|FHWA > Engineering > Pavements > Concrete > High Performance Concrete Pavements: Project Summary > Chapter 5|
High Performance Concrete Pavements
|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.
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).
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.
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.
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