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www.dot.state.pa.us
Steven L. Koser, P.E. Pennsylvania Department of Transportation
Bituminous PWT (Percent Within Tolerance)
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Spec Limits and Goal Posts are Similar
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Bituminous PWT (Percent Within Tolerance) Steven L. Koser, P.E. - - PowerPoint PPT Presentation
Bituminous PWT (Percent Within Tolerance) Steven L. Koser, P.E. - - PowerPoint PPT Presentation
Bituminous PWT (Percent Within Tolerance) Steven L. Koser, P.E. Pennsylvania Department of Transportation www.dot.state.pa.us 1 Spec Limits and Goal Posts are Similar www.dot.state.pa.us 2 Quality Measure: Percent Within Tolerance (PWT)
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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%
1.0
- r 100%
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Standard Deviation
- A measure of the variability (i.e. spread) of data
Spread
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PWT
- Efficiently captures mean and standard deviation
in one quality measure
X
3s 2s 1s
- 3s
- 2s
- 1s
X - mean s - standard deviation
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Number of States using PWT for Hot Mix Asphalt
5 10 15 20 25 30
2010 2008
2014
Number of Agencies
Source FHWA 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
paym ents for loose adherence to targets
- Moves focus to targets (NOT
minimums)
Advantages of PWT
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- Adds bonus structure (maximum 4% )
- Adds m ix 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
- PW T specification (50% mix, 50% density)
- 30% asphalt content
- 10% # 200 sieve
- 1 0 % prim ary 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)
- Allow s contractor to term inate 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 ) m ethods thru CT process:
- 1. PWT-LTS (Laboratory Testing Section)
- Fully approved (includes FHWA)
- Acceptance at LTS
- PWT-LTS Use Guidelines/ District Memo
- 2. PWT-HOLA (Hands On Local Acceptance)
- Fully approved (includes FHWA)
- Department Acceptance, Contractor Lab
- 3. PWT-LA (Local Acceptance)
- Contractor Results, Department Verification, F-test
and t-test (Not Practical)
Current Status
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- Very sim ilar to current process
- Allows a contractor option to expedite
sam ple 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
- 2 Standard Work Day Turnaround Goal at LTS
PWT-LTS
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PWT-HOLA
- HMA/ WMA Material
sam ples collected as usual
- Acceptance testing
performed at:
- Proficient producers
lab
- or another mutually
acceptable lab
- No LTS acceptance
testing (except for dispute resolution situation)
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Mixture Sample Collection
Contractor Pulls Sample Contractor Transports Sample Representative Tests Sample Locally Representative 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 will need to
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
will need AMRL on-site proficiency assessment
- Every two years
- Assessment on the
equipment to be used for acceptance
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Independent Assurance
- Required by 23 CFR 637
- First lot and randomly once for
every ten thereafter
- Performed at the LTS on split
samples
- Ensures sampling and testing is
performed correctly
- Ensures testing equipment
used is properly calibrated and
- perating 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 equipment for
Department use
- Representative reviews
equipment
- Can remove equip. not meeting
requirements from service
- Department Acceptance
- Accessibility to local lab
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Sample Transportation and Security
- Tamper proof
coolers with clasps and unique, unopened padlock
- Must be capable of
relocking for storage
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Sample Transportation and Security
- Alternative: Coolers
with uniquely numbered security tags
- Only one lot per
container
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Sample Security
- Sealed containers first inspected for security. Upon
- pening, samples and paperwork to be examined.
- If 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 to begin once lot
is complete
- LA testing takes priority
- ver other testing
- Contractor’s technician
may be present to witness, but not required
- Contractor may saw cut
density cores for testing
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- Projects advertised after October 13,
2015 (considered)
- PWT-HOLA available as of January 15,
2016
- PWT-LTS Incentive/ Disincentive
Spreadsheet
2016 Construction Season
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Challenges
- Budget
- Test Turnaround Time (PWT-LTS)
- Oven Correction Factor (PWT-LTS)
- Manpower/ Equipment (PWT-HOLA)
- AMRL (PWT-HOLA)
- Standard Deviation
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Taking on the Challenge
- Expedited Sample Delivery (PWT-LTS)
- Dispute Resolution
- Training (PWT-HOLA)
- AMRL (PWT-HOLA)
- Standard Deviation
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