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Publication Number: FHWA-RD-01-169
Date: October 2005
Rehabilitation of Jointed Portland Cement Concrete Pavements: SPS-6, Initial Evaluation and Analysis
Chapter 7. INITIAL PERFORMANCE TRENDS
The LTPP sections have been surveyed periodically under the monitoring program to collect time-series performance data for each SPS-6 section. Monitoring activities include longitudinal profile, deflection testing, manual distress, faulting, transverse profile (or rutting), PASCO, and friction data. These data are available for evaluating the performance of each PCC pavement rehabilitation treatment. This chapter provides an initial review and evaluation using some of the key performance trends for the core sections of the SPS-6 experiment. Note that this initial evaluation of performance trends is only cursory; it is not within the scope of this study to conduct a comprehensive evaluation at this time. In addition, the oldest section is only 10 years old and, therefore, the results should only be considered as early trends. The longitudinal profile and surface distress (including transverse cracking, faulting, reflection cracking, fatigue cracking, and rutting) were selected for this preliminary review. An analysis of the deflection data will require an extensive evaluation of the backcalculation results, which is beyond the scope of this initial study.
The most important issue to be addressed in this evaluation is the relative performance of the different rehabilitation techniques. Because each experiment encompasses a range of rehabilitation techniques with widely varying levels of corrective effort, a comprehensive and fair comparison of the effectiveness of these techniques is difficult. For example, if one rehabilitation technique exhibits less transverse cracking, but more faulting than another, it would be difficult to say which one provided "better" performance. Therefore, it is nearly impossible to directly correlate the various surface distresses within the different rehabilitation techniques. For this reason, the surface distresses can be used to directly compare the pavement performances of similar rehabilitation techniques; however, these distresses cannot be used to correlate the performances of the different rehabilitation techniques.
However, one measure of performance that all techniques must ultimately satisfy is smoothness. The overall performance of all sections included in this report will be evaluated using the IRI. However, the development of various distresses is also important and it is critical that the performance of each rehabilitation technique be compared using a combination of the smoothness and key distress types.
The SPS-6 sections can be separated into three pavement categories: bare PCC, AC overlay of nonfractured PCC, and AC overlay of fractured PCC. Within each pavement category, direct comparisons of performance based on distress are also possible as described below:
These monitoring data are summarized in table 79. Table 79 shows that all three rehabilitation techniques can be compared using the IRI, and that the distresses cannot be directly compared in all three rehabilitation techniques. However, within each rehabilitation technique, the distress data can be directly compared for all sections.
Because the IRI values can be used to directly correlate the performance of all rehabilitation techniques, this chapter will first discuss the relative roughness performance of each technique. This will be followed by a comparison of the distress levels for all core sections within each rehabilitation technique.
IRI PERFORMANCE TRENDS
The IRI of the SPS-6 rehabilitated sections over time depends on both the initial IRI and the change in IRI over time. Figure 15 shows a plot of the IRI of all sections over time. The wide range of IRI values over time illustrates the variation in smoothness because of the various rehabilitation techniques.
The initial IRI for the control sections and the minimum and maximum preparation of PCC without diamond grinding are typically quite high, ranging from about 2 to 4 m/km (127 inches/mi to 253 inches/mi). Thus, even the repair of all deteriorated areas of JRCP or JPCP does not result in a smooth pavement. Additional measures, such as diamond grinding or overlay placement, are needed to restore smoothness. Figure 15 shows that the initial IRI for all of the AC overlays and for the maximum preparation of PCC sections (with diamond grinding) is approximately 1 m/km (63.36 inches/mi), ranging from 0.7 to 1.5 m/km (44 to 95 inches/mi). Thus, properly rehabilitated PCC pavements can be restored to a smoothness level similar to that of new construction.
IRI Over Time
The change in IRI since rehabilitation is of interest to show how each rehabilitation technique performs over time. The existing pavement condition, subgrade, traffic, and climatic effects will contribute to the performance of each rehabilitation alternative. Thus, the following is only general early observations, and a detailed analysis of each SPS-6 site is needed to determine the specific findings.
