Transcript HMA Construction Program

HMA Construction Program
Module 10 – Quality Control /
Quality Assurance
Module 10 Objectives
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Objective of Quality Control
Objective of Quality Assurance
Four Types of Specifications
Population, lot, sample, and specimen
Random sampling and testing plans
Control charts
Applicable QC/QA tests
Quality Trends in Construction
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Customer-driven quality initiatives
ISO 9000-based quality systems
Project-focused quality efforts
Focus on customer satisfaction
The definition of “quality”
Senior leadership involvement
Quality Pavements: Don’t Begin
and End with Material Inspection
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Pavement design
Subgrade preparation
Base construction
Management philosophy
Specification Evolution
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Method or Recipe (Past)
End Result (Quasi-Present)
Quality Assurance (Present)
Performance Based (Future?)
Method or Recipe (Past)
COUNTY
CITY
STATE
VILLAGE
Department of Transportation Library
Method Specification
• Owner designs project and sets
specifications
• Contractor identifies material sources
• Contractor supplies representative
samples
• Agency conducts mix design
Method Specification (continued)
• Contractor begins production of mixture
• Agency conducts gradation and asphalt
content tests at plant and makes plant
adjustments
• Agency checks pavement density
• Pay adjustments, if any, are made
Problems with Method
Specifications
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Mix design – plant specific
Types of tests inadequate
Economic incentive – materials
Adjustments at plant affect density
Frequent disagreements
– Agency makes changes which affect pay
– Referee testing often required
End Result Specifications
• Specifying agency/contractor
– Sets limits
– Defines the desired quality of the finished
product
End Result Specifications (continued)
• Becoming more prevalent
• Agency or contractor designs project and
provides expected results for:
– Materials used,
– Volumetrics,
– Smoothness, and
– Density
End Result Specifications (continued)
• They typically require the:
– Contractor to do quality control testing
– Agency to do assurance testing and
conduct an acceptance program for
payment
• Consultants can play the role of
either the contractor or the agency in
terms of testing.
Common factors are used in end-result
specifications for acceptance of
materials and finished
pavements
Quality Assurance Specifications
• Separates responsibility for process
control and product acceptance
• Ensures that inspection
plays an essential role
Performance Based Specifications
• Performance of the final, in-place
product, is measured; not how it was
built
• Performance-based test methods have not
been fully developed
Performance Based
• Superpave Technology
• Warranties
• Rut Testers
The primary goal of a
QUALITY ASSURANCE SYSTEM
is to provide CONTROL and
maintain ASSURANCE. This
partnering approach will help to
maintain program credibility.
Objectives of a Quality Control
System
• Produce a quality product
• Assure that the final product meets job
specification
• Satisfy the customer’s needs, as
economically as possible
QC is the CONTROL portion of the
inspection system. QC ensures the
production of uniform materials that
meet required specifications through
periodic inspection and testing.
QC is the producer’s responsibility!
QA is the ASSURANCE portion of the
inspection system. QA assures the owner
that the producer’s test results are
accurate. Random sampling and testing
are at greater intervals than the
producer’s process.
QA is the buyer’s responsibility!
Testing Responsibility
• Shifting from agency to contractor
• Certification training programs
Quality Control Work Chart
Q u a lity Assu ra n c e
Bu y e r
O rg a n iza tio n
Ag e n c y
S e lle r
C o n tra c to r
Q u a lity C o n tro l
S u p e rviso r
Laydow n
C re w C h ie f
H o t M ix F a c ility
Ow ner
In d e p e n d e n t
Assu ra n c e
F a c ility
Q u a lity C o n tro l
F o re m a n
T e c h n ic ia n
Typical QC/QA Sampling and
Testing Procedures
• Pre-production
• Job Mix Formula approval and
verification
• QC during production by contractor
• Production and in-place acceptance by
owner
Pre-Production QC/QA
• Plant Considerations
• Aggregate, asphalt cement, and additives
for mix design
• Consider anticipated process adjustments
– Cause and effect
– Economics
Job Mix Formula Approval
and Verification
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Aggregate gradation
Aggregate physical properties
Asphalt content
Volumetric analysis
Stability or strength testing, where
applicable
• Moisture susceptibility
QC During Production by
Contractor
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Aggregate gradation
Asphalt content
Volumetric analysis
In-place density
QA During Production by Agency
Random production and in-place acceptance
testing by the owner is similar to contractor
testing, plus measurements of:
– Thickness
– Smoothness
– Overall profile and workmanship
Independent Assurance
In order for the QC/QA program to
maintain the highest level of accuracy and
credibility, owners should maintain an
Independent Assurance Group. Typically
separate, the group randomly reviews both
parties’ procedures and addresses
discrepancies.
