Superpave TM Mix Design Marshall Mix Design 1. Select suitable - - PowerPoint PPT Presentation

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Superpave TM Mix Design Marshall Mix Design 1. Select suitable aggregates 2. Select a suitable asphalt binder 3. Select appropriate mixing and compaction temps 4. Select a suitable aggregate structure 5. Mix and compact samples in the lab

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SLIDE 1

SuperpaveTM Mix Design

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SLIDE 2

CIVL 3137 2

Marshall Mix Design

1. Select suitable aggregates 2. Select a suitable asphalt binder 3. Select appropriate mixing and compaction temps 4. Select a suitable aggregate structure 5. Mix and compact samples in the lab 6. Analyze mix volumetrics (air voids, etc.) 7. Select the optimum asphalt content 8. Evaluate moisture susceptibility

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SLIDE 3

CIVL 3137 3

Superpave Mix Design

1. Select suitable aggregates 2. Select a suitable asphalt binder 3. Select appropriate mixing and compaction temps 4. Select a suitable aggregate structure 5. Mix and compact samples in the lab 6. Analyze mix volumetrics (air voids, etc.) 7. Select the optimum asphalt content 8. Evaluate moisture susceptibility

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SLIDE 4

CIVL 3137 4

Superpave Specimens

SUPERPAVE Marshall 6"

4"

4700 g Aggregate

1200 g Aggregate

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SLIDE 5

Why 4700‐g Specimens?

  • The larger specimens better accommodate

larger NMAS mixes (up to 1½ inches). Marshall specimens 2½ inches high can be dominated by a single large aggregate particle.

CIVL 3137 5

4.0" 2.5" 6" 4.5"

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SLIDE 6

CIVL 3137 6

Gyratory Compactor

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SLIDE 7

CIVL 3137 7

Gyratory Compaction

 = 1.25º 30 rpm P = 600 kPa

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SLIDE 8

Why Gyratory Compaction?

  • Gyratory compaction produces a kneading

motion that better replicates what happens beneath the rollers during compaction on the road surface.

 = 1.25º

CIVL 3137 8

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SLIDE 9

Superpave Mix Design Approach

  • Select suitable materials and determine the

proper mixing and compacting temperatures.

  • Determine the best aggregate blend from among

several trial blends using specimens compacted at one trial asphalt content.

  • Estimate the correct asphalt content for the best

blend using the results from that one trial.

  • Determine the optimum asphalt content using

specimens compacted at four different asphalt contents around the estimate.

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SLIDE 10

CIVL 3137 10

  • 1. Select suitable aggregates

Source: NCEES FE Supplied Reference Handbook

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SLIDE 11

CIVL 3137 11

  • 2. Select a suitable asphalt binder

76 70 64 58 52 46 ‐4 ‐10 ‐16 ‐22 ‐28 PG70‐22 PG64‐16

Lowest Annual 1‐day Pavement Temperature Highest Annual 7‐day avg. Pavement Temperature

40 34 28

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SLIDE 12
  • 3. Determine relevant temperatures

CIVL 3137 12 Peanut Butter Ketchup Chocolate Syrup Honey Tomato Juice Vegetable Oil

AASHTO T-245 MARSHALL MIXING TEMP. RANGE (170 +/- 20 cSt) AASHTO T-245 MARSHALL COMPACTING TEMP. RANGE (280 +/- 30 cSt)

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SLIDE 13
  • 4. Create several aggregate blends

CIVL 3137 13

Blend 1 Blend 2 Blend 3

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SLIDE 14
  • 5. Select a Trial Binder Content

CIVL 3137 14

NMAS (mm) Aggregate Relative Density and Absorption 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6

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SLIDE 15

A Question to Ponder

  • Why does the trial binder content drop with

increasing NMAS?

NMAS (mm) Aggregate Relative Density and Absorption 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6

CIVL 3137 15

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SLIDE 16

CIVL 3137 16

Effect of NMAS on Surface Area

surface area = 11 ft2 surface area = 22 ft2

10" effective asphalt volume  aggregate surface area

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SLIDE 17

Another Question to Ponder

  • Why does the trial asphalt content increase

with increasing aggregate absorption?

