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Publication Number: FHWA-HRT-04-032
Date:

Key Findings From LTPP Analysis 2000-2003

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PAVEMENT REHABILITATION

With a large portion of the national highway system at or beyond its original design life, pavement rehabilitation has come to the forefront as a key activity for highway agencies. The magnitude of the challenges faced by agencies as they pursue the rehabilitation of our highway system is tremendous. LTPP analysis has begun to provide some of the many answers that highway agencies need as they address this challenge. The following re key findings from several LTPP analyses of pavement rehabilitation.

  1.  
  2. Rehabilitation of Rigid Pavements
  3. Rehabilitation of Flexible Pavements

Rehabilitation of Rigid Pavements

  1. Findings of the SPS-6 Experiment

    The primary objective of the SPS-6 experiment (rehabilitation of jointed PCC pavements) is to examine the effects of different rehabilitation techniques on JPCP or JRCP. Based on pavement preparation, the rehabilitation techniques investigated can be separated into three pavement categories: exposed PCC, AC overlay of non-fractured PCC, and AC overlay of fractured PCC. Within each category, direct comparisons of performance based on distress are described below.

    Report No. FHWA-RD-01-169

    • Exposed PCC: The rehabilitation techniques in this category involve the restoration techniques other than overlay, including full-depth repair, diamond grinding, joint sealing, and addition of retrofitted edge drains. faced by agencies as they pursue the rehabilitation of our
      •  
      • If the pre-rehabilitated section has significant roughness, a diamond grinding should be fully considered or the section will retain its roughness. Full-depth repairs do not remove significant roughness from a JPCP or JRCP by themselves.
      • Both routine and premium pavement preparation treatments reduce the amount of transverse cracking immediately after rehabilitation. Routine preparation treatment includes limited patching, crack repair and sealing, and stabilization of joints. Premium preparation treatment includes subsealing, subdrainage, joint repair and sealing, full-depth repairs with restoration of load transfer, diamond grinding, and shoulder rehabilitation.
      • Premium pavement preparation with diamond grinding reduces the amount of faulting to zero immediately after rehabilitation.
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    • AC overlay of non-fractured PCC: This rehabilitation technique involves applying varying degrees of pre-overlay repairs and placing an AC overlay.
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      • The AC overlay of non-fractured PCC reduces the roughness immediately after rehabilitation to a smooth level (1.0 m/km (5.3 ft/mile)).
      • The sections with AC overlay of non-fractured PCC exhibit a faster increase in IRI over time than does the fractured PCC.
      • The sections with AC overlay of non-fractured PCC exhibit a lower increase in IRI over time than do premium preparation PCC sections.
      • The routine and premium preparation sections with 102-mm (4-inch) AC overlays exhibited no reflective cracking within the first year after construction.

    Report No. NCHRP 20-50(3/4)

    • The rigid pavement rehabilitation treatments in the SPS-6 experiment (rehabilitation of jointed PCC pavements) can be ranked from most to least effective with respect to IRI, rutting, and cracking in the following order:
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      • 203-mm (8-inch) overlay of cracked/broken and seated pavement.
      • 102-mm (4-inch) overlay of either intact or cracked/broken and seated pavement, with or without sawing and sealing of transverse joints, and with either minimal or intensive pre-overlay repair.
      • Concrete pavement restoration with diamond grinding, full-depth repair, and joint and crack sealing.
      • Concrete pavement restoration without diamond grinding, but with full-depth repair, and joint and crack sealing.
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    • Of the SPS-6 test sections that received diamond grinding, most also received full-depth repair, joint resealing, and crack sealing. In addition to those four techniques, some sections also received subdrainage retrofitting, undersealing, and/or load transfer restoration. The last three techniques do not appear to have produced significantly lower long-term roughness levels, compared to sections that received only diamond grinding, full-depth repair, and joint and crack sealing.
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  2. Findings of the SPS-6 and GPS-7B Experiments

    Report No. NCHRP 20-50(3/4)

    • The rutting data from the SPS-6 (rehabilitation of jointed PCC pavements) and GPS-7B (new AC overlays on PCC pavements) experiments indicate that, on average, 6 mm (0.24 inches) of rutting develops in the first year after placement of an AC overlay of either an intact or a cracked/broken and seated concrete pavement. This may be due to compaction of the AC overlay by traffic, and appears to be independent of the overlay thickness, mixture type, pre-overlay preparation, and pre-overlay rutting level.
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    • No significant differences were detected in crackingbased on 8 years of data:
      • Between minimal (i.e., without milling) and intensive (i.e., with milling) pre-overlay preparation.
      • Between sections with versus without sawed and sealed joints.
      • Between 102-mm (4-inch) overlays with sawed-andsealed joints versus those over cracked/broken and seated pavements.
      • Between 102-mm (4-inch) versus 203 mm (8-inch) overlays of cracked/broken and seated pavements.
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    • In 102-mm (4-inch) AC overlays of intact slabs, no significant differences were detected in roughness based on 6 years of data:
      • Between minimal and intensive pre-overlay preparation.
      • Between sections with versus without sawing and sealing of transverse joints.
      • Between overlays with sawed and sealed joints versus overlays of cracked/broken and seated slabs.
      • As expected, among overlays of cracked/broken and seated slabs, the 203-mm (8-inch) overlays have significantly lower long-term roughness than the 102-mm (4-inch) overlays.

