High Performance Concrete Pavements Project Summary
Chapter 5. ILLINOIS 1 (I-55 SB, Williamsville)
This project was the first constructed by the Illinois Department of Transportation (IDOT) to evaluate alternative dowel bars for use in jointed concrete pavements. Constructed in 1996, the project is located on the exit ramp of a weigh station in the southbound direction of I-55 (milepost 107) near Williamsville, just north of Springfield (see Figure 5). Although not a TE-30 project, it did serve as a springboard for future IDOT projects evaluating alternative dowel bars under the TE-30 program.
Figure 5. Location of IL 1 project.
On most concrete pavements, steel dowel bars are used at transverse joints to provide positive load transfer between adjacent slabs. However, even if epoxy coated, these dowel bars are susceptible to corrosion, which can create locked or "frozen" joints that can spall and crack the concrete, significantly reducing the service life of the pavement. The purpose of this study, therefore, is to compare the performance of non-corrosive type 'E' fiberglass and polyester dowels to the performance of conventional epoxy-coated dowel bars in a side-by-side field evaluation project.
Project Design and Layout
This project was constructed in 1996 and consists of a 280-mm (11.25-in.) slab placed on a 100-mm (4-in.) bituminous aggregate subbase (BAM) (Gawedzinski 2000). In accordance with IDOT practices at the time, the jointed concrete pavement was constructed as a hinge-joint design, in which conventional doweled transverse joints are spaced at 13.7-m (45-ft) intervals and intermediate "hinge" joints containing tie bars are placed at 4.6-m (15-ft) intervals between the doweled joints (see Figure 6); this pavement is essentially a jointed reinforced design with the reinforcing steel concentrated at locations where the pavement is expected to crack. The hinge joints contain number 6 epoxy-coated tie bars, 900-mm (36-in.) long and placed at 450-mm (18-in.) intervals across the joint (Gawedzinski 2000). Preformed compression seals (32-mm [1.25-in.] wide) are placed in the doweled transverse joints and a hot-pour joint seal placed in the tied hinge joints (Gawedzinski 2000).
Figure 6. Illinois DOT hinge joint design (IDOT 1989).
The pavement was paved 4.9-m (16-ft) wide, and a 3.0-m (10-ft) tied portland cement concrete (PCC) shoulder was placed adjacent to the mainline exit ramp. The shoulders were tied using number 6 epoxy-coated tie bars, 900 mm (36 in.) long and placed at 762-mm (30-in.) intervals (Gawedzinski 2000).
Seven joints (excluding hinge joints) are included in the project, the layout of which is shown in Figure 7. The first two regular transverse joints of the project contain conventional epoxy-coated steel dowel bars (38-mm [1.5-in.] diameter). The next four regular transverse joints contain type 'E' fiberglass and polyester bars (38-mm [1.5-in.] diameter and 450-mm [18-in.] long). The fiberglass and polyester resin bars were manufactured by RJD Industries of Laguna Hills, California. The final regular transverse joint in the project contains conventional epoxy-coated steel dowel bars.
Figure 7. Layout of IL 1 project.
State Monitoring Activities
IDOT collects traffic data from the sorter scale located at the entrance ramp of the weigh station. Traffic totals from the period from September 1996 to September 1999 are summarized in Table 4 (Gawedzinski 2000).
|TRUCK TYPE||NUMBER OF VEHICLES||ACCUMULATED 18-KIP ESAL APPLICATIONS|
All seven joints in the project are evaluated at least semi-annually by IDOT to assess their performance. This evaluation consists of both distress surveys and nondestructive testing using the falling weight deflectometer (FWD). Results from the FWD testing program are plotted in Figures 8 and 9 (Gawedzinski 2000). Figure 8 shows the load transfer efficiency (LTE) across each of the seven joints as a function of time, whereas Figure 9 shows the maximum joint deflection measured at each joint as a function of time.