Process Control Plan
• Assignment of QC responsibilities
• Type and frequency of tests
• Record of plant inspections and
calibrations
• Documentation
• Criteria for action
Assigning QC Responsibilities
S e lle r
C o n tra cto r
Q u a lity C o n tro l
Laydow n
S u p e rviso r
C re w C h ie f
H o t M ix F a c ility
Ow ner
F a c ility
Q u a lity C o n tro l
C re w C h ie f
T e c h n ic ia n
Type and Frequency of Tests
• Sampling and testing mix components
(Plant)
• Sampling and testing mixture produced
(Plant/Field)
• Analysis of results
• Evaluation of compliance with
specification limits
HMA Sampling and Testing
It is crucial that the producer and
agency use the same test methods and
equipment specifications in order to
compare test results appropriately.
Analysis of Test Results
• Does the mix comply with specification
limits?
– Current results vs. previous results
– Job Mix Formula, JMF (+/-)
– Single test vs. moving average
Sample Process Control Chart
Percent AC
6.1
Upper Control Limit
5.9
Job Mix
Formula
5.7
5.5
Lower Control Limit
5.3
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Test Number
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 = Running Average  = Individual Test Results
Sample Process Control Chart
6.3
6.1
Percent AC
Upper
5.9
Job Mix
Formula
5.7
5.5
Lower
5.3
5.1
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Test Number
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Control Charts
• What is plotted?
– Control sieves
• Max, 4.75 mm, 600 µm, 75 µm
(#4, #30, #200)
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Asphalt Content
Max. Theoretical Sp. Gr.
Laboratory Sp. Gr.
Voids and VMA
Pavement in-place density
Benefits of Control Charts
Benefits of Control Charts
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Early detection of trends
Establish process capability
Decrease inspection frequency
Permanent record of quality
Provide a basis for acceptance
Instill quality awareness
Taking corrective measures
Evaluating data for cost savings
Recording and reporting
Plant Inspections and Calibrations
• Control cold feeds and hot bins
• Facility operations and controls
QC / QA
• Documentation
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Day to day results
Problems with incoming products
Adjustments made to trend towards JMF
Others
QC / QA
• Criteria for action
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Specification tolerances
Timely response for adjustments
Adjusted job mix formula
Others
Total Variability
• Variability – Everything varies
• Assignable variability can be eliminated
IF we identify the cause
Scientific Tools to Use in the
Treatment and Analysis of Data
• Statistics
• Random sampling
Statistics
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Central tendency or average
Dispersion or range
Standard deviation or variability
Degrees of freedom (n-1)
Outliers
Normal Distribution is
most important for
highway materials
Statistics (continued)
• Sampling vs. complete enumeration
– Population
– Sample
– Data
• Controlled conditions
Population or Lot
Sample from the
Population or Lot
Sample #1
Sample #2
Sample #3
Random Sampling
• Any portion of the population has equal
chance of being selected
• Bias is introduced when judgment is used
• Use random number tables
Lots and Sublots
LOT
Random
Sampling
SUBLOT
Stratified
Random
Sampling
QC / QA Sampling Example
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Lot size: 1,000 meters
Pavement width: 3.6 meters
5 cores per lot
Lot begins at Sta. 100+000
LOT
100+000
5 equally sized sub-lots
Random Number Table
X (longitudinal) 0.74
0.60
0.01
0.27
0.43
Y (transverse)
0.29
0.21
0.78
0.01
0.43
0.28
0.37
0.00
0.49
0.97
0.73
0.08
0.87
0.32
0.97
0.72
0.14
0.09
0.70
0.41
QC / QA Sampling Example (cont’d)
• Sub-lot #1
– Length = 200 meters
– Random numbers: 0.74 and 0.29
• Measure up from Sta. 100+000
– X = 0.74 x 200 meters = 148 meters
– Y = 0.29 x 3.6 meters = 1.0 meters
QC / QA Sampling
• Participant Example:
– Lot size: 2,000 meters
– Pavement width: 3.6 meters
– 5 cores per lot
– Lot begins at Sta. 200+000
Random Number Table
0.74
0.60
0.01
0.27
0.43
0.29
0.21
0.78
0.01
0.43
0.28
0.37
0.00
0.49
0.97
X (longitudinal)
0.73
0.08
0.87
0.32
0.97
Y (transverse)
0.72
0.14
0.09
0.70
0.41
QC / QA Sampling
• Participant Example (cont’d.):
– Sub-lot #1
• Length = 400 meters
• Random numbers: 0.73 and 0.72
– Measure up from Sta. 200+000
• X = 0.73 x 400 meters = 292 meters
• Y = 0.72 x 3.6 meters = 2.6 meters
Process Acceptance Criteria
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Materials
Thickness tolerance
Pavement density
Pavement smoothness
Materials
