Superpave mix design

Source Asphalt Institute, Superpave mix design. Superpave Series No. 2 (SP-2), 3rd Edition, Lexington, USA Asphalt Institute, 2001. With permission. 

85/80 denotes that 85% of the coarse aggregate has one fractured face and 80% has two or more fractured faces. 

The required minimum values for coarse and fine aggregate limits proposed as a function of traffic level and layer thickness ( 100 mm or 100 mm) are given in Table 5.6. 

Apart from the above consensually decided properties, aggregates should meet the requirements for resistance to degradation in the Los Angeles machine (ASTM C 131 2006 and C 535 2012 or AASHTO T 96 2010), soundness of aggregates (ASTM C 88 2013 or AASHTO T 104 2011) and contaminants such as clay lumps and friable particles in aggregates (ASTM C 142 2010 or AASHTO T 112 2012). A short description of tests for the determination of the above properties is given in Chapter 2. 

The AC mix design in the United States is suggested to be conducted with the Superpave methodology. 

---

Asphalt Institute recommended cold mix method Resistance to plastic flow of bituminous mixtures using Marshall Apparatus Immersion—Marshall method Immersion—Marshall method Superpave mix design... 

The term asphalt binder has been utilised in the Superpave mix design method to classify the grade of asphalt cement used in an asphalt mix based on expected performance under specific environmental conditions and anticipated traffic loading. Asphalt binder according to ASTM D 8 (2013) is an asphalt which may or may not contain an asphalt modifier . 

Bitumen selection is based on either penetration or viscosity-graded specifications determined by ASTM D 946 (2009) and ASTM D 3381 (2012) or AASHTO M 226 (2012), respectively, or, when Superpave mix design is followed, on performance-graded specifications according to ASTM D 6373 (2007) or AASHTO M 320 (2010). 

The fundamental difference between the Superpave and the Marshall methodology is the way specimens are compacted. In the Superpave mix design methodology, the specimens are compacted with the gyratory compactor (Table 5.8) (ASTM D 4013 2009) and the relative density... 

The final step on the Superpave mix design procedure is the determination of the moisture sensitivity of the target mix. 

According to the American practice, the resistance to permanent deformation, or resistance to rutting as it is called, of the bituminous mixtures is determined with the recently introduced flow number test. The test is a uniaxial repeated (dynamic or cyclic) compression test executed with a test device specially developed for Superpave mix design procedure. The test device is known as AMPT, which is also capable of determining the dynamic modulus of the mixture. The test is carried out at an elevated temperature determined from the average 7-day maximum pavement temperature 20 mm below the surface (see Section 7.6.23). The test is carried out in accordance to AASHTO TP 79 (2013). 

The wheel-tracking test using the APA for evaluating the rut resistance of bituminous mixtures is carried out in accordance to AASHTO T 340 (2010). The test is used as part of fundamental performance tests for Superpave mix design. 

McDaniel R., H. Soleymani, and R.M. Anderson. 2001. Recommended Use of Reclaimed Asphalt Pavement in the Superpave Mix Design Method Guidelines. Research Results Digest 253. Washington, DC Transportation Research Board. 

In American standards, as in European standards, ACs are also designated by the maximum aggregate size. Mixture and gradation limits specified by ASTM 3515 (2010) and control points, shown in boldface, specified by Superpave mix methodology (Asphalt Institute SP-2 2001) for dense AC are given in Table 5.4. It is stated that ASTM 3515 (2010) has been withdrawn in 2009 and has not been replaced. However, to the author s opinion, ASTM 3515 (2010) gradation limits are still helpful to determine the gradation envelope of dense AC until a replacement comes out. 

According to the Superpave methodology (AASHTO M 323 2013 Asphalt Institute SP-2 2001), which sooner or later will completely replace Marshall mix design, the AC is currently designed with volumetric criteria, once the materials (bitumen and aggregates) have been chosen. 

The steps followed in AC mix design by Superpave procedure are summarised below ... 

The only mix design practice for WMA available at the period of writing this book was the one prepared by the NCHRP and proposed to be added as an appendix to AASHTO R 35 (2012) for Superpave volumetric design of HMA. The mix design practice for WMA is described in NCHRP Report 691 (2011), Appendix A, and its basic features are outlined below. 

AASHTO M 323. 2013. Superpave volumetric mix design. Washington, DC American Association of State Highway and Transportation Officials. 

The Superpave asphalt mix design system includes the performance grade (PG) asphalt binder specification. The Superpave asphalt binder tests try to determine physical properties that can be directly related to field performance in terms of ratting, fatigue cracking and low temperature cracking. Superpave characterizes asphalt at the actual pavement temperatures it will experience, and at the periods of time when distresses are most likely to occur. A part of the Superpave binder specification is... 

The American Superpave design methodology was developed bearing in mind the use of performance-related requirements. At present, the Superpave design selects the bitumen on the basis of performance-related specifications but the target asphalt mix is still determined on the basis of volumetric properties. 

---