Rehabilitation of Jointed Portland Cement Concrete Pavements: SPS-6, Initial Evaluation and Analysis

Chapter 8. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

The SPS-6 experiment, Rehabilitation of Jointed Portland Cement Concrete Pavements, is one of the key experiments in the LTPP program. The main objective of this experiment is to determine the effectiveness of different rehabilitation techniques and strategies and their contributions to pavement performance and service life. There are some concerns about the ability of the SPS-6 experiment to meet expectations, given that several SPS-6 sites were not constructed. In addition, some construction deviations and data collection deficiencies exist for the SPS-6 sites that were constructed.

This study presents the first comprehensive evaluation of the SPS-6 experiment. First, this chapter summarizes the experiment site factors, data availability, and data completeness for the SPS-6 experiment. Next, this chapter provides a convenient summary of the conclusions drawn from the early performance trends identified in this report. This is followed by a brief summary of some of the States' expectations for the SPS-6 experiment. Finally, this chapter provides the research team's recommendations for improving the SPS-6 experiment, its data availability, expectations for the SPS-6 experiment, and future data collection and analysis topics.

SUMMARY

A summary of experiment site factors and data availability and completeness is provided below:

SPS-6 Experiment Site Factors Summary

Fourteen SPS-6 sites have been constructed throughout the United States. Each SPS-6 site was selected to fulfill a portion of the original SPS-6 design factorial. Once these sections were constructed, a review of the climatic data resulted in several sites being reclassified in the wet-freeze zone (as shown in table 81). This reclassification completes the wet-freeze design factorial. This will allow a complete analysis of the wet-freeze climatic areas, which encompass a large geographic region of the United States. Unfortunately, many sites are now missing from the wet-no freeze, dry-freeze, and dry-no freeze zones. Thus, there is excellent coverage in the wet-freeze climatic zones for both JPCP and JRCP, and excellent coverage for JPCP in wet-no freeze climatic zones. Unfortunately, there is no coverage for either JPCP or JRCP in dry climatic zones. Note that this will only be important if increased precipitation significantly affects the performance of rehabilitated JRCP and JPCP.

It is also important to consider the variations in the design properties associated with each experiment section and variations in the monitoring interval from that designated by the SPS-6 experimental plan. All of these deviations from the requirements of the SPS-6 experimental plan must be considered during all future analytical efforts.

Notes:

• Each * indicates that an additional site is needed to complete the original design matrix.
• Bolded sections were originally in another cell of the design matrix.
• Italicized sections indicate that the site did not meet the minimum traffic requirements.
• MO(A) is the second SPS-6 site constructed in Missouri; the first site is designated as MO.

Data Availability and Completeness Summary

Data availability and completeness for the SPS-6 experiment are good overall. A high percentage of the SPS-6 data are at level E; however, a significant amount of data was not available at the time of analysis, especially traffic, distress surveys, and key materials testing data. These deficiencies need to be addressed before serious analysis of the SPS-6 experiment can occur. This includes:

• Data that were not available at the time of the study and are required by the LTPP data collection guidelines (unavailable data).
• Data elements that are important to future research, but are not required by the LTPP data collection guidelines for SPS-6 (missing data elements).

Unavailable Data

This section summarizes the data that were unavailable at the time of the study and are required by LTPP data collection guidelines. It should be stressed that there are numerous reasons why some important data may not be available from the publicly released IMS database at the time of analysis. The following are some possible examples:

• Data are yet to be collected or the laboratory tests have not yet been performed.
• Data are under regional review.
• Data have failed one of the quality checks and are being reviewed.
• Data have failed one of the quality checks and were identified as anomalies.
• Data need to be quality checked.

As such, the unavailable data identified in this section do not necessarily mean that the data were not collected or submitted by the States. There are several instances where data may get held up and not reach level E. Note that the results reported in this section are based on level E data only. The LTPP program is embarking on a systemwide effort to resolve all unavailable data so that they will be available to future researchers. Some data have already been located during the course of this study.

Table 82 summarizes data availability and completeness by some of the key data types, while table 83 summarizes data availability and completeness for the key data types that are to be monitored over the long term. Note that any rating of "Fair" or "Poor" means that these sites would not meet analytical needs and, therefore, must be improved as soon as possible. The SPS-6 data deficiencies are summarized below:

• Alabama and Missouri (A): Sites are newly constructed and data processing is underway.
• Indiana: Design thicknesses are in the database in place of the as-constructed thicknesses.
• Traffic data are deficient or there are negative ESAL values for 6 of 14 sites (40 percent).
• All States (except Arizona) need to conduct some of the materials testing.
• Some of the monitoring data from immediately before and after construction were not collected or are not yet available in the database.
• Most of the long-term monitoring data are at level E.

