Construction QC/QA Representative Samples 1

Quality Control / Quality Assurance

Obtaining a representative sample

Senior/GraduateHMA Course

Construction QC/QA Representative Samples 2

Sample Size

• Mixture Component Variability

• Confidence Level

• Error or Bias From True Value

• Effect on Performance

Construction QC/QA Representative Samples 3

Frequency of Sampling/Testing

• Mixture Production Variability

• Effect on Performance

• Previous History

• Compliance With Specifications

Construction QC/QA Representative Samples 4

SAMPLING

• Preliminary Investigation of the Potential

Source

• Control of Product at the Source of Supply

• Control of Operations at the Site of Use

• Acceptance or Rejection of Material

Construction QC/QA Representative Samples 5

SIZE AND NUMBER OFSAMPLES

D 3665 Random Sampling of Construction Materials

E 105 Probability Sampling of Materials

E 122 Choice of Sample Size to Estimate the Average Quality of a Lot or Process

E 141 Acceptance of Evidence Based on the Result of Probability of Sampling

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SAMPLE SIZE

Nominal

Maximum Size Minimum Mass, lbs.

No. 8 4

No. 4 4

3/8 8

1/2 12

3/4 16

1 20

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Types of samples to be taken

• Aggregate

• Asphalt binder

• HMA mixture

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Sampling at Point of Shipment Delivery

• By bleeder valve or tap in transfer line or at back of truck

– During unloading, center 1/3 of load

Safety equipment is a must

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• Draw and discard at least a gallon of binder to clear line

Sampling Truck

Construction QC/QA Representative Samples 10

• Immediately take at least a quart sample

Sampling Truck

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Protection and Preservation• Take care not to contaminate containers• Fill and immediately seal

– Don’t immerse in solvent

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Protection and Preservation

• Store so that emulsions are protected from freezing

• Avoid transferring from one container to another

• Retain samples not tested (point of delivery)

• Take precautions to avoid contamination during

sampling, handling, shipping and storage

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Sampling at Plant Tank

• Same sampling directions apply to sampling the plant tank

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Sampling Bituminous Paving Mixtures

• Accurate test results depend upon a uniform, representative sample being collected.

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Sample Location

• At the plant– From the truck – most common– From plant discharge– From cold feed (gradation only)

• At the roadway– Behind the paver (11 states)– From the windrow

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Which is the best location?

WHY?

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Truck sampling

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Loose HMA

RTSD

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Sampling – Roadway

• Approximately equal increments• Make vertical face with shovel

750 mm (30 in.) parallel to centerline• Pull material back 300 mm (12 in.)

Construction QC/QA Representative Samples 21

Sampling – Roadway (continued)

• Place scoop on pavement next to vertical face and fill scoop

Obtain material to full depth• Close lid and remove scoop when full• Repeat to obtain required sample size

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Sampling from the roadway

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Sampling – Paver

• Obtain samples at end of auger using square shovel

• Place shovel in front of auger extension with blade flat on surface

• Allow front face of auger stream to cover shovel

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Sampling – Paver (continued)

• Remove shovel before auger reaches it Lift shovel vertically

• Repeat until sample size reached

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Sampling from Paver

WHAT ARE THE PROBLEMS WITH

THIS?

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“Sampling The Windrow”

Solution

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Sampling Loose HMA?

See any problems with this?

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Effect of Sampling Location on Gradation Variability

0

1

2

3

4

5

6

3/4"

1/2"

3/8" #4 #8 #16

#30

#50

#100

#200

Sieve Size

Sta

nd

ard

Dev

iati

on

s

Coldfeeds (n=45)

Loose HMA (n=45)

Cores (n=46)

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Sample Splitting

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Sample Splitting

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Segregated Samples from the Same Mix

Coarse Portion

3.79% Asphalt Binder

Fine Portion

5.21% Asphalt Binder

Construction QC/QA Representative Samples 32

Questions?