Pavement Types

Hard surfaced pavements, which make up about 67 percent of U.S. roads and 70 percent of Washington State roads are typically categorized into flexible and rigid pavements:

  • Flexible pavements.  Those which are surfaced with bituminous (or asphalt) materials.  These types of pavements are called “flexible” since the total pavement structure “bends” or “deflects” due to traffic loads.  A flexible pavement structure is generally composed of several layers of materials which can accommodate this “flexing”.
  • Rigid pavements.  Those which are surfaced with portland cement concrete (PCC).  These types of pavements are called “rigid” because they are substantially stiffer than flexible pavements due to PCC’s high stiffness.

Each of these pavement types distributes load over the subgrade in a different fashion.  Rigid pavement, because of PCC’s high stiffness, tends to distribute the load over a relatively wide area of subgrade.  The concrete slab itself supplies most of a rigid pavement’s structural capacity.  Flexible pavement uses more flexible surface course and distributes loads over a smaller area.  It relies on a combination of layers for transmitting load to the subgrade.  This Guide focuses on flexible pavements.

In general, both flexible and rigid pavements can be designed for long life (e.g., in excess of 35 years) with only minimal maintenance.  Both types have been used for just about every classification of road.  Certainly there are many different reasons for choosing one type of pavement or the other, some practical, some economical, and some political.  As a point of fact, 95 percent of U.S. paved roads are surfaced with bituminous (asphalt) materials (FHWA 2009).

HMA Mix Types

The most common type of flexible pavement surfacing in the U.S. is hot mix asphalt (HMA).  Hot mix asphalt is known by many different names such as hot mix, asphalt concrete (AC or ACP), asphalt, blacktop or bitumen.  For clarity, this Guide makes a conscious effort...

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Standard Washington State Hot Mix Asphalt Types

This section lists the standard HMA  mixes used in Washington State both today and prior to changing from the Hveem mix design method.  Most modern HMAs are listed to designate both the nominate maximum aggregate size of the mix and the PG (Performance Grade) of...

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Recycled HMA

HMA is one of the most recycled products in the U.S.  As much as 100 million tons of HMA are milled off roads during resurfacing and widening projects each year.  Of this amount, 80 million tons (80 percent) are recycled as "reclaimed asphalt pavement" (RAP)...

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Asphalt Treated Base (ATB)

Asphalt treated base (ATB) is a dense-graded (but more permeable) HMA with a wide gradation band and lower asphalt content intended for use as a stabilizing base course and intended to be used in conjunction with a top/ wear course of street/ highway grade HMA...

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"Superpave" is an overarching term for the results of the asphalt research portion of the 1987 - 1993 Strategic Highway Research Program (SHRP).  Superpave consists of (1) an asphalt binder specification, (2) an HMA mix design method and (3) HMA tests and performance...

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