Wisconsin Asphalt Pavement Association - Back to Basics … · 2017. 12. 8. · •Gyratory Compactor, VMA used to determine minimum %AC •Consensus aggregate properties on blend

Back to Basics - Volumetrics

November 28, 2017

Paul Eggen, P.G.

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2

Informed by and “borrowing” from. . .

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“I learn something new every day. The problem is, most of it is stuff that I probably should already

know.”Unknown

History of Mix Design & Volumetrics

1905• Clifford Richardson - New York Testing Co.• Calculates VMA and adjusts for correct %AC

1920’s• Hubbard Field Method - Asphalt Association• Used lab compacted specimens and volumetric

analysis.

1932• Hveem Design Method - California• Determined Asphalt content based on aggregate

surface area (film thickness)

4History of Asphalt Mix in North America – Asphalt Magazine


1930’s• Marshall Mix Design - Mississippi• Used Voids and VFA

1962

• Asphalt Institute updates MS-2• Incorporates VMA into Marshall Design• VMA requirements based on NMAS


Rutting in the 1980s eventually led to Superpave

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1993

• SuperPave Volumetric Mix Design – SHRP• Gyratory Compactor, VMA used to determine

minimum %AC• Consensus aggregate properties on blend.

2000• WisDOT adopts Superpave mix design

methodology


ASPHTEC-1, January 1992 8

Terminology

•Volumetric – Of or relating to measurement by volume.

•Gravimetric – Of or relating to measurement by weight.

•Empirical – Based on observation or experience rather than logic or theory (measured).

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10Gerry Huber – Heritage Research Group, 2017

Terminology: Specific Gravity

• Relates Density of an Object to the same Volume of Water

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D = G x 1.000Density in g/cm3 specific

gravityof object

density of water

The “Rosetta Stone” for asphalt mix volumetrics


• Specific Gravity Terms “G”• Gmb - bulk specific gravity of the compacted mix. (Gyratory Puck or Pavement Core)

• Gb - specific gravity of the binder (~1.03)

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Teminology: Specific Gravity

• Specific Gravity Terms “G”• Gmm - theoretical maximum specific gravity of the mix. Uncompacted, no air voids. (Rice test)

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•Specific Gravity Terms “G”•Gmb - bulk specific gravity of the compacted mix. (Gyratory Puck or Pavement Core)

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•Specific Gravity Terms “G”•Gb - specific gravity of the binder (~1.03)

•Gsb - bulk specific gravity of the aggregate

•Gse - effective specific gravity of the aggregate

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Terminology

• Air voids (Va) – Total volume of air in a compacted mix. (3%-4%)

• Va = 100 x (Gmm – Gmb)/Gmm

• Low voids – potential for rutting• High voids – lower compaction and loss of durability

• Voids are a big deal!18

Terminology

• Effective Asphalt Content (Pbe) – % of non-absorbed asphalt

• Pbe = Pb – Pba• Pba calculated using Gseand Gsb

• Gravimetric

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Voids in Mineral Aggregate (VMA)

•Definition: volume of intergranular void space in a compacted mix % by volume total mix.

•VMA = 100-[Gmb x (100-Pb)/Gsb)•Strongly influenced by gradation. • Increased VMA = Increased Asphalt Content = Increased Film Thickness

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airasphalt

agg

VOL MASS

VMA

Absorbed ACTotalVolume

Effective AC

12.5 mm Mix - .45 Power Curve

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100.094.4

23.6

12.79.37.56.14.84.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Sieve Size raised to 0.45 Power

Perc

ent P

assi

ng

Blend No. 58-4 Max Dens Cahill Specs

9.5 mm Porous - .45 Power Curve

Mix VMA RequirementsVoids in the Mineral Aggregate

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5 9.5 15.0 (15.5)4 12.5 14.0 (14.5)3 19 13.02 25 12.01 37.5 11.0

Nom Max Size(Grade) (mm)

Minimum VMA%

% binder

VM

A

VMA vs. Asphalt Content

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Terminology

•Voids Filled with Binder (VFB or VFA) – The percentage of VMA filled with asphalt binder.

•VFB = 100 x (VMA-Va)/VMA•Generally required to be between about 65 –75%.

•Volumetric

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Why Focus on Effective Binder Content?

Why not just focus on total binder content?



Superpave fixed the rutting problem but lowered effective asphalt contents which

led to loss of durability

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WisDOT Aggregate Specifications

Minimum VMA requirements increased for LT and MT mixes

Increase Asphalt Content by Lowering Voids

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Determine Asphalt Content @ 4.0% Voids

LT 40MT 75HT 100

Mixture Type

DesignGyrations

% binder

air voids

Use linear regression to determine asphalt content at 3.0% air voids

4.0%

Asphalt Content @ 4.0% & 3.0% Voids

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Increase in Pb goes directly to Pbe = increased film thickness

Bottom Line - VMA is King

•Allows for increased effective asphalt volume (film thickness) while maintaining voids.

•Improves durability while maintaining rut resistance.

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39Dave Johnson – Asphalt Institute, 2016

Not to be confused with “Balanced Mix Designs”

Calculating Effective Binder Content

What goes into the calculation?
















Bottom Line - VMA is King

•Allows for increased effective asphalt volume (film thickness) while maintaining voids.

•Improves durability while maintaining rut resistance.

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Volumetrics

•Relatively inexpensive testing and can be quickly determined.

•Has been used to predict performance in past.

•Will likely still play a role in the age of performance testing (surrogate properties).

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airasphalt

agg

VOL MASS

VMA

Absorbed ACTotalVolume

Effective AC

Thank you!!

Questions?

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Documents

Wisconsin Asphalt Pavement Association - Back to Basics … · 2017. 12. 8. · •Gyratory Compactor, VMA used to determine minimum %AC •Consensus aggregate properties on blend