Why Adjusted AFT.PPT · 2020-03-31 · Why AFT instead of VMA? There is little correlation between the nominal maximum aggregate size and overall gradation, or aggregate surface area

WhyAdjusted AFT ?j

5 Basic Options for % AC5 Basic Options for % AC

• Specify a Minimum % AC

• Specify a Minimum VMA• Specify a Minimum Vbep y be

• Specify a Minimum AFT

• Specify a Minimum Adjusted AFT• Specify a Minimum Adjusted AFT

Adjusted AFT and VMA are both intended jto provide an adequate effective AC volume (Vb )volume (Vbe).

VMA is based on the Nominal Maximum Aggregate Sizegg g

AFT is based on the calculated Aggregate Surface Area (SA), which is basically an “Index”.

Why AFT instead of VMA?

There is little correlation between the nominal maximum aggregate size and overall gradation, or aggregate surface area (SA)

The Calculated “SA” represents a gradationThe Calculated SA represents a gradation similar to a Fineness Modulus

“SA” can account for changes in Aggregate S ifi G itSpecific Gravity

• VMA = Vb + VVMA Vbe + Va

• AFT = V /SAAFT Vbe/SA

h• “SA” represents the aggregate gradation

• As “SA” increases Vb must alsoAs SA increases, Vbe must also increase in order to maintain a specific AFTAFT

• AFT, Aggregate SA and Vbe are independent of the degree ofindependent of the degree of compaction at Design (i.e. the

b f bl ti )number of blows or gyrations)

• VMA and VFA are dependent on the degree of compaction at Design

The Primary Difference

betweenbetween

Asphalt Pavement Mixture

and

Aggregate Base

S C

Aggregate Base

is

ASPHALT CEMENT

Inadequate

Asphalt Film Thickness (AFT) p ( )or

Effecti e AC Vol me (V )Effective AC Volume (Vbe)May Result iny

“St i i ” R li“Stripping” or Raveling

Stripping on TH 12

Stripping on TH 10

Stripping on TH 101

More Stripping o e S pp gon TH 101

Stripping on TH 242

St i i TH 47Stripping on TH 47

Stripping on TH 55

Stripping on TH 7Stripping on TH 7

More StrippingMore Stripping on TH 7

Raveling on TH 12

More Raveling on TH 12

Raveling on Schmidt Lake Road

Raveling on TH 21

More Raveling on TH 21

E iExcessive

Asphalt Film Thickness (AFT) or

Effective Asphalt Volume (Vbe) p ( be)May Result in

RuttingRutting

Rutting on TH 41

Rutting on TH 41

Rutting on TH 494

Edge of Bridge Shadow

Measures Tried to ProvideMeasures Tried to Provide Adequate Effective AC Volume

Mi i T l A h l C C• Minimum Total Asphalt Cement Content

• Minimum Voids in Mineral Aggregate (VMA)

• Minimum Asphalt Film Thickness (AFT)

Mi i T l AC CMinimum Total AC ContentDoes Not Account for:

• Changes in AC Absorption• Changes in AC Absorption

• Changes in Gradation or Aggregate Surface Area

Minimum VMA• Accounts for Changes in AC Absorption

• Includes Both Vbe and Air Voids

• Based on Very Poor Correlation with Aggregate Surface AreaAggregate Surface Area

E th Additi f S d• Encourages the Addition of Sand

• VMA is dependent on Design Compaction

Minimum AFTAd antagesAdvantages

• Accounts for AC Absorption by using Effective AC Content

• Has a Direct Correlation with AggregateHas a Direct Correlation with Aggregate Surface Area

• Can Account for Changes in Aggregate S ifi G itSpecific Gravity

Minimum AFTProblems

• “Normally” the Minimum Required Effective AC Volume (Vbe) is Directly Proportional to the Aggregate Surface Area (This is probably not necessary).

• A Gradation is Required for Each AFT CalculationCalculation

MINIMUM VMA CRITERIAMINIMUM VMA CRITERIA

ASPHALT INSTITUTE

(Based on 4% Design Air Voids)

MIX DESIGN (MS-2)

Nominal Maximum Maximum

ASPHALT INSTITUTE

Minimum

1.5"

Nominal MaximumAggregate Size

Maximum Aggregate Size

25.0 mm (1")

% VMA

12.0

Minimum

1"

3/4" 14.0

19.0 mm (3/4")

12.5 mm (1/2")

13.0

1/2"

3/8" 17.04.75mm (#4)

15.09.5 mm (3/8")

Illustrations of Poor CorrelationIllustrations of Poor Correlationbetween

Maximum Aggregate Size andand

Aggregate Gradation

C O M P A R I S O N O F S P E C . 2 3 6 0 , G R A D A T I O N S A & B M I X T U R E S( 2 0 0 1 T r i a l M i x D a t a )( 2 0 0 1 T r i a l M i x D a t a )

