DIGEST 2006 - Sabita

ecommendations (R69/97 for
bituminous mix design) involves
an analytical study prior to
verification by mechanical testing.
This analytical study is supported
by a software package called
PRADO (Programmes for Asphalt
Mix Design and Optimisation).
This method aims to achieve the
best possible compromise between
various (and sometimes
conflicting) requirements such as
dealing with both resistance to
fatigue and rutting of the mix. In
Volumetric and mastic
evaluation of dolerite and
quartzite mixes:
Theoretical volumetric calculations
using PRADO software were done
for both the designs incorporating
both dolerite and quartzite. The
results of the volumetric analysis
(estimating VIM, VMA and the
filler/binder ratio - by both mass
and volume – and the stiffening
effect of the mastic) over a range
of binder contents were calculated
as follows:
Dolerite
Quartzite
Binder content (%)
4
4.5
5
5.5
4
4.5
5
5.5
Estimated VIM (%)
PRADO
7.7
6.5
5.3
4.1
6.2
5.1
4.0
2.9
VIM (%) laboratory
7.7
5.4
4.0
3.6
6.8
4.9
3.2
1.5
Estimated VMA (%)
PRADO
VMA (%) laboratory
Filler/binder ratio (by
mass)
Filler/binder ratio (by
volume)
T R&B increase (mastic vs
binder)
17.1
17.5
1.4
0.49
11.9
17.1
16.7
1.24
0.44
10
17.1
16.5
1.12
0.39
8.7
17.1
17.4
1.02
0.36
7.7
15.3
15.7
15.9
0.60
21.7
15.3
15.1
1.41
0.53
17.4
15.3
14.7
12.7
0.48
14.6
15.3
14.4
1.16
0.43
12.5
Table 2: PRADO Mix Design Estimates Versus Actual Volumes
this approach, the stability of the
mix can be ensured by making use
of intergranular friction while
avoiding overfilling the mineral
skeleton with mastic (i.e. with
filler and binder). This mastic
should only fill part of the voids in
the mineral aggregate and should
also have the right consistency
(i.e. the correct proportion of filler
and binder).
Dolerite aggregate evaluation
results
In general the estimated VIM and
VMA values as predicted by
PRADO are slightly higher than the
values obtained in the laboratory.
From Table 2 it can be seen that
the increase in the Ring & Ball
temperature of the mastic
105