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Publication Number: FHWA-HRT-10-066
Date: October 2011

 

Impact of Design Features on Pavement Response and Performance in Rehabilitated Flexible and Rigid Pavements

Chapter 8. Study Findings, Conclusions, and Recommendations

This chapter provides the findings and conclusions from the analysis of preventive maintenance treatments and performance of different pavement rehabilitation alternatives. Recommendations for future research are provided at the end of the chapter.

Preventive Maintenance Treatments

The findings presented in this section are based on the analysis of 81 SPS-3 flexible pavement sites and 34 SPS-4 rigid pavement sections subjected to different preventive maintenance treatments. Most of the flexible pavement sites were monitored for at least 4 years, and about 22 percent of the sites were monitored for 10 years or more. Most of the rigid pavement sites were monitored for at least 4 years.

Preventive Maintenance Effectiveness for Flexible Pavements

From the analysis of SPS-3 sites, the following effects of preventive maintenance treatments on pavement performance were observed:

IRI:

Rutting:

Fatigue cracking:

Preventive Maintenance Effectiveness for Rigid Pavements

The study of the SPS-4 sites showed that the performance of the joint/crack sealed sections and undersealed sections was not significantly different from the performance of control sections. Additionally, no meaningful difference between the two treatments was found. The analysis was weakened by the small number of sites and only 4 years of performance history that included recorded surveys with undersealing treatment. While 34 sites included the survey measurements for joint/crack sealed sections, only 10 sites had data for undersealed sections.

Rehabilitated Flexible Pavements

The findings presented in this section are based on the analysis of 18 SPS-5 rehabilitated flexible pavement experimental sites with 162 core test sections. Most of the sections were monitored for at least 9 years.

Evaluation of Rehabilitation Strategies with Respect to Performance

To analyze data from the SPS-5 experiment, a gradual statistical analysis was used  in which the data from each site were analyzed first, followed by a consolidated analysis of all sites simultaneously in search for general trends and broader conclusions about pavement performance and its dependency on design features and site conditions. The results obtained in the consolidated analysis mostly agree with the results found in the individual site analyses. A summary of the analysis findings with respect to major pavement performance indicators is provided below.

IRI:

Rutting:

Fatigue cracking:

Transverse cracking:

Longitudinal cracking (in wheel paths):

In terms of the effect of design features or construction practices, the following conclusions were made:

Overlay thickness:

Milling:

RAP mixes:

Evaluation of Rehabilitation Strategies with Respect to Structural Responses

For evaluation of structural responses, a maximum FWD deflection measured under the center of the load was used as a structural response indicator. The study concentrated on evaluating FWD maximum deflections against the average pavement performance during the service life of SPS-5 sites. As with the analysis of pavement performance presented above, a gradual statistical analysis was used beginning with the analysis of individual sites, followed by a consolidated analysis of all sites simultaneously. The results from the consolidated analysis supported the findings from the analysis of individual sites. A summary of the analysis findings with respect to structural response is as follows:

In terms of the effect of design features or construction practices, the following conclusions were made:

Overlay thickness:

RAP mixes:

Milling:

Evaluation of Structural Responses Immediately After Rehabilitation and Future Performance

The objective of this evaluation was to identify trends in the relationship between response measured after the rehabilitation and the observed performance in subsequent years of the pavement's service life. Only long-term performance was used for this analysis, which included performance data of 5 years or more. The following summarizes the analysis findings:

IRI:

Rutting:

Fatigue cracking:

Transverse cracking:

Longitudinal cracking:

Rehabilitated Rigid Pavements

Findings presented in this section are based on the analysis of 14 SPS-6 rehabilitated rigid pavement sites, specifically 8 JPCP and 6 JRCP. Most of the sections were monitored for at least 6 years. The findings from the analysis are described separately for JPCP and JRCP sites.

Evaluation of JPCP Rehabilitation Strategies with Respect to Performance

The results from the statistical analysis led to the following conclusions with respect to major pavement performance indicators, total cracking and IRI:

Total cracking:

IRI:

It should be noted that the best performance alternative may not be the lowest cost alternative. Selection of a rehabilitation alternative must also consider the cost and long-term maintenance.

The analysis of impact of site conditions led to the conclusion that different climate regions and surface conditions did not have a significant impact on roughness and total cracking performance for the rehabilitation strategies included in the SPS-6 JPCP experiment.

Effect of PCC Restoration Prior to Overlay

The impact of PCC restoration preoverlay treatments on performance of overlaid sections was investigated in the JPCP sites of the SPS-6 experiment. Transverse cracking was the only distress for which statistical differences were found between the four treatments. The conclusions from this study were as follows:

The analysis of impact of site conditions led to the following additional conclusions:

Effect of PCC Restoration Without Overlay

Three sections in each SPS-6 site did not receive overlays as part of their rehabilitation strategies. These sections were used to evaluate the impact of PCC restoration on performance. The small number of sections available for this study significantly reduced the power of the analysis and the chances of finding statistical differences among the treatment alternatives.
No statistical differences in performance were found for short-term performance. The only performance indicator that showed statistical differences between the treatments was long-term roughness. From the analysis of long-term roughness, the findings supported by the statistical analysis were as follows:

An attempt was made to evaluate the impact of site conditions on performance; however, the results were not statistically significant.

Evaluation of JRCP Rehabilitation Strategies with Respect to Performance

Similar to JPCP findings, the results of the JRCP analyses suggested that rehabilitation strategies with HMA overlays improved roughness performance, while strategies without overlays were better at improving total cracking development and propagation. The main conclusions were
as follows.