7 0

8 0

G r a d a t i o n B ( A v g . + 1 S D )

5 0

6 0

G r a d a t i o n B ( A v g . - 1 S D )G r a d a t i o n A ( A v g . + 1 S D )G r a d a t i o n A ( A v g . - 1 S D )

4 0

5 0

PASS

ING

G r a d . B i s 3 / 4 " M a x ( M i n V M A = 1 4 . 0 )G r a d . A i s 1 / 2 " M a x ( M i n V M A = 1 5 . 0 )

2 0

3 0

PER

CEN

T

0

1 0

# 2 0 0 # 1 0 0 # 5 0 # 3 0 # 1 6 # 8 # 4

S IE V E S IZ E

C O M P A R I S O N O F S P E C . 2 3 6 0 , G R A D A T I O N S B & C M I X T U R E S( 2 0 0 1 T r i a l M i x D a t a )( 2 0 0 1 T r i a l M i x D a t a )

7 0

8 0

G r a d a t io n C ( A v g . + 1 S D )G d t i C ( A 1 S D )

5 0

6 0

G r a d a t io n C ( A v g . - 1 S D )G r a d a t io n B ( A v g . + 1 S D )G r a d a t io n B ( A v g . - 1 S D )

4 0

5 0

PASS

ING

G r a d . C i s 1 " M a x ( M i n V M A = 1 3 . 0 )G r a d . B i s 3 / 4 " M a x ( M i n V M A = 1 4 . 0 )

2 0

3 0

PER

CEN

T

0

1 0

# 2 0 0 # 1 0 0 # 5 0 # 3 0 # 1 6 # 8 # 4

S IE V E S IZ E

C O M P A R I S O N O F S P E C . 2 3 5 0 , G R A D A T I O N S # 3 & # 5 M I X T U R E S( 2 0 0 1 T r i a l M i x D a t a )( 2 0 0 1 T r i a l M i x D a t a )

8 0

9 0

G r a d a t i o n # 3 ( A v g . + 1 S D )G r a d a t i o n # 3 ( A v g . - 1 S D )

6 0

7 0

G r a d a t i o n # 5 ( A v g . + 1 S D )G r a d a t i o n # 5 ( A v g . - 1 S D )

4 0

5 0

PASS

ING

G r a d . 3 i s 3 / 4 " M a x ( M i n V M A = 1 4 . 0 )G r a d . 5 i s 3 / 8 " M a x ( M i n V M A = 1 5 . 0 o r 1 7 . 0 )

2 0

3 0

PER

CEN

T P

0

1 0

# 2 0 0 # 1 0 0 # 5 0 # 3 0 # 1 6 # 8 # 4

S IE V E S IZ E

C O M P A R I S O N O F S P E C .2 3 5 0 , G R A D A T I O N S # 3 & # 4 M I X T U R E S( 2 0 0 1 T r i a l M i x D a t a )( 2 0 0 1 T r i a l M i x D a t a )

7 0

8 0

G r a d a t i o n # 3 ( A v g . + 1 S D )G d t i # 3 ( A 1 S D )

5 0

6 0

G r a d a t i o n # 3 ( A v g . - 1 S D )G r a d a t i o n # 4 ( A v g . + 1 S D )G r a d a t i o n # 4 ( A v g . - 1 S D )

4 0

5 0

PASS

ING

G r a d . 3 i s 3 / 4 " M a x ( M i n V M A = 1 4 . 0 )G r a d . 4 i s 1 / 2 " M a x ( M i n V M A = 1 5 . 0 )

2 0

3 0

PER

CEN

T

0

1 0

# 2 0 0 # 1 0 0 # 5 0 # 3 0 # 1 6 # 8 # 4

S IE V E S IZ E

C O M P A R I S O N O F S P E C . 2 3 5 0 , G R A D A T I O N S # 2 & # 3 M I X T U R E S( 2 0 0 1 T r i a l M i x D a t a )( 2 0 0 1 T r i a l M i x D a t a )

7 0

8 0

G r a d a t i o n # 2 ( A v g . + 1 S D )G r a d a t i o n # 2 ( A v g - 1 S D )

5 0

6 0

G r a d a t i o n # 2 ( A v g . - 1 S D )G r a d a t i o n # 3 ( A v g . + 1 S D )G r a d a t i o n # 3 ( A v g . - 1 S D )

4 0

PASS

ING

G r a d . 2 i s 1 " M a x ( M i n V M A = 1 3 . 0 )G r a d . 3 i s 3 / 4 " M a x ( M i n V M A = 1 4 . 0 )

2 0

3 0

PER

CEN

T

0

1 0

# 2 0 0 # 1 0 0 # 5 0 # 3 0 # 1 6 # 8 # 4

S IE V E S IZ E

3/4" MAXIMUM SIZE AGGREGATE (Based on 2003 Contractor Production Data)

90

100

A 2 Std D

70

80

ng

Avg. + 2 Std. Dev.Avg. - 2 Std. Dev.