*For Indiana, design values were used as actual pavement layer thicknesses.

Detailed data availability and completeness assessments are provided in the following sections for traffic, materials, and monitoring data.

Traffic Data

The SPS-6 experimental design calls for traffic data to be collected using a combination of permanent and portable equipment by the individual States. Table TRF_MONITOR_BASIC_INFO was examined to identify SPS-6 records with annual ESAL estimates. As discussed in this report, Alabama, Arkansas, Missouri (A), and Tennessee do not have any traffic data in the IMS database. Because these sections are relatively new to the program, they probably have traffic information. However, as of August 1999, information had not yet been entered into the database. The remaining sites have 1 to 9 years of traffic data available, depending on the age of the site. In addition, Arizona and California have negative ESAL values for most of the AC-overlaid sections and, therefore, have a non-level E record status. Reportedly, these values have been corrected since these data were originally extracted from the IMS database.

Materials Testing Data

Data availability and completeness assessment results for the key AC and PCC materials testing tables show that none of the materials tests meets the required number of tests initially established by the LTPP program. It is important to point out that, even though all of the materials tests have not been conducted, many States have conducted some of these tests. In addition, many States are looking into and addressing their materials testing deficiencies. As of the time of this report, very little materials testing data were available for the sites in Alabama, Arkansas, and Missouri (A) because of the relatively young ages of these sites. In addition, California, Indiana, and South Dakota had very little materials testing data available when this report was prepared. The remaining eight sites have completed a significant portion of the materials testing results. Arizona has the most complete set of materials testing results in the IMS database based on the data extracted from the IMS database for this report.

Monitoring Data

Seven types of monitoring data are included in the LTPP IMS: (1) automated distress, (2) manual distress, (3) friction, (4) longitudinal profile, (5) cross profile, (6) deflection, and (7) dynamic load response. Using the minimum requirements for the collection of monitoring data noted in these tables, an assessment of data availability and completeness follows:

• Long-term monitoring data were not yet releasable at the time of this data analysis for Alabama, Arkansas, Missouri (A), and Tennessee.
• Longitudinal profile data are acceptable for most sites. Long-term monitoring was typically conducted at an interval averaging less than 3 years.
• Deflection data are complete, with a long-term monitoring interval averaging 3 years or less.
• Faulting data are, on average, at an interval of 3 years or less.
• Rutting data are, on average, at an interval of 2 years or less.
• Combined distress data result in periodic surveys within an average interval of 2 years, except for Arizona, which is at an interval of 2.4 years.
• Friction testing was not available for nine sites. However, sites with friction data have a relatively good monitoring period that averages 3 years or less.

Missing Data Elements

The following data elements or information were not included in the SPS-6 data collection plan; however, they will probably be needed for future analyses of the data. These data elements or activities are recommended for future data collection activities for the SPS-6 experiment:

• Measure the dynamic modulus in uniaxial compression over a temperature range for hot mix asphalt (HMA) mixtures.
• Measure the performance grade of the asphalt that was used in the HMA layers and measure the aging that has occurred since construction.
• Measure the indirect tensile strain at failure in accordance with the method identified in National Cooperative Highway Research Program (NCHRP) Report 338. This value can be easily measured during the indirect tensile strength test.

CONCLUSIONS

Conclusions drawn from the early performance trends identified in this report are provided below.

Early Performance Trends Summary

Note that these performance trends represent early findings and that these results may be altered once all of the data have been collected and a more thorough investigation has been conducted in the future. This includes detailed analysis of every SPS-6 site. Tables 84 through 87 show the preliminary performance trends for each general type of rehabilitation treatment applied.

N/A: Surveys for section ***604 are not sufficient to identify preliminary trends

N/A: Surveys for section ***604 are not sufficient to identify preliminary trends.

Bare PCC Pavements

Roughness

• Control sections (maintenance only) and minimum-preparation sections (without diamond grinding) exhibit the roughest pavements. Even those sections having the maximum preparation, but no diamond grinding exhibited considerable roughness or IRI. Thus, if the pre-rehabilitated section has significant roughness, diamond grinding should be thoroughly considered or the section will retain its roughness. By themselves, full-depth repairs did not remove significant roughness from JRCP or JPCP.
• Maximum preparation with diamond grinding resulted in initially smooth pavements (initial IRI about 1.0 m/km (63.36 inches/mi)) that were similar to AC overlays. The IRI of these sections did increase over time (more so than for the AC overlays), probably because of more joint and crack faulting in some sections.

