Rehabilitation of Asphalt Concrete Pavements: Initial Evaluation of The SPS-5 Experiment-Final Report

Chapter 3. Project Requirements

A set of requirements was placed on each SPS-5 project to be built as part of the LTPP program. These included limitations on the rehabilitation of the test sections and specifications covering the types of materials to be used, the materials tests to be conducted, and the monitoring to be conducted by the Regional Coordination Office (RCO) during the life of the project. Each of these requirements is described in this chapter.

CONSTRUCTION REQUIREMENTS

Each region received, construction requirements from the "Construction Guidelines" section of the Specific Pavement Studies of Rehabilitation of Asphalt Concrete Pavements (SPS-5) Guide.⁽²⁾ These guidelines would ensure adequate attention to the details of construction operations.

The guidelines included several special considerations: The SPS-5 projects could not be built in areas where lanes were being widened. Seal coats and geotextiles were not allowed on these test sections. The projects could not include retrofitted edge drains, lane additions, or shoulder construction. Surface friction courses could be used if required by the agency, but they were restricted to 19 mm and were not considered part of the HMA overlay thickness. If the HMA surface of the control section was stripping, a seal coat could be placed on its surface if that represented a standard agency practice.

Control Section

The control section on each project was to have only a limited amount of activity. A control section provides an indication of the performance of the pavement if no rehabilitation has been done. Therefore, it was important for construction activity on the control section to be limited to a minimum. Repairs on these sections were limited to those maintenance activities needed to sustain safety and functionality. The application of a seal coat or chip seal was to be delayed at least one year after construction of the other test sections.

Levels of Surface Preparation

The factorial had two levels of pavement preparation: minimal and intensive.

Minimal surface preparation was used on test sections 02 through 05, and included patching and placing a level-up course for ruts deeper than 13 mm. Patches were to be used in areas with localized failures. These areas included severe fatigue cracks, potholes, deep depressions, and cracks greater than 19 mm wide. The area to be patched was to be cleaned of loose material and a tack coat used to ensure a good bond of the patch material. The patch material was to be a dense-graded HMA. A level-up layer of a fine-graded HMA mixture could be placed only when the ruts were greater than 13 mm deep, and placement was confined to wheel paths.

If the original pavement included a porous friction course (PFC), this material could be milled off. The PFC was removed only if the prior experience of the State highway agency (SHA) indicated that this material would adversely affect the performance of the overlay. Milling of the PFC was not to extend into the surface course of the flexible pavement.

Intensive surface preparation was used on sections 06 through 09. As stated in chapter 2, this level of preparation included milling, patching of distressed areas and potholes, and crack sealing. No seal coats or geotextiles were to be placed on these test sections. Milling was required on all of these test sections to a depth of 38 to 51 mm to remove oxidized or stripped material. The milled surface was cleaned with a power broom and then the milled material was replaced with an equal thickness of the HMA overlay mixture, excluding any PFC material that was removed.

HMA Mixture Designs and Materials

HMA mixture designs for both the recycled and virgin mixtures were to meet the following requirements:

• If a Marshall mix design was used:

  Compaction	75 blows
  Stability (minimum)	8000 newtons
  Flow	8 mm–14 mm
  Compaction	3 to 5 percent

• If a Hveem mix design was used:

  Stability value (minimum)	37 newtons
  Swell (maximum)	8 mm
  Design air voids	3 to 5 percent

• All new aggregates were to have 60 percent of the material retained on the No. 4 sieve with two fractured faces. The aggregate blend should be a dense-graded gradation.
• Experimental modifiers and additives were not allowed.
• The recycled mix should include 30 percent RAP. The RAP should not be from a mix with a history of stripping or high abrasion.
• The reclaimed coarse aggregate should have 100 percent passing the 38-mm sieve and a maximum of 25 percent passing the 9.5-mm sieve.
• Lift thickness was to be no more than 76 mm.
• Longitudinal joints were to be located within 0.3 m of the center of the lane or within 0.3 m of the center of two adjacent lanes.
• Transverse joints were to be located outside of the test sections.

MATERIALS SAMPLING AND TESTING

Materials sampling and testing were required for each material placed and on the existing pavement before placement of the overlay to evaluate differences between the test sections and projects within the SPS-5 experiment. The material properties being measured are those commonly used for design and those needed to assess the response characteristics of HMA mixtures.

