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Utah Demonstration Project: Precast Concrete Pavement System on I-215
I-215 is a busy interstate belt route southeast of Salt Lake City. The HfL project was conducted on the SB lanes of I-215 in the vicinity of the entry ramp from 3900 South. The general project location is shown in Figure 1. Here, the SB direction of I-215 has three lanes, and a shoulder, as seen in Figure 2. A portion of the project also includes a merge area, as seen in Figure 2.
Figure 1. Location of project on I-215 southeast of Salt Lake City.
Figure 2.Project location and plan on southbound I-215.
Figure 3. Southbound project view showing three lanes, merge area, and shoulder.
The 2009 average daily traffic for this section was 68,000 (in two directions), which includes a mix of commuter and truck traffic. The a.m. hourly peak was close to 4,500 vehicles, and the p.m. hourly peak was close to 2,500 vehicles in the SB direction alone. This is also a major route to Salt Lake City International Airport and a major truck route for SB traffic from I-80 to I-15. The relatively high peak hour urban traffic volumes make long-term lane closures highly disruptive, so UDOT sought to minimize the impact of construction on traffic.
The pavement was in poor condition when measured in 2008. The existing nondoweled concrete pavement was constructed in 1976 and was well beyond its 20- to 30-year design life. Pavement repairs had not been made since original construction. The existing concrete pavement also showed signs of surface polishing and cracking and corresponding reduction in skid resistance. UDOT estimated that about 1,500 square yards required full-depth replacement, which would cause enormous disruptions to traffic if performed traditionally. The pavement condition was assessed as fair. Pavement joints had debris and missing materials, which also contributed to cracking and spalling. Figures 3 through 7 show the pavement condition in May 2011.
Figure 4. Photos. Shattered slabs with longitudinal and transverse cracking on I-215.
Figure 5. Map. High-severity spalling and polishing of PCC surface on I-215.
Figure 6. High-severity cracks and spalls on the on-ramp slabs on I-215.
Figure 7. Photo. Severely deteriorated cracks and spalls filled with HMA on I-215.
The innovation on this project was the use of APC techniques, specifically PCPS. UDOT chose to use precast pavement panels with a placement time of 7 to 10 hours. Using precast pavements allowed for offsite construction with a better cure environment and offpeak construction, compared to traditional cast-in-place construction with a minimum 7- to 10-day cure time and limited control of the cure environment.
UDOT's goals for using APC were the following:
Using APC to address the pavement deficiencies and the knowledge and abilities of the contractor and designer, UDOT hoped to achieve best-value improvements. UDOT considered the use of PCPS for rapid repair because it is a technology that could improve safety, reduce congestion, and improve pavement performance, all of which are key elements of the HfL program.
UDOT's goal for the project was to demonstrate how APC technologies can be used to reduce construction impacts while improving safety and durability. UDOT planned to use APC with other programs, such as accelerated bridge construction. HfL's promotion of PCPS as a Vanguard Technology encouraged UDOT to submit an HfL project application.
The design for the project began with a scanning study of other States with experience using PCPS, followed by a lessons-learned report. A brainstorming meeting was held with UDOT engineers, fabricators, consultants, and contractors to discuss lessons learned from the scanning study. Based on the lessons learned and the meeting, the concept plans and work approach were developed. Six test panels were placed in fall 2010 for evaluation over the winter. Lessons learned from placement of the test panels were used to modify and improve plans for placement of the I-215 panels. Key design challenges included the following:
Geometry and Fit
Geometry and fit were important technical issues that needed to be resolved, particularly with a curved horizontal alignment. Curved horizontal alignment creates potential for fit issues with an estimated calculated chord offset as high as 0.25 in. A key question was whether to use curved or straight panels. The decision was made to use 12-foot (ft) straight panels rather than curved panels, vary the joint width, and saw cut and grout as needed. This was done with a goal to develop standardized sizes and shapes and to have flexibility for starting and stopping points of the project. Another issue considered during design was that the existing longitudinal joint would be irregular after removal of the old PCC, creating potential fit problems. The decision was made to saw cut the existing longitudinal joint to improve the fit between the lane 2 pavement and the new lane 3 panels. During construction, some of the new panels were also saw cut to improve fit.
Lifting of Panels
Key decisions needed to be made to reduce stresses and potential cracking of the panels during transportation, lifting, and placement. The panels were reinforced with #4 deformed steel bars to support panel weight during lifting. Reusable swivel lifting devices used for heavy loads were specified. These lifting devices have angular load capacity because of the swivel, and a smaller hole is needed for the swivel lifting devices compared to conventional lifting bolts.
Grade Preparation and Profile Leveling
Decisions on grade preparation and profile leveling were made with a goal to minimize the time spent preparing the grade and placing panels because of the short nighttime timeframe (7- to 10-hour closures) to remove and replace the existing pavement. Decisions were made to adjust the panel elevation using leveling screws, eliminate the sand bed, and use urethane or concrete grout injection under the panels to provide uniform support to the panels.
Grout was specified to be pumped in the grout ports of the panels to flow between the panel and the base material, filling voids and providing uniform support to the panels. Prototype tests showed 100 percent coverage for both urethane and concrete grout options. Field tests showed that both materials performed well over the winter. The decision made was that both materials were acceptable. However, urethane was chosen for this project because of its shorter cure time.
