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

15h ROAD PAVEMENTS FORUM

East LondonMay 2008

HMA Task Group

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

HMA Progress

Issue Groups

• Mix Design– Many activities on research and

development• Gautrans forensic study

• APT

• Rut Challenge

– Implementation Lacking

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

Mix Design Implementation

• Performance – need criteria– Rutting• Rut testing devices

– Cracking• Lots of cracking – water sensitive bases• Variability

– Permeability• Water sensitive bases• Variability

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

Variability and Risk

Pavement Design

• Implementation– Pavement designs need to be improved and

to take available materials into account– Specifications need revision

Variability and Risk

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

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

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.

HMA Task Group

Core

• A Taute

• D Rossmann

• H Marais

• PA Myburgh

• B Verhaeghe

Corresponding

• JA Grobler, D Pretorius

• JC vd Walt, E Sadzik, S Oloo

• J Wise AN Other

• T Distin, L Sampson

• E Denneman

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

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.

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

Binder Content Pay Factors – CAPSA07

Density Pay Factors – CAPSA07

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?

Problem Statement

Improved siewe ,stockpile method at plant

9092949698

100

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 STD ST 1 ST 1 ST 1 ST 2 ST 2 ST 3 ST 3 ST 4 ST 4 ST 5 ST 5 ST 5 ST 5

6.7 % passing

Lower Limit

80

85

90

95

100


4.75 % passing

Upper Limit

Lower Limit

60

65

70

75

80


2.36 mm

Upper Limit

Lower Limit

30354045505560


1.18 mm

1.18 mm

20

25

30

35

40


0.600 mm

Upper Limit

1015202530


0.300 mm

0.300 mm

510152025


0.150 mm

0.150 mm

0.05.0

10.015.020.0


0.075 mm

0.075 mm

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

Crusher Dust Variability - Individual Sieves

Crusher Dust Variation

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

9.5 6.7 4.75 2.36 1.18 0.600 0.300 0.150 0.075

Sieve Size

Valu

e_ Stdev

Spec Max

Control Stdev


0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

9.5 6.7 4.75 2.36 1.18 0.600 0.300 0.150 0.075

Sieve Size

Valu

e_ Stdev

Spec Max

Control Stdev


0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

9.5 6.7 4.75 2.36 1.18 0.600 0.300 0.150 0.075

Sieve Size

Valu

e_ Stdev

Spec Max

Control Stdev

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

•

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

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.

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.

Illustrative Weighted Sum of DifferencesSingle source – crusher run

Consider weighted sum of standard deviations

• Sum the weighted value of standard deviations on selected sieves.

• Use same weightings as on differences

Example of Sum of weighted std dev per sieve

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

Proposed Pay Factor for Grading Consistency

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

Example 1 – Lot with medium variability and low difference

SampleDate

Source/ MixTonnage

Lane

Lot No Target SPEC 78 79 80 81 82 83 84 Avg Std Dev Weight (Sum 12)

Position 15.82 15.7 15.6 15.5 15.4 15.27 15.18

Weight (Sum 12)

Binder Content 5.1 4.8 - 5.4 5.57 5.29 4.85 5.37 5.41 5.54 5.43 5.35 0.24 0.92

SIEVE SIZE

26.5 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.019.0 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.013.2 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.09.5 98 94 - 100 99 99 99 98 99 98 100 98.86 0.69 0.9 1 0.96.7 85 80 - 90 87 83 81 84 84 85 90 84.86 2.91 0.1 1 0.14.75 69 65 - 73 72 66 60 67 65 69 73 67.43 4.43 1.6 1 1.62.36 43 39 - 47 47 43 38 43 43 46 47 43.86 6.37 0.9 2 1.71.18 29 25 - 33 31 29 26 29 29 30 31 29.29 1.70 0.3 1 0.3

