1. Innovations in HMA RPF May 2006

2. Content Proposed HMA trials High Modulus Asphalt Bailey method of design

3. HMA Trials A GPTRW/Sabita – joint venture

4. Content Background Meeting on 23 March 2006 Forensic study Issues Way forward

5. Background Negative perceptions on hma wc performance –based on wide range of causative factors –adversely influence the use of a key road building material Ensure that technology is sound and up- to-date to render the product cost-effective Welcome the opportunity to cooperate with GPTRW to respond to the challenge

6. Meeting on 23 March 2006 Attendance –Senior staff of 4 Sabita members active in Gauteng (and consultant) –GPTRW –CSIR BE –L Sampson –P Myburgh Agenda –Forensic study –Defining issues –Way forward

7. Forensic study In preliminary phase Identified three key issues: –Performance widely scattered - distress in a notable proportion of roads sampled –Prevalence of permanent deformation at intersections –Lack of correspondence of approved job- mixes and site materials in several instances

8. Issues defined The trials project should cover two main areas: –Mix designs for adequate performance –Quality management systems Job-mix proposals Aggregate uniformity and relevance

9. Mix designs Aggregate shape, grading and binder content Dogged adherence to COLTO grading envelopes to current aggregate shape Resultant low binder content/low VIM –Premature brittleness –Lack of resistance to permanent deformation Need to differentiate between intersections and open road conditions

10. Mix designs/cont… High crusher sand content vis-à-vis availability (60+% -4.75mm) Layer thickness/NMAS ratios (NCHRP: 3 – 4) Need to understand and incorporate methods to assess aggregate packing (e.g. “Bailey method” published by TRB)

11. Mix design/cont… Possibly move to stone skeleton mixes (as opposed to sand skeleton ones) Ultimately strive for balance: –Durability –Fatigue strength –Resistance to permanent deformation

12. Way ahead Joint enthusiasm to proceed with trial sections Mixes would be evaluated by laboratory and APT methods Process - joint venture of road authority consultants and suppliers/contractors –Enhanced expertise base –Advance implementation of findings

13. Way ahead/cont… The four contractor/suppliers would partner with specialist HMA design consultants Designs based on commercially available binders to be submitted by end June for use on: –Intersections –Open highway Each trial would constitute: –60 tons (160m x 3.7m x 40mm) COLTO gradings would NOT be a point of departure

14. Way ahead/cont… Job-mix relevance and aggregate consistency will be key Completion of forensic study MMLS and laboratory testing of mats HVS testing to commence in Oct/Nov Formation of broader industry advisory group to monitor and evaluate

15. Conclusion Joint venture presents a model for future cooperation between road authorities, suppliers/contractors and consulting engineers to mobilise experience and expertise to respond to technical challenges Springboard for future initiatives

16. High modulus asphalt French initiative Enrobé à Module Élevé (EME) – locally called HiMa Tested in the UK (TRL) Introduction to SA being investigated (both roads and airports)

17. What is EME/HiMa? Base course - high content of hard bitumen Low air voids High elastic stiffness High deformation resistance Good fatigue resistance Impermeable and durable Aggregate angularity and cleanliness defined Hard grades of bitumen (15/25pen) Use in France for 20 years Tested and reported on by TRL (UK) 2005

18. TRL report TRL 636) EME designed and tested and compared with HDM Aggregate size – 20mm Binder richness modulus 3.65 (b.c. 6%) Air voids (120 gyrations) 1.8% Complex modulus (15°C, 10Hz) 14 GPa Binder penetration (25 °C) 18 R&B SP 66

19. TRL conclusions EME superior to HDM in many respects: –More deformation resistant –Superior load spreading capability –More durable and impermeable –Reduced layer thickness – 25mm for 80 m –esa’s –Trials based on French method – needs to be verified for other methods and conditions

20. HiMa in SA? Bitumen meeting HiMa requirements can be made available Prospect of incorporating trial sections into the GPTRW joint venture on asphalt Ultimately present another option to consider in the heavy duty pavement sphere.

21. Bailey method Published as TRB Circular E-C044 (2002) Bailey method for Gradation Selection in Hot- mix Asphalt Mixture Design It presents: A systematic approach to blending aggregates that provides aggregate interlock as the backbone of the structure and a balanced continuous gradation to complete the mixture

22. Basic principles Definition of coarse and fine aggregate Aggregate packing –Coarse aggregates create voids –Fine aggregates that can fill these voids Combination of aggregates (by volume) Analysis of blends

23. Combination process Boundary of coarse and fine aggregate (PCS = 0.22 of NMPS) Loose and rodded unit weights – voids Mix type –Coarse graded – coarse aggregate skeleton –Fine graded – load carried by fine aggregate, Meeting aggregate ratios to ensure packing is as intended and not interfered with

24. Calculations