Comparison of Results of Example II with the 30-20-10 rule of SMA Composition

According to the rule described in Section 6.2.2, proper stone-to-stone contact is created if the percentage of aggregate passing the 0.075 mm, 2.36 mm, and

4.75 mm sieves equals 10%, 20%, and 30%, respectively. Table 6.11 shows the comparison between the achieved result of Stage 4 and ratios according to the 30-20-10 rule.

There are some noticeable differences. First, the 30-20-10 SMA should contain more aggregates larger than 2.36 mm (80%), whereas the relevant SMA of Example I was designed at only 75% on the 2.0 mm sieve. With regard to particles larger than

Recommended Ratios of SMA 0/11S according to German DAV Handbook Compared with the result of sMA design in example ii

0

10

20

30

40

50

60

70

80

90

100

FIGURE 6.8 SMA mix of Example II, Stage 4, adjusted to the ratios recommended by the German DAV handbook compared with its original gradation and Zichner’s proportions.

TABLE 6.11

Recommended SMA Ratios according to the 30-20-10 rule Compared with the result of sMA Designed in example ii

4.75 mm, the result obtained in Example II is consistent with the requirement con­cerning 30%. Figure 6.9 shows the SMA corrected in such a way that its ratios are in conformity with the assumptions of the 30-20-10 rule.

The SMA designed according to the 30-20-10 rule is more gap graded than our SMA in Example II, which is especially evident in the percent passing the 2.0-mm sieve. In general, mixtures with such a strong gap in grading are harder to compact and are more permeable. On the other hand, one can get very strong skeleton with such a clear gap grading (stone-to-stone contact).