0.600 21 17 - 25 22 21 20 21 21 22 22 21.29 0.76 0.3 1 0.30.300 15 12 - 18 15 14 14 15 14 15 15 14.57 0.53 0.4 1 0.40.150 10 8 - 12 11 11 10 11 11 11 11 10.86 0.76 0.9 2 1.70.075 7 6 - 8 8.3 7.7 7.3 7.7 7.5 7.9 8 7.77 0.66 0.8 2 1.5

18.81 6.1 12 8.5 89

Abs (Target -

Avg)

Weighted Diff

Pay Factor

Percentage Passing

LOT A6 Km 15.839 to Km 15.10022/11/2007A/C MED

357.08West Bound Fast Lane

Example 2: Lot with low variability but higher difference

SampleDate

Source/ MixTonnage

Lane

Lot No Target SPEC 60 61 62 63 64 29./11 30./11 AVG STD.

Position 17.28 17.14 16.98 16.84 16.72 Plant Plant DEV.Binder Content 5.1 4.8 - 5.4 4.81 4.75 4.86 4.94 4.71 5.15 4.97 4.88 0.15 1.01

SIEVE SIZE

26.5 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.019.0 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.013.2 100 100 100 100 100 100 100 100 100 100.00 0.00 0.0 0 0.09.5 98 94 - 100 99 98 99 99 99 99 99 98.86 0.38 0.9 1 0.96.7 85 80 - 90 83 82 82 84 81 86 84 83.14 1.68 1.9 1 1.94.75 69 65 - 73 68 66 67 67 67 72 67 67.71 1.98 1.3 1 1.32.36 43 39 - 47 43 44 42 43 43 47 45 43.86 3.35 0.9 2 1.71.18 29 25 - 33 27 28 27 28 28 29 30 28.14 1.07 0.9 1 0.9

0.600 21 17 - 25 20 20 19 20 20 19 20 19.71 0.49 1.3 1 1.30.300 15 12 - 18 14 13 13 14 13 13 14 13.43 0.53 1.6 1 1.60.150 10 8 - 12 10 10 10 10 10 10 10 10.00 0.00 0.0 2 0.00.075 7 6 - 8 7.7 7.4 7.5 7.6 7 6.5 7.4 7.30 0.83 0.3 2 0.6

10.31 8.9 12 10.0 100

Percentage Passing

Pay Factor

Abs (Target -

Avg)

Weighted Diff

Weight (Sum 12)

LOT 11 Km 17.3 to Km 16.614/11/2007A/C MED

280West Bound Fast Lane

Resulting Pay Factors for 10 lots

11 12 13 14 15 16 17 18 19 20Spec Weights

98 1 0.8 0.6 1.2 1.1 1.3 0.8 1.0 0.8 1.2 1.085 1 1.7 2.9 2.0 0.9 0.8 0.2 1.8 0.7 2.3 0.869 1 1.7 2.8 2.2 1.9 0.3 2.3 0.3 3.3 4.4 2.443 1 2.0 1.2 0.8 1.6 2.0 0.8 2.8 0.7 0.1 0.229 2 1.0 0.6 1.2 0.6 0.0 1.2 3.0 0.3 0.2 2.021 1 1.1 0.1 1.4 0.3 0.3 0.3 1.0 0.3 0.2 0.815 1 1.4 0.5 1.0 0.6 0.5 0.3 0.5 0.2 0.1 1.010 2 0.2 1.3 0.4 0.9 1.5 1.5 2.5 1.3 1.8 0.87 2 0.7 1.3 0.8 1.4 1.7 1.6 2.4 1.7 2.0 1.0

Sum WAbs 12 9.8 10.7 9.8 8.0 6.9 8.4 14.1 8.5 11.2 9.0100.4 90.5 92.5 96.0 98.2 89.2 83.8 94.9 89.5 94.1 92.9

11.0 12.6 13.8 14.0 12.5 20.5 14.8 13.4 16.0 15.6

Absolute Value of Weighted Deviation of Lot from target

Lot Number

Pay Factor

Sum of Weighted Stdev for lot (SWStd)

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.

Documents

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