Long-Term Pavement Performance Maintenance and Rehabilitation Data Collection Guide

Appendix A. Standard Codes

Experiment Type Definitions

General Pavement Studies

(01) Asphalt Concrete Pavement with Granular Base

Acceptable pavements for this study include a dense-graded HMAC surface layer, with or without other HMAC layers, placed over untreated granular base. One or more subbase layers may also be present, but are not required. A treated subgrade is classified as a subbase layer. "Full depth" AC pavements—defined as an HMAC surface layer combined with one or more subsurface HMAC layers beneath the surface layer with a minimum total HMAC thickness of 152 mm (6 inches) placed directly over a treated or untreated subgrade—are also allowed in this study. Two or more consecutive lifts of the same mixture design are to be treated as one layer.

Seal coats or porous friction courses are allowed on the surface, but not in combination. For example, a porous friction course placed over a seal coat is not acceptable. Seal coats are permissible on top of granular layers. At least one layer of dense-graded HMAC is required, regardless of the existence of seal coats or porous friction courses.

(02) Asphalt Concrete Pavement with Bound Base

Acceptable pavements for this study include a dense-graded HMAC surface layer with or without other HMAC layers, placed over a bound base layer. To properly account for a variety of bound base types in the sampling design, two classifications of binder types, bituminous and nonbituminous, are defined as factor levels. Bituminous binders include asphalt cements, cutbacks, emulsions, and road tars. Nonbituminous binders include all hydraulic cements (those that harden by a chemical reaction with water and are capable of hardening under water), lime, fly ashes, and natural pozzolans, or combinations thereof. Stabilized bases with lower quality materials such as sand asphalt or soil cement are also allowed. Stabilization practices of primary concern for this study are those in which the structural characteristics of the material are improved due to the cementing action of the stabilizing agent. (Thus, the description of the study actually refers to treatments improving the structural properties of the base materials.) Two or more consecutive lifts of the same mixture design are to be treated as one layer. One or more subbase layers may be present but are not required.

Seal coats or porous friction courses are permitted on the surface but not in combination, e.g., a porous friction course placed over a seal coat is not acceptable. Project selection is often favorable to those constructed on both fine and coarse subgrades.

(03) Jointed Plain Concrete Pavement—JPCP

Acceptable pavements for this study include a jointed, unreinforced PCC slab placed over an untreated granular base, HMAC, or stabilized base. One or more subbase layers may also be present, but are not required. The joints may have either no load transfer devices or smooth dowel bars. A seal coat above a granular base layer is permissible. Jointed slabs with load transfer devices other than dowel bars and pavements placed directly over a treated or untreated subgrade are not acceptable.

(04) Jointed Reinforced Concrete Pavement—JRCP

Acceptable projects include jointed reinforced PCC pavements with doweled joints spaced between 66 and 213 m (20 and 65 ft). The slab may rest directly on a base layer or on unstabilized coarse-grained subgrade. A base layer and one or more subbase layers may exist, but are not required. A seal coat is also permissible over a granular base layer. JRCPs placed directly over a fine-grained soil/aggregate layer or a fine-grained subgrade will not be considered for this study. JRCPs without load transfer devices or using devices other than smooth dowel bars at the joints are not acceptable.

(05) Continuously Reinforced Concrete Pavement—CRCP

Acceptable projects include continuously reinforced PCC pavements placed directly over a base layer or upon unstabilized coarse-grained subgrade. One or more subbase layers can exist but are not required. A seal coat (prime coat) is permissible just above a granular base layer. CRCPs placed directly over a fine-grained soil/aggregate layer or a fine-grained subgrade are not acceptable for this study.

(06) AC Overlay of AC Pavement

Pavements in the GPS–6A, 6B, 6C, 6D, and 6S experiments include a dense-graded HMAC surface layer with or without other HMAC layers placed over an existing AC pavement.

The designation 6A refers to those sections that were overlaid before acceptance in the GPS program.

The 6B, 6C, 6D, and 6S designation refers to LTPP sections on which an overlay was placed after the section had been accepted into the LTPP program.

Seal coats or porous friction courses are allowed, but not in combination. Fabric interlayers and SAMIs are permitted between the original surface and the overlay. The total thickness of HMAC used in the overlay is required to be at least 25.4 mm (1.0 inch).

(07) AC Overlay of Concrete Pavement

Pavements classified in the GPS–7A, 7B, 7C, 7D, 7F, 7R, and 7S experiments primarily consist of JPCP, JRCP, and CRCP pavements in which a dense-graded HMAC surface layer with or without other HMAC surface layers was constructed.

The exception is the 7R classification that has been added to account for PCC pavement test sections rehabilitated using CPR techniques. (To date, no test sections have been classified in the 7R category.)

