Assessing Quality of Asphalt Paving Jobs to Determine Contractor Pay

1
Assessing Quality of Asphalt Paving Jobs to
Determine Contractor Pay

• Robin C. Wurl
• James R. Lundy
• 2003 Quality Productivity Research Conference

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Contractors Employed for Asphalt Paving Jobs in
Oregon

• Job price established prior to commencing
• At job completion, quality of pavement assessed
• If pavement quality exceeds expectations
• Contractor receives pay bonus
• If pavement quality below expectations
• Contractor is given a pay penalty

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Bonus or Penalty is Determined by a Pay Factor

• Pay Factor
• Index between 0.75 and 1.05
• Multiplied by original job price to determine
  final payout figure
• Final Payout (Job Price) x (Pay Factor)

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Pay Factor is a Function of the Expected Quality
Level
Pay Factor
Expected Quality Level Exceeded
1.05
1.00
Expected Quality Level Attained
0.95
0.90
0.85
0.80
Quality Level UnacceptableTear out and replace
0.75
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Goal Map Job Quality to a Pay Factor

• Statistically quantify quality of pavement job
• Map statistical quality measure of job to pay
  factor

Statistical Quality Level of Job
Job Pay Factor
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Nature of Pavement Mixes

• Multiple Quality Characteristics (QCs)
• X1, X2, , Xp
• Target values for QCs may change during job
• Process adjustments in beginning of production
• Changes in raw materials during production
• QCs not all equally important

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The Measure of Quality is Based on Loss Function

• Consider univariate case X mix quality
  characteristic T target of quality
  characteristic
• Quadratic Loss Function
• Expected Loss

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Quality Measures
Measure of Deviation from Target
Measure of Variability
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Multiple QCs and Target Changes During Job
kth QC
jth target change within kth QC
ith observation within jth target change within
kth QC
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Quality Measures are Estimated for Each QC and
Target

• Estimate deviation from targetwith

• Estimate variabilitywith

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Quality Measures are Averaged Over Target Changes

• Use number of observations per target in weighted
  average of quality measures

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Individual Quality Measures are Mapped to Pay
Factor Values

• Specific point values of quality measures mapped
  to equitable pay factor
• Mappings determined from expertise about process
• Straight units (not squared) for quality measures
  

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Linear Interpolation is Used Create Continuous
Mapping Function
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Account for Unequal Importance of QCs

• Assign weights to QCs to account for different
  relative importance
• wk - relative importance weight of QC

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Intermediate Pay Factor Values Computed for
Quality Measures

• Deviation from target
• Variability

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Intermediate Pay Factor Value Computed for a
Specific QC

• For kth QC

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Pay Factor for the Overall Job is Computed

• Overall

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Example Asphalt Paving Job

• X1 ? Air voids in pavement mix ()
• Target T1 4 and changes to 4.3
• Relative importance w1 0.4
• X2 ? In-place density of pavement ()
• Target T2 93
• Relative importance w2 0.6

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Quality Measures Computed within Each Target
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Quality Measures Averaged Over Target Changes
Number of observations for target 1
Number of Observations for target 2
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Deviation from Target for Air Voids Mapped to
Individual Pay Factor
Deviation from Target
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Quality Measures Mapped to Pay Factor Values
Intermediate Pay Factorfor Deviation from
Target
Overall Pay Factor