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 It is becoming increasingly apparent that ongoing negative perceptions in the industry regarding the performance of hot-mix asphalt, particularly wearing courses, are not in the interests of this sector and may prove to militate against the ongoing traditional use of this product in a market currently experiencing a growth phase. These negative perceptions have a wide range of causative factors, some of them more well-founded than others. Suffice it to say that all is not well in the house of hotmix design and certain aspects of quality management of hot mix asphalt wearing courses. We, as a road industry, cannot allow a situation whereby ongoing shortcomings in engineering practice will adversely influence the ongoing use of a key road building material. We should renew our efforts to ensure that the technology surrounding wearing course asphalt especially is sound and up-to-date to render the product cost-effective and, hence, competitive. Only by doing so, can negative perceptions and disadvantageous pavement selection policies be challenged or averted The willingness of Gautrans to jointly seek resolution to the problem is sincerely welcomed by the industry. A collaborative effort of client, advisor and provider is surely the best way forward.It is becoming increasingly apparent that ongoing negative perceptions in the industry regarding the performance of hot-mix asphalt, particularly wearing courses, are not in the interests of this sector and may prove to militate against the ongoing traditional use of this product in a market currently experiencing a growth phase. These negative perceptions have a wide range of causative factors, some of them more well-founded than others. Suffice it to say that all is not well in the house of hotmix design and certain aspects of quality management of hot mix asphalt wearing courses. We, as a road industry, cannot allow a situation whereby ongoing shortcomings in engineering practice will adversely influence the ongoing use of a key road building material. We should renew our efforts to ensure that the technology surrounding wearing course asphalt especially is sound and up-to-date to render the product cost-effective and, hence, competitive. Only by doing so, can negative perceptions and disadvantageous pavement selection policies be challenged or averted The willingness of Gautrans to jointly seek resolution to the problem is sincerely welcomed by the industry. A collaborative effort of client, advisor and provider is surely the best way forward.

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 NOT ONLY enhance expertise base; Advance implementation of findings and lesions learntNOT ONLY enhance expertise base; Advance implementation of findings and lesions learnt

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 The four contractor/suppliers represented at the meeting would partner with specialist HMA design consultants to design the following mixes (ie two submissions from each partnership) for improved performance using commercially available binders: One for intersections; One for general use. The designs should be submitted to GDPTRW (Ms Sadzik) by 31 May 2006 and distributed to the working group for discussion at the next meeting of 20 June 2006 at 11:00 at GDPTRW.The four contractor/suppliers represented at the meeting would partner with specialist HMA design consultants to design the following mixes (ie two submissions from each partnership) for improved performance using commercially available binders: One for intersections; One for general use. The designs should be submitted to GDPTRW (Ms Sadzik) by 31 May 2006 and distributed to the working group for discussion at the next meeting of 20 June 2006 at 11:00 at GDPTRW.

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 The current HVS schedule would dictate that HVS testing would begin in Oct/Nov 2006. However, completion of phase 2 of the Forensic study, and significant MMLS and laboratory testing would be required before that time as inputs to the overall project. The project advisory group not represented at the meeting (D Rossmann, F Hugo, E Fletcher and M Henderson) should also be invited to the meeting of 20 June and a broader industry advisory group should be formed. Mr Verhaeghe (the project[PM1] leader) of the CSIR would also attend the meeting.  [PM1]Which project?The current HVS schedule would dictate that HVS testing would begin in Oct/Nov 2006. However, completion of phase 2 of the Forensic study, and significant MMLS and laboratory testing would be required before that time as inputs to the overall project. The project advisory group not represented at the meeting (D Rossmann, F Hugo, E Fletcher and M Henderson) should also be invited to the meeting of 20 June and a broader industry advisory group should be formed. Mr Verhaeghe (the project[PM1] leader) of the CSIR would also attend the meeting.  [PM1]Which project?

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