Frequently Asked Questions (FAQ)

This section contains some of the more frequently asked pavement questions.  Each question is linked to a place in this document that provides the answer.

General

• How do I find a Washington Asphalt Pavement Association member paving contractor in my area?

• Where can I find more information like this on hot mix asphalt (HMA) pavements?

• What is hot mix asphalt (HMA)?

• Is there a difference between tar and asphalt?

• What is a pavement's purpose?

• How much do we use roads in the U.S.?

Pavement Types

• What types of pavement are there?

• Are there different kinds of hot mix asphalt?

• What is Superpave?

• What is Stone Matrix Asphalt (SMA)?

• What is asphalt treated base (ATB)?

• What is RAP and how is it used?

• What types of standard HMA mixes are used in Washington State (e.g., Class A, Class G, etc.)?

• What is a Modified Class B mix?

Materials

• What is the difference between maximum aggregate size and nominal maximum aggregate size?

• What is the PG asphalt binder grading system?

• What is an asphalt binder modifier?

Design Factors

• What is the difference between a CBR, R-Value and resilient modulus and how do I correlate them to one another?

• What is an equivalent single axle load (ESAL)?

• What is frost heave and should I worry about it?

Mix Design

• What is a job mix formula (JMF)?

• What are the differences between the Hveem, Marshall and Superpave methods?

Structural Design - Design Catalog

• How thick should I make my pavement?

• What are the basic structural elements in a pavement?

• What is a Perpetual Pavement?

Construction

• How should I prepare the surface over which I plan to place a new pavement or overlay?

• What is "Rice density"?

• Why are density measurements given as a percentage?

• Why are density and compaction so important?

Pavement Evaluation

• What is IRI?

• How are pavements evaluated?

• What is a life cycle cost analysis and are there any tools to help me perform one on a proposed pavement?

Maintenance & Rehabilitation

• What is a bituminous surface treatment, or chip seal?

• Are all overlays used to increase the structural capacity of a pavement?

General Guidance

• Do you have any pavement design and construction guidance?

• There is something wrong with my pavement.  What is it and how do I fix it?

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