50

60

cent

Pas

sin

SA = 39.4 SF/Lb

20

30

40

Perc

0

10

20

SA = 20.7 SF/Lb

#200 #100 #50 #30 #16 #8 #4

Sieve Size

How is Aggregate Surface Area Calculated?

It is based on the Aggregate Gradation,d S f A F t li t d i thand Surface Area Factors listed in the

Asphalt Institutes MS-2 as part of the Hveem Design Method

Based on the Asphalt Institutes MS-2

SA = Calculated Surface Area in SF/ Lb.Based on the Asphalt Institutes MS 2

SA = 2 + .02a + .04b + 0.08c + .14d + .30e + .60f + 1.60g

Where:

a,b,c,d,e,f and g are % of total aggregate passing

respectively the #4, #8, #16, #30, #50, #100 and #200 sieves,

Aggregate SA Adjustmentgg g j

• The SA factors are generally based on anThe SA factors are generally based on an aggregate specific gravity (Gsb) of 2.650.

• Aggregates with higher Gsb’s will have less SA per pound than those with lower Gsb’sSA per pound than those with lower Gsb s

• The aggregate SA can be adjusted based on• The aggregate SA can be adjusted based on the minus #4 Gsb As follows:

Adjusted SA = SA(2 650/ #4G )Adjusted SA = SA(2.650/-#4Gsb)

AGGREGATE SURFACE AREA VS SIEVE SIZE

My Verification

AGGREGATE SURFACE AREA VS. SIEVE SIZE(Assuming Spherical Shape)

Relative Aggregate Sieve Size Surface Area Surface Area

#/(mm) (Per Unit Wt.) (SF/Lb) 1" (25) 1.0 0.44

3/4" (19) 1.3 0.573/8" (9.5) 2.6 1.13#4 (4.75) 5.3 2.31#8 (2.36) 11 4.77

#16 (1.18) 21 9.16#30 (0 60) 42 18 31#30 (0.60) 42 18.31#50 (0.30) 83 36.19

#100 (0.15) 167 72.81#200 (0.075) 333 145.19( )

Assuming Spherical particles with a Specific Gravity = 2.65

The calculated aggregate SAThe calculated aggregate SA is not exact,,

b ll blbut generally reasonably represents the gradationrepresents the gradation.

SURFACE AREA CALCULATIONS2001 TM Data Mix Type 2360 Grad. #B Avg. - 1 SD

MS II My CalculationsSieve SA SA SA SASize % Passing Factor (SF/Lb) % Retained Factor (SF/Lb)

3/4" (19mm) 100 0.02 2.00 0 0.006 0.003/8" (9.5mm) 79 NA NA 21 0.011 0.24

y

3/8 (9.5mm) 79 NA NA 21 0.011 0.24#4 (4.75mm) 54 0.02 1.08 25 0.023 0.58#8 (2.36mm) 38 0.04 1.52 16 0.048 0.76

#16 (1.18mm) 26 0.08 2.08 12 0.092 1.10#30 (0.60mm) 17 0.14 2.38 9 0.183 1.65( )#50 (0.30mm) 10 0.30 3.00 7 0.362 2.53

#100 (0.15mm) 4 0.60 2.40 6 0.728 4.37#200 (0.075mm) 2.7 1.60 4.32 1.3 1.452 1.89

* (0.038mm) 1.8 NA NA 0.9 2.9 2.74** (0.019mm) 1.1 NA NA 0.6 5.8 3.56

18.78 19.42MS II SA = My SA =

* Assumes 65% of the Material Passing the 0.075mm Sieve Passes 0.038mm ** Assumes 65% of the Material Passing 0 038mm Passes 0 019mm

#200 (0.075mm) 2.7 1.60 4.32 1.3 1.452 1.89* (0.038mm) 1.9 NA NA 0.8 2.9 2.35** (0.019mm) 1.3 NA NA 0.6 5.8 3.29

** Assumes 65% of the Material Passing 0.038mm Passes 0.019mm

18.78 18.75

* Assumes 70% of the Material Passing the 0.075mm Sieve Passes 0.038mm ** Assumes 70% of the Material Passing 0.038mm Passes 0.019mm

