15 h ROAD PAVEMENTS FORUM East London May 2008 HMA Task Group

1. 15h ROAD PAVEMENTS FORUMEast LondonMay 2008HMA Task Group

2. Resolution #2 From last November • That an RPF task group be established under the leadership of Arthur Taute to coordinate activities relating to HMA design, quality assurance, performance and specifications in line with the recommendations of CAPSA’07

3. HMA Progress

4. Issue Groups • Mix Design • Many activities on research and development • Gautrans forensic study • APT • Rut Challenge • Implementation Lacking

5. Mix Design Issues • Aggregate Packing • Bailey • DASR • (Dominant Aggregate Size Range) – Denneman SATC 2007 • Binder Stiffness • Problems with current specification that it can span across several performance grades – Bahia/ Marais/ AsAc • Binder Durability • Johan Muller

6. Mix Design Implementation • Performance – need criteria • Rutting • Rut testing devices • Cracking • Lots of cracking – water sensitive bases • Variability • Permeability • Water sensitive bases • Variability

7. Performance Investigations • Premature Cracking and Rutting as well as Inconsistency between design and actual asphalt laid • Gauteng Forensic Study • Inappropriate use (tender mixes at intersections) • Gauteng Forensic Study • Permeability • Rossmann et al CAPSA07 • Rutting • Verhaeghe et al CAPSA07 • APT - Rut Challenge - Gautrans/Sabita - CSIR/Industry

8. Variability and Risk

9. Pavement Design • Implementation • Pavement designs need to be improved and to take available materials into account • Specifications need revision

10. Variability and Risk

11. Issue Groups • Quality Management • Components • Problems with binder consistency • Problems with aggregate consistency • Implementation • Quality problems in practice • Entire process that can influence quality needs improvement – from design and specification through procurement, mix design and approval, manufacture and construction

12. Construction Issues • Variability within lots • Consistency throughout project • Uniformity across length and breadth of lanes • Diversity of aggregate supply • Regularity of supply and surface • Homogeneity of materials

13. Problem Statement • We can be as smart as we like on HMA design etc but then we have to be able to implement the design. • With new mix paradigm (AC and very heavy loads), variability issues are over-riding any design processes and decisions in respect of the performance of the product.

14. HMA Task Group Core Corresponding JA Grobler, D Pretorius JC vd Walt, E Sadzik, S Oloo J Wise AN Other T Distin, L Sampson E Denneman • A Taute • D Rossmann • H Marais • PA Myburgh • B Verhaeghe

15. How do we improve implementation in the light of the following • Design – lack of resources • Specification - no new criteria - old • Procurement – cheapest price • Mix design approval – cumbersome - discourages changes during works • Manufacture – commercial interests • Construction – focus on doing whatever one needs to, to get acceptance • Acceptance testing – statistical methods which assume reasonable uniformity and do often not reject substandard materials

16. Can Pay Factors Help? • USA – common • RSA do have some penalties and partial payment but no bonus for good quality work. • Clients feel they deserve quality but are not always getting it unless the CE and contractor are “special” • May allow for some discounts by those who know they can rely on PF>1 • PF should not be considered as a bonus but rather payment for better quality.

17. Proposed Pay Factors in Sabita Manual and at CAPSA • Bonus/penalty for riding quality – some benefits but limited general acceptance • Sabita Manual 5 – proposed but not retained – specification issue • CAPSA proposals for PF based on consistency and average of • Binder Content • Density • Now Aggregate Gradation

18. Binder Content Pay Factors – CAPSA07

19. Density Pay Factors – CAPSA07

20. Aggregate Gradation • Substantial variation between individual samples. Many points on the road that are out of specification. • Lot averages generally OK • What do to about lots that do not meet specification ? • How to encourage conformance?

21. Problem Statement

22. Problem Statement • Variation occurs through all sieve sizes of source material • It is possible to reduce variation by premixing before loading into bins • Propose a Pay Factor to accommodate the additional costs

23. Crusher Dust Variability - Individual Sieves

24. Grading Pay Factor • Need a Pay Factor that provides an indication of the deviation of the average grading of a lot from the target. • Consider the sum of the absolute values of the difference between the percentage passing each sieve in a lot and the target grading • Problem is that there can be substantial variation within a lot but the average can be OK • Therefore need a parameter provides and indication of this variability

25. Grading Pay Factor Contd. • Certain sieves are more critical than others • Eg current spec allows +- 5, +-4, +-3 and +-2 for various sieves with the 0.150 and 0.075 being the most critical (+-2) • The 2.36 mm sieve is also critical in continuously graded mixes. • Therefore the absolute value of the differences needs to be weighted differently for various sieves

26. Grading Pay Factor Contd. • Must try to ensure consistency when applying the Pay Factor across different mixes and gradations • Therefore need to standardize on number of sieves being considered and weighting that is applied.

27. Consider weighted sum of differences • Sum the weighted absolute value of differences between actual grading and target grading on selected sieves. • Use weightings to correspond to current allowable variation • Add extra weight for other important sieves.

28. Illustrative Weighted Sum of DifferencesSingle source – crusher run

29. Consider weighted sum of standard deviations • Sum the weighted value of standard deviations on selected sieves. • Use same weightings as on differences

30. Example of Sum of weighted std dev per sieve

31. Proposed Criteria • Use weighting of 1 on all sieves and 2 on 2.36mm, 0.150mm and 0.075mm for medium graded asphalt • Use a total weighting of 12 • Vary the weighting and critical sieves depending on mix design and critical issues. • Use values for Sum Weighted Std Dev as follows: • <12 – low variability • 12- 17 medium variability • >17 high variability

32. Proposed Pay Factor for Grading Consistency

33. Pay Factor • Pay Factor Grading • SStd>17 = 1.06 – 2 x WD (max 1.0 min 0.85) • SSTd>12 <17 = 1.12 - 2 x WD (max 1.05 min 0.85) • SStd<12 = 1.20 – 2 * WD (max 1.10 min 0.85) • WD = Weighted sum of absolute values of differences between actual % passing and target % passing on sieves from 6.37mm to 0.075mm (9 sieves) where weight is 1 for all sieves except 2.36mm, 0.150mm and 0.075mm where it is 2. • SWStd = Sum of Weighted Stdev for the lot on same 9 sieves using the same weighting

34. Example 1 – Lot with medium variability and low difference

35. Example 2: Lot with low variability but higher difference

36. Resulting Pay Factors for 10 lots

37. Action Plan • Mix Design • Need criteria for various rut testing devices – ongoing research rut challenge etc • Need criteria for permeability – problem is mix variability resulting in variable results • Need to start implementing Pay Factors • Require trial specification and feedback throughout industry. • Have used riding quality Pay Factors with success in the past – therefore should be able to use others. • Need to assess how to combine Pay Factors – consider multiplication • Need to start the debate and start moving away from what we were doing.