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Jaco Liebenberg Dennis Rossmann Philip Joubert

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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

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slide1

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
Overview
  • Introduction to project
  • Structural design limitations
  • Mix design requirements
  • Mix design process
  • Mix design performance tests & results
  • Construction
introduction
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)

13 mm Bitumen rubber seal

40 mm AC

40 mm AG

125 mm AC

300 mm C3 subbase

150 mm G7 selected

CBR 3 subgrade

introduction1
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
pavement design options
Pavement Design Options

? mm Concrete overlay

? mm overlay

40 mm AC

125 mm AC

300 mm C3 subbase

150 mm G7 selected

CBR 3 subgrade

pavement design options1
Pavement Design Options

40 mm AC

125 mm AC

300 mm C3 subbase

150 mm G7 selected

CBR 3 subgrade

pavement design options2
Pavement Design Options

300 mm C3 subbase

150 mm G7 selected

CBR 3 subgrade

structural design
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
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
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%
trial sections
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
Deformation and rutting resistance
  • MMLS testing and Hamburg wheel tracking tests
    • Also discussed in paper by Hugo et.al
fatigue resistance
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
adopted mix design
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
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
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