MS II SA = My SA =

MS II My Calculations

SURFACE AREA CALCULATIONS2001 TM Data Mix Type 2350 Grad. #5 Avg. + 1 SD

Sieve SA SA SA SASize % Passing Factor (SF/Lb) % Retained Factor (SF/Lb)

3/4" (19mm) 100 0.02 2.00 0 0.006 0.003/8" (9 5mm) 100 NA NA 0 0 011 0 00

MS II My Calculations

3/8 (9.5mm) 100 NA NA 0 0.011 0.00#4 (4.75mm) 89 0.02 1.78 11 0.023 0.25#8 (2.36mm) 72 0.04 2.88 17 0.048 0.81

#16 (1.18mm) 52 0.08 4.16 20 0.092 1.83#30 (0.60mm) 35 0.14 4.90 17 0.183 3.11#50 (0.30mm) 20 0.30 6.00 15 0.362 5.43

#100 (0.15mm) 10 0.60 6.00 10 0.728 7.28#200 (0.075mm) 5.5 1.60 8.80 4.5 1.452 6.53

* (0.038mm) 3.6 NA NA 1.9 2.9 5.58** ( ) 2 3 NA NA 1 3 5 8 7 26** (0.019mm) 2.3 NA NA 1.3 5.8 7.26

36.52 38.09

* Assumes 65% of the Material Passing the 0.075mm Sieve Passes 0.038mm** Assumes 65% of the Material Passing 0 038mm Passes 0 019mm

MS II SA = My SA =

#200 (0.075mm) 5.5 1.60 8.80 4.5 1.452 6.53* (0.038mm) 3.9 NA NA 1.7 2.9 4.79** (0 019mm) 2 7 NA NA 1 2 5 8 6 70

Assumes 65% of the Material Passing 0.038mm Passes 0.019mm

(0.019mm) 2.7 NA NA 1.2 5.8 6.7036.52 36.74

* Assumes 70% of the Material Passing the 0.075mm Sieve Passes 0.038mm** Assumes 70% of the Material Passing 0.038mm Passes 0.019mm

MS II SA = My SA =

Examples ofExamples of

Aggregate SAvs

% Passing Various Sieves% Passing Various Sieves

SA vs. % Passing 3/4" Sieveg(2003 Project Data)

50

R2 = 0.03540

45

gate

SA

30

35

ed A

ggre

g(S

F/Lb

)

25

Cal

cula

te

15

20

93 94 95 96 97 98 99 100 101

C

PERCENT PASSING 3/4" SIEVE

SA vs. % Passing 1/2" Sieveg(2003 Project Data)

40

R2 = 0.03235

gate

SA

25

30

d A

ggre

g(S

F/Lb

)

20

25

Cal

cula

ted (

1570 75 80 85 90 95 100

C

PERCENT PASSING 1/2" SIEVE

There is virtually no correlationThere is virtually no correlation between the percent passing the

¾” or ½” sieves and the Aggregate Surface Area (SA)Aggregate Surface Area (SA)

SA vs % Passing #4 SieveSA vs. % Passing #4 Sieve (2004 Project Data)

40

R2 = 0.257

35

ate

SA

30

d A

ggre

ga(S

F/Lb

)

25

Cal

cula

ted (

2025 30 35 40 45 50 55 60 65 70 75 80 85

C

% Passing #4 Sieve


40

R2 = 0.424

35

ate

SA

30

d A

ggre

ga(S

F/Lb

)

25

Cal

cula

ted (

2020 25 30 35 40 45 50 55 60 65

C

% Passing #8 Sieve

SA vs % Passing #16 SieveSA vs. % Passing #16 Sieve(2004 Project Data)

40

R2 = 0.56535

ate

SA

30

d A

ggre

ga(S

F/Lb

)

25

Cal

cula

ted (

2015 20 25 30 35 40 45 50 55

C

% Passing #16 Sieve


40

R2 = 0.66335

40

te S

A

30Agg

rega

tSF

/Lb)

25

alcu

late

d (S

2010 15 20 25 30 35 40 45

Ca

10 15 20 25 30 35 40 45

% Passing #30 Sieve


40

R2 = 0.687

35

ate

SA

30

d A

ggre

g(S

F/Lb

)

25

Cal

cula

ted (

205 10 15 20 25 30

C

5 10 15 20 25 30% Passing #50 Sieve


40

R2 = 0.71535

ate

SA

30

d A

ggre

ga(S

F/Lb

)

25

Cal

cula

ted

204 5 6 7 8 9 10 11 12

C

% Passing #100 Sieve


40

R2 = 0.54835

ate

SA

30

d A

ggre

ga(S

F/Lb

)