Transverse Cracking

• Both minimum- and maximum-rehabilitation treatments reduce the amount of transverse cracking immediately after rehabilitation because of full-depth repairs and slab replacements.
• The rate of increase in transverse cracking is somewhat less for the control section. The minimum-preparation section (***602) has a higher rate of increase in transverse cracking, while the maximum-preparation section (***605) has the highest rate. The cause of these trends needs to be explored on a site-by-site basis.

Faulting

• The control section had the least change in joint faulting over time. This can be explained by the fact that all of the slabs within this section have reached equilibrium and have reduced movement.
• Maximum-preparation rehabilitation with diamond grinding reduces the amount of faulting to zero immediately after rehabilitation.
• Minimum- and maximum-preparation sections had a higher rate of increase in faulting over time than the control section. This may be partially caused by the fact that most of these sections were diamond ground, giving a zero faulting, and then a more rapid increase followed over time at both the regular joints and the joints of the new full-depth repairs.
• Faulting of the maximum-preparation sections is projected to equal that of the control sections after about 12 years, on average.
• The major advantage of maximum preparation over minimum preparation in the early analysis appears to be the smoothness resulting from diamond grinding.

AC Overlay of Nonfractured PCC

Roughness

• AC overlay of nonfractured PCC reduces the roughness immediately after rehabilitation, typically to a smooth level (1 m/km (63.36 inches/mi)).
• These sections are experiencing a faster increase in IRI over time than the AC overlay of fractured PCC.
• These sections are experiencing a lower increase in IRI over time than the maximum preparation PCC sections.
• The amount of preparation (minimum or maximum) did not yet appear to have a significant effect on the IRI of AC nonfractured JRCP or JPCP. This may change as the pavements age.

Reflection Cracking

• Neither the minimum- nor maximum-preparation sections with 102-mm (4-inch) AC overlays had any reflection cracking within the first year after construction.
• Reflective cracking survey information for the minimum-preparation sections with a 102-mm (4-inch) AC overlay with sawed and sealed joints (***604) appears to be inconsistent from survey date to survey date. It is recommended that these inconsistencies be addressed before this rehabilitation alternative is further evaluated.
• Maximum-preparation sections had very little change or increase in reflection cracking, while minimum-preparation sections had a slightly higher increase in reflection cracking over time.

AC Overlay of Fractured PCC

Roughness

• AC overlay of fractured PCC had a low IRI immediately after rehabilitation (typically 1.0 m/km (63.36 inches/mi)).
• This rehabilitation had the lowest rate of increase in IRI after rehabilitation than any of the other rehabilitation alternatives.

Fatigue Cracking

• Both crack/break and seat rehabilitation techniques with 102-mm (4-inch) and 203-mm (8- inch) AC overlay show low amounts of fatigue cracking over time.

Transverse Cracking

• As these pavement sections continue to age, a direct comparison should be made between the transverse (reflection) cracking occurring for the nonfractured PCC rehabilitation and that found for the fractured PCC rehabilitation. This should be done, site-by-site, for each SPS-6 experiment to obtain the maximum trends and findings for each rehabilitation alternative.

STATE EXPECTATIONS

One national workshop was held recently where input was received from the States on the SPS-6 experiment. The meeting was held on April 28, 2000, in Newport, RI. The research team made presentations at the conference on the status of SPS-6 data collection, data availability, near- and long-term LTPP products, and the analysis of SPS-6 data. Several participating States made presentations on the status and analyses of their SPS-6 projects and their expectations for the SPS-6 experiment. There were many discussions on future directions for the SPS-6 experiment and analyses of the data.

In general, the States are satisfied with the SPS-6 experiment and fully expect to get valuable information about the different rehabilitation features included in the SPS-6 experiment. Many States have been conducting and are planning their own analyses on their SPS-6 projects. Some of these analyses have already yielded useful results. The States would like to see a focus on implementation of SPS-6 findings as they evolve over time.

First and foremost, what the States want from the SPS-6 experiment are the effects on pavement performance and the cost-effectiveness of the experimental design factor features, such as:

• Condition of existing pre-rehabilitated jointed plain concrete.
• Pre-restoration effectiveness.
• Pre-overlay effectiveness.
• AC overlay thickness.
• Fractured versus nonfractured influence.
• Diamond grinding effectiveness.
• Edge drain effectiveness.

