Technical information

2-7
Figure 2.2.4: Sub-layering of HMA in test sections N1 to N8 (Timm and Priest, 2006).
Table 2.2.1 presents the individual mixture design parameters for mixes 1 to 4
which were paved in the N1 and N2 sections. It may be seen that the surface mixes 1
and 3 differ by the type of binder and corresponding preparation temperatures. SBS
modified PG 76-22 was used for Mix 1, and unmodified PG 67-22 was used for Mix 3.
Both mixes (see Figure 2.2.5) were designed with a ‘wearing’ (dense) gradation having
a nominal maximum aggregate size (NMAS) of 9.5 mm (3/8 in.) and a compactive
effort of 80 gyrations. At the optimum binder content (i.e., 6.13% effective), the
samples had 4.3% air voids and 17.9% VMA. Similar to the surface mixes, the
intermediate and bottom mixes (mixes 2 and 4) differed by the type of binder. SBS
modified PG 76-22 was used for Mix 2, and unmodified PG 67-22 was used for Mix 4.
Both mixes (see Figure 2.2.5) were designed with a ‘Base’ (also dense) gradation
having a NMAS of 19 mm (3/4 in.) and a compactive effort of 80 gyrations. At
optimum binder content (4.27% effective), the samples had 4.3% air voids and 14.5%
VMA.