25

Cal

cula

ted

202.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

C


Another Option besides “SA” that could have been used

to Representto Represent Aggregate Gradation gg g

would have beenFineness Mod l sFineness Modulus

F I N E N E S S M O D U L U S V s . S U R F A C E A R E A( 2 0 0 4 P r o je c t D a t a )

5 . 0 0

4 . 5 0

4 . 7 5

R 2 = 0 . 6 6 5

4 . 0 0

4 . 2 5

odul

us

3 5 0

3 . 7 5

4 . 0 0

inen

ess

M

3 . 2 5

3 . 5 0

2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0

Fi

S A ( S F / L b )

Consider:Consider:

AGGREGATE SURFACE AREA "INDEX"AGGREGATE SURFACE AREA "INDEX"Aggregate Surface Area in SF/Lb.

Asphalt Film Thickness in Microns

ASPHALT FILM THICKNESS "INDEX"

Asphalt Film Thickness (AFT)i i l this simply the:

Effective AC Volume (Vbe)

Divided by the

Aggregate Surface Area (SA)gg g ( )

A S P H A L T F IL M T H IC K N E S S C A L C U L A T IO N

A F T ( i n m i c r o n s ) =P b e x 4 8 7 0

1 0 0 x P s x S A

P b e =

P

E f f e c t i v e A s p h a l t C o n t e n t ( % o f T o t a l M i x t u r e W e i g h t )P e r c e n t A g g r e g a t e i n M i x t u r e / 1 0 0

W h e r e :

P s =

S A = C a l c u l a t e d S u r f a c e A r e a i n S F / L b .( i e . D e c i m a l )P e r c e n t A g g r e g a t e i n M i x t u r e / 1 0 0

S A = 2 + . 0 2 a + . 0 4 b + 0 . 0 8 c + . 1 4 d + . 3 0 e + . 6 0 f + 1 . 6 0 gW h e r e :

# 4 , # 8 , # 1 6 , # 3 0 , # 5 0 , # 1 0 0 a n d # 2 0 0 s i e v e s , r e s p e c t i v e l y a , b , c , d , e , f a n d g a r e % o f t o t a l a g g r e g a t e p a s s i n g t h e

Examples of

AFTAFT vs

% Passing Various Sieves

AFT vs % Passing #4 SieveAFT vs. % Passing #4 Sieve (2004 Projects)

213.0

R2 = 0.168

11.0

12.0

cron

s)

9.0

10.0

d A

FT (M

i

6 0

7.0

8.0

Cal

cula

ted

5.0

6.0

30 35 40 45 50 55 60 65 70 75 80 85

C

% Passing #4 Sieve

AFT vs. % Passing #8 Sieve g(2004 Projects)

R2 = 0.21913.0

R 0.219

11.0

12.0

rons

)

9.0

10.0

d A

FT (M

icr

7.0

8.0

Cal

cula

ted

5.0

6.0

15 20 25 30 35 40 45 50 55 60 6515 20 25 30 35 40 45 50 55 60 65

% Passing #8 Sieve


13.0

R2 = 0.28311.0

12.0

cron

s)

9.0

10.0

d A

FT (M

i

6 0

7.0

8.0

Cal

cula

ted

5.0

6.0

15 20 25 30 35 40 45 50 55

C

% Passing #16 Sieve


13.0

R2 = 0.38811.0

12.0

icro

ns)

9.0

10.0

d A

FT (M

7.0

8.0

Cal

cula

ted

5.0

6.0

10 15 20 25 30 35 40 45

C

10 15 20 25 30 35 40 45% Passing #30 Sieve


13.0

R2 = 0.49511.0

12.0

cron

s)

9.0

10.0

d A

FT (M

i

6 0

7.0

8.0

Cal

cula

ted

5.0

6.0

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

C

% Passing #50 Sieve


13.0

R2 = 0.66011.0

12.0

cron

s)

9.0

10.0

d A

FT (M

i

6 0

7.0

8.0

Cal

cula

ted

5.0

6.0

4 5 6 7 8 9 10 11 12

C

% Passing # 100 Sieve


13.0

R2 = 0.48511.0

12.0

cron

s)

9.0

10.0

d A

FT (M

i

6 0

7.0

8.0

Cal

cula

ted

5.0

6.0

2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0

C


Some Methods to Increase AFT:

• Reduce the % passing the #30, #50, #100 and/or #200 sieves

• Increase the amount of crushed material• Waste the baghouse fines• Completely redesign the mixture• Completely redesign the mixture

The Primary Difference

betweenbetween

Asphalt Pavement Mixture

and

Aggregate Base

S C

Aggregate Base

is

ASPHALT CEMENT

REDUCED PAY FACTORSFOR

MIXTURE PRODUCTION FAILURES

Pay FactorsIndividual Moving AverageItem

75%Gradation 95%

NACoarse and Fine AggregatCrushing 90%

75%

75%Asphalt Binder Content 85%

VMA 85%

g

70% 50%Production Air Voids

Asphalt Film Thickness No Current Requirement

(Isolated and Individual)