• Process control by contractor
• Assurance sampling and testing done
randomly, and less frequently, by owner
Thickness Tolerance
• Can be checked with cores
• Yield checks during paving
• Use of stringline
– Initial HMA course
– Ski used on subsequent courses
• Smooth surface to pave on
Pavement Density
• Types of density specifications
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Laboratory density
Maximum theoretical density
Control strip
Method specification (ordinary compaction)
Laboratory Density
• Compares cores to field-produced mix
density
– Field mix compaction same as mix design
– Mix design properties verified
– End result specification
Percent Density =
In-Place Density
x 100
Laboratory Density
Maximum Theoretical Density
(Rice)
• Unit weight of mix in “voidless” state
• Core density is compared to MTD
• Relative density is in-place air voids
Percent of MTD =
In-Place Density
x 100
Max. Theor. Density
Control Strip Density
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Requires control strip at start of each lift
Minimum tonnage or area
After constructed, density tests taken
Test results compared to lab or MTD
– Number of tests is specified
– Is compaction adequate?
• Field density is the reference target
• 100% of target is desired
Control Strip Precautions
• These factors can affect density:
– Mix temperature
– Asphalt content
– Gradation
– Rolling technique
Reference Density Comparison
100
% of
Maximum 99
Theoretical
Density
98
0
97
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100
96
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99
95
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98
94
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97
93
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100
96
92
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99
95
91
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For 4% Voids
Mix Design
% of
Laboratory
Density
% of
Control Strip
Density
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In-Place
Air
Voids
Method Specification
• No reference density
• Spells out rolling operation
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Number of rollers
Types of rollers
Number of passes
Temperature measurements
“Free of roller marks”
• Very subjective specification
Pavement Smoothness
• Provide better ride
• Less damage to pavement
• Measurements must be accurate,
repeatable, and hopefully related to what
we feel when we drive the road
• Specifications should be set to how much
we can realistically improve the
smoothness of a road
• Corrections?
Pavement Smoothness
Measurements
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Straight edge
Profilograph
Profilometer
Mays Meter
LISA
Pavement Smoothness
Measurements (continued)
• Straight edge
– Typically 3 meters long
– Measure deviations > 6 mm
– Some have wheels (rolling straight edge)
• Local requirements?
– 3 mm in 3 meters
– 6 mm in 3 meters (sidestreets)
– 5 mm in 5 meters
Pavement Smoothness
Measurements (continued)
• Profilograph
– Most common is “California Style”
• 8 meter long aluminum truss
• Center mounted measuring wheel
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Standard testing distance = 0.15 km
Blanking band (5 mm)
Measurement in mm/km
Manual -vs- computer output
Local requirements?
Pavement Smoothness
Measurements (continued)
• Profilometer
– Self contained truck or trailer
– Uses accelerometers and distance measuring
equipment
– Computer processed information
– Used at highway speeds
– High initial investment
• Not easy to correlate different methods
Pavement Smoothness
Measurements (continued)
• Mays Meter – trailer device for
measuring roughness
• LISA
– Lightweight inertial surface analyzer or
quick response profilometer
– Laser sensor and an accelerometer
– Travels at 15 to 30 kph
QC / QA Review
The primary goal of a
QUALITY ASSURANCE SYSTEM
is to provide CONTROL and
maintain ASSURANCE. This
partnering approach will help to
maintain program credibility.
QC / QA Review
Implementing a Quality CONTROL
Program
• Management commitment
• Quality statement
• Developing a Quality Control
manual
QC / QA Review
Implementing a Quality ASSURANCE
Program
• Process Quality Control
• Acceptance sampling, testing and inspection
• Independent Assurance
Quality Control with
Quality Assurance
Credibility is another way of saying,
“You can believe me!”
Module 10 Objectives Review
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Objective of Quality Control
Objective of Quality Assurance
Four Types of Specifications
Population, lot, sample, and specimen
Random sampling and testing plans
Control charts
Applicable QC/QA tests