Back to Basics - Volumetrics
November 28, 2017
Paul Eggen, P.G.
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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
History of Mix Design & Volumetrics
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
5History of Asphalt Mix in North America – Asphalt Magazine
Rutting in the 1980s eventually led to Superpave
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History of Mix Design & Volumetrics
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
7History of Asphalt Mix in North America – Asphalt Magazine
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
Terminology: Specific Gravity
• 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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Terminology: Specific Gravity
•Specific Gravity Terms “G”•Gmb - bulk specific gravity of the compacted mix. (Gyratory Puck or Pavement Core)
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Terminology: Specific Gravity
•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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16Gerry Huber – Heritage Research Group, 2017
17Gerry Huber – Heritage Research Group, 2017
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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20Gerry Huber – Heritage Research Group, 2017
21Gerry Huber – Heritage Research Group, 2017
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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28Gerry Huber – Heritage Research Group, 2017
29Gerry Huber – Heritage Research Group, 2017
Why Focus on Effective Binder Content?
Why not just focus on total binder content?
31Gerry Huber – Heritage Research Group, 2017
32Gerry Huber – Heritage Research Group, 2017
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?
41Gerry Huber – Heritage Research Group, 2017
42Gerry Huber – Heritage Research Group, 2017
43Gerry Huber – Heritage Research Group, 2017
44Gerry Huber – Heritage Research Group, 2017
45Gerry Huber – Heritage Research Group, 2017
46Gerry Huber – Heritage Research Group, 2017
47Gerry Huber – Heritage Research Group, 2017
48Gerry Huber – Heritage Research Group, 2017
49Gerry Huber – Heritage Research Group, 2017
50Gerry Huber – Heritage Research Group, 2017
51Gerry Huber – Heritage Research Group, 2017
52Gerry Huber – Heritage Research Group, 2017
53Gerry Huber – Heritage Research Group, 2017
54Gerry Huber – Heritage Research Group, 2017
55Gerry Huber – Heritage Research Group, 2017
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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