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CHAPTER 5
Mixture Volumetric Composition
Chapter 5 of the Manual discusses the volumetric composition of HMA mixtures. The chapter
includes a significant amount of introductory material, including the definitions of many terms
related to HMA composition and various relationships between HMA compositional factors
such as voids in mineral aggregate (VMA) and air voids and pavement performance. Much of
the second half of the chapter is devoted to a detailed description of volumetric analysis of HMA
mixtures, including numerous equations and example calculations. The primary source for the
terminology and equations given in this chapter is AASHTO R 35, Superpave Volumetric Design
for Hot-Mix Asphalt. In some cases, the Asphalt Institute's MS-2 and SP-2 manuals were also
used as references since these manuals are also referenced in AASHTO R 35 (2, 3).
The critical information in Chapter 5 is the various equations presented for calculating various
factors of HMA volumetric composition, such as air void content, VMA, and effective binder
content. There are many different ways of calculating these factors, and many different forms of
what are, in many cases, identical mathematical relationships. Furthermore, all of the equations
given in Chapter 5 can be derived from fundamental physical relationships among volume fraction,
mass fraction, specific gravity, density, and absorption. These relationships--and the resulting
mathematical equations--are often represented through the use of a phase diagram. Although
a very useful concept, the phase diagram approach to volumetric analysis has not been included
in the Manual because it was believed that its interpretation would be too challenging for many
technicians and some engineers. Table 2 lists sources for the various equations presented in
Chapter 5; again, it should be noted that all of these equations can be derived from the physical
relationships involved, but it is useful to show other references using the same or similar equations
in discussion of HMA volumetric composition and analysis.
Table 2. Sources for equations in chapter 5.
Equation
No. For Calculation of Source
5-1 Bulk specific gravity of compacted specimen AASHTO T 166
5-2 Maximum specific gravity of loose mixture AASHTO T 209
5-3 Bulk specific gravity of aggregate blend AASHTO R 35; TAI SP-2, MS-2
5-4 Air void content of compacted specimen,% by mixture volume AASHTO R 35, T 269
5-5 Total asphalt binder content of mixture,% by mixture mass By definition
5-6 Total asphalt binder content of mixture,% by mixture volume By definition
5-7 Absorbed asphalt binder content,% by mixture volume By Definition
5-8 Effective asphalt binder content,% by mixture volume By Definition
5-9 Effective asphalt binder content,% by mixture mass By Definition
5-10 Absorbed asphalt binder content,% by mixture mass By Definition
5-11 Voids in mineral aggregate,% by mixture volume AASHTO R 35
5-12 Voids filled with asphalt,% by volume AASHTO R 35
5-13 Apparent film thickness NCHRP Report 567 (4)
5-14 Aggregate specific surface (method 1) NCHRP Report 567 (4)
5-15 Aggregate specific surface (method 2) NCHRP Report 567 (4)
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