AR-160 AR-20 AR-40 AR-HO AR-tO
Older system that measures needle penetration. Asphalt is sampled at 77" F (25 "Cl- Still in use in Canada and in some states.
Newer system introduced in 1972. Scientifically measures viscosity of the asphaltât 140"F (60*C). Most states use this system.
A variation of I he more standard viscosity graded system. Measures asphalt after simulated aging. Used in several western states.
* Consult local highway departments for criteria of local grading systems. Local criteria are oflen slight modifications of the above specifications, altered to suit local conditions.
t The hard-sofl scale is used to indicate relative hardness within each grading system and not as a comparison of hardness from one grading system to another. The grades toward the harder, or thicker, end of the spectrum tend to be used in heavier traffic conditions or warmer climates. Cooler climates or lighter loads utilize grades inward ihe softer end of the spectrum.
Technically, the term asphalt refers only to asphalt cement or "binder," the basic cementitious material that is eventually mixed with aggregate to form pavements. In common usage, however, the terms asphalt, asphalt pavement, asphalt concrete, and bituminous concrete refer to the many available mixtures of asphalt and aggregate that are used for various purposes in landscape construction.
This section focuses exclusively on asphalt when used for paving, etc. although asphalt cement or binder is also commonly used as a sealant and as an adhesive (mastic)
The American Society for Testing and Materials (ASTM) and the American Association of State Highway and Transportation Officials (AASHTO) have established specifications on the manufacture and use of asphalt cement or binder products, and asphalt concrete mixtures commonly used in the United States. These specifications were used as a guide for data shown in this section.
It should be noted that in 1994 the industry formally accepted and began to implement the results of a ten year research effort conducted under the US Federal Strategic Highway Research Program (SHRP). This resulted in developing a new system for the design of asphalt paving to be known as Superpave. They are in the process of introducing a new designation for asphalt cement which hence-forth is to be called an "asphaltic binder." This binder will be known as PG (Performance Graded) binder and the new specifications for this asphaltic binder will be shown as a higher positive number followed by a negative number as for example PG 64-22. The first number represents a hot pavement design criteria In degrees centigrade and the second number represents the low or cold pavement design criteria in degrees centigrade. The grades will vary by 6 degree increments on both the high and low ends.
Since these new specifications are not officially available at the time of publication of this handbook (1997), the U.S. readers of this Section are urged to seek the latest detailed data from either national or local sources. Every major governmental unit throughout the world has established a set of standard specifications for asphaltic cement or binders that should be used as a guide to the production of quality asphalt pavements within its jurisdiction. Local standards and practices should always be consulted for the appropriate designs and specifications for any specific region or area.
2.0 asphalt cement or binder
2.1 Properties of Asphalt Cement or Binder
Asphalt cement or binder has several important properties that effect how this materia! can be used for various purposes and conditions.
Thermopiasticity: Asphalt cement or binder is an adhesive which deforms under loads or liquefies with heat. These properties cause it to be classified a flexible type ol pavement.
Viscosity and Crades: The viscosity of asphalt is directly influenced by tempera-lure. A temp era tu re/viscosity slope can be plotted to define the temperature for mixing and compaction. An increase in temperature means a decrease in viscosity.
Asphalt cement or binder can have grades of hardness or viscosity (Table 820-1). Each grade is intended for specific purposes.
There are three different methods for grading asphalt cement or binders used in the United States and Canada. All three grade asphalt according to degree of hardness. Table 8202 lists various grades of asphalt's from each method that are appropriate for roads, depending on climatic conditions.
Weathering: The oxidation of the surface and the evaporation of lighter hydrocarbons (volatilization) causes asphalt to lose its plasticity and to become brittle with age Properly sloped subbases and subgrades, proper compaction of layers, and timely sealing and surfacing treatments keep weathering to a minimum.
Insolvency: Asphalt is resistant to the chemical effects of water and of most salts, acids, and alkali's except petroleum-based materials, such as gasoline and oil-based paints if applied in concentrated amounts. Tar sealers are used on asphalt surfaces where concentrated spillage is expected
Color Asphalt is naturally black, but certain proprietary products or paving processes can alter that color. (Refer to 7.3 Colored Asphalt Pavements in this section for more information.)
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