Asphalt Film Thickness No Current Requirement

Approximate AFT’sppof some

1960’, 70’s and 80’s Projects

(Based on Mn/DOT Test Results)(Based on Mn/DOT Test Results)

APPROXIMATE AFT 1963 Thru 1965 Projects 2331 & 2341 Non Wear

11.0

9.0

10.0

ons)

Avg. AFT = 6.5 Microns

7.0

8.0

e AF

T (M

icro

4.0

5.0

6.0

Appr

oxim

ate

2.0

3.0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

A

1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5

Project I.D.

APPROXIMATE AFT 1963 Thru 1965 Projects

2351 Binder13.0

Avg AFT = 11 1 Microns

10.0

11.0

12.0

cron

s)

Avg AFT = 11.1 Microns

7 0

8.0

9.0

te A

FT (M

ic

5.0

6.0

7.0

Appr

oxim

at

2.0

3.0

4.0

60 61 62 63 64 65 66 67 68 69 7060 61 62 63 64 65 66 67 68 69 70

Project I.D.

A P P R O X IM A T E A F T 1 9 6 3 T h r u 1 9 6 5 P r o j e c t s

W e a r M i x t u r e s

1 2 .0

A g A F T 7 8 M ic r o n s

9 0

1 0 .0

1 1 .0A v g A F T = 7 . 8 M ic r o n s

7 .0

8 .0

9 .0

Mic

rons

)

4 0

5 .0

6 .0

xim

ate

AFT

(M

2 .0

3 .0

4 .0

71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43

App

rox

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

P r o je c t I . D .

1 9 7 8 T R IA L M IX A F T ( 2 3 3 1 N o n W e a r )

1 0 .0

A v g . A F T = 6 . 7 M ic r o n s

8 .0

9 .0

6 .0

7 .0

(Mic

rons

)

4 .0

5 .0

oxim

ate

AFT

2 .0

3 .0

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3

App

r

P r o je c t I . D .

1978 TRIAL MIX AFT (2331 & 2341 Wear)

15.0

16.0


12.0

13.0

14.0

cron

s)

Avg. 2361 AFT = 11.7 Microns

8 0

9.0

10.0

11.0

ate

AFT

(MIc

5.0

6.0

7.0

8.0

Appr

oxim

a

2.0

3.0

4.0

34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 803 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8

Project I.D.

1980 PROJECT AFT (Non Wear Mixtures)

10.0

Average AFT = 5.6 Microns

8.0

9.0g

6.0

7.0

(Mic

rons

)

4.0

5.0AFT

2.0

3.0

2 3 4 5 6 7 8 9 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 441 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4

Project I.D.

1980 PROJECT AFT (2331 & 2341 Wear Mixtures)

12 0

13.0

Avg. 2331 & 2341 AFT = 6.8 Microns

10.0

11.0

12.0g


7.0

8.0

9.0

(Mic

rons

)

5.0

6.0AFT

2.0

3.0

4.0

1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 421 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4

Project I.D.

1982 PROJECT AFT(Non Wear Mixtures)

10.0

Average AFT = 5.1 Microns

8.0

9.0g

6.0

7.0

(Mic

rons

)

4.0

5.0AFT

2.0

3.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Project I.D.

1982 PROJECT AFT (2331 & 2341 Wear)

11.0 Avg. 2331 & 2341 Wear = 6.6 Microns

8 0

9.0

10.0 Avg. 2361 Wear = 11.3 Microns

6.0

7.0

8.0

(Mic

rons

)

4.0

5.0

AFT

2.0

3.0

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

Project I.D.

1984 TRIAL MIX AFT (2331 Non Wear)

11 0

12.0


9.0

10.0

11.0

cron

s)

7.0

8.0

ate

AFT

(Mic

4.0

5.0

6.0

Appr

oxim

a

2.0

3.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Project I.D.

1984 TRIAL MIX AFT(2331 & 2341 Wear)

16.0

17.0


13.0

14.0

15.0

16.0

cron

s)


10.0

11.0

12.0

ate

AFT

(Mic

7.0

8.0

9.0

Appr

oxim

a

4.0

5.0

6.0

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 863 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8

Project I.D.

1986 TRIAL MIX AFT(2331 Non Wear)

13 0

14.0


10 0

11.0

12.0

13.0

cron

s)


8.0

9.0

10.0

ate

AFT

(Mic

5.0

6.0

7.0

Appr

oxim

a

2.0

3.0

4.0

1 3 5 7 9 1 3 5 7 9 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 771 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 6 6 6 6 6 7 7 7 7

Project I.D.

