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
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Publication Number: FHWA-HRT-06-068
Date: March 2006
Long-Term Pavement Performance (LTPP) pavement test sections should remain inservice for as long as possible so that performance trends can be established. Since the pavement test sections used in the LTPP program are located on public roads, however, some form of modification to the pavement structure will ultimately occur to keep the road in a safe and serviceable condition.
The terms maintenance and rehabilitation are used in the LTPP program to classify how various treatments that alter a test section's structure are documented in the database. This is an important distinction, since classification of some of these treatments may differ from highway agency terminology. For example, thin overlays that some agencies may classify as maintenance are classified by the LTPP program as rehabilitation since the data forms for overlays of any thickness are the same.
Maintenance activities include seal coats, crack sealing, patching, joint sealing, grinding, milling less than 25.4 millimeters (mm) (1 inch) deep, and grooving. Limitations on maintenance are intended to eliminate those activities that would reduce or destroy the amount of information that can be obtained from a test site. Maintenance of nonpavement related items such as guard rails, lighting, and signs are not affected by these guidelines.
Rehabilitation activities include overlays and associated pretreatments (patching, milling, joint repair, etc.), inlays (mill and fill), pressure relief joints in portland cement concrete (PCC) pavements, subsealing or undersealing, retrofitted subdrainage, joint load transfer restoration, and shoulder restoration.
A maintenance control zone beginning 152.4 meters (m) (500 feet (ft)) before the monitoring site and ending 76.2 m (250 ft) past the monitoring site has been established around each LTPP test section or project to coordinate maintenance activities in the area and to reduce the influence of other maintenance activities on the performance of the test section. Therefore, these guidelines pertain only to the maintenance activities within this maintenance control zone. The control zones should receive attention only in response to a direct pavement need in accordance with guidelines. In addition, all maintenance treatments within a zone should be performed using the corresponding highway agency's standard procedures and materials.
For General Pavement Studies (GPS) test sections, the maintenance control zone is located adjacent to the ends of the test section. For Specific Pavement Studies (SPS) projects, the maintenance control zone is established before the beginning of the first test section and terminated after the end of the last test section. For SPS sites with test sections located more than 1.6 kilometers (km) (1 mile (mi)) apart, the maintenance control zone should be established for each group of test sections.
Rehabilitation work, or any activities that will significantly alter the pavement performance, should not be performed on the test sections during the study period. These activities include extensive milling, grinding, grooving, or use of heater planer, undersealing, overlays (hot-mix asphalt concrete (HMAC)/PCC), slab jacking, retrofitting underdrains or edge drains, and other specific types of activities that affect the structural response of the monitoring site.
If these measures are applied to the pavement outside of the maintenance control zone, transitions the distance from these treatments to the control zone should be of sufficient length (recommended 61 m (200 ft) from the beginning or end of the control zone) to ensure the monitoring site is not influenced. If any of these types of treatments are planned for an area adjacent to a control zone, or for adjoining lanes or shoulders, the Regional Support Contractor (RSC) must be notified as soon as possible.
Although application of these treatments is strongly discouraged during the LTPP monitoring performance period, at some point the condition of the test section will deteriorate to a level that requires some type of extensive rehabilitative measure. In this event, the RSC should be notified to coordinate the last round of evaluation measurements. Since large amounts of information have been collected on these monitoring sites, these sections should be included as part of a rehabilitated pavement study. If the section is continued as one of the LTPP rehabilitation experiments, then data on the types of treatments should be collected following the guidelines established in chapter 4 of this guide.
Safety-related maintenance required by the participating agency's standards may be performed at any time. Safety-related maintenance used in this context refers to spot patching of potholes, punchouts, blowups, or other surface defects as well as restoration of friction resistance. For slowly deteriorating safety conditions, it would be desirable to notify the LTPP RSC in advance of any corrective action so that an observation of the pavement condition before application of the treatment can be made.
Until the end of 2003, restoration and rehabilitation were permitted on LTPP test sections as long as the guidelines for monitoring continuation specified in this document were followed.
When restoration or rehabilitation treatments are applied, the distance from these treatments to the monitoring section should be of sufficient length to ensure that performance of the test section is not influenced. If any of these types of treatments are planned for the pavement surrounding a test section or project, or for an adjoining lane or shoulder, the RSC must be notified as early as possible to enable adequate monitoring of pavement condition before treatment application. For test sections that will remain in study after a rehabilitation treatment, it is important that appropriate LTPP rehabilitation forms be completed to document treatment application. These forms can be obtained from the LTPP RSC and should be completed and returned to the RSC as soon as possible following the rehabilitation treatment.
The following chapters provide descriptions of the data forms used in collecting information about the maintenance or rehabilitation treatments applied to the LTPP test sections and guidelines for completing these forms. These chapters also address the restrictions placed on each type of treatment to keep these sections in the study for as long as possible.