DIGEST 2006 - Sabita

decided rather to use the old TRH8
coarse envelope (13mm nominal
aggregate type). The first contract
where the dolerite TRH8 coarse
mix was used successfully was the
ORTIA Echo taxiway contract. On
the following ORTIA contract
(Yankee taxiway) the grading
adopted was slightly finer on the
2.36mm sieve, which resulted in
lower gyratory voids and higher
MMLS3 rutting values.
Subsequently, to ensure
compliance with more stringent
performance-related specifications,
it was decided to revert
back to the original Echo taxiway
contract grading with only slight
changes to optimise the mix.
These included adjustments in the
grading to maintain VMA values in
the region of 16, which satisfy the
rut criteria without causing binder
starvation of the mix, i.e. maintaining
a film thickness of 7.5µm.
With the very high volume of work
that had to be completed before
the end of 2006, it was decided to
prepare a quartzite design as a
Performance required Fundamental mix property Simulation testing
to confirm
performance
• Mix 1: Highly trafficked (>ES10) wearing course:
• High rut resistance
and durability;
• Acceptable fatigue
resistance;
• Acceptable friction (no
fattening/bleeding).
• Grading to be a 13.2mm nominal
aggregate, coarse graded type to
ensure compactability; 2.36mm
key compositional point to be set
to ensure VMA target obtained;
filler set to obtain a filler/binder
(F/B) ratio of ≈ 1.3. The grading
curve to be smooth to ensure
compactability and prevent
segregation;
• % passing 0.075mm (filler) to be
relatively high to stiffen mix (F/B
≈ 1.3 – 1.45);
• Adequate VMA to get enough
binder in (for durability/fatigue)
while still preventing closing up
of the mix (i.e. Marshall voids =
5.0 and terminal voids in SP
gyratory >3%);
• Binder penetration – 60/70 -
40/50 Pen;
• Film thickness > 7.5µm
(minimum binder content of
4.5%)
• MMLS3 @ 50°C
on briquette/field
cores;
• Mod Lottman;
• 4 Pt beam fatigue
test @ 200µm
and 350µm;
• Gyratory curve to
300 gyrations.
Mix 2: Highly trafficked (>ES10) wearing course for high shear intersection
areas:
• Very high rut
resistance and
durability;
• Acceptable fatigue
resistance;
• Acceptable friction (no
fattening/bleeding)
• As above with binder type to be
40/50 Pen. and F/B slightly
higher (±1.40) with film
thickness > 7µm
Table 1: Fundamental Design Principals
As above
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