1986 TRIAL MIX AFT (2331 Shoulder Wear)

13 0

14.0


10 0

11.0

12.0

13.0

cron

s)


7 0

8.0

9.0

10.0

ate

AFT

(Mic

5.0

6.0

7.0

Appr

oxim

a

2.0

3.0

4.0

78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 001

Project I.D.

1986 TRIAL MIX AFT(2331 & 2341 Wear)

15 0

16.0Avg. 2331 & 2341 AFT = 9.4 Microns


12 0

13.0

14.0

15.0

cron

s)

Avg. 2361 AFT 13.9 Microns

9 0

10.0

11.0

12.0

ate

AFT

(Mic

7.0

8.0

9.0

Appr

oxim

a

4.0

5.0

6.0

01 04 07 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 200

203

206

209

212

215

218

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2

Project I.D.

AVERAGE AFT

2331 & 2341 2331, 2341 & 2351 2351 2361YEAR NON WEAR WEAR NON WEAR WEAR

1963-65 6.5 7.8 11.1 NA1978 6.7 9.3 NA 11.71980 5 6 6 8 NA 9 11980 5.6 6.8 NA 9.11982 5.1 6.6 NA 11.31984 7.4 9.6 NA ?1986 7 8 9 4 NA 13 91986 7.8 9.4 NA 13.9

Some Comments

concerning

VMA AFT and VVMA, AFT and Vbe

Mn/DOT’s current minimum VMA requirements vary fromVMA requirements vary from

12.5% to 15.0%

Depending on max. aggregate sized t i #8 iand percent passing #8 sieve.

The Sixth Edition of the Asphalt Institutes MS 2 also lists a MinimumInstitutes MS-2 also lists a Minimum

VMA of 17%* for a Mixture with3/8”Maximum Sized Aggregate

* 4% Design Air Voids* 4% Design Air Voids

This results in a VMA Range of 4.5%(17.0 – 12.5) for our normally used(17.0 12.5) for our normally used

Asphalt Mixture Gradations

MINIMUM VMA CRITERIAMINIMUM VMA CRITERIA

ASPHALT INSTITUTE

(Based on 4% Design Air Voids)

MIX DESIGN (MS-2)

Nominal Maximum Maximum

ASPHALT INSTITUTE

Minimum

1.5"

Nominal MaximumAggregate Size

Maximum Aggregate Size

25.0 mm (1")

% VMA

12.0

Minimum

1"

3/4" 14.0

19.0 mm (3/4")

12.5 mm (1/2")

13.0

1/2"

3/8" 17.04.75mm (#4)

15.09.5 mm (3/8")

VMA includes both V and VVMA includes both Vbe and Va

As a result, in order to achieve the desired minimum Vbe:

The minimum required VMA h ld i h h V d ishould vary with the Va during

mix production

Example of VMA vs Vbeas Va Changes

• If VMA = 14.0 and Va = 4.0; Vbe = 10.0%• If VMA = 14.0 and Va = 5.0; Vbe = 9.0%a ; be

• If you assume that a Vb of 10% providesIf you assume that a Vbe of 10% provides the desired amount of AC for a specific gradation, the mixture could have 10% less g ,Vbe than desired and still fully meet the VMA criteria if the Va increases from 4.0 to 5.0%, while the VMA remains at 14.0%.

In order to maintain an AFT ofIn order to maintain an AFT of 8.0 Microns over our normal

range of aggregate surface areas the V would have a Range ofthe Vbe would have a Range of

about 6.5%

AFT Spec. vs. Vbe Spec.p be p

• A “normal” AFT spec. requires the Vbe toA normal AFT spec. requires the Vbe to be directly proportional to the aggregate surface area (SA).su ace a ea (S ).

A Eff ti AC V l (V ) ld• An Effective AC Volume (Vbe) spec. would allow the Vbe to be proportional, but not di tl ti l t th tdirectly proportional, to the aggregate surface area. However, “Steps” would be req ired as the SA changedrequired as the SA changed.

