Back to Basics - Volumetrics November 28, 2017

Transcription

1 Back to Basics - Volumetrics November 28, 2017 Paul Eggen, P.G. 1

2 Informed by and borrowing from... 2

3 I learn something new every day. The problem is, most of it is stuff that I probably should already know. Unknown 3

4 History of Mix Design & Volumetrics s 1932 Clifford Richardson - New York Testing Co. Calculates VMA and adjusts for correct %AC Hubbard Field Method - Asphalt Association Used lab compacted specimens and volumetric analysis. Hveem Design Method - California Determined Asphalt content based on aggregate surface area (film thickness) History of Asphalt Mix in North America Asphalt Magazine 4

5 History of Mix Design & Volumetrics 1930 s 1962 Marshall Mix Design - Mississippi Used Voids and VFA Asphalt Institute updates MS-2 Incorporates VMA into Marshall Design VMA requirements based on NMAS History of Asphalt Mix in North America Asphalt Magazine 5

6 Rutting in the 1980s eventually led to Superpave 6

7 History of Mix Design & Volumetrics 1993 SuperPave Volumetric Mix Design SHRP Gyratory Compactor, VMA used to determine minimum %AC Consensus aggregate properties on blend WisDOT adopts Superpave mix design methodology History of Asphalt Mix in North America Asphalt Magazine 7

8 ASPHTEC-1, January

9 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). 9

10 Gerry Huber Heritage Research Group,

11 Terminology: Specific Gravity Relates Density of an Object to the same Volume of Water D = G x Density in g/cm 3 specific gravity of object density of water The Rosetta Stone for asphalt mix volumetrics 11

12 Terminology: Specific Gravity Specific Gravity Terms G G mb - bulk specific gravity of the compacted mix. (Gyratory Puck or Pavement Core) G b - specific gravity of the binder (~1.03) 12

13 Teminology: Specific Gravity Specific Gravity Terms G G mm -theoretical maximum specific gravity of the mix. Uncompacted, no air voids. (Rice test) 13

14 Terminology: Specific Gravity Specific Gravity Terms G G mb - bulk specific gravity of the compacted mix. (Gyratory Puck or Pavement Core) 14

15 Terminology: Specific Gravity Specific Gravity Terms G G b - specific gravity of the binder (~1.03) G sb - bulk specific gravity of the aggregate G se - effective specific gravity of the aggregate 15

16 Gerry Huber Heritage Research Group,

17 Gerry Huber Heritage Research Group,

18 Terminology Air voids (V a ) Total volume of air in a compacted mix. (3%-4%) V a = 100 x (G mm G mb )/G mm Low voids potential for rutting High voids lower compaction and loss of durability Voids are a big deal! 18

19 Terminology Effective Asphalt Content (P be ) % of non-absorbed asphalt P be = P b P ba P ba calculated using G se and G sb Gravimetric 19

20 Gerry Huber Heritage Research Group,

21 Gerry Huber Heritage Research Group,

22 Voids in Mineral Aggregate (VMA) Total Volume VOL VMA air asphalt MASS Effective AC Absorbed AC agg Definition: volume of intergranular void space in a compacted mix % by volume total mix. VMA = 100-[G mb x (100-P b )/G sb ) Strongly influenced by gradation. Increased VMA = Increased Asphalt Content = Increased Film Thickness 22

23 12.5 mm Mix -.45 Power Curve 23

24 9.5 mm Porous -.45 Power Curve Percent Passing Sieve Size raised to 0.45 Power Blend No Max Dens Cahill Specs 24

25 Mix VMA Requirements Voids in the Mineral Aggregate VMA Nom Max Size (Grade) (mm) Minimum VMA % (15.5) (14.5) % binder 25

26 VMA vs. Asphalt Content 26

27 Terminology Voids Filled with Binder (VFB or VFA) The percentage of VMA filled with asphalt binder. VFB = 100 x (VMA-V a )/VMA Generally required to be between about 65 75%. Volumetric 27

28 Gerry Huber Heritage Research Group,

29 Gerry Huber Heritage Research Group,

30 Why Focus on Effective Binder Content? Why not just focus on total binder content?

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32 Gerry Huber Heritage Research Group,

33 Superpave fixed the rutting problem but lowered effective asphalt contents which led to loss of durability 33

34 WisDOT Aggregate Specifications Minimum VMA requirements increased for LT and MT mixes

35 Increase Asphalt Content by Lowering Voids 35

36 Determine Asphalt 4.0% Voids Mixture Type Design Gyrations LT 40 MT 75 HT 100 air voids 4.0% % binder Use linear regression to determine asphalt content at 3.0% air voids

37 Asphalt 4.0% & 3.0% Voids Increase in P b goes directly to P be = increased film thickness 37

38 Bottom Line - VMA is King Allows for increased effective asphalt volume (film thickness) while maintaining voids. Improves durability while maintaining rut resistance. 38

39 Not to be confused with Balanced Mix Designs Dave Johnson Asphalt Institute,

40 Calculating Effective Binder Content What goes into the calculation?

41 Gerry Huber Heritage Research Group,

42 Gerry Huber Heritage Research Group,

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55 Gerry Huber Heritage Research Group,

56 Bottom Line - VMA is King Allows for increased effective asphalt volume (film thickness) while maintaining voids. Improves durability while maintaining rut resistance. 56

57 Volumetrics Total Volume VOL VMA air asphalt MASS Effective AC Absorbed AC agg 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). 57

58 Thank you!! Questions? 58