A general sampling and testing plan was created for use as a guideline.⁽¹⁾ This guideline was used to develop a sampling and testing plan specific to each project. Because each owner agency was allowed to add supplemental test sections, the number of tests varies for each project (test numbers increase with an increase in test sections). These plans were created before the 15 construction of each individual project. The plans provided the location of each sample to be taken, where each sample should be sent, and specified the tests to be performed on each sample.

Samples taken from the project include:

• Bulk samples from the upper 305 mm of the subgrade.
• Thin-walled tube samples of the subgrade to 1.2 m from the top of the subgrade.
• Jar samples of the subgrade.
• Bulk samples of any unbound base layer.
• Jar samples of any unbound base layer.
• Cores of any bound base layer.
• Cores of the asphalt surface and binder.
• Bulk samples of the asphalt mixes used in the overlay.
• Bulk samples of the asphalt cement used in all mixes.
• Cores of the overlay materials being placed.

In addition to each of these samples, bulk samples were to be taken of the asphalt cement, aggregates, and uncompacted asphalt concrete mixes to be stored long term. Auger probes were to be performed in the shoulder of each test section to a depth of 6 m. This allowed determination of the depth to a rigid layer. Finally, as part of the field activities during the construction of the project, nuclear density and moisture testing was conducted on top of the bulk sampling areas for the subgrade, and on the top of each layer in each test section.

The testing of these samples was split between the FHWA and the owner agency. The FHWA was responsible for the resilient modulus tests, creep compliance tests, and associated tests (tests for which results are required before running the resilient modulus tests). For instance, the protocol for determining the resilient modulus on unbound materials was dependent upon the material classification. Therefore, the FHWA laboratory determined the classification of the material before running the resilient modulus test. The owner agencies were responsible for all other laboratory material tests. Tables 4 and 5 illustrate the tests that were to be performed and the minimum number required.

MONITORING REQUIREMENTS

Performance Data

The several different types of performance data used to monitor the SPS-5 projects are:

• Manual and photographic distress surveys. The photographic distress surveys are performed by PASCO, while the manual distress surveys are performed by RCO personnel.
• Deflection basin measurements are collected by the RCOs using a Dynatest® falling weight deflectometer (FWD).
• Transverse profile measurements can be taken at the same time as the distress surveys. As part of a manual distress survey, the surveyor takes transverse profile measurements using a FACE Company Dipstick®, while the PASCO units take the transverse profiles in addition to the photographic distress surveys.
• Friction measurements are collected by each individual agency responsible for constructing the project.

Initial monitoring of these performance indicators was to be performed on the test sections 6 months before construction was initiated and within 6 months after construction was completed.

Long-term monitoring was to be performed every other year, but could be postponed for up to one year. The RCOs are responsible for maintaining the data-collection schedule. However, there can be numerous reasons why a RCO was unable to satisfy the monitoring frequency requirements in place when a project was built; some are:

• Egress restrictions imposed by the contractor until that project was accepted by or turned back over to the owner agency.
• Weather conditions, especially on projects built in the northern part of North America and completed during the fall months.
• Equipment breakdowns or maintenance requirements.
• Scheduling difficulties.

As of January 1, 1999, friction measurements were no longer required on any test section. All data collected are submitted and stored in the IMS.

Traffic Data

Traffic data are to be collected on each of the projects. The requirement as of the time of this report stated that automatic vehicle classification (AVC) data are to be collected continuously on SPS-5 test sections. The term "continuous data" is defined as the "use of a device that is intended to operate throughout the year and to which the SHA or Canadian Province commits the resources necessary to both monitor the quality of the data being produced and to fix problems quickly upon determination that the equipment is not functioning correctly."⁽⁷⁾ This level of data collection is necessary to provide accurate traffic loading measurements. In addition to continuous AVC data, weigh-in-motion (WIM) data are to be collected a minimum of 2 days per year.

Climatic Data

Climatic data are obtained from the National Oceanic and Atmospheric Administration (NOAA). These data are collected from four to five NOAA weather stations surrounding the project. The data are then averaged using a weighting procedure. This procedure gives weights based on the distance of the weather station from the project. The closer the weather station is to the project, the larger the weight used in the averaging. The data collected from NOAA include information about the temperature, rainfall, wind, and solar radiation.

Each SPS-5 project was to meet these monitoring minimum requirements. Any deviation from these requirements could affect the results that can be obtained from data analysis. The next chapter examines how each project has deviated from these requirements and how these deviations can be expected to affect results obtained from this experiment.