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%

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Sieve Size (mm)

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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

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fte

r 1

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0 r

ep

itit

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s (

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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

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0.0007Hamburg wheel tracking

Mix

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/pa

ss

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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

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Repetitions

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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