www.dot.state.pa.us

Steven L. Koser, P.E.Pennsylvania Department of Transportation

Gary L. Hoffman, P.E.PA Asphalt Pavement Association

Bituminous PWT(Percent Within Tolerance)

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Spec Limits and Goal Posts are Similar

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Quality Measure:Percent Within Tolerance (PWT)

• Estimates the percentage of material within specification limits– Assumes normal distribution– Area equals 1.0 or 100%

1.0or 100%

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Standard Deviation

• A measure of the variability (i.e. spread) of data

Spread

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Standard Deviation: Equation

• Sample standard deviation (s)

s =∑(Xi - X)2

s = - 1∑(Xi - X)2

n - 1

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PWT

• Efficiently captures mean and standard deviation in one quality measure

X 3s2s1s-3s -2s -1s

X - means - standard deviation

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QL → PWLL

Percent Within Tolerance

• Lookup estimated PWL from Q for a specified number of samples (n)

X 3s2s1s-3s -2s -1s

PWLL

LSL

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Percent Within Tolerance

• Lookup estimated PWL from Q for a specified number of samples (n)

X 3s2s1s-3s -2s -1s

QU → PWLU PWLU

USL

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+ - 100 =

Percent Within Tolerance

PWLL

LSLUSL

PWLU

USL

X

LSL

PWL

PWLU + PWLL - 100 = PWL

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Payment Plan with Incentive

Pay Incentive

Pay Disincentive

AQL=90

10095 105

9080 100

Pay factors

Estimated PWL

70

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Number of States using PWT forHot Mix Asphalt

0

5

10

15

20

25

30

2010 20082014Num

ber o

f Age

ncie

s

SourceFHWA QA Assessment

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•Tighter adherence to producing job mix formula

•Tighter adherence to field density spec. requirements

What Does PWT Drive?

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•Well suited for low bids to achieve quality

•Contractors = bonuses for tighter adherence to targets

•Contractors = reduced payments for loose adherence to targets

•Moves focus to targets (NOT minimums)

Advantages of PWT

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•Adds bonus structure (maximum 4%)

•Adds mix gradation (PCS) as part of payment

•Modifies current “goal posts” approach for 100% payment (good or no good)

•Results in many fewer 100% payments and spreads these out (bonus and penalty)

What’s different with PWT spec?

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• Current specification (50% mix, 50% density)

• 25% asphalt content• 25% #200 sieve• 50% field density

• PWT specification (50% mix, 50% density)• 30% asphalt content• 10% #200 sieve• 10% primary control sieve (new)• 50% field density

Payment Equation Changes

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•Defective lots can be left in place at 70% pay by DE (previously 50% pay)

•Allows contractor to terminate lot Allows contractor to limit risk when

early QC results indicate an issue Must stop paving 90% maximum pay Must R&R if defective by test results

Common to All PWT Specs

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•Three (3) methods thru CT process:1. PWT-LTS (Laboratory Testing Section)

• Fully approved (includes FHWA)• Acceptance at LTS• PWT-LTS Use Guidelines/District Memo

2. PWT-LA (Local Acceptance)• Producer/Contractor Results, Department Verification, F-test and t-test (Not Practical)

3. PWT-HOLA (Hands On Local Acceptance)• Department Acceptance, Producer/Contractor Lab

Current Status

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2016 Construction Season•Projects advertised after October 13, 2015 (considered)

•Districts decide if PWT-LTS is viable

•Gain experience with PWT

•PWT-LTS Incentive/Disincentive Spreadsheet

PWT-LTS

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•Very similar to current process

•Allows contractor option to expedite sample delivery to Harrisburg

Inspection staff secures samples Secure samples given to contractor Contractor delivers to LTS at his cost LTS verifies security prior to testing Priority given to expedited samples Test Turnaround Goal (Days)

PWT-LTS

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What is Local Acceptance?

•HMA/WMA Material samples collected as usual

•Acceptance testing performed at:

•Proficient producers lab

•or another mutually acceptable lab

•No LTS acceptance testing (except for dispute resolution situation)20

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Mixture Sample Collection

Contractor Pulls Sample

Contractor Transports

Sample

Representative Tests Sample

LocallyRepresentative Splits Sample

LTS Tests IA Sample

Representative Secures Sample

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Gmm Verification Testing

• Federal Aid Projects & Projects on the NHS• Local Testing

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Staffing LA Testing

•Districts allocate certified plant inspectors to perform testing

•Shortage in qualified staff• Use Consultants?

•May need to coordinate testing for out of District sources

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Contractor’s Lab Assessment

•Local acceptance lab needs AMRL on-site proficiency assessment

•Every 2-years

•Assessment of equipment used for acceptance testing

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Independent Assurance

• Required by 23 CFR 637

• First Lot & randomly once every 10 Lots thereafter

• Performed at LTS on splitsamples

• Ensures testing equipment used is:

• properly calibrated• operating correctly

• Ensures sampling & testing is performed correctly

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Local Acceptance QC Plan

•Separate LA QC Plan required to detail specifics

•3 weeks before paving

•Must identify lab and equipment for testing

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Local Acceptance Equipment Requirements

•Dedicated equip. for Dept. use

•Dept. Representative:•Reviews equipment•Disapproves equip. not meeting requirements

•Provides Final Lab Acceptance

•Dept. Rep. accessibility to local lab

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Sample Transportation and Security

• Tamper proof coolers with:

• Clasps• unique, unopened padlock

• Capable of relocking for storage

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Sample Transportation and Security

• Alternative: Coolers w/uniquely numbered security tags

• Only 1 lot per cooler

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Sample Security

• Sealed containers:• Inspected for security• @ opening, samples & paperwork examined

• Evidence of compromised security Dept. may:

• Reject for testing• Suspend paving operations • and require additional samples to be taken

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Sample Paperwork

•Paperwork (TR-447) is the same

•Worksheets keep records of test results

•Paperwork to be retained for 3-years

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Lot Testing

•Testing begins when lot is complete

•LA testing takes “priority” over other testing (i.e., QC)

•Contractor’s tech. may witness not required

•Contractor may saw cut density cores for testing

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Department Concerns/Issues

Equipment:•Enough equipment

• Inspectors familiar with equipment

•Space for QC testing AND acceptance testing @ same time

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Department Concerns/Issues

Manpower:•Need more trained & certified inspectors•Challenge dedicated LA testing staff, ANDmeet all other Materials Unit duties (i.e., aggregate, concrete, SOS, records audits, etc.)

Training:•Many inspectors are certified, but have little experience doing testing

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Cons

PWT-LTS• Oven

Correction Factor

• Test Turnaround Time

PWT-HOLA• Manpower• Equipment• IA• AMRL

PWT-LA• Manpower• Equipment• IA• AMRL• Large Projects

Only• F-test/t-test

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Pros

PWT-LTS• Manpower• Equipment• All Projects

PWT-HOLA• Oven

Correction Factors

• Test Turnaround

• Gmm Verification

• Staff Knowledge

• AMRL• All Projects

PWT-LA• Oven

Correction Factors

• Test Turnaround

• Gmm Verification

• Staff Knowledge

• AMRL

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Questions?

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