innovations on the asphalt mix design for the rehabilitation of national route 3 between...
TRANSCRIPT
Innovations on the Asphalt Mix Design for
the Rehabilitation of National Route 3
between Mariannhiill and Key Ridge
Jaco Liebenberg
Dennis Rossmann
Philip Joubert
Overview
• Introduction to project• Structural design limitations• Mix design requirements• Mix design process• Mix design performance tests & results• Construction
CBR 3 subgrade
Introduction
• N3/1&2 Mariannhill – Key Ridge• Main link Durban - Gauteng• Constructed in 1985• 40 to 50 million E80’s• Constructed as• Maintenance
– 1994/5 (+14 years)
• Identified for Rehabilitation– 2006 (+20 years)
150 mm G7 selected
40 mm AG
125 mm AC
300 mm C3 subbase
40 mm AC
13 mm Bitumen rubber seal
Introduction
• Major typical defects– Rutting in slow lane– Some isolated rutting in middle lane– Cracking and pumping in slow lane
• Design traffic
• Design requirements– Slow lane: Substantial pavement required– Middle lane: Some repairs required– Fast lane: None required
Slow lane Middle lane
15 years 70 million 22 million
30 years 185 million 54 million
Pavement Design Options
40 mm AC
125 mm AC
150 mm G7 selected
300 mm C3 subbase
CBR 3 subgrade
? mm overlay? mm Concrete overlay
Pavement Design Options
40 mm AC
125 mm AC
150 mm G7 selected
300 mm C3 subbase
CBR 3 subgrade
Pavement Design Options
150 mm G7 selected
300 mm C3 subbase
CBR 3 subgrade
Structural design
• Stabilised subbase performed well– Only localised repairs required– Not thick enough for traffic volume (req 450 mm)
• Asphalt inlay considered most appropriate– Mix design to compliment structural design– Stiff as possible (req: E = 4 000 Mpa)
• Slow lane– Signs of stripping in lower part of layer replace all asphalt– Selective repairs of subbase
• Middle lane– Some cracking and deformation Only repair upper 80 mm
• Fast lane– Only Isolated repairs
• New surfacing over full width
Paper discuss process to consider for restrictions in structural design by optimising the asphalt mix design
Mix design requirements
• Primary requirements– Rut resistant– Stiff (≈ 4 000 MPa)– Fatigue resistant
• Secondary requirements– Low permeability– Good moisture susceptibility
• Mix design process– Standard mix design process– 2 mix designs in parallel – selection process– Much emphasis on performance testing– Performance tests on mixes from trial sections
Mix design
• Aggregate and grading – Coarse aggregate quartzite– Fine aggregate: quartzite & tillite mix– Bailey method to determine optimum grading– Contained 15 % RAP
• Binders– Two binders evaluated– A-P1 (4% EVA) with Optimum binder Content @ 4.2%– vs. A-E2 (3.5% SBS) with Optimum binder Content @ 4.4%
• Min component of mix design:– Performance under accelerated testing
• 6 trial sections constructed– Directly north of toll Plaza in slow lane– A-P1 mix: 3.9% 4.2% and 4.5%– A-E2 mix: 4.0% 4.3% and 4.6%
0.01 0.1 1 10 1000
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Sieve Size (mm)
% P
as
sin
g
Trial sections
• From trial sections (extracted from pavement)– 228 cores– 16 beams
• Tested for– Rut resistance under MMLS and Hamburg wheel tracking– Moisture susceptibility under MMLS and mod. Lottmann– Permeability– Fatigue
Deformation and rutting resistance
• MMLS testing and Hamburg wheel tracking tests– Also discussed in paper by Hugo et.al
4.2% A-P1
4.5% A-P1
4.3 % A-E2
4.5 % A-E2
MMLS Dry, 7200/hr, 60 °C Yes Yes Yes Yes
MMLS Dry, 2400/hr, 60 °C Yes No Yes No
MMLS Wet, 7200/hr, 60 °C Yes No Yes No
Hamburg Yes Yes Yes Yes
A-P1 (3,9%) A-P1 (4,2%) A-P1 (4,5%) A-E2 (4,1%) A-E2 (4,4%) A-E2 (4,7%)0
0.5
1
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3.5MMLS
MMLS dry @ 7 200/hour
MMLS wet @ 7 200/hour
Mix
Ru
t a
fte
r 1
00
00
0 r
ep
itit
ion
s (
mm
)
A-P1 (3,9%) A-P1 (4,2%) A-P1 (4,5%) A-E2 (4,1%) A-E2 (4,4%) A-E2 (4,7%)0
0.0001
0.0002
0.0003
0.0004
0.0005
0.0006
0.0007Hamburg wheel tracking
Mix
Ru
t ra
te (
mm
/pa
ss
)
Fatigue resistance
• Coarse rut resistant mixes generally poor fatigue• Beams extracted from pavement
– 6 beams for 4.2% A-P1 tested– 6 beams for 4.3% A-E2 tested
• Fatigue test– 4 point bending beam– Constant strain
10 000 100 000 1 000 000 10 000 0000
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Repetitions
Str
ain
(m
e)
A-P1
A-E2
Adopted mix design
• A-P1 mix considered most appropriate mix– Better rut resistance– Better moisture susceptibility– Fatigue comparable to A-E2, within acceptable guidelines
• A-E2 probably suitable as well• Performance tests A-P1
Construction
• High level of control comfort design intent is built• Tight control of
– Mix properties– Compaction
• Ability to project trends and act pro-actively• Construction quality
– No rejected work or rework on Asphalt base– Some issues recently with UTFC currently being investigated
Conclusions
• Limitations during structural design• Possible to optimise mix design to compliment
structural design– Require cooperation
• Asphalt mix design process– Benefits not a standalone process– Tie in with pavement design
• Attention to mix design – mix appropriate for application – considers unique requirements for application