Abbreviation for the Strategic Highway Research Program. This multi-year in depth federal research project provides much of the data used in determining today’s most effective paving and pavement maintenance designs, materials, and methods.

The part of a paving machine which spreads, smoothes, and provides the initial compaction of the asphalt. Screeds actually “float” over the asphalt and their adjustment determines the finished thickness as well as the crown or valley profile of the asphalt mat.

Application of a sealant (usually coal-tar emulsion or asphalt emulsion type) to preserve, protect, and beautify asphalt pavements. Generally used on low traffic streets or off-street locations.

The degree to which a paved surface is angled to aid in the drainage of water.

Slurry Seal
A sealcoating process generally used on runways, streets, and roadways. In this process the coating is manufactured by the application equipment as it is being applied. A closely specified blend of graded asphalt emulsion, additives, and aggregate slurry seal is generally classified as Type I, II, or III depending on the size of aggregate used. A large aggregate slurry seal with additional polymers may also be referred to as microsurfacing. Used infrequently on parking areas due to the potential for tracking in hot weather.

Stone Base
The layer in the pavement system below the asphalt binder and driving surface. The base usually consists of crushed stones of varying sizes and gradations.

The soil prepared to support a structure or a pavement system. It is the foundation for the “pavement structure.”

Subgrade Failure
Subgrade failures occur when the prepared soil beneath the asphalt structure can no longer adequately support the weight of the structure or the traffic. Subgrade failures can occur for a number of reasons, including: ground water, excessive load counts (too much weight), and inadequate design. The failure can be corrected by excavating the soft material from the affected area and replacing it with compacted soil or bridging stone material.

Is short for “Superior Performing Asphalt Pavement”. It is an asphalt design philosophy that uniquely designs roads, parking lots and other asphalt structures according to the environment. Variables such as weather, the amount of traffic, the type of traffic, etc. are taken into account.

Asphalt mix where the largest stone used is no larger than 1/8 an inch (typically #8 gradation). Surface mixes are usually laid at a minimum depth of 1inch compacted.

Tack Coat
Asphalt oil, usually emulsion type, applied to existing pavement during repairs or overlay paving to create a bond between the old and new asphalt.

The result of products or materials being “picked up” by car tires, shoes, shopping cart wheels, etc. and being carried from the pavement or “tracked” onto surfaces where the material is not desired.

Transverse Crack
A break in the asphalt pavement that is at a ninety degree angle to the direction of the roadway or the direction in which the asphalt was laid.

Transverse Joint
A joint in the asphalt pavement that is at a ninety degree angle to the direction of the roadway or the direction in which the asphalt was laid.