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 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 laneMiddle lane 15 years70 million22 million 30 years185 million54 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 = 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 ( ≈ 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 4.2% –vs. A-E2 (3.5% SBS) with Optimum binder 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 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 °CYes MMLS Dry, 2400/hr, 60 °CYesNoYesNo MMLS Wet, 7200/hr, 60 °CYesNoYesNo HamburgYes

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 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