Figure 16 graphically shows the change in average IRI values for all of the core SPS-6 sections throughout their entire life since rehabilitation. The data plotted in this graph show that for the first year after construction, there is very little change in roughness for all types of rehabilitation. After rehabilitation, each of the pavement sections has a widely varying rate of increase in IRI, with some holding constant and others increasing greatly. Sections showing more than a 1.0 m/km (63.36 inches/mi) increase in IRI include the control section, the minimum-preparation bare PCC, the maximum-preparation bare PCC, and the minimum preparation with 102-mm (4-inch) AC overlay sections.
A statistical analysis software program was used to identify the preliminary trends that are developing based on the available data. In addition, this program was used to identify significant differences within each of the rehabilitation techniques. This information was then used to statistically group all of the rehabilitation techniques based on similar performance trends, as shown in table 80. It is important to note that this preliminary analysis did not include the effects of climate, traffic, initial pavement condition, or base or subgrade materials (other factors that obviously affect performance).
Table 80 shows that there is a significant influence in pavement smoothness based on the rehabilitation technique used. Based on the Duncan Group and a 5-percent confidence level, it can be noted that the bare PCC pavement sections are performing significantly differently than the AC-overlaid PCC pavements. In addition, the AC overlay of fractured PCC is performing significantly differently than the nonfractured PCC pavements. Therefore, three distinct performance trends are developing based on the rehabilitation technique used.
It is important to note that the fractured PCC pavement sections with a 102-mm (4-inch) AC overlay may be statistically grouped with either the nonfractured PCC pavements or the fractured PCC pavements. It is anticipated that, as this rehabilitation technique continues to age, these pavement sections will become more significantly similar to one of these distinct rehabilitation techniques.
Figure 15. IRI since rehabilitation for all core SPS-6 sections.
1 m/km = 63.36 inches/mi
Figure 16. Change in IRI since rehabilitation for all core SPS-6 sections.
1 m/km = 63.36 inches/mi
Based on this statistical comparison of the core pavement sections, it can be noted that the rate of increase in IRI since rehabilitation is lowest for the AC-overlaid PCC pavements (and even lower for the fractured PCC with thicker AC overlays) and is highest for the bare PCC pavements. It is important to remember that smoothness is not the only pavement performance indicator and, therefore, it is important that the development of the various distresses also be considered. Each of these rehabilitation techniques has widely different costs. Thus, one alternative may not perform as well as another, but may still be more cost-effective.
SURFACE DISTRESS PERFORMANCE TRENDS
As discussed above, the distress data collected for each section can be compared for each distinct rehabilitation technique. Therefore, this section will compare the distress performance trends within each distinct rehabilitation technique (bare PCC, AC overlay of nonfractured PCC, and AC overlay of fractured PCC).
As indicated in table 79, transverse cracking and faulting can be used to compare the performance of all bare PCC rehabilitated concrete pavements. Therefore, the control (***601), minimum-preparation (***602), and maximum-preparation (***605) sections can be directly compared to each other as follows:
Figure 17 shows the length of the transverse cracking for all three bare concrete sections. From this figure, it can be observed that cracking gradually increases with age and that the minimum- and maximum-preparation sections generally have more transverse cracking than the control section. The scatter is so great that this difference may not be significant.
It appears that the control section and the minimum-preparation sections have approximately the same increase in transverse cracking (slope) per year. It can also be noted that the maximum-preparation section has a higher rate of transverse cracking per year than the other two sections. There are no obvious reasons for this result, and a detailed analysis of each SPS-6 site is needed to ascertain the cause. The rate of increase in transverse cracking for each rehabilitation treatment will become more distinct as the pavement sections continue to age.
Figure 17. Total transverse cracking for bare PCC pavement sections.
1 m = 3.28 feet
The average joint faulting values and their associated trends for the bare concrete sections are shown in figure 18. From this figure, it can be noted that there is very little increase in the amount of faulting for the control sections, while both the minimum- and maximum-preparation sections are showing an increase in faulting since rehabilitation occurred. Both rehabilitation alternatives can be projected to reach the same magnitude of faulting as the control section after about 10 to 12 years.
