U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
|This report is an archived publication and may contain dated technical, contact, and link information|
Publication Number: FHWA-HRT-01-167
Date: April 2005
Structural Factors of Jointed Plain Concrete Pavements: SPS-2—Initial Evaluation and Analysis
Chapter 6. initial Evaluation of Key Performance Trends
This chapter provides an initial review and evaluation of the key performance trends for the SPS-2 project. Note that this initial evaluation is cursory in nature, because it is not within the scope of this study to conduct a comprehensive evaluation. Furthermore, the long-term performance may be different from short-term performance. The following key performance data are reviewed:
The SPS-2 project sites are relatively young pavements, ranging from 2 years old in Wisconsin to 7.5 years old in Kansas. Therefore, as expected, most SPS-2 sections are showing good performance and low distress levels. Table 52 summarizes the SPS-2 sections showing noticeable distress, along with key pavement design factors. (Noticeable distress is defined as a section that has a mean edge faulting greater than 1.0 mm or that exhibits longitudinal or transverse cracking.) As of January 2000, only 43 out of 155 sections (28 percent) showed any noticeable distress.
Because of the very low distress level of most sections, distress prediction models were not developed at this time. However, an initial evaluation of what affects the distressed sections was conducted. The results of the distress and profile data review and evaluation are presented in the following sections.
Note that these are early performance trends; the long-term performance may be different.
The distribution of the mean joint faulting values (the lane at edge) in SPS-2 sections, recorded as of January 2000, is illustrated in figure 13. Note that these values are the maximum mean faulting values recorded over the life of the section to date.
Ninety-five percent of the SPS-2 sections (148 sections) currently have a mean edge faulting less than 1 mm. Of the seven sections having greater than 1-mm faulting, six were constructed with an aggregate base and one was constructed with a lean concrete base. Additionally, three sections are from the heavily trafficked Michigan SPS-2 project site, and two sections are from the Nevada SPS-2 project site.
Table 52. SPS-2 sections with noticeable distress.
Figure 13. Distribution of the mean joint faulting values for SPS-2 sections (total 155 sections).
Figure 14. Mean edge joint faulting for different categories.
The mean edge faulting for different groups of design features or site conditions is depicted in figure 14. The following conclusions can be drawn from this initial evaluation:
An example of a faulting time history trend using data from the Michigan SPS-2 project site is provided in figure 15. Faulting measurements from different sections were averaged by base types. The aggregate base type shows the highest faulting trend over time.
The distribution of the transverse cracking is depicted in figure 16. As of January 2000, 82 percent of the sections had zero transverse cracks. However, 5 percent (eight sections) of the SPS-2 sections showed more than 50 percent slabs cracked. As shown in table 52, all eight sections are from at the Nevada SPS-2 project site, which was less than 4.5 years old. This excessive early cracking appears to indicate serious construction problems at the site. A review of the field distress maps will be very helpful in explaining these cracking observations.
Figure 15. Sample faulting time history plot-heavily trafficked Michigan SPS-2 sections by base types.
Due to the excessive cracking at the Nevada site, the cracking data from that site were not included in the following evaluation. The mean percentage of slabs cracked transversely, grouped by design features or site conditions, is given in figure 17. The following preliminary conclusions can be drawn from these mean value comparisons:
A sample time history for transverse cracking, using data from the Michigan SPS-2 project site, is shown in figure 18. Section 260218, which has a very thin slab and LCB, shows the highest level of cracking. Nine of 12 sections (75 percent) show no transverse cracking.
The distribution of longitudinal cracking is shown in figure 19. As of January 2000, 78 percent of the sections have no longitudinal cracks, whereas 4 percent (6 sections) have more than 50 m longitudinal cracking. Five of these six sections are at the Nevada SPS-2 project site, which was less than 4.5 years old at that time. Again, this excessive early cracking indicates serious construction problems at the site, and a review of the field distress maps will be very helpful in explaining these cracking observations. The Nevada site data were not included in the following plots and analyses.
Figure 16. Distribution of the transverse cracking for SPS-2 sections (total 155 sections)
Figure 17. SPS-2 mean percentage of slabs cracked transversely for different categories.
Figure 18. Sample time history plot for transverse cracking, Michigan SPS-2 project site.
The average total longitudinal crack length per section for different groups of design features or site conditions is given in figure 20. The conclusions drawn from these comparisons are very similar to those for transverse cracking.
A sample time history for the longitudinal cracking, using data from the Michigan SPS-2 project site, is provided in figure 21. Again, section 260218 shows the highest level of cracking. Ten out of 12 sections (83 percent) show no longitudinal cracking.
Pavement smoothness affects ride quality, and therefore is a very important performance indicator. In this study, the initial IRI and the IRI over time were both evaluated.
Figure 19. Distribution of the longitudinal cracking for SPS-2 sections (total 155 sections).
Figure 20. SPS-2 mean total longitudinal cracking for different categories.
Figure 21. Sample time history plot for longitudinal cracking-heavily trafficked Michigan SPS-2 project.
The initial IRI measurements represent the smoothness of the pavement soon after construction. Previous studies showed that initial smoothness significantly affects future smoothness of the pavements. For SPS-2 sections, the distribution of the initial IRI is shown in figure 22. The mean initial IRI was 1.30 m/km, and ranged from 0.76 to 2.19 m/km.
The effects of the key design features on initial IRI were analyzed statistically. An analysis of variance (ANOVA) was conducted that showed the following factors as significant:
The mean initial IRI values for different design features and site conditions are shown in figure 23.
Figure 22. Distribution of the initial IRI for SPS-2 sections (total 155 sections, mean = 1.30 m/km).
Figure 23. SPS-2 mean initial IRI for different site conditions and design features.
The IRI of each SPS-2 section was measured over time. The maximum value over time was determined and analyzed (typically, this occurred at the latest survey date). Distribution of the maximum IRI of all SPS-2 sections as of January 2000 is shown in figure 24. A majority of the SPS-2 sections (66 percent) are still very smooth, with an IRI less than 1.5 m/km. However, three sections are very rough, with an IRI greater than 2.5 m/km. These three sections are all in Michigan (sections 260214, 260217, and 260218).
It is a common belief that smoothness or IRI over time is a function of the initial IRI, cumulative traffic, and surface distresses. A multiple regression analysis was conducted on the maximum IRI, and the following regression model was developed:
(1)IRI = 0.08777 + 0.993 * Init_IRI + 0.1630
R2 = 72% SEE = 0.192 N = 56
This model shows that the initial IRI, joint faulting, and total KESALs (Age * annual KESALs) affect future IRI values. Transverse cracking and longitudinal cracking did not show significant effects on future IRI. This may be due to the low severity levels of these cracks at SPS-2 sections.
The SPS-2 sections are relatively young, and a large majority show little distress. As of January 2000, only 43 of 155 sections (28 percent) are showing any noticeable distresses. Ninety-five percent of the SPS-2 sections have less than 1 mm of edge joint faulting. Eighty-seven percent of the SPS-2 sections show zero transverse cracking, and 78 percent of the sections have zero longitudinal cracking.
Based on the preliminary statistical analyses and comparisons, the following preliminary and early performance trends are observed (note that long-term performance may be different from short-term performance):
Figure 24. Distribution of the IRI for SPS-2 sections (January 2000) (total 155 sections).