The designation 7A refers to sections that were overlaid prior to acceptance in the GPS program. The 7B, 7C, 7D, 7F, and 7S designations refer to those test sections on which an overlay was placed after the section had been accepted into the LTPP program.

The PCC slab may rest upon a combination of the base and/or subbase layers. The existing concrete slab can also be placed directly over lime or cement-treated fine or coarse-grained subbase or over untreated coarse-grained subgrade soil. Slabs placed directly over untreated fine-grained subgrade are not acceptable.

Seal coats or porous friction courses are permissible but not allowed in combination. Fabric interlayers and SAMIs are acceptable when placed between the original surface (concrete) and the overlay. Overlaid pavements involving aggregate interlayers and open-graded AC interlayers are not included in this study. The total thickness of HMAC used in the overlay is required to be at least 38 mm (1.5 inches).

(09) Unbonded JCP Overlays of Concrete Pavement

Acceptable projects for this study include unbonded JPCP, JRCP, or CRCP overlays with a thickness of 129 mm (5 inches) or more placed over an existing JPCP, JRCP, or CRCP pavement. An interlayer used to prevent bonding of the existing and the overlay slabs is required. The overlaid concrete pavement can rest on a base and/or a subbase or directly on the subgrade.

Specific Pavement Studies

(01) Structural Factors for Flexible Pavements

The experiment on Strategic Study of Structural Factors for Flexible Pavements (SPS–) examines the performance of specific HMAC-surfaced pavement structural factors under different environmental conditions. Pavements within SPS– must start with the original construction of the entire pavement structure or removal and complete reconstruction of an existing pavement. The pavement structural factors included in this experiment are in-pavement drainage layer, surface thickness, base type, and base thickness. The experiment design stipulates a traffic loading level in the study lane in excess of 100,000 80-kN (18-kip) equivalent single axle load (ESAL) per year. The combination of the study factors in this experiment result in 24 different pavement structures. The experiment is designed using a fractional factorial approach to enhance implementation practicality. This permits the construction of 12 test sections at 1 site and the construction of a complementary 12 test sections on a similar subgrade type at another site within the same climatic region.

(02) Structural Factors for Rigid Pavements

The experiment on Strategic Study of Structural Factors for Rigid Pavements (SPS—) examines the performance of specific JPCP structural factors under different environmental conditions. Pavements within SPS— must start with the original construction of the entire pavement structure or the removal and complete reconstruction of an existing pavement. The pavement structural factors included in this experiment are in-pavement drainage layer, PCC surface thickness, base type, PCC flexural strength, and lane width. The experiment requires that all test sections be constructed with perpendicular doweled joints at 4.9-m (15-ft) spacing and stipulates a traffic loading level in the lane in excess of 200,000 ESAL/year. The experiment is designed using a fractional factorial approach to enhance implementation practicality. This permits construction of 12 test sections at 1 site and construction of a complementary 12 test sections on a similar subgrade type at another site within the same climatic region.

(03) Preventive Maintenance Effectiveness of Flexible Pavements

The experiment on Preventive Maintenance Effectiveness of Flexible Pavements (SPS–3) examines the performance of four preventive maintenance treatments (cracking seal, chip seal, slurry seal, and thin overlay) on AC surfaced pavement sections within the four climatic regions, on the two classes of subgrade soil. The experimental design stipulates that the effectiveness of each of the four treatments be evaluated independently. The effectiveness of combinations of treatments is not considered. Therefore, each site includes four treated test sections in addition to a control section. In most cases the control, or "do nothing" section, is classified as a GPS test section.

(04) Preventive Maintenance Effectiveness of Jointed Concrete Pavements

The experiment on Preventive Maintenance Effectiveness of Jointed Concrete Pavements (SPS–4) was designed to study the effects of crack/joint sealing and undersealing on jointed PCC pavement structures. Both JRCP and JPCP are included in the study. Undersealing is included as an optional factor and is only performed on a section for which the need for undersealing is indicated. The experimental design stipulates that the effectiveness of each of the two treatments be evaluated independently. The effectiveness of combinations of treatments is not considered. Each test site includes two treated test sections in addition to a control section. The treatment sections on joint/crack seal test sites consists of one section in which all joints have no sealant, and one in which a watertight seal is maintained on all cracks and joints.

(05) Rehabilitation of Asphalt Concrete Pavements

The experiment on Rehabilitation of Asphalt Concrete Pavements (SPS–5) examines the performance of eight combinations of AC overlays on existing AC-surfaced pavements. The rehabilitation treatment factors included in the study are intensity of surface preparation, recycled versus virgin AC overlay mixture, and overlay thickness. The experimental design includes all four climatic regions and conditions of existing pavement and stipulates a traffic loading level in the study lane in excess of 100,000 ESALs/year.