A gradual decrease in overall load transfer efficiency is observed in Figure 8, with the conventional steel dowel bars consistently showing higher levels of load transfer then the fiber composite bars. But, as seen in Figure 9, the largest deflection is consistently shown by one of the conventional doweled joints, although the other two conventional doweled joints show consistently low deflections. LTE values less than 70 percent provide very low stress load transfer, and the results of the LTE testing suggest that many of the joints are exhibiting an unacceptable LTE level after only 7.5 years.
Figure 8. Load transfer efficiency on IL 1 (Gawedzinski 2000).
Figure 9. Maximum joint deflections on IL 1 (Gawedzinski 2000).
After about 4 years of service, this project is performing well. None of the joints is exhibiting any signs of distress. IDOT will continue monitoring the project to assess the relative performance of the different dowel bar types.
Interim Project Status, Results, and Findings
Truck data continues to be gathered from the sorter scale installed in the entrance ramp of the weigh station. Equivalent single-axle loads (ESALs) were computed using scale vendor software and standard IDOT design coefficients. Reported ESAL counts are lower than actual applied ESALs due to the failure of the hard drive on the sorter scale computer for a 13.5-month period from January 23, 2002, to March 13, 2003. ESAL counts for the missing period were projected using the truck data previously gathered from the scale and manual counts obtained from scale operators. Cumulative ESAL estimates are provided in Table 5 (Gawedzinski 2004).
Visual observations of the joints show no obvious signs of pavement distress; neither faulting nor spalling was evident at any of the seven joints. The original construction had the joints sealed with a preformed elastomeric joint seal material compressed into a 15.75-mm (0.62-in.) wide joint. Over time, the preformed elastomeric joint material has been pushed deeper into the saw cut, especially in the wheelpaths. Deflection LTE and joint deflection values were determined for each of the seven pavement joints. The average values were determined from deflections measured as simulated 4-, 8-, and 12-kip loads were applied to the pavement on the approach and leave sides of the joints. The joints were tested at both inner and outer wheelpaths and at the center of the lane for a total of 18 tests per joint.
Figure 10 (Gawedzinski 2004) provides a summary of the LTE verses ESALs, as measured over time. Figure 11 (Gawedzinski 2004) provides a graph of average pavement temperature at a 4-in depth verses LTE.
Figure 10. Load transfer efficiency vs. ESALs (Gawedzinski 2004).
Figure 11. Load transfer efficiency vs. pavement temperature (Gawedzinski 2004).
Current Observations (Gawedzinski 2004)
The Williamsville site is 7.5 years old and has been subjected to over 10.1 million ESALs. The joints at Williamsville show very little sign of distress or damage. The preformed elastomeric joint seal is still intact, showing only that it is deeper in the joints under the wheelpaths. Overall, only very minor spalling is displayed at the joints; however, it is not known if this was due to damage during the cutting of the original saw cuts or if it has occurred over time.
Evaluation of the FWD data indicate that, on average, the fiber composite dowel bars perform somewhat less effectively than the carbon steel control dowel bars. Graphs showing the individual joint performance show that changes in deflection and LTE are related to the "overall pavement system" performance, rather than changes in individual joint performance. Dips and spikes in deflection and LTE are similar to some degree for all of the joints, rather than the joints behaving individually, but many of the joints (especially those equipped with FRP bars) are approaching (or have fallen below) the minimum acceptable LTE level of 70 percent.
More frequent FWD testing is planned for the Williamsville site in order to evaluate what causes this response for the bars. Data show LTE and joint deflection do not appear to be affected by changes in pavement temperature. It is unknown what the moisture content is at the dowel bar/joint interface and how much the moisture content effects LTE and joint deflections.
Points of Contact
Illinois Department of Transportation
Bureau of Materials and Physical Research
126 E. Ash Street
Springfield, IL 62704
Gawedzinski, M. 2000. TE-30 High Performance Rigid Pavements Illinois Project Review. Illinois Department of Transportation, Springfield.
---. 2004. TE-30 High Performance Rigid Pavements: An Update of Illinois Projects. Illinois Department of Transportation, Springfield.
Illinois Department of Transportation (IDOT). 1989. Mechanistic Pavement Design. Supplement to Section 7 of the Illinois Department of Transportation Design Manual. Illinois Department of Transportation, Springfield.