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Publication Number: FHWA-RD-01-166
Date: November 2003

Structural Factors for Flexible Pavements—Initial Evaluation of The SPS-1 Experiment Final Report

PROJECT REQUIREMENTS

Each SPS-1 project had to meet certain criteria. There were limitations on the methods and materials used in construction of the sections, as well as requirements for testing and continued monitoring. Each of these criteria is outlined in this chapter.

CONSTRUCTION MATERIAL REQUIREMENTS

Construction requirements were provided in the "Construction Guidelines" section of the Specific Pavement Studies of Structural Factors for Flexible Pavements (SPS-1) Guide.(4) The overall length of each section was required to be 183 m with 152.4 m for monitoring and 15.25 m on each end for materials sampling. The distance between each of these sections had to be long enough to allow sufficient space for changes in materials and thicknesses during construction. The suggested length for these transitions was 30.5 m.

Subgrade Requirements

The finished subgrade elevations were not to vary from the design by more than 12 mm. This was to be determined using rod and level readings taken on the lane edge, outer wheel path, midlane, inner wheel path, and the inside lane edge at 15-m intervals throughout the project. Surface irregularities were not to exceed 6 mm between two points in any direction in a 3.05-m interval. If a working platform at the top of the subgrade was required, adding lime, portland cement, or other suitable material to the subgrade to alter the index properties of the soil could create it. The strength of the subgrade was not to be unduly increased.

Base Layers

Two types of bases are included in each project—drained and undrained. The drained bases include a permeable asphalt treated base with edge drains. The undrained bases consist of dense graded materials. The undrained bases were used on sections 1–6 and 13–18, and were defined as dense graded aggregate base (DGAB), asphalt treated base (ATB), or a combination of these two materials. The requirements for the DGAB were as follows:

The requirements for the ATB layer were as follows:

Sections 7–12 and 19–24 incorporate the drained bases. Each of these sections includes a PATB layer with edge drains to permit water to drain out of the pavement structure. The requirements for the PATB layer were as follows:

Drainage Materials

Filter fabrics were to be used on sections that include PATB layers. These were specified to prevent clogging of the PATB layer. The filter fabrics used were to meet the American Association of State Highway and Transportation Officials-American Building Contractors-American Road and Transportation Builders Association Task Force 25 recommendations, which include the following requirements:

Edge drains were to be installed on sections containing a PATB layer to collect water draining from the permeable base. The requirements on these drains were as follows:

Drainage pipes were to be sized for the expected flows determined as part of design. Discharge outlet pipes were to be located at maximum intervals of 76.2 m. Outlets were to be at least 152 mm above the expected 10-year flow elevation of the collector ditches to prevent backflow.

It should be noted that the construction requirements did not include video inspection of the edge drains after construction of the project or site was completed.

HMA Layers

The HMA surface had to meet the following requirements, as a minimum:

The shoulders placed on these projects had to be a minimum of 1.2-m wide. If possible, the shoulders were to be paved full-width with the surface course to eliminate longitudinal joints. If this was not possible, then the shoulders were to be paved such that the longitudinal joint was to be at least 305 mm outside the travel lane.

Surface friction courses were allowed on the sections if these layers were required by the participating agency. The friction courses were required to be no thicker than 19 mm and were not to be considered as part of the AC thickness required for any specific test section in the experiment.

MATERIALS SAMPLING AND TESTING

Sampling and testing were required on each of the materials being placed. The materials characterization is necessary to evaluate differences between the sections and between projects within the experiment. The parameters measured are those used in most design procedures and those used to assess important performance characteristics of these materials.

A general sampling and testing plan was created for use as a guideline.(4) >This guideline was then used to develop the sampling and testing plan specific to each project. Because each State was allowed to add supplemental test sections, the number of tests may vary from project to project (test numbers increasing with increase in test sections). These plans were created prior to the construction of each individual project and provided the location of each sample to be taken, where the sample should be sent, and the tests that were to be performed on each sample.