In addition to the structural design features, the States also want to know which major site condition factors influence the performance of rehabilitated concrete pavement, including:

• Climate.
• Traffic volume.
• Traffic loading.

Other specific expectations from the States include:

• Maximum years of service life for rehabilitated pavements.
• Next-best alternative.
• Dollar design.
• Standard solutions for a given pavement condition.
• Best rehabilitation methods for minimizing reflection cracking.
• State-specific findings.

As for future analytical plans for the SPS-6 experiment, the States believe that it is worthwhile to first fill in the missing data (backcasting, if necessary, to obtain traffic and materials data). It is believed that many fundamental studies can be conducted to see how SPS-6 sections are responding to loading and environmental stresses. It was also suggested that an integrated analytical plan is needed for future research.

This evaluation has shown that several significant problems will limit the results that can be obtained from the SPS-6 experiment. Specifically, the SPS-6 projects have construction and rehabilitation deviations. In addition, significant materials and traffic data are missing from some sites or sections. The missing traffic data and key materials data must be obtained or forecasted before meaningful global analysis can be performed.

However, this does not mean that many important and useful findings and results cannot be obtained from the SPS-6 experiment. Some interesting and important early trends have already been identified that will be useful for the rehabilitation of jointed plain concrete, even though the sections are less than 10 years old. As time and traffic loadings accumulate on the SPS-6 sites, much more valuable performance data will be obtained.

Because of FHWA's intense ongoing effort to obtain missing data (construction, materials, traffic, and monitoring), valuable results can be obtained from the SPS-6 sites. It is further believed that even more results can be obtained if a concerted effort is made to perform proper analyses of the data.

RECOMMENDATIONS

Finally, this chapter provides the research team's recommendations for improving the SPS-6 experiment, data availability, expectations for the SPS-6 experiment, and future data collection and analysis topics as follows.

Missing SPS-6 Experiments

It is recommended that the following sites be constructed:

• Construct additional sites in dry climatic regions (assuming that States such as Arizona and California agree) so that the findings can be extended to these regions. There are currently no SPS-6 sites within a dry climatic region. Precipitation and temperature are known to affect diamond-ground joints and may affect HMA overlays over conventional and cracked and seated pavements as well.

Missing SPS-6 Data

Significant efforts should be put forth to obtain the following missing data:

• Materials: Extensive data are currently missing. It is important that these data be obtained and moved to level E in the database or the evaluation of various rehabilitation treatments will be hampered.
• Traffic: Data at level E are limited or missing for a large number of sites.
• Pavement structure data (primarily thickness): Data at level E are limited or missing for about 25 percent of the sites.
• Monitoring: Data are very limited at four sites; joint faulting is limited. Pre- and post-rehabilitation testing are missing for most sections.

Expectations From SPS-6 Experiments

The overall objective is for SPS-6 performance results to provide the SHAs with documented findings to help them improve their management, design, construction, and materials procedures for the rehabilitation of jointed concrete pavements. The following specific expectations for the SPS-6experiments are recommended:

Effects of Specific Design, Climate, and Traffic

• Effects of level of pre-restoration preparation for bare JPCP and JRCP on performance (faulting, transverse cracking, joint spalling, IRI).
• Effects of level of pre-HMA overlay preparation on performance (rutting, reflection/transverse cracking, IRI).
• Effects of HMA-overlaid sawed and sealed joints on performance (reflection/transverse cracking, IRI).
• Effects of cracking and seating of JRCP and JPCP prior to HMA overlay on performance (rutting, reflection/transverse cracking, IRI).
• Effects of HMA overlay thickness over cracked and seated JRCP and JPCP on performance (rutting, reflection/transverse cracking, fatigue, longitudinal cracking, IRI).
• Effects of climatic region on the performance of various rehabilitation treatments (temperature, precipitation).
• Effects of traffic loading on the performance of various rehabilitation treatments.

Data for Use in Calibration of Mechanistic-Empirical Distress Models

• 2002 Design Guidedistress models:
  • Data for use in empirical performance modeling (for pavement management).
  • Data for use in a variety of mechanistic modeling (backcalculation, structural analysis, and reflection cracking).

Data for Use in a Variety of Cost-Benefit Analyses

Future Data Collection

The following are recommended:

• Routine current data collection:
  • Weigh-in-motion (WIM) and automatic vehicle classification (AVC) traffic monitoring: Ensure that LTPP guidelines are followed.
  • Resolve irregular distress measurements over time for each SPS-6 section (wild swings of distress quantities over time) and resolve saw and seal reflection/transverse cracking interpretation problems.
• Collect new data:
  • None recommended.

