ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 358

been subjected to traffic for a number of years. The initial compaction level
was implemented to assist with identifying “tender” mixes. A tender mix
lacks stability during construction, and hence will displace under the rollers
rather than densifying. For the initial stage of determining the design aggre-
gate structure, samples are compacted with gyrations. The volumetric
properties are determined by measuring the bulk specific gravity of the
compacted mix and the maximum theoretical specific gravity of a loose
mix with the same asphalt content and aggregate composition. The volumet-
ric parameters, VTM, VMA, and VFA, are determined and checked against
the criteria. Two additional parameters are evaluated in the Superpave
method: percent of

N ini

N des

G mb

G mm

G mm at N ini , and the dust-to-effective binder content

ratio. The percent of G mm at N ini is determined as

Percent G mm,Ndes h des
h ini

Percent G mm,Nini = (9.11)

where and are the heights of the specimen at the initial and design
number of gyrations, respectively. Note that the percent

h ini h des

G mm,Ndes is equal to

(100-VTM).
The dust-to-effective binder ratio is the percent of aggregate passing the
0.075 mm (#200) sieve divided by the effective asphalt content, computed as

a G se - G sb
G sb G se

P ba = 100 b G b (9.12)

a P ba
100

P be = P b - b P s (9.13)

P D
P be

D/B = (9.14)

where

D/B = dust to binder ratio

absorbed binder based on the mass of aggregates
specific gravity of aggregate
dust, or % of aggregate passing the 0.075mm sieve
effective binder content

P ba = percent

G sb = bulk

P D = percent

P be = percent

The Superpave method requires determining the volumetric properties
at 4% VTM. The samples prepared for the evaluation of the design aggregate
content are not necessarily at the binder content required for achieving this
level of air voids. Therefore, the results of the volumetric evaluation are
“corrected” to four percent air voids, as

P b,est = P bt - 0.4 1 4 - VTM t 2 (9.15)

(9.16) VMA est = VMA t + C 1 4 - VTM t 2

C = 0.1 for VTM t 6 4.0%

C = 0.2 for VTM t Ú 4.0%

100 VMA t

- 4.0

VFA est = (9.17)

VMA t