Innovations in HMA

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