Recommended Future Analyses for SPS-6 Experiment

As stated previously, the SPS-6 test sections are currently developing initial performance trends. Currently, no long-term performance trends have been identified and only a few sections have been taken out of service. The real benefit from this experiment will occur over the next 10 to 15 years as more and more test sections exhibit higher levels of distress, magnifying the effects of the experimental factors on performance.

This report focuses on the quality and completeness of the SPS-6 construction and monitoring data and on the adequacy of the experiment to achieve the original expectations and objectives. Detailed analysis of the effects of different rehabilitation alternatives on performance was outside the scope of this study. Thus, future studies using the SPS-6 experiment data should be planned and prioritized so that they can be initiated as the SPS-6 projects exhibit higher levels of distress.

These future studies should be planned in two stages, focusing on local and national expectations for the experiment. The first stage is to conduct a detailed assessment or case study on each experimental cell in the experiment to ensure data adequacy, assess construction deficiencies, and support local interests and expectations, while the second stage evaluates the effects of different rehabilitation alternatives across the entire national experiment. Both analytical stages are briefly discussed in the following sections. A third analytical stage will ultimately be needed after the sections are 10 to 15 years of age to fully reap the benefits of the SPS-6 experiment.

Initial Stage: Analysis of Local Expectations or Experimental Factorial Cells

Each major cell in the SPS-6 experiment consists of a duplicated project. Each SPS-6 site constitutes a full factorial of design factors and makes it possible to evaluate the performance results for each experimental factor for those site conditions. A detailed evaluation of the replicated projects within each major cell should be completed as soon as possible to ensure that all of the required data exist and to examine any construction anomalies. The objectives of the case studies in the first stage are to:

• Resolve construction and monitoring data anomalies and experimental cell differences for those projects that changed cell locations from the original experimental design as they relate to the specific cell in the experiment.
• Conduct comparative analyses of the individual test sections at each site, including the supplemental test sections, to identify the differences in pavement performance and response. These comparative studies should include performance measures, material properties, and as built conditions.
• Determine the effects of any construction difficulties, problems, and material noncompliance issues with the SPS-6 project specifications, if any, on pavement performance and response at each site.
• Develop findings regarding comparisons made between the companion projects and test sections and prepare a case study report that will be useful for the SHAs involved (the report will also be useful for the national studies).

This first analytical stage is considered absolutely essential prior to initiation of the second analytical stage.

Second Stage: Analysis of National Expectations or Experimental Findings

The second analytical stage should not be pursued until the first analytical stage has been completed. It is expected that the analyses performed at this stage will be coordinated with the Strategic Plan for LTPP Data Analysis. The SPS-6 experiment can contribute to the following specific analyses outlined in the strategic plan:

• Relationships to enable interchangeable use of laboratory- and field-derived material parameters (Strategic Plan No. 2B).
• Procedures for determining as-built material properties (2C).
• Estimation of material design parameters from other materials data (2E).
• Information as to the relationship between as-designed and as-built material characteristics (2F).
• Recommendations for climatic data collection to adequately predict pavement performance (3D).
• Models relating functional and structural performance (4C).
• Calibrated relationships (transfer functions) between pavement response and individual distress types (5C).
• Quantitative information on the performance of maintenance and rehabilitation treatments, including the effect of pretreatment conditions (6A).
• Guidance on the timing and selection of pavement maintenance and rehabilitation options, and the expected performance life of each (6B).
• Quantitative information on the impact of design features on measured pavement responses (deflections, load transfer, strains, etc.) (7A).
• Quantitative information on the impact of design features on pavement distress (7B).

In summary, the following future analytical objectives are recommended for the SPS-6 experiment. These analytical topics are discussed in more detail in figures 22 through 26.

1. Perform site-by-site analyses of SPS-6 projects to resolve data problems and the impact of construction anomalies on the performance of individual test sections (initial stage (figure 22)).
2. Determine the effects of the SPS-6 experimental factors on the performance of the rehabilitation of JPCP and JRCP (figure 23).
3. Conduct cost-benefit analyses of SPS-6 site data to determine the cost-effectiveness of various rehabilitation design features (figure 24).
4. Calibrate and validate relationships (transfer functions) between pavement structural response and individual distress types (figure 25).
5. Determine the optimum rehabilitation techniques for jointed concrete pavement design features for specific site conditions and traffic loading (study of the SPS-6 experimental factors) (figure 26).

The full results from the SPS-6 experiment will require 10 to 15 years of monitoring for the majority of the sections. Additional studies beyond those proposed will be required.