PC = aC, (d)"n (Eq. 5-1)
and
PFA aF- d)a A (Eq. 5-2)
Where
PeA or PFA = percent of material by weight passing a given sieve having
opening of width d,
aca = constant (intercept) for the coarse aggregate,
aFA = constant (intercept) for the fine aggregate,
d = sieve opening width, mm,
nCA = slope (exponent) for the coarse aggregate,
nFA = slope (exponent) for the fine aggregate.
The method used for determining the "break" between coarse and fine aggregate is based
on the Bailey method (Vavrik et al., 2001). The primary control sieve defining the break
between fine and coarse aggregate in the mix is determined as follows to find the closest
sieve size:
PCS = NMPS x 0.22 (Eq. 5-3)
Where
PCS = Primary control sieve for the overall blend (i.e., division between coarse and
fine aggregate),
NMPS = Nominal maximum particle size for the overall blend as defined in
Superpave, which is one sieve larger than the first sieve that retains more than 10%.
The 0.22 value used in the equation was determined empirically, as discussed by Vavrik
et al. (2002). For example, for a 12.5-mm nominal maximum size mix, the primary
control sieve is 2.36 mm (NMPS x 0.22 = 2.750), whereas for a 19.0-mm nominal
maximum size mix, the primary control sieve is 4.75 (NMPS x 0.22 = 4.180).
Table 5-1 presents the power law coefficients for the fine and the coarse aggregate
portions of the mixtures studied. Generally, the R2 values obtained indicate a fairly good