NMAS (mm) Aggregate Relative Density and Absorption 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6

CIVL 3137 17

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SLIDE 18

CIVL 3137 18

Mix Volumetrics

Aggregate Particle (MG ,VG) Water Permeable Voids Effective Asphalt (MBE ,VBE) Absorbed Asphalt (MBA ,VBA) absorbed asphalt volume  aggregate absorption

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SLIDE 19

A Final Question to Ponder

  • Why does the trial asphalt content decrease

with increasing aggregate relative density?

NMAS (mm) Aggregate Relative Density and Absorption 2.65 / 0.8% 2.65 / 1.6% 2.70 / 0.8% 2.70 / 1.6% 9.5 8.3 8.9 8.1 8.7 12.5 5.0 5.6 4.9 5.5 19 4.4 5.0 4.3 5.0 25 4.1 4.7 4.0 4.6

CIVL 3137 19

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SLIDE 20

Binder Content

Gs = 2.65 Gs = 2.70 Assume two 2-cm-diameter aggregate spheres each with a 0.05-cm-thick asphalt cement coating

CIVL 3137 20

m 1.03 0.9970 g cm 4 3 π 1.05 cm 1.00 cm 0.658 g

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SLIDE 21

Binder Content

Gs = 2.65 m 2.65 0.9970 g cm 4 3 π 1 cm 11.07 g

CIVL 3137 21

P m m m

  • 0.658

0.658 11.07 0.056 5.6%

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SLIDE 22

Binder Content

Gs = 2.70 m 2.70 0.9970 g cm 4 3 π 1 cm 11.28 g

CIVL 3137 22

P m m m

  • 0.658

0.658 11.28 0.055 5.5%

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SLIDE 23
  • 6. Select the compaction effort

CIVL 3137 23

< 0.3 0.3 to < 3 3 to < 30 30 +

Source: ASTM D6925 ‐ 06

N = number of revolutions in the gyratory compactor

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SLIDE 24

CIVL 3137 24 7

115 100 10 7 1 75

As the number of gyrations increases, the height of the specimen decreases, so the more gyrations the denser the specimen. This is the same idea behind using more blows per side in the Marshall specimen.

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SLIDE 25

CIVL 3137 25 7

Nmax 100 10 Nini 1 Ndes

For a given traffic level, we want to know the specimen density after Nini, Ndes, and Nmax gyrations.

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SLIDE 26

Superpave Compaction Levels

  • Ninitial is used to gage how well the asphalt mix will compact

during construction. If it compacts too quickly (the air voids are too low) the mix may be tender during construction and unstable when subjected to traffic.

  • Ndesign is the number of gyrations required to produce a

sample with the same density as that expected in the field after being subjected to further compaction due to traffic. The asphalt mix should have 4% air voids at this density.

  • Nmax is the number of gyrations required to produce a

sample with greater density than is expected in the field after many years of traffic. If the mix compacts too much (the air voids are too low), it could bleed.

CIVL 3137 26

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SLIDE 27

Compaction Requirements

CIVL 3137 27

AIR VOIDS (VTM)  11% 4%  2% N = number of revolutions in the gyratory compactor

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SLIDE 28

Compaction Requirements

CIVL 3137 29 Source: NCEES FE Supplied Reference Handbook

N = number of revolutions in the gyratory compactor

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SLIDE 29

Initial Trial

  • Compact two specimens (4700 g of aggregate each)

to Ndes gyrations.

  • Determine the mix volumetrics (VTM, VMA, VFA).
  • Estimate the asphalt content that will produce a

mix with exactly 4% air voids at Ndes gyrations.

  • Estimate VMA, VFA and %Gmm@Nini for a specimen

with exactly 4% air voids.

  • If the VMA, VFA and %Gmm@Nini requirements are

met, this is a suitable aggregate blend.

