Below is a description of each of the Specific Pavement Study (SPS) experiments. When constructing SPS projects, States and Provinces had the option of adding sections of particular interest to them. The data for these supplemental sections are not generally available. Please contact the LTPP Customer Support Service Center for additional information on obtaining this data.

SPS-1: Strategic Study of Structural Factors for Flexible Pavements

The SPS-1 examines the effects of climatic region, subgrade soil (fine- and coarse-grained), and traffic rate (as a covariate) on pavement sections incorporating different levels of structural factors. These factors include drainage (presence or lack of it), asphalt concrete (AC) surface thickness (102 mm and 178 mm), base type (dense-graded untreated aggregate and/or dense-graded asphalt-treated), and base thickness (203 mm and 305 mm for undrained sections and 203 mm, 305 mm and 406 mm for drained sections). The study design stipulates a traffic loading level in the study lane in excess of 100,000 Equivalent Single Axle Loads (ESALs) per year.

SPS-2: Strategic Study of Structural Factors for Rigid Pavements

SPS-2 examines the effects of climatic region, subgrade soil (fine- and coarse-grained), and traffic rate (as a covariate) on doweled jointed plain concrete pavement (JPCP) sections incorporating different levels of structural factors. These factors include drainage (presence or lack of it), concrete thickness (203 mm and 279 mm), base type (dense-graded aggregate and lean concrete), concrete flexural strength (3.79 and 6.21 MPa at 14 days), and lane width (3.9 m and 4.6 m). The study requires that all test sections be constructed with perpendicular joints at 4.9 m spacing and stipulate a traffic load level in the lane in excess of 200,000 ESALs per year.

SPS-3: Preventive Maintenance Effectiveness of Flexible Pavements

SPS-3 compares the effectiveness and mechanisms by which the selected maintenance treatments preserve and extend pavement service life, safety, and ride quality. The overall goal was not to compare the performance of one treatment to another, but to compare the change in performance of the treated section to the untreated section. The study factors for flexible pavements include: climatic zone, subgrade type (fine or coarse), traffic loading (greater or less than 85,000 ESALs/year), initial condition (good, fair, or poor), and structural adequacy (high or low). The maintenance treatments applied were slurry seal, chip seal, crack seal and thin overlay.

SPS-4: Preventive Maintenance Effectiveness of Rigid Pavements

SPS-4 compares the effectiveness and mechanisms by which the selected maintenance treatments preserve and extend pavement service life, safety, and ride quality. The overall goal was not to compare the performance of one treatment to another, but to compare the change in performance of the treated section to the untreated section. The study factors for flexible pavements include climatic zone, subgrade type (fine or coarse), subbase (granular or stabilized), and traffic loading (greater or less than 85,000 ESALs/year). The maintenance treatments applied were joint seal and joint seal with under seal.

SPS-5: Rehabilitation of Asphalt Concrete Pavements

SPS-5 examines the effects of climatic region, condition of existing pavement (fair and poor), and traffic rate (as a covariate) on pavement sections incorporating different methods of rehabilitation with AC overlays. These rehabilitation methods include surface preparation (routine preventive maintenance and intensive preparation with cold milling and associated repairs), type of asphalt overlay (virgin and recycled), and overlay thickness (51 and 129 mm). The study design stipulates a traffic loading level in the study lane in excess of 100,000 ESALs per year. The combination of study factors in this experiment result in eight different rehabilitation options to be constructed at each test site.

SPS-6: Rehabilitation of Jointed PCC Pavements

SPS-6 examines the effects of climatic region, type of pavement (plain and reinforced), condition of existing pavement (fair and poor), and traffic rate (as a covariate) on pavement sections incorporating different methods of rehabilitation with and without AC overlays. The rehabilitation methods include surface preparation (a limited preparation and full concrete pavement restoration) with a 102 mm thick AC overlay or without an overlay, crack/break and seat with different AC overlays (102 mm and 203 mm), and limited surface preparation with a 102 mm thick AC overlay with sawed and sealed joints. The experiment design stipulates a traffic-loading level in the study lane in excess of 200,000 ESALs/year. The combination of study factors results in seven different rehabilitation options constructed at each site. Sites are located only in wet-freeze and wet-no-freeze zones.

SPS-7: Bonded PCC Overlays on Concrete Pavements

SPS-7 examines the effects of climatic region, type of pavement (jointed and continuously reinforced), and condition of existing pavement and traffic (as covariates) on pavement sections incorporating different rehabilitation methods and concrete overlays. These rehabilitation methods include different surface preparation methods (cold milling plus sand blasting and shot blasting), bonding agents (neat cement grout or none), and overlay thickness (76 mm and 127 mm). The study design stipulates a traffic loading level in the study lane in excess of 200,000 ESALs/year. The combinations of study factors result in eight different overlay options that must be constructed at each site.

SPS-8: Study of Environmental Effects in the Absence of Heavy Loads

The study of Environmental Effects in the Absence of Heavy Loads examines the effect of climatic factors, subgrade type (frost-susceptible, expansive, fine, and coarse), on pavement sections incorporating different designs of flexible and rigid pavements and subjected to very limited traffic as measured by the ESAL accumulation. Pavement structure includes two levels of structural design for each class of pavement. Flexible pavement sections consist of 102 mm and 178 mm of AC surface on a 102 and 305 mm thick dense-graded untreated granular base respectively. Rigid pavement test sections consist of 203 mm and 279 mm thick doweled jointed plain concrete slabs on 152 mm thick dense-graded granular base. The study design stipulates the traffic volume in the study lane be at least 100 vehicles per day but not more than 10,000 ESALs in a year. The combination of study factors results in two flexible and two rigid sections. The flexible and rigid sections may be constructed at the same or different sites.

SPS-9: Validation of SHRP Asphalt Specification and Mix Design (Superpave)

As a part of the Strategic Highway Research Program (SHRP), conducted between 1987 and 1993, an extensive amount of research and development was conducted to improve the performance of AC. These activities conducted under the framework of the Asphalt Research Program investigated the chemical and physical properties of the asphalt binder. It also involved the development of accelerated tests for asphalt aggregate mixtures. The validation of the resulting performance-based asphalt and asphalt-aggregate mixture specification is being performed through controlled sections. The study design incorporates climatic conditions as defined by moisture (four levels) and pavement temperatures (four levels for minimum design temperature and four levels for maximum design temperature), asphalt-aggregate mix design, and traffic loading that must be at least 50,000 ESALs in the outside lane. At each site, both a State or Provincial mixture design and a SHRP Mixture and Design Analysis System section are built. Other mixes, such as Stone Mastic Asphalt, may also be constructed.

SPS-10: Warm-Mix Asphalt Overlay of Asphalt Pavements

The study of Warm-Mix Asphalt Overlays of Asphalt Pavements examines the long-term performance of warm mix asphalt pavements against hot-mix asphalt. The experiment consists of three core test sections:

• Hot-mix asphalt. 
• Warm-mix asphalt using foaming technology.
• Warm-mix asphalt using a chemical additive technology.

The overlays are between 2 and 4 inches in thickness, dense graded and the asphalt must contain 10 to 25 percent recycled mix.