Asphalt Basics

For more information, please visit Mn/Road.

1. Terms
2. Mix Descriptions and Characteristics
3. Mix Design

1. Terms

AASHTO - American Association of State and Highway Transportation Officials.
ADT or AADT - Average Daily Traffic.
Apparent specific gravity of asphalt mixture - A ratio of the unit weight of an asphalt mixture (excluding voids permeable to water) to the unit weight of water.
Bulk specific gravity of asphalt mixture - Ratio of the unit weight of an asphalt mixture (including permeable and impermeable voids) to the unit weight of water.
Cement treated base - A base layer constructed with good quality, well-graded aggregate mixed with up to 6% cement.
Effective specific gravity of an asphalt mixture - Ratio of the unit weight of an asphalt mixture (excluding voids permeable to asphalt) to the unit weight of water.
Emulsion - A mixture of asphalt cement with water. Asphalt emulsions are produced by adding a small amount of emulsifying soap to asphalt and water. The asphalt sets when the water evaporates.
ESAL - Equivalent Single Axle Load. A unit used to quantify various types of axle loadings into a single design number for pavement design. Defined as one 18,000 pound four-tire dual axle load.
MST - Moisture Sensitivity Test. Also known as TSR or
Modified Lottman. This test attempts to predict whether a mixture is susceptible to stripping. It compares wet strength to dry strength, and identifies adhesion and cohesion problems.
Plant mix - An asphalt concrete mixture that is not prepared at the paving site. Resilient Modulus: May be referred to as modulus of elasticity. It is not the same as the modulus of subgrade reaction, k although the two are related. For positive values of the resilient modulus, MR » k x 19.4. The resilient modulus is also approximately equal to 1500 times the California Bearing Ratio (CBR).
Saw and seal - Saw and seal involves sawing newly placed bituminous > >pavement to control thermal cracking.
Subbase - A layer of aggregate of planned thickness and quality placed on the existing soil as a foundation for the base. Subgrade: The portion of a roadbed surface which has been prepared as specified, upon which a subbase, base, base course, or pavement is to be constructed.
Tack coat - The initial application of asphalt material to an existing asphalt or concrete surface to provide bond between the existing surface and the new material.
Total voids in an asphalt mixture - Total volume of air in the asphalt mixture.
VMA - Voids in Mineral Aggregate. Measure of unabsorbed asphaltand air voids.
Voids filled with asphalt - The portion of the voids in mineral aggregate of an asphalt mixture which excludes the air voids, as well as the asphalt absorbed by the aggregate.

For more information on asphalt terms, visit:
The Asphalt Institute
Bituminous Mixture Labs

2. Mix Descriptions and Characteristics

In 1997, Min/DOT adopted the Performance Grading (PG) system to classify asphalt binder. The technical memo outlining this change can be found on the Mn/DOT web site.

Information regarding the PG system can also be found on the
Mn/DOT web site.

Note: All Mn/DOT technical memorandums can be found here.

Binder Guidelines

Less than 1 million ESAL's:
Overlays:
PG 58-28
New construction:
PG 58-34 Top 4" (for all counties)
PG 52-34 Below 4" (for Districts 1 and 2)
PG 58-28 Below 4" (for Districts 3 through 8)

Cost Information

Assistance with mix selection is available here.

Two mixtures are specified in the newest Mn/DOT standard specifications:

Regardless of the specification used, users must ensure that all testing is consistent with the Material Control Schedule Users must also coordinate with the Mn/DOT District Lab.

3. Mix Design

More information is available from the Asphalt Institute FAQ.