The requirements for gradation of SMA mixtures have been provided in the European standard PN-EN 13108-5 (see Chapter 14). This standard does not set out the criteria and conditions for selecting the particular gradation of a mixture. Establishing these criteria remains the responsibility of each CEN-member state. In Figures 14.2 through 14.5, examples of gradation limits are presented.
6.2.1 Original Zichner’s Proportions
In his publications (Zichner, 1971; Zichner, 1972) Dr. Zichner described a recommended composition of an SMA mixture as follows:
• The stone content should be about 65-80% (m/m), preferably 70-75%, using only crushed stones.
• The main rule governing gradations is that the mixture is composed “so that the percentage of the coarser size is greater than that of the smaller size.”
• Mastic content is 20-35% (m/m).
• 23-28% of the mastic is a binder.
• For layers with different thicknesses, different types of stones should be used as follows:
• Thickness less than 3 cm—stone fractions 2/5.6 and 5.6/8 mm in proportions of 25 and 75%, respectively
• Thickness 3-4.5 cm—stone fractions 2/5.6, 5.6/8, and 8/12 mm, or only 5.6/8 and 8/12 mm
• Thickness greater than 4.5 cm—stone fractions 2/5.6, 5.6/8, 8/12, and 12/18 mm
• Only manufactured sand should be used in the mastic.
Looking at Zichner’s MASTIMAC and MASTIPHALT gradation curves presented in Chapter 1 (see Figure 1.1), we can find approximate contents of aggregate fractions (Table 6.4).
The proportions of different fractions of coarse aggregates used in current German SMA mixtures are presented also in Chapter 2 (see Table 2.1) after the German DAV Handbook (Druschner and Schafer, 2000).