Samples taken from the project include:

In addition to each of these samples, bulk samples were to be taken of the asphalt cement, aggregates, and uncompacted AC mixes to be stored long term. A series of auger probes were to be performed in the shoulder of each test section to a depth of 6 m. This allows for the 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 divided between FHWA and the SHAs. FHWA conducted the resilient modulus tests, creep compliance tests, and other associated tests. The associated tests are those for which the results are required prior to running the resilient modulus tests. For instance, the protocol for determining the resilient modulus on unbound materials is dependent upon the material classification. Table 4 lists the tests that were to be performed and the minimum number required.

MONITORING REQUIREMENTS

The monitoring of these projects includes several different types of data—distress surveys, deflection measurements, transverse profile measurements, friction measurements, and longitudinal profile measurements. Each of these measurements has different frequency requirements, as noted in the following paragraphs, but these frequencies have been revised over time. The detailed review on the data completeness and availability was based on the cited reference. There can be numerous reasons why a regional coordination office (RCO) was unable to satisfy the monitoring frequency requirements that were in place when a project was built. Some of these reasons are as follows:

Distress Surveys

A distress survey was to be performed on the sections within 6 months of construction. A manual distress survey is to be performed on the sections biennially, with the exception of the "weak" sections. These weak sections are numbers 1, 9, 13, and 21, and they are surveyed annually. (5) >If necessary, the surveys may be postponed up to 1 year. In addition to the manual surveys, video distress surveys are performed.

Deflection Surveys

Deflection measurements are to be collected using a falling weight deflectometer (FWD) from 1 to 3 months after the project has been constructed.(6) Long-term monitoring of these projects is to be completed biennially, except for the "weak" sections. This testing can also be postponed up to 1 year if necessary. Sections 1, 9, 13, and 21 were to be tested every 6 months, but this testing can be postponed up to 6 months.

Table 4. Required testing for the SPS-1 experiment.

Material Type and Properties

LTPP Protocol

Minimum No. of Tests per Layer

Subgrade (when embankment ³ 1.2 m)
No Testing

Subgrade
Sieve Analysis
P51
6
Hydrometer to 0.001 mm
P42
6
Atterberg Limits
P43
6
Classification (visual-manual on thin-wall tubes)
P52
6
18
Moisture-Density Relations
P55
6
Resilient Modulus
P46
6
Unit Weight (only if thin-wall tubes available)
P56
6
Natural Moisture Content
P49
6
Unconfined Compressive Strength (only if thin-wall tubes available)
P54
6
Permeability
P57
3

Permeability

P48

6
Embankment < 1.2 m

Sieve Analysis

P51
6

Hydrometer to 0.001 mm

P42

6

Atterberg Limits

P43

6

Classification

P52

6

Moisture-Density Relations

P55

6

Resilient Modulus

P46

6

Natural Moisture Content

P49

6
Permeability
P48
6
Embankment ³ 1.2 m
Sieve Analysis
P51
6
Hydrometer to 0.001 mm
P43
6
Atterberg Limits
P42
6
Classification (visual-manual on thin-wall tubes)
P52
6
Moisture-Density Relations
 
18
Resilient Modulus
P55
6
Unit Weight (only if thin-wall tubes available)
P46
6
Natural Moisture Content
P56
6
Unconfined Compressive Strength
(only if thin-wall tubes available)
P49
P54
6
6
Permeability
P57
3

Permeability

P48
6
Unbound Granular Base
Particle Size Analysis
P41
3
Sieve Analysis (washed)
P41
3
Atterberg Limits
P43
3
Moisture-Density Relations
P44
3
Resilient Modulus
P46
3
Classification
P47
3
Permeability
P48
3
Natural Moisture Content
P49
3

Permeable Treated Asphalt Base

Asphalt Content (Extraction)

P04

3

Extracted Aggregate: Gradation of Aggregate

P14
3
Asphalt Treated Base
Core Examination/Thickness
P01
34
Bulk Specific Gravity
P02
34
Maximum Specific Gravity
P03
3
Asphalt Content (Extraction)
P04
3
Moisture Susceptibility
P05
3
Resilient Modulus

