Construction of a Precast Prestressed Concrete Pavement Demonstration Project on Interstate 57 Near Sikeston, Missouri
Chapter 1. Introduction
Transportation agencies are continually seeking new techniques for rapid pavement construction and rehabilitation that will help them to minimize disruption to the motoring public. This need is particularly critical in urban areas where traffic delays caused by construction can result in substantial user costs. Precast concrete pavement has received renewed attention in recent years as a construction technique to meet this need. Precast concrete pavement not only provides a rapid construction solution that minimizes lane closure time for construction, but also provides a high-performance, long-term solution and not just a "quick fix."
Recent efforts by the Federal Highway Administration (FHWA) have led to numerous advances in precast pavement technology. In 2000 an FHWA-sponsored feasibility study was completed by the Center for Transportation Research (CTR) at The University of Texas at Austin, which examined the use of prestressed precast concrete panels for expedited pavement construction.(1) To evaluate the viability of the concept developed through the feasibility study, a subsequent FHWA-sponsored implementation study, conducted by CTR, resulted in the construction of a 0.7-km (2,300 ft) precast prestressed concrete pavement (PPCP) pilot demonstration project near Georgetown, Texas, in 2002,(2) followed by a second demonstration project in El Monte, California, in 2004.(3,4)
The success of the initial precast prestressed pavement demonstration projects in Texas and California led to the construction of additional demonstration projects. In 2003, FHWA initiated a series of precast prestressed pavement demonstration projects, including projects in Missouri, Texas, and Iowa. The intent of these demonstration projects was to evaluate the precast prestressed pavement concept for various applications while also familiarizing State highway agencies with precast pavement technology. The demonstration project constructed near Sikeston, Missouri, is described herein.
FHWA Demonstration Projects
One of the primary goals of the FHWA-sponsored PPCP demonstration projects is to examine various applications of precast pavement for expedited pavement construction. The first two projects in Texas and California have demonstrated the viability of PPCP construction for two different applications.
Interstate 35 Frontage Road-Georgetown, Texas(2)
Completed in spring 2002, the I-35 frontage road pilot project was the first FHWA project demonstrating the viability of the precast prestressed pavement concept. While not constructed under traffic and short time windows, this project was intended to evaluate the design details and construction procedures for use on future projects. Approximately 0.7 km (2,300 ft) of precast prestressed pavement was constructed the full width of the roadway. Both "full-width" and "partial-width" panels were utilized. The full-width panels spanned the entire 11 m (36 ft) width of the roadway, including two traffic lanes and inside and outside shoulders. The partial-width panels were constructed in two adjacent sections, one 6 m (20 ft) wide and the other 5 m (16 ft) wide, to achieve the full 11-m (36 ft) roadway width. The adjacent sections were tied together with additional transverse post-tensioning. Several aspects of precast concrete pavement were demonstrated by this project:
- Overall feasibility of constructing a PPCP.
- Use of an armored expansion joint in the precast panels.
- Use of central stressing with precast, post-tensioned pavement panels.
- Use of non-match-cast precast panels with interlocking keyways.
- Installation of precast panels over a hot-mix asphalt leveling course.
- Construction of precast pavement on a vertical curve.
- Lane-by-lane construction of precast pavement using partial-width precast panels.
Interstate 10-El Monte, California(3,4)
The second PPCP demonstration project was constructed by the California Department of Transportation in April 2004. PPCP was incorporated into a project to widen eastbound I-10 near El Monte. A 76-m (248 ft) section of PPCP was installed adjacent to the existing main lanes, adding 8.2 m (27 ft) of traffic lanes and a 3-m (10 ft) shoulder to the existing pavement. The project included several unique aspects of PPCP construction:
- Incorporation of a change in pavement cross slope into the surface of the precast panels.
- Nighttime installation of precast panels during a 5-hour construction window.
- Installation of precast panels over a lean concrete base.
- Use of epoxy-coated strands for longitudinal post-tensioning.
- Use of a nonarmored dowelled expansion joint.
- Diamond grinding of the finished surface to achieve pavement smoothness requirements.
Interstate 57-Sikeston, Missouri
The most recently completed demonstration project, constructed on I-57 near Sikeston, is described in more detail in this report. The project also demonstrated several aspects of PPCP construction:
- Incorporation of a pavement crown into the precast panels,
- Post-tensioning from the joint panels as opposed to central stressing.
- Use of a "header-type" nonarmored expansion joint.
- Use of a noncontinuous keyway along the panel joints.
- Installation of precast panels over a permeable asphalt-treated base.
- Diamond grinding of the finished surface to achieve smoothness requirements.
