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Jaco Liebenberg Dennis Rossmann Philip Joubert

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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Jaco Liebenberg Dennis Rossmann Philip Joubert

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  1. Innovations on the Asphalt Mix Design for the Rehabilitation of National Route 3 between Mariannhiill and Key Ridge Jaco Liebenberg Dennis Rossmann Philip Joubert

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

  3. 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

  4. 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

  5. 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

  6. Pavement Design Options 40 mm AC 125 mm AC 300 mm C3 subbase 150 mm G7 selected CBR 3 subgrade

  7. Pavement Design Options 300 mm C3 subbase 150 mm G7 selected CBR 3 subgrade

  8. 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

  9. 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

  10. 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%

  11. 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

  12. Deformation and rutting resistance • MMLS testing and Hamburg wheel tracking tests • Also discussed in paper by Hugo et.al

  13. 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

  14. 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

  15. 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

  16. 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

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