(06) Rehabilitation of Jointed Portland Cement Concrete Pavements

The experiment on Rehabilitation of Jointed Portland Cement Concrete Pavements (SPS–6) examines the performance of seven rehabilitation treatment options as a function of climatic region, type of pavement (plain and reinforced), and condition of existing pavement. The rehabilitation methods include surface preparation (a limited preparation and full CPR) with a 102-mm- (4-inch-) thick AC overlay or without an overlay, crack/break and seat with two AC overlay thicknesses (102 mm and 203 mm) (4 inches and 8 inches), and limited surface preparation with a 102-mm- (4-inch-) thick AC overlay with sawed and sealed joints.

(07) Bonded Concrete Overlays of Concrete Pavements

The experiment on Bonded Concrete Overlays on Concrete Pavements (SPS–7) examines the performance of eight combinations of bonded PCC treatment alternatives as a function of climatic region, pavement type (jointed and continuously reinforced), and condition of existing pavement. The rehabilitation treatment factors include combinations of surface preparation methods (cold milling plus sand blasting, and shot blasting), bonding agents (neat cement grout or none), and overlay thickness (76 and 127 mm) (3 and 5 inches). The experimental design stipulates a traffic loading level in the study lane in excess of 200,000 ESAL/year.

(08) Environmental Effects in the Absence of Heavy Loads

The experiment on Environmental Effects in the Absence of Heavy Loads (SPS–8) examines the effect of climatic factors in the four environmental regions, subgrade type (frost-susceptible, expansive, fine, and coarse) on pavement sections incorporating flexible and rigid pavement designs that are subjected to limited traffic loading. The experimental design requires either two flexible pavement structures or two rigid pavement structures to be constructed at each site. The two flexible pavement sections consist of a 102-mm (4-inch) AC surface on a 102-mm- (8-inch-) thick untreated granular base, and a 178-mm (7-inch) AC surface over a 305-mm- (12-inch-) thick granular base. The two rigid pavement test sections consist of doweled JPCP with 203-mm (8-inch) and 279-mm (11-inch) PCC surface thickness on 152-mm- (6-inch-) thick dense-graded granular base. The pavement structures included in this study match pavement structures included in the SPS– and — experiments. The experiment design stipulates that traffic volume in the study lane be at least 100 vehicles per day but not more than 10,000 ESALs/year. The flexible and rigid pavement sections may be constructed at the same site or at different sites.

(09) Validation of SHRP Asphalt Specifications and Mix Design

The SPS–9P pilot effort was initiated at the end of the SHRP program with the objective of gaining experience in implementing the Superpave specifications. Test sections classified as SPS–9P were constructed using a very limited set of guidelines. In some instances, specifications were based on interim Superpave specifications that were changed at a later date. Many of the test sections were constructed before material sampling and testing guidelines were established.

The SPS–9A experiment, Superpave Asphalt Binder Study, requires construction of a minimum of two test sections at each project site. Construction may include new construction, reconstruction, or overlay. The minimum test sections consist of (1) Highway agencies' standard mix, (2) Superpave Level 1 designed standard mix, and (3) Superpave mix with alternate binder grade either higher or lower than the specified Superpave binder. The minimum of two test sections at some sites results from the agency's declaration that the Superpave test section is the same as the standard agency mixture. This experiment will provide the opportunity to evaluate and improve the practical aspects of implementing the Superpave mix design through a hands-on field trial by interested highway agencies. It will also make it possible to compare the performance of the Superpave mixes against mixes designed with current highway agencies' asphalt specifications, asphalt-aggregate specifications, and mix design procedures. Finally, there will be an opportunity to test the sensitivity of the Superpave asphalt binder specifications relative to low temperature cracking, fatigue, and permanent deformation distress factors.

JPCP – Jointed Plain Concrete Pavement, JRCP – Jointed Reinforced Concrete Pavement, CRCP – Continuously Reinforced Concrete Pavement
* "Composite Pavements" are pavements originally constructed with an AC wearing surface over a PCC slab (1986 AASHTO Guide for Design of Pavement Structures).

* Originally taken from Oil and Gas Journal, March 20, 1989, pp. 72–89 and updated October 1993.

Taken from Manual Series No. 5 (MS-5), "A Brief Introduction to Asphalt," and Specification Series No. 2 (SS-2), "Specifications for Paving and Industrial Asphalts," both publications by the Asphalt Institute.

Note: LTPP only studies outside lanes.

Note: The recycling agent groups shown in this table are defined in ASTM D4552.

Previous | Table of Contents