Benefits of Precast Concrete Pavement
While the benefits of precast prestressed concrete pavement have been documented more thoroughly elsewhere,(2,3,5) the following is a summary of some of these benefits:
Reduced User Delays
Perhaps the most apparent benefit of precast concrete pavement is rapid construction-not in terms of the placement rate, but in terms of how quickly the pavement can be opened to traffic. Because precast panels are fabricated and cured off site, they are able to withstand traffic loading almost immediately after they are installed. This permits precast pavement panels to be installed during nonpeak travel times such as at night or during weekend closures, minimizing the impact of construction on the motoring public. By limiting construction to nonpeak travel times, user delays and associated user delay costs can be minimized. This is where the primary economic benefit of precast concrete pavement will be realized.
Improved Quality and Performance
Expedited pavement construction is of little benefit if the pavement constructed is not a long-term solution. Precast concrete panels provide a long-term solution and not just a temporary "quick fix." Because precast concrete panels can be fabricated in a controlled environment, there is a high degree of quality control over their production. Precast concrete fabrication facilities offer a tremendous degree of flexibility over the concrete mixtures and materials used as well as the curing processes. Concrete mixtures are batched very consistently and hauled only short distances from the batch plant to the forms, minimizing the probability of variations in the mixture used for the panels. This proximity permits the use of a mixture with a very low water-to-cementitious materials ratio and optimal air void characteristics and also permits the use of lightweight aggregates to reduce the weight of the precast panels for shipping.
Curing of concrete pavements is critical. Precast fabrication facilities allow precast pavement panels to be cured under many different conditions. Steam curing, wet-mat curing, or heavy applications of curing compound are all techniques that can be utilized at precast fabrication plants. The result of improved curing operations is a more durable pavement surface with reduced "built-in curl" from moisture gradients in the panels.
Pavement performance is further enhanced through the incorporation of prestressing, which helps to reduce or even eliminate cracking. Because a compressive stress is induced in the pavement slab through prestressing, cracking will only occur if tensile stresses exceed the combination of the concrete's tensile strength and prestress force. This can result in a significant savings in maintenance costs over the life of the pavement and may even prevent the occurrence of major pavement failures. A cast-in-place, post-tensioned pavement, 150 mm (6 in.) thick, constructed near Waco, Texas, in 1985 has demonstrated the improved performance that can be achieved with prestressing.(6)
Prestressing also benefits performance by giving the precast panels a certain ability to "span" voids beneath the pavement. This ability is beneficial when the precast panels must be installed over a base that is not perfectly flat or contains "soft" areas or is one in which voids are expected to form over time.
Reduced Slab Thickness
Another benefit of incorporating prestress into precast concrete pavement is a reduction in required slab thickness. By inducing a compressive stress in the pavement slab, stresses in a thinner pavement slab caused by traffic loading can be limited to those of a much thicker slab, providing an equivalent design life to a thicker pavement slab. A reduction in slab thickness not only results in material savings, but also allows for "in kind" slab replacement. For example, an existing pavement slab 200 mm (8 in.) thick could be replaced with PPCP that is 200 mm (8 in.) thick and will have an equivalent design life to a much thicker (e.g., 300-mm [12 in.]) slab. This possibility is particularly beneficial for replacing pavement beneath bridge overpasses where a certain level of clearance must be maintained.
Extended Construction Season
Perhaps a less-obvious benefit of precast concrete pavement is the potential it provides for extending the construction season. Precast panels can be installed in colder (and hotter) temperatures that would normally prohibit cast-in-place pavement construction.
The primary objective of this report will be to summarize the PPCP demonstration project on I-57 near Sikeston, Missouri, including the design, fabrication, panel installation, instrumentation, and evaluation of the project. The report also presents recommendations for future PPCP projects based on lessons learned from this project. The following is a summary of the remaining chapters of this report:
Chapter 2 presents the precast pavement concept developed through the feasibility study, described previously. This includes the panel types, base preparation, panel assembly, post-tensioning, and grouting.
Chapter 3 presents the details of the Missouri Demonstration Project, including the scope of application and the project layout.
Chapter 4 presents the design, design considerations for PPCP, design procedure, and final design recommendations.
Chapter 5 discusses the fabrication of the precast panels, including the panel details and fabrication and handling procedures.
Chapter 6 discusses the construction of the precast pavement on site. The chapter covers base preparation, transportation, panel placement, post-tensioning, and grouting.
Chapter 7 presents the instrumentation and evaluation of the demonstration project by the FHWA project team and by a research team from the University of Missouri-Columbia. The chapter includes some of the significant findings from the instrumentation program, including performance and condition of the pavement during the 1st year in service.
Chapter 8 presents the overall project evaluation, including an assessment of design, fabrication, construction, and cost. Recommendations are also given for future precast pavement projects based on lessons learned from this project.
Chapter 9 presents a summary of the project and recommendations for future projects based on observations from the Missouri demonstration project.