Rehabilitation of Flexible Pavements

  1. Findings of the SPS-5 Experiment
    The performance of the rehabilitation techniques in the SPS-5 experiment (rehabilitation of AC pavements) is presented in four categories: the AC overlay thickness, the age of overlay, milling with overlays, and the overlay mixture type (with or without recycled asphalt pavement).
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    • AC overlay thickness. Report No. NCHRP 20-50(3/4)
      • Overlay thickness and pre-overlay roughness level are the two factors that most influenced the performance of asphalt overlays of asphalt pavements in the SPS-5 experiment with respect to roughness, rutting, and fatigue cracking.
      •  
      Report No. FHWA-RD-01-168
      • Overlay thickness does not appear to have a strong effect on the occurrence of longitudinal cracking in the wheel path and rutting. There is no apparent effect on roughness based on these early observations (5 years after rehabilitation).
      •  
      Report No. FHWA-RD-00-029
      • Compared to thinner (51-mm (2-inch)) overlays, thicker (127-mm (5-inch)) overlays consistently have less longitudinal cracking outside the wheel path.
      •  
    • Age of AC overlay. Report No. FHWA-RD-01-168
      • Age of overlay was found to be the leading contributing factor to four of the six distresses studied in the SPS-5 experiment (rehabilitation of AC pavements): fatigue cracking, rutting, transverse cracking, and initial pavement smoothness.
      • Age of the overlay and the climatic factors (temperature and precipitation) have a significant effect on the fatigue cracking at each project. The thickness of the overlay was less significant than these two factors based on these early observations (5 years after rehabilitation).
      • Age of the overlay and precipitation were found to have an important effect on the rut depths. However, increased precipitation may not be the sole factor related to increased rut depths.
      • Age of the overlay, pavement condition before overlay, and milling were found to be important relative to pavement smoothness.
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    • Milling with overlays. Report No. FHWA-RD-00-29
      • The data consistently show fewer transverse cracks on milled surfaces, compared to unmilled surfaces, before overlay placement. This seems logical, because removal of the top material from the original AC layer should reduce the effects of the cracks in the original pavement on the overlay.
      • The amount of transverse cracking is dependent on the original pavement condition before overlay placement. The overlays placed on pavements classified in good condition exhibit less transverse cracking than on pavements classified in poor condition.
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    • Report No. FHWA-RD-01-168
      • The data show that milling offers no consistent advantage for resisting longitudinal cracking outside the wheel path during the early life of an overlay. Milling has little effect in the short run.
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    • Overlay mixture type (with or without recycled asphalt pavement). Report No. FHWA-RD-00-029
      • There is no advantage to using one mixture type over the other (virgin versus recycled mixtures) in reducing the number of transverse cracks.
      • Compared to virgin mixes, recycled AC mixtures resisted longitudinal cracking outside the wheel path substantially better in at least five projects constructed.
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  2. Findings of the GPS-6 Experiment Report No. FHWA-RD-00-029
    •  
    • The GPS-6 (including GPS-6A: existing AC overlays on AC pavements and GPS-6B: new AC overlays on AC pavements) data show that fatigue cracking and longitudinal cracking in the wheel path are related. Specifically, the longitudinal cracking in the wheel path will eventually propagate or evolve into fatigue cracking with continued traffic loading.
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    • GPS-6A (existing AC overlays on AC pavements) data show that overlay designs that provide pavement structure consistent with traffic expectations can be expected to perform well for more than 10 years.
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  3. Findings of the SPS-5 and GPS-6B Experiments Report No. NCHRP 20-50(3/4)
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    • Similar to the results from the SPS-6 (rehabilitation of jointed PCC pavements) and GPS-7B (new AC overlays on PCC pavements) experiments, the rutting data from the SPS-5 (rehabilitation of AC pavements) and GPS-6B (new AC overlays on AC pavements) experiments indicate that, on average, about 6 mm (0.24 inches) of rutting develops in the first year after placement of an AC overlay of an AC pavement. This may be due to compaction of the AC overlay by traffic and appears to be independent of the overlay thickness, mixture type, pre-overlay preparation, and preoverlay rutting level.
    •  
    • No significant differences were detected in rutting based on 10 years of data between:
      • Virgin versus recycled mixtures.
      • Minimal versus intensive pre-overlay preparation.
      • Thin (51-mm (2-inch)) versus thick (127-mm (5-inch)) AC overlays.

 

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