Load Transfer Devices
The existing pavement does not have load transfer at the joints. A key design question was whether load transfer devices (dowel bars) were needed and whether they would damage the adjacent panels. The decision made was to use 1.5-in × 18-in dowel bars at transverse joints (six for the 12-ft × 12-ft slabs and three for the 6-ft × 12-ft slabs) and to saw cut the dowel bar slots and joint sealant reservoir after placement of the panels for better alignment and to avoid fit problems.
Figure 8 is a typical cross-section showing the transverse view and the side view of the PCPS slab. As shown in the figure, two sizes of panels (49 12 ft × 12 ft and seven 6 ft × 12 ft) were used on this project. The 12-ft × 12-ft panel was used on lane 3, while both 12-ft × 12-ft and 6-ft × 12-ft panels were used in the merge area of the on-ramp to SB I-215.
Figure 8. Transverse view and side view showing the PCPS slab panels to be placed.
Figure 9 and Figure 10 show the typical plan views and section views for the 12-ft × 12-ft panels and the 6-ft × 12-ft panels, respectively. The key features of the PCPS panels are summarized as follows:
9. Typical plan view and section view for 12-ft × 12-ft panels.
Figure 10. Typical plan view and section view for 6-ft × 12-ft panels.
Figure 11. Load transfer device details.
Figure 12. Lifting device details.
Figure 13. Leveling bolt detail.
The construction project was awarded to Kilgore Contracting and the precast panels were made by Harper Precast. The I-215 construction project included replacing distressed pavement slabs with precast concrete pavement panels. Figures 14 through 17 show the casting of the precast panels at Harper Precast. The panels were placed during a 7- to 10-hour nighttime window with closure of the rehabilitated lane and the adjacent lane. The third lane (lane 1) was open to traffic throughout the construction. All lanes were open to traffic during daytime hours. Special provisions required the following:
Table 1 shows the contractor’s nightly activity schedule
After lane closures, barrier placement, mobilization, and preparation, the project started with removal and hauling of the existing pavement (lane 3), as shown in Figure 18 and Figure 19. Note the jagged longitudinal edge of the existing pavement (lane 2) in Figure 18. These longitudinal edges were saw cut for better panel fitting and grout containment, as shown in Figure 19. Per specifications, the existing base material was excavated, repaired, regraded, and compacted with a vibrating plate compactor, as shown in Figure 20. The base was specified to be finished with plus or minus 0.5 in of the desired profile. Sand bedding material was used to fill void areas as needed. The leveling plates were placed directly on the prepared compacted base, as shown in Figure 21. The panels were moved into place using a crane and supported at four points using lifting swivels, as shown in Figure 22 and Figure 23. A field decision was made to taper cut some of the panels (Figure 24) by 1 to 1.5 in to account for the horizontal curvature of the existing roadway.
Once the panels were placed on the prepared base, they were leveled using leveling bolts to within final grade tolerance of 0.25 in, as shown in Figure 25 and Figure 26. Preformed strip seal was used to seal the longitudinal joint and prevent grout from flowing out of these joints, as shown in Figure 27. Urethane leveling grout was injected through the grout injection hole, as shown in Figure 28 and Figure 29, to fill voids and support the panels. The urethane grout was specified to develop 90 percent of its full compressive strength of 90 pounds per square inch within 30 minutes of injection at 40º F or greater. The leveling bolts were specified to be removed or field cut at a minimum of 1 in below the top surface of the panel. Lifting block-outs, grout ports, and leveling bolt hardware block-outs were repaired using specified cement grout. Longitudinal or transverse joints in excess of 0.5 in were filled with specified encasement grout. Dowel slots were cut in at the transverse joints to retrofit the panels with dowel bars, as shown in Figure 30 and Figure 31. The final constructed project is shown in Figure 32.
Figure 14. Completed form ready for concrete pour.
Figure 15. Pouring concrete in form to precast the panel.
Figure 16. Removal of grout tube and bolt locator jigs.
Figure 17. Finished top of precast panel ready for curing.
Figure 18. Removal of existing deteriorated pavement (lane 3).
Figure 19. Hauling of existing pavement (lane 3).
Figure 20. Placing and compacting the base course fill material.
Figure 21. Leveling plates placed directly on top of the compacted base.
Figure 22. Placement of precast panel on the prepared base.
Figure 23. Steering precast panel into place onto the prepared base.
Figure 24. Cutting panels to 1- to 1.5-in taper to account for horizontal curvature of existing roadway.
Figure 25. Leveling bolts used to level the panels on the leveling plates.
Figure 26. Panels leveled using leveling bolts to within final grade tolerance of 0.25 in.
Figure 27. Placing preformed strip seal to contain grout.
Figure 28. Urethane grout injected through the grout injection hole.
Figure 29. Urethane grout injection closeup.
Figure 30. Placement of dowel bars into dowel slot.
Figure 31. Transverse joint with grout-filled dowel bar slots.
Figure 32. Placed panels and project open to traffic before diamond grinding for ride quality.