October 2007 issue of TCP, “Paving the Way” presented an emerging market for precast concrete: highway pavement. Several precast/prestressed concrete pavement demonstration projects had been completed throughout the U.S. Today, precast pavement can safely be considered a mature technology, providing highway agencies with yet another tool to help them get in, get out, and stay out.
The increased adoption of precast pavement has been fueled by several factors. First, the success of initial demonstration projects and recent “production” projects has increased contractors’ comfort level with the technology as an alternative to other rapid construction options, such as rapid-strength concrete and asphalt.
Some of the initial precast pavement demonstration projects are now more than 10 years old and have exhibited excellent performance, proving that precast pavement is indeed a long-lasting solution. Precast producers have also embraced this technology and have taken many steps to promote and improve awareness within the industry.
Finally, with its increased use and greater awareness, the unit cost of precast pavement has sharply decreased. This makes it more competitive with other rapid construction techniques — particularly considering the long-lasting nature of the product.
Precast pavement in brief
Precast pavement is an alternative to hot-mix asphalt and cast-in-place concrete pavement. Although it can be used for new construction, its most beneficial use has been for reconstruction and rehabilitation of existing concrete pavements. This includes reconstruction of long continuous sections of pavement, as well as isolated slab repairs.
The primary advantage of precast panels is they do not require curing time in the field. The panels can essentially be installed and opened to traffic immediately, making this an ideal technology for projects where construction is limited to short (four- to eight-hour) work windows. Precast pavement is considered to be a long-term reconstruction/rehabilitation solution, and not just a temporary quick fix.
The two primary types of precast pavement used in the U.S. to date are precast/prestressed concrete pavement (PPCP) and jointed precast pavement systems (JPPS). With PPCP, the panels are typically pretensioned during fabrication and post-tensioned together onsite, providing a continuous prestressed pavement slab.
With JPPS, the panels are interconnected similarly to cast-in-place pavement using dowels. JPPS panels are typically either heavily reinforced or pretensioned.
PPCP passes the test
In 2009, PPCP technology was really put to the test with projects in Delaware and Virginia. Both projects required that all reconstruction of the existing pavement be limited to overnight work windows to minimize disruptions to the traveling public. In Delaware, the contractor had to work between 7 p.m. to 5 a.m. each night to remove the existing 12-inch-thick concrete pavement, place a 4-inch pervious concrete base, install 8-inch precast panels, and post-tension them together so they could be opened to traffic each day. Just a few months later, a section of Interstate 66 in Northern Virginia that carries more than 180,000 vehicles per day was reconstructed using PPCP. As in Delaware, construction activities were limited to 9 p.m. to 5 a.m. each night to ensure the pavement was open to daytime traffic.
Both of these projects successfully demonstrated the viability of PPCP as a rapid reconstruction technique for deteriorated concrete pavement under the strictest time constraints. However, the success of these projects led to deployment on a much larger scale elsewhere.
California leads the way
After a successful PPCP demonstration project on Interstate 10 in 2004, the California Department of Transportation (Caltrans) appears to have embraced precast pavement technology. In 2011, Caltrans District 4 (Oakland-Bay Area) deployed PPCP on a large scale, for the rehabilitation of about 7.5 miles of Interstate 680 near Dublin.
The project consisted of spot reconstruction of isolated areas of three of the four lanes of I-680 in both the northbound and southbound directions for a total of about 5.5 lane-miles of precast pavement (PPCP and JPPS). Similar to the projects in Delaware and Virginia, all reconstruction activity was restricted to the hours of 8 p.m. to 5 a.m. This included removing the existing concrete pavement, placing a rapid-setting lean concrete base, and installing and post-tensioning the precast panels.
Precast supplier Con-Fab Corp. of Lathrop, Calif., proposed an innovative modification that further improved efficiency. Two-way pretensioned precast panels were oriented in the direction of traffic, allowing the contractor to install up to 36 feet of precast pavement with each panel. These two-way pretensioned panels were also used for isolated single-slab replacement portions of the project.
The success of the I-680 project has led to additional jobs in Northern California, including Interstate 80 east of Sacramento and Interstate 580 near Pleasanton/Livermore, comprising just more than 6.5 lane miles of precast pavement. Both are currently in construction.
Meanwhile in Southern California, where precast pavement was first introduced, PPCP has been specified for the reconstruction of a 9.2-mile section of Interstate 710. The project will utilize about 4300 precast panels for 36 lane-miles of new concrete pavement. When completed, it will be the largest PPCP project ever constructed in the U.S.
Additional projects totaling about nine additional lane-miles are currently planned for Interstate 5 truck lanes and Interstate 405.
California has also utilized a proprietary precast pavement system which uses reinforced panels and doweled joints to effectively replace existing jointed concrete pavement in-kind. This system has been successfully deployed on a large scale in New York and New Jersey, and for smaller projects in several other states.
Not just for reconstruction
In addition to reconstruction applications, Caltrans has found perhaps a much larger potential for using precast pavement in slab repairs. Seeking an alternative to the traditional approach of rapid-strength concrete for isolated slab replacements, Caltrans maintenance forces have demonstrated the viability of precast pavement slabs for this purpose.
These slab replacement panels are typically reinforced and utilize dowels to provide load transfer between the precast panels and existing pavement. To date, more than 230 precast panels have been used for slab repairs in greater Los Angeles including two bus pads along urban arterials.
Caltrans has utilized both proprietary and in-house systems for these slab repairs. Its innovative system uses embedded leveling screws to raise or lower precast panels to match the elevation of the existing pavement. Rapid-strength grout pumped beneath the panels provides support.
National and international appeal
While California has deployed precast pavement on perhaps the largest scale to date, other states including New York, New Jersey, and Illinois continue to use both PPCP and JPPS extensively. These states have developed standard specifications, and in some cases generic precast pavement system designs that will further the use of this technology.
Internationally, a project completed in 2011 in Indonesia featured 88 lane miles of PPCP for new construction, further demonstrating the viability and wide variety of applications for precast pavement. TCP
- David Merritt is project manager for The Transtec Group Inc., an Austin-Texas based engineering firm specializing in pavements and pavement materials. Email email@example.com.