How to Ensure Quality and Incentive Pay on CDOT Projects ‐ RMACES ‐June 24, 2015

Craig Wieden, Region 2 Materials Engineer

Quality Assurance Panel Presentation  

CDOT Region 2• Encompasses 14 Counties in SE Colorado • Approximately 2,500 Centerline Lane Miles 

of Roadways• Terrain – Mountains to Eastern Plains • High Elev. ‐ 11,539 Feet at Hoosier Pass• Low Elev. – 3,365 Feet – Kansas Border• Roadways

• Interstate Highways (125,000 AADT)• Low volume rural roads (40 AADT)

• Air Temps from 110ºF to -50ºF

Contractors:• Urban areas – fixed asphalt plants• Rural areas – mobile plantsMaterial Sources:• Hard Rock Quarries• Alluvial and River Deposits

• CDOT HMA Acceptance Criteria• Voids Acceptance

• AC Content• Air Voids• Voids in Mineral Aggregate• Mat Density • Joint Density

• Gradation Acceptance• AC Content• Gradation• Mat Density• Joint Density

15%25%45%15%

10%30%10%35%15%

Voids Acceptance Weighting

Gradation Acceptance Weighting

Voids Acceptance Maximum PF

How to Ensure Quality

• Mix Design• Consistency/Uniformity of materials• Process Control (Quality Control) for:

• Production• Placement

• Plant Capabilities and Control

Good Quality Example

Mix Design and Materials• 18% - ½” Rock• 41% - Crusher Fines• 10% - Clean Crusher Fines• 11% - Natural Sand• 19% - Fractionated RAP• 1% - Hydrated Lime

Production Targets set were:• AC – 5.4%• Air Voids – 3.2%• VMA – 14.6%

Mix Design Fine Aggregate Angularity – 46.4

Aggregates

½” Rock

Natural Sand

Clean Crusher Fines

RAP

Crusher Fines

Production Gradations

Good Quality AC Content and Volumetrics

• Total of around 27,000 tons of HMA produced• AC content target was 5.4%

• Average AC (28 tests) was 5.47%• AC Standard Deviation was 0.08%

• Air Voids Target was 3.2%• Average Air Voids were 3.3%• Air Voids SD was 0.5% 

• VMA Target was 14.6 (14.7 after 1st 3 Tests)• Average VMA was 14.8• VMA SD was 0.3%

What do these kind of numbers result in?

AC content – Quality Level of 99.514Air Voids – Quality Level of 99.175VMA – Quality Level of 99.982

PF’s for all three elements were 1.055.  Which is the maximum allowable PF for this quantity of HMA.

Poor Quality Example

Initial Mix Design and Materials• 20% - 9/16” Rock• 49% - Crusher Fines• 20% - Natural Sand #1• 10% - Natural Sand #2• 1% - Hydrated Lime

Mix Design Fine Aggregate Angularity – 45.7

Production Targets set were:• AC – 5.7%• Air Voids – 3.6%• VMA – 14.7%

Aggregates

9/16” Rock

Natural Sand #2

Natural Sand #1Crusher Fines

Production Gradations

AT‐1• AC ‐ 5.51%• Air Voids – 2.0• VMA – 13.0

INFO 1• AC ‐ 5.38%• Air Voids – 1.6• VMA – 12.7

Production Targets• AC – 5.7%• Air Voids – 3.6%• VMA – 14.7%

Poor Quality Example

Re-Design and Materials• 20% - ½” Rock• 44% - Crusher Fines• 20% - Natural Sand #1• 15% - Washed Sand• 1% - Hydrated Lime

Mix Design Fine Aggregate Angularity – 45.2

Production Targets set were:• AC – 5.7%• Air Voids – 3.6%• VMA – 15.3%

Production Gradations

1st Rep• AC ‐ 5.25%• Air Voids – 3.0• VMA – 13.7

1st 10K• AC ‐ 5.37%• Air Voids – 3.7• VMA – 14.6

Production Targets• AC – 5.7%• Air Voids – 3.6%• VMA – 15.3%

2nd 10K• AC ‐ 5.71%• Air Voids – 3.6• VMA – 15.1

AC Content and Volumetrics

• Total of around 15,000 tons of top mat HMA produced• AC content target was 5.7%

• Average AC (16 tests) was 5.46%• AC Standard Deviation was 0.18%

• Air Voids Target was 3.6%• Average Air Voids were 3.2%• Air Voids SD was 0.9% 

• VMA Target was 15.3 (14.6 after 1st 3 Tests)• Average VMA was 14.4• VMA SD was 0.63%

What do these kind of numbers result in?

AC content – Quality Level of 59Air Voids – Quality Level of 78.2VMA – Quality Level of 94.1

PF for AC content – 0.836PF for Air Voids – 0.952PF for VMA – 1.042

Summary

• Start with a good mix design• Use good materials – angular and clean builds VMA• Rounded improves workability, but tends to collapse VMA• What might work for gradation acceptance may not work on 

volumetric acceptance • Control your materials!

• Consistent and Uniform• Know your production capabilities

• Baghouse rejection and metering• Stockpile moisture influence on your plant

• Use your process control• It’s a contract requirement, but is beneficial if used correctly

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Thank you 

Questions and Comments?

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