CIVL 3137 30

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SLIDE 30

CIVL 3137 31

115 100 10 1

Ndes

115 100 10 7 1 75

Assume 2 million ESALs for the sake of this example Nini = 7, Ndes = 75, Nmax = 115

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SLIDE 31

CIVL 3137 32

Mix Volumetrics

(Taken from The Asphalt Institute Manual ES‐1, Second Edition)

Weigh in Air Weigh in Water

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SLIDE 32

CIVL 3137 33

Calculate Gmb @ Ndes

in air mb des SSD in water

W G @ N W W  

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SLIDE 33

Calculate %Gmm at Nini

CIVL 3137 34

mb des des mm ini mm ini

G @ N H %G @ N 100% G H           

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SLIDE 34

CIVL 3137 35

115 100 10 1 115 100 10 7 1 75

Assume 2 million ESALs for the sake of this example Nini = 7, Ndes = 75, Nmax = 115

(Nini , Hini) (Ndes , Hdes)

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SLIDE 35

CIVL 3137 36

115 100 10 1 115 100 10 7 1 75

(7, 125.8) (75, 111.5)

Assume Gmm = 2.403 at the trial binder content Assume Gmb = 2.369 after Ndes = 75 gyrations

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SLIDE 36

Calculate %Gmm at Nini

CIVL 3137 37

mb des des mm ini mm ini mm ini

G @ N H %G @ N 100% G H 2.369 111.5 %G @ N 100% 87.3% 2.403 125.8                       

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SLIDE 37

CIVL 3137 38

Voids in Total Mix (Air Voids)

mb des mm

G @ N VTM 1 100% G         

Gmb = bulk specific gravity of compacted mixture

D 2726 ‐ Bulk Specific Gravity and Density

  • f Compacted Bituminous Mixtures

Gmm = maximum specific gravity of the mixture

D 2041 ‐ Theoretical Maximum Specific Gravity and Density of Bituminous Paving Mixtures

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SLIDE 38

CIVL 3137 39

Voids in Mineral Aggregate

 

mb des b sb

G @ N 1 P VMA 1 100% G          

Gmb = bulk specific gravity of compacted mixture Gsb = bulk specific gravity of the aggregate blend Pb = asphalt binder content of mixture

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SLIDE 39

CIVL 3137 40

Voids Filled with Asphalt

VTM VFA 1 100% VMA         

VFA is the percentage of the available space between the aggregate particles (the VMA) that is occupied by asphalt binder rather than by air voids.

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SLIDE 40

Estimate Pb @ 4% Air Voids

CIVL 3137 41

 

b b

P @4% P 0.4 4% VTM   

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SLIDE 41

CIVL 3137 42

1 2 3 4 5 6 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) Air Voids (%)

Marshall Mix Design

0.4 1

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SLIDE 42

Estimate Pb @ 4% Air Voids

CIVL 3137 43

   

b b b b

P @4% P 0.4 4% 2.6% P 0.4 1.4% P 0.56%       

Assume VTM = 2.6%

To increase air voids, you’ll have to reduce binder content

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SLIDE 43

Estimate Pb @ 4% Air Voids

CIVL 3137 44

   

b b b b

P @4% P 0.4 4% 5.4% P 0.4 1.4% P 0.56%        

Assume VTM = 5.4%

To decrease air voids, you’ll have to increase binder content

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SLIDE 44

Estimate VMA @ 4% Air Voids

CIVL 3137 45

   

if VTM < 4% VMA@4% VMA 0.1 4% VTM if VTM > 4% VMA@4% VMA 0.2 4% VTM      

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SLIDE 45

Estimate VMA @ 4% Air Voids

CIVL 3137 46

   

VMA@4% VMA 0.1 4% 2.6 VMA 0.1 1.4% VMA 0.14%       

Assume VTM = 2.6%

If you increase the air voids the VMA will increase

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SLIDE 46

Estimate VMA @ 4% Air Voids

CIVL 3137 47

   