Total cracking:

IRI:

The sawed and sealed joints did not deteriorate significantly on these sections, and they became an effective control of reflection cracking. If they were removed from total cracking, the sawed and sealed sections would have shown similar performance to other HMA overlays.

Effect of PCC Restoration Prior to Overlay

The impact of PCC restoration treatments on the performance of overlaid sections was investigated in JRCP sites of the SPS-6 experiment. Transverse cracking was the only distress for which statistical differences were found between the four treatments. The conclusions from this study were as follows:

The sawed and sealed joints did not deteriorate significantly on these sections, and they became an effective control of reflection cracking. If they were removed from total cracking, the saw and sealed sections would have shown similar performance to other HMA overlays.

Effect of PCC Restoration Without Overlay

Three sections in each SPS-6 site did not receive an overlay as part of their rehabilitation strategies. These sections were used to evaluate the impact of PCC restoration on performance. Distresses common to rigid pavements were used as performance measures. The only performance indicator that showed statistical differences between the treatments was short-term transverse reflection slab cracking. The findings from this statistical analysis were as follows:

Evaluation of Rehabilitation Strategies with Respect to Structural Responses

FWD deflections were used as the response measure of the pavement structure. Deflections at the center of the slab and at the transfer joints were used in this study. JPCP and JRCP structures were evaluated independently. Sections that received an HMA overlay were monitored like flexible pavements, and deflections at the center of the lane were used.

There were limitations due to the amount of data available, especially after the data were grouped by pavement structure type and surface. Because of the small sample size (eight sites), the statistical power of the analysis was low, and no statistical differences were found in the pavement response of JPCP structures.

The only analysis that provided some statistically meaningful results was the evaluation of maximum deflection at the center lane of overlaid JRCP structures. The results suggested that crack/break and seat significantly increased the overall deflections measured on the pavement surface. The remaining treatments interchangeably provided equivalent maximum deflection magnitudes. These results were expected since crack/break and seat was an alternative in which the concrete slab was reduced to smaller pieces resulting in lower stiffness, and this increased the maximum deflection at the center of the slab.

Evaluation of Structural Responses Immediately After Rehabilitation and Future Performance

The objective of this study was to identify trends in the relationship between response measured immediately after the rehabilitation and the observed performance in the subsequent years of the pavement's service life. LTE between slabs and maximum deflection at the center of the slab were used when the surface remained concrete slabs after rehabilitation. Maximum deflection at the center of the lane was used when the surface changed to HMA after rehabilitation.

LTE Versus Performance in JPCP

Only transverse slab cracking exhibited a clear trend with LTE values in no overlaid JPCP sections, indicating that as the efficiency of the load transfer increased, the amount of transverse slab cracking decreased. This trend suggested that good load transfer joint restoration was important to mitigate the development and propagation of slab cracking.

Maximum Deflection at Center of Slab Versus JPCP Performance

The trend between performance based on roughness and deflection measured at the center of the slab suggested that the higher the deflection, the smoother the JPCP over time. This trend was not what would normally be expected. The level of slab cracking also showed an inverse trend with maximum deflection measured at the center of the slab. The trend suggested that slabs with higher deflections under FWD loading were less likely to develop cracking. A possible explanation was that stiffer subgrades resulted in higher slab curling and warping stresses, which led to increased slab cracking. This same result was found in MEPDG.(1) While stiffer foundations reduced axle load stresses, they increased curling and warping stresses, which often tended to dominate cracking.

Faulting was also investigated, and the observed trend suggested that faulting was inversely proportional to deflection measured at the center of the slab. High deflection values yielded low faulting, although the trend was weak and depended on only one or two points. There was no logical explanation for this result.

Maximum Deflection at Center of Lane Versus Performance of Overlaid JPCP

For sections that received an overlay as part of the rehabilitation strategy, there was a clear indication that overlaid JPCP with high deflections were more likely to become rougher pavements in the long term compared to sections with low deflection values.

Overlaid JPCP sections with high center lane deflections were more likely to experience higher rutting than sections with low deflection values. Since all rutting occurred in the HMA layer, the cause for this result was not explainable unless the HMA was so soft that it contributed significantly to the total deflection. Normally, nearly all deflection was in the foundation for JPCP.

The fatigue cracking trend suggested that high fatigue cracking was expected when deflection values were high. High longitudinal cracking values were observed when maximum deflections at the center of the lane were low, which indicated that the pavement structure was less deformable and more susceptible to surface tensile stresses, which was an important contributor to the development and propagation of longitudinal cracking.

Response Versus Performance in JRCP

The investigation of possible trends between response and performance in JRCP structures did not result in any meaningful conclusions. Different performance measures were analyzed against LTE, maximum deflection at the center of the slab, and maximum deflection at the center of the lane; however, no relevant conclusion was determined.

Findings from MEPDG Analyses

MEPDG analysis was used to compare MEPDG-predicted performance of rehabilitated pavement sections with field-measured data and to verify current calibration against predictions of rehabilitated pavement structures. The following summarizes the findings from the MEPDG analysis.

The findings for the roughness model are as follows:

The findings for the rutting model are as follows:

The finds for cracking models for HMA overlays are as follows:

Recommendations for Future Research

The following list provides suggestions for future research to further build on the knowledge gained from this study.

Researchers could monitor or create a new LTPP experiment to examine new and rehabilitated sections, including the following focus areas:

Another possible research plan includes future improvements of MEPDG models, including the following:

The recommendations for technology transfer are as follows:

 


The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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