P07

9
Tensile Strength
P07
12
Extracted Aggregate:
Specific Gravity:
   
Coarse Aggregate
P11
3
Fine Aggregate
P12
3
Gradation of Aggregate
P14
3
National Aggregate Association (NAA) Test for Fine Aggregate Particle Shape
P14A
3
Asphalt Cement:
Abson Recovery
P21
3
Penetration at 25 °C and 46 °C
P22
3
Specific Gravity at 16 °C
P23
3
Viscosity at 60 °C and 135 °C
P25
3
Asphalt Cement (from Tanker or Plant):
Penetration at 25 °C and 46 °C

P22

3
Specific Gravity at 16 °C
P23
3
Viscosity at 60 °C and 135 °C
P25
3
Asphalt Concrete Surface and Binder

Core Examination/Thickness

P01

60

Bulk Specific Gravity
P02
60
Maximum Specific Gravity
P03
3
Asphalt Content (Extraction)
P04
3
Moisture Susceptibility
P05
3
Creep Compliance
P06
3
Resilient Modulus
P07
18
Tensile Strength
P07
24
Extracted Aggregate
Specific Gravity:
P11
3
Coarse Aggregate
P12
3
Fine Aggregate
P14
3
Gradation of Aggregate
P14A
3
NAA test for Fine Aggregate Particle Shape
 
3
Asphalt Cement:
Abson Recovery
P21
3
Penetration at 25 °C, 46 °C
P22
3
Specific Gravity at 16 °C
P23
3
Viscosity at 60 °C, 135 °C
P25
3
Asphalt Cement (from Tanker):
Penetration at 25 °C, 46 °C
P22
3
Specific Gravity at 16 °C
P23
3

Viscosity at 60 °C, 135 °C

P25
3

Transverse Profiles

Transverse profile measurements are to be taken at the same frequency, and at the same time, as the distress surveys.(5) As part of a manual distress survey, the surveyor takes transverse profile measurements using a FACE Dipstick ®. The PASCO units take automated transverse profile surveys in addition to the automated distress surveys.

Longitudinal Profiles

Longitudinal profile measurements are to be taken on the sections within 3 months after construction.(7) >These measurements can be postponed up to 3 additional months. The "weak" sections (sections 1, 9, 13, and 21) are monitored every 6 months but monitoring can be postponed up to 6 additional months. The other sections are to be monitored biennially. These tests can be postponed up to 1 year, if necessary.

Friction Surveys

Friction measurements were to be taken from 3 to 12 months after the sections were constructed. Long-term monitoring is to be conducted biennially. However, as of January 1, 1999, friction measurements are no longer required on any test section.(8) These measurements are considered optional and the data are being stored in the national IMS database, if collected.

Traffic Data

Traffic data are to be collected on each of the projects as well. The current requirement states that weigh-in-motion (WIM) data are to be collected continuously on SPS-1 sections. Continuous data collection is defined as the "use of a device that is intended to operate throughout the year and to which the SHA 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."(9) WIM devices are to be calibrated biannually. This level of data collection is considered necessary to provide accurate traffic loading measurements.

Climatic Data

Each SPS-1 project was to include the installation of an automated weather station (AWS).(10) The site is to be located close enough to the project to provide weather data that is representative of the weather on the project. The equipment installed at these locations includes a rain gauge. A desiccant, humidity indicator, and conduit putty are used to measure humidity. A wind monitor is included in the installation to measure wind speeds. Equipment also is included to determine the cloud cover and temperature at the site. All of this data is collected and stored by a datalogger. The data is downloaded from the datalogger at least every 6 months.

In addition to the AWS used to collect weather data, data are obtained from four to five National Oceanic and Atmospheric Association (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 includes information about the temperature, rainfall, wind, and solar radiation.

Each of the SPS-1 projects was supposed to meet these minimum requirements. Any deviation from these requirements could affect the results obtained from the analysis of the data. The next chapter examines how each of the SPS-1 projects have deviated from the requirements and how these deviations can be expected to affect the results that can be achieved from this experiment.

 


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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