VMA@4% VMA 0.2 4% 5.4 VMA 0.2 1.4% VMA 0.28%        

Assume VTM = 5.4%

If you decrease the air voids the VMA will decrease

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SLIDE 47

VMA Criteria

Nominal Maximum Aggregate Size Minimum VMA (percent) 9.5 mm 15.0 12.5 mm 14.0 19.0 mm 13.0 25.0 mm 12.0 37.5 mm 11.0

This is the same as the Marshall criteria

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SLIDE 48

Estimate VFA @ 4% Air Voids

CIVL 3137 49

4% VFA 1 100% VMA         

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SLIDE 49

VFA Criteria

Traffic (million ESALs) Design VFA (percent) < 0.3 65 – 80 0.3 to 3.0 65 – 78 > 3.0 65 ‐ 75

This is similar to the Marshall criteria

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SLIDE 50

Estimate %Gmm @ Nini

CIVL 3137 51

 

mm ini mm ini

%G @ N %G @ N 4% VTM   

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SLIDE 51

Estimate %Gmm @ 4% Air Voids

CIVL 3137 52

 

mm ini

%G @ N 86.3% 4% 2.6% 86.3% (1.4%) 84.9%      

Assume VTM = 2.6%

If you increase the air voids the density will decrease

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SLIDE 52

Estimate %Gmm @ 4% Air Voids

CIVL 3137 53

 

mm ini

%G @ N 86.3% 4% 2.6% 86.3% ( 1.4%) 87.7%       

Assume VTM = 5.4%

If you decrease the air voids the density will increase

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SLIDE 53

Compaction Requirements

CIVL 3137 54 Source: NCEES FE Supplied Reference Handbook

N = number of revolutions in the gyratory compactor

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SLIDE 54

Optimum Asphalt Content

  • If our estimated VMA, VFA and Gmm@Nini at

4% air voids meet the requirements, we have assembled a suitable aggregate structure.

  • To determine the final binder content, we’ll

compact four new specimens to Ndes gyrations using the adjusted binder content and binder contents that are 0.5% less, 0.5% more and 1.0% more than the adjusted binder content.

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SLIDE 55

Optimum Asphalt Content

  • We will then calculate and plot VTM, VMA,

VFA and %Gmm@Nini as a function of binder content.

  • We will interpolate the final binder content as

that one that gives exactly 96% Gmm (4% VTM) at Ndes gyrations and check to make sure that binder content also produces suitable VTM, VMA, VFA and %Gmm@Nini.

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SLIDE 56

CIVL 3137 58

1 2 3 4 5 6 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) VTM (%)

VTM Results

Assume estimated AC @ 4% air voids = 4.8%

Final

  • ptimum

4.6%

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SLIDE 57

CIVL 3137 59

13 14 15 16 17 18 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) VMA (%)

VMA Results

Final VMA 14.6%

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SLIDE 58

VMA Criteria

Nominal Maximum Aggregate Size Minimum VMA (percent) 9.5 mm 15.0 12.5 mm 14.0 19.0 mm 13.0 25.0 mm 12.0 37.5 mm 11.0

This is the same as the Marshall criteria

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SLIDE 59

CIVL 3137 61

50 60 70 80 90 100 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) VFA (%)

VFA Results

Final VFA 71%

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SLIDE 60

VFA Criteria

Traffic (million ESALs) Design VFA (percent) < 0.3 65 – 80 0.3 to 3.0 65 – 78 > 3.0 65 ‐ 75

This is similar to the Marshall criteria

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SLIDE 61

CIVL 3137 63

80 82 84 86 88 90 3.5 4.0 4.5 5.0 5.5 6.0 6.5 Asphalt Content (%) Gmm (%)

%Gmm @ Nini Results

Final %Gmm 83.5%

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SLIDE 62

Compaction Requirements

CIVL 3137 64 Source: NCEES FE Supplied Reference Handbook

N = number of revolutions in the gyratory compactor

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SLIDE 63

Optimum Asphalt Content

  • Finally, we will compact two more specimens

made at the optimum asphalt content to Nmax gyrations and check to make sure the %Gmm is less than 98%.

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SLIDE 64

CIVL 3137 70

CAUTION: FE Reference Handbook

Source: NCEES FE Supplied Reference Handbook