Status of QDMR / AAPA Alliance SMA Specification Development. Jason Jones - Senior Engineer (Road Surfacing)

Transcription

1 Status of QDMR / AAPA Alliance SMA Specification Development Jason Jones - Senior Engineer (Road Surfacing)

2 Historical Development of SMA Specifications Development of specification through trials in the mid to late 1990 s Early mixes were used successfully on heavily trafficked roads SMAs desired for open surface texture noise & spray and claimed long life. MRS11.33 (12/99) Mixes were permeable SAMI seals were sometimes not used Stripping issue identified in early 2002 Symptoms include:- White fines on the surface Water retention Binder migration (blobs of bitumen on surface) Lower AC layer turns to granular whilst surfacing hangs on Rutting

3 Outcomes of Asphalt Stripping

4 Historical Development of SMA Specifications MRS11.33A Coarser grading Lower design voids Mandatory inclusion of hydrated lime Higher compaction standard 93% CV MRS11.33B (Supp Spec) Peninsula District & South Coast Hinterland District Coarser gradation Removal of oversize stone Permeability issues remained unresolved

5 Historical Development of SMA Specifications Consultation with international experts in 2004 USA experts Larry Michael and Richard Schreck visited Queensland Workshops with industry and QDMR Specification changes suggested Aims: Improve durability by reducing its permeability Improve its workability to achieve increased densities Benchmark local conditions with proven USA systems

6 Historical Development of SMA Specifications QDMR / AAPA Alliance SMA Working Group developed a specification based on Maryland / Virginia DOT experience Finer gradation Relaxed filler requirements Design voids 3.0% (50 blows Marshall) Free binder volume requirement introduced Lower binder modification Compaction standard 94% CV Production and placement trial Specification known as Gateway Trial Supplementary Specification

7 QDMR / AAPA Alliance Gateway SMA Trial Gateway Trial Supplementary Specification 4 trial sections on Gateway Motorway 4 asphalt suppliers using different mix designs Constructed April June 2005 Performance of site was monitored Report on trial completed early 2007 Input by Main Roads and industry

8 Outcomes of Gateway Trial Permeability was reduced Workability was improved Performance was mixed? Many factors affected performance Binder selection Design voids selection Filler properties Mix volume ratio

9 Contractor A Field Density less than specified compaction standard Layer thickness 40mm Contractor B Binder Softening Point = 54.5 o C Binder Consistency = 720Pa.s Mastic Consistency = 8,920Pa.s Binder Softening Point = 65.5 o C Binder Consistency = 2,280Pa.s Mastic Consistency = 65,500Pa.s

10 Contractor C Contractor D Binder Softening Point = 53.0 o C Binder Consistency = 744Pa.s Mastic Consistency = 14,400MPa Binder Softening Point = 63.5 o C Binder Consistency = 1,550Pa.s Mastic Consistency = 51,600MPa

11 Situation after Gateway Trial More permeable mixes: MRS11.33, MRS11.33A & MRS11.33B Rutting / flushing concerns: Gateway and Anzac Avenue trials

12 What Controls Rut Resistance in SMA? Many views on subject Grading Design Voids Binder Filler Mastic Fine aggregate and so on

13 Was the USA Type Grading that Influential? SM14 Wheel Tracking 16 Final Rut Depth (mm) Fixed Binder Fraction Gateway Spec Grading MRS11.33A SM12

14 SMA Specification Status (Aug 2006) MRS11.33 (12/99) was withdrawn All interim versions were withdrawn, except for: MRS11.33A (03/06) MRS11.33 (04/06) Interim specifications to be used only after consultation with Pavements & Materials Branch.

15 Hope Island Road Trial Incorporation of learnings from Gateway Motorway / Anzac Avenue trials: A0.6S polymer modified binder Tighter control on filler properties Mix volume ratio mm layer thickness High compaction standard 94% CV Gritting for improved early skid resistance was also trialled.

16 Surface Texture Hope Is Rd Texture Depth for SMA - Hope Island Road Texture Depth (mm) Gritted Not Gritted OWP BWP IWP Wheel Path Not gritted section S/B IL data Ch 0-80m excluded from the analysis

17 Surface Texture - Gateway Contractor A Contractor B Contractor C Contractor D Texture Depth (mm) Austroads investigatory level for surface texture depth in wheel path (freeways and other high-class facilities with free-flowing traffic conditions) OWP BWP IWP Chainage

18 Hope Island Road Trial Were the performance problems of Gateway and Anzac Avenue trials resolved? Difficult to say: Performance has been acceptable Traffic volume considerably less than Gateway Motorway and Anzac Avenue

19 Where to from here? SM14 still in development phase: Permeability needs to be balanced with rut resistance and texture Pavements & Materials Branch has drafted a revised specification based on progress to date Preliminary discussions with AAPA members and Metropolitan District Concerns within QDMR that specification has not been proven in heavy traffic situations What functional requirements does Main Roads want for high speed environments? Follow other SRAs and international trends: Smaller nominal size mixes

20 What About SM10? Renewed interest in SM10 for 80km/h speed environments Withdrawn with MRS11.30 (12/99) Main Roads currently reviewing existing SM10 sites

21 The End Questions?