U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-RD-07-052
Date: September 2007
Layer: That part of the pavement produced with similar material and placed with similar equipment and techniques. The material within a particular layer is assumed to be homogeneous. The layer thickness can be equal to or less than the core thickness or length.
Sample: A representative portion of material from one or more pavement layers received from the field. A sample can be a core, block, chunk, piece(s), bulk, thin-walled tube or jar sample.
Test Specimen: That part of the layer which is used for or in the specified test. The thickness of the test specimen can be equal to or less than the layer thickness.
Core: An intact cylindrical specimen of the pavement material that is removed from the pavement by drilling at the designated location. A core can consist of, or include, one, two, or more different layers.
Block: A block sample of the pavement material is removed by sawing at the test pit area through the full depth of the pavement. A block sample can consist of, or include, one, two, or more different layers. Chunks and/or pieces are retrieved from the field if a block sample cannot be recovered. Chunks and pieces are always smaller than a block sample.
Chunks: Chunks (large pieces) of material extracted from the full thickness of each layer in the test pit area and/or the 12-inch (305-mm) diameter BA... type borehole(s). An undisturbed block sample (12 inch [305 mm] square) may also be taken from the field in certain cases. A chunk is always smaller than a block sample. If chunks or block samples of the designated material cannot be recovered, then smaller pieces of the material are collected in the field for shipment to the laboratory.
Pieces: Very small chunks of material extracted from the full thickness of each layer in the test pit area and/or the 12-inch (305-mm) diameter BA... type borehole(s). An undisturbed block sample (12-inch [305-mm] square), or a chunk sample may also be taken from the field in certain cases. A chunk is always smaller than a block sample and a piece is always smaller than a chunk sample. Pieces are recovered only if block or chunk samples could not be recovered in the field.
Bulk Samples: That part of the pavement material that is removed from an unbound base or subbase layer or from the subgrade. Bulk samples are retrieved from the borehole(s) and the test pit at the designated locations. The bulk sample of each layer is shipped in one or more bag(s) to the laboratory. The material from one layer should never be mixed with the material from another layer even if there is less than the desired amount to perform the specified tests.
Test Sample: That part of the bulk sample of an unbound base or subbase layer or subgrade which is prepared and used for the specified test. The quantity of the test sample may be the same but will usually be less than the bulk sample.
Asphaltic Concrete (AC): Thoroughly controlled paving mixtures coarse and fine aggregates or fine aggregate above, with or without mineral filler, uniformly mixed with asphalt, and compacted into a uniform dense mass. For purposes of this Guide, AC material generally consists of hot-laid, hot-mixed AC (HMAC) paving mixtures used in bituminous surface, wearing and binder courses, and other HMAC layers beneath the AC surface.
Portland Cement Concrete (PCC): A combination of portland cement, water, and aggregates bound together into a uniform, dense mass. For purposes of this Guide, the material consists of pavement quality portland cement concrete used in the PCC surface layer of PCC pavements.
Treated Base or Subbase Material: Treated base or subbase materials are bound or stabilized base or subbase layers. These terms (treated, bound, stabilized) are used interchangeably in reference to base and subbase layers containing a cementing or binding type of agent. For allowable LTPP terminology and codes, see Table 4.30 of this Guide.
Asphalt Treated Base or Subbase (ATB): Asphalt treated base and subbase materials (also known as bituminous treated materials) include soils, aggregate and soil-aggregate mixtures bound by asphalt cement, emulsified asphalt, cutback asphalt, tar, or bitumen. Examples are asphalt treated aggregate base, soil-asphalt, and sand-asphalt. Typically these materials are produced by cold-mix and mixed-in-place procedures. For the purposes of this Guide, the ATB materials do not include AC materials described in (j) above with the exception of HMAC layers beneath AC surfaces.
Other than Asphalt Treated Base or Subbase (OTB): Other than asphalt treated base and subbase materials include all types of treated materials for which asphalt cement, emulsified asphalt, cutback asphalt, tar or bitumen were not used as a binding agent. Typical OTB materials range from very strong and durable to weak and less durable treated materials. Examples of very strong material are lean concrete, econocrete, and CTB. The following materials may range from strong to weak; soil cement, lime stabilized materials, lime-, flyash-treated soils. Materials stabilized with chemicals, industrial wastes, and different kinds of proprietary products are also included in the category of OTB materials.
Treated Subgrade: Treated subgrade materials are bound or stabilized layers of subgrade soils. The terms (treated, bound, stabilized) are used interchangeably in reference to the treated subgrade containing a cementing or binding type of agent. Table 4.27 and Table 4.30 should be consulted to assign appropriate LTPP terminology and codes for the description of treated subgrade material and type of treatment respectively. The treated subgrade may be asphalt treated material (for example, ATB) or other than asphalt treated material (for example, OTB, lime, cement, lime-, and cement-flyash, polymer, and chemical treated subgrade; but not lean concrete and econocrete).
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