It is important to note that both the minimum- and maximum-preparation sections had reduced faulting values for several years after rehabilitation was completed because of diamond grinding, which reduces faulting to zero. The minimum-preparation sections, on average, had slightly more faulting than the maximum-rehabilitation alternative. This may be partially explained by the fact that most of the maximum-preparation sections had diamond grinding performed, while the minimum-preparation sections may or may not have had this treatment. At this time, it is difficult to tell if the increase in roughness (slope) for both the minimum- and maximum-rehabilitation treatments is significantly different. As these pavement sections continue to age, it is expected that the performance of the minimum- and maximum-preparation sections will become more distinct. These data trend lines show that the faulting of the maximum-preparation (with diamond grinding) sections will not equal the control section until after about 12 years.
Figure 18. Mean joint faulting for bare PCC sections.
1 mm = .039 inch
AC Overlay of Nonfractured PCC
As indicated in table 79, reflection cracking can be used to compare the performance of all AC overlays of PCC pavements. Therefore, the minimum preparation with a 102-mm (4-inch) AC overlay (***603), the minimum preparation with a 102-mm (4-inch) AC overlay with sawed and sealed joints (***604), and the maximum preparation with a 203-mm (8-inch) AC overlay (***606) can be directly compared with each other.
Transverse Reflection Cracking
Figure 19 shows the linear amount of reflection cracking for the AC overlay of nonfractured PCC sections. It is important to note that the minimum-preparation section with a 102-mm (4-inch) AC overlay with sawed and sealed joints (***604) has many survey dates with extremely high values of reflection cracking and a considerable amount of variability. It appears that the survey techniques are not consistent from survey to survey. These discrepancies may be a result of some confusion by the survey crew regarding the changing definition of reflection cracking distress over the life of the LTPP program. These discrepancies should be addressed and corrected in the database before further conclusions can be reached.
In addition, none of these sections exhibited reflection cracking during the first year following rehabilitation. However, it can be noted that most of the reflection cracking appeared during the second year after rehabilitation. Also, it can be noted that there is a relatively small increase in the length of the reflection cracking over time (slope of the line) for all of the rehabilitation techniques. Therefore, it appears that most reflection cracking will typically occur within a 2 year period after rehabilitation. In addition, the amount of reflection cracking does not significantly increase after this period; however, it is expected that these cracks will continue to deteriorate
Figure 19. Total reflection cracking for nonfractured PCC pavement sections.
1 m = 3.28 ft
AC Overlay of Fractured PCC
As indicated in table 79, fatigue and rutting can be used to compare the performance of all AC overlays of nonfractured PCC pavements. Therefore, the cracked/broken and seated PCC with 102- and 203-mm (4- and 8-inch) AC overlays (***607 and ***608, respectively) can be directly compared with each other.
Wheelpath fatigue and the associated trends for the AC overlay of fractured PCC pavements are shown in figure 20. Many of the fractured PCC sections have not exhibited any fatigue cracking since rehabilitation. However, some sections are showing a tendency toward fatigue cracking. Of those sections with fatigue cracking, it can be noted that the increase in cracking over time for both rehabilitation alternatives appears very similar. As these pavement sections continue to age, these performance trends will become more distinct.
Figure 20. Total fatigue cracking for fractured PCC pavement sections.
1 square meter = 10.8 square feet
The average rutting values (combined values of the mean left and right wheelpath rut depths obtained from the MON_T_PROF_INDEX_SECTION table) and their associated trends are shown in figure 21. From this figure, it can be noted that there is a very wide amount of scatter in the rutting data. Both of the crack/break and seat rehabilitation alternatives appear to be rutting at similar rates. As these pavement sections continue to age, these performance trends will become more distinct.
An important comparison is the extent of transverse cracking (including all reflection cracking) between the fractured and nonfractured slab sections. This would indicate whether the fractured slab treatment had any effect on the reduction of transverse cracking. This comparison will require the direct comparison of transverse cracking between nonfractured and fractured sections at each SPS-6 site. No initial performance trends have been determined yet because these sections are still relatively young. As these sections continue to age, it is expected that valuable findings will be obtained regarding the influence of various levels of maintenance on PCC pavements.
Figure 21. Average rut depth for fractured PCC pavement sections.
1 mm = .039 inch
More Detailed Analysis
The previous performance trends should be considered only as tentative and general. Each SPS-6 site must be analyzed separately and specific findings should be determined at each site. Then these findings need to be combined and synthesized to produce an overall set of findings and trends. An overall analysis of all SPS-6 site data is beyond the scope of this initial analysis; however, this needs to be done in the future.