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CHAPTER 7 Selection of Asphalt Concrete Mix Type Chapter 7 provides engineers and technicians with guidance on the selection of HMA mix types for different applications. In most cases, when an engineer or technician is performing a mix design, the mix type will be specified by the owner or agency requesting the mix design. However, this may not always be the case--especially for private paving work, where the owner may not have any idea what type of mix is best suited for her or his particular application. Fur- thermore, because selection of mix type is a direct function of where within a pavement the mix is located, Chapter 7 also discusses the topic of pavement structure in some detail. The primary reference for Chapter 7 is a publication of the National Asphalt Pavement Asso- ciation (NAPA): HMA Pavement Mix Type Selection Guide (33). Some additional information is given on lift thickness, based on NCHRP Report 531 (32), and on pavement structure and mix type selection for perpetual pavements, based on TRB Circular 503 (34). The figures and tables presented in Chapter 7 are not highly technical in nature, instead pre- senting, for the most part, general knowledge concerning pavement types and pavement struc- ture. Figure 7-1 presents the different types of pavement structures incorporating HMA in new construction. Figure 7-2 is similar, but presents different types of pavement structures using HMA that result from pavement maintenance operations. The traffic levels listed in Table 7-1 are defined in both AASHTO M 323 and R 35. However, the descriptions of typical traffic and road types for the different traffic levels occurs only in AASHTO R 35. Table 7-2, giving recommended lift thicknesses for different mix types and NMAS, is taken directly from NCHRP Report 531 (32), while Table 7-3 is a summary of infor- mation taken from NAPA's publication HMA Pavement Mix Type Selection Guide (33). 240