V b e V s . S A V s . A F Tb e( B a s e d o n 2 0 0 4 T e s t D a t a )

1 8 . 0

1 9 . 0

1 4 0

1 5 . 0

1 6 . 0

1 7 . 0

A F T = 1 0 . 0 M i c r o n s

1 1 . 0

1 2 . 0

1 3 . 0

1 4 . 0

% V

be

8 . 0

9 . 0

1 0 . 0

%

5 . 0

6 . 0

7 . 0

2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1

A F T = 6 . 0 M i c r o n s

2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1

A g g r e g a t e S A ( S F / L b )

An “Adjusted” AFT Specification

• Allo s the V to ha e a Range of abo t• Allows the Vbe to have a Range of about 4.5%, to basically match current Asphalt Institute VMA criteriaInstitute VMA criteria

• Eliminates the need for “steps” in the minimum Vb requiredminimum Vbe required

• Allows both Individual and Moving Average Specification requirementsAverage Specification requirements

• Example: Adj AFT = AFT + 0 06(SA 28)• Example: Adj. AFT = AFT + 0.06(SA-28)

R e q u i r e d V b e N e c e s s a r y t o P r o v i d e a n A F T ,b e

o r A d j u s t e d A F T , o f 8 . 0 M i c r o n s( B a s e d o n 2 0 0 4 P r o j e c t T e s t D a t a )

1 6 0

1 4 . 0

1 5 . 0

1 6 . 0

V b e R e q u i r e d f o r A F T t o E q u a l 8 . 0 M i c r o n s

1 1 . 0

1 2 . 0

1 3 . 0

Vbe

8 . 0

9 . 0

1 0 . 0% V

V b e R e q u i r e d f o r A d j . A F T t o E q u a l 8 . 0 M i c r o n s B a s e d o n " A d j A F T " A F T 0 0 6 ( S A 2 8 )

6 . 0

7 . 0

2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 4 0 4 1

" A d j . A F T " = A F T + 0 . 0 6 ( S A - 2 8 )

A g g r e g a t e S A ( S F / L b )

A i t V RApproximate Vbe Ranges:

4.5% for VMA Criteria

6.5% for “Normal” AFT

4 5% for “Adjusted” AFT4.5% for “Adjusted” AFT

Some “Experts” believe that VMA combined with VFA andVMA combined with VFA and Fines/Effective AC is adequate

for specifying the minimum Vbe.

We’ve already discussed the yproblems with VMA. Now we’ll

co er VFA and P /Pcover VFA and P200/Pbe

VFA

VFA d f h “ id fill d i hVFA stands for the “voids filled with asphalt” and is the Percent Vbe as compared to the total Percent VMA.

If a mixture has a Vbe of 9.5% and a A f 14 0% h A ld bVMA of 14.0%, the VFA would be

68%.

VFA CriteriaVFA Criteria• VFA criteria is usually based on Mixture Type

or Traffic Level, and is listed as a range.

• VFA criteria is not based on the gradation: either maximum aggregate size or aggregate surface area

• Our VFA specs require between 65% and 78% for Wear, and between 70% and 83% for Non-Wear at Design

MINIMUM VMA VS. AGGREGATE SURFACE AREA(Mixtures with 8 Microns AC Film Thickness and 3% Air Voids)

Min Req Min Req Minimum % of VMAMin. Req. Min. Req. Minimum % of VMAAggregate ACeff ACeff Min. VMA Total VMA Which

SA SA Volume Volume for (for 3% Voids is ACeff

(SF/Lb.) (SF) (gal/CF) (CF/CF) ACeff and ACeff) (VFA)

15 2256 0.443 0.059 5.9 8.9 6620 2949 0.579 0.077 7.7 10.7 7225 3612 0.709 0.095 9.5 12.5 7630 4250 0.834 0.112 11.2 14.2 7935 4865 0.955 0.128 12.8 15.8 8140 5462 1.072 0.143 14.3 17.3 83

MINIMUM VMA VS. AGGREGATE SURFACE AREA(Mixtures with 8 Microns AC Film Thickness and 4% Air Voids)

Min. Req. Min. Req. Minimum % of VMAAggregate ACeff ACeff Min. VMA Total VMA Which

SA SA Volume Volume for (for 4% Voids is ACeff

(SF/Lb.) (SF) (gal/CF) (CF/CF) ACeff and ACeff) (VFA)

15 2234 0.439 0.059 5.9 9.9 5920 2916 0.572 0.077 7.7 11.7 6625 3574 0 702 0 094 9 4 13 4 7025 3574 0.702 0.094 9.4 13.4 7030 4210 0.827 0.111 11.1 15.1 7335 4819 0.946 0.127 12.7 16.7 7640 5402 1.061 0.142 14.2 18.2 78

Fines to Effective AsphaltFines to Effective Asphalt(P200/Pbe)

• The P200/Pbe ratio may limit the P200, but it has little if any affect on the remaining y gsieves.

• In the SA calculation, the P200 generally accounts for only 20% to 30% of the Totalaccounts for only 20% to 30% of the Total calculated SA. 70% to 80% comes from the other sievesother sieves.

AFT vs #200/PbAFT vs. #200/Pbe (2004 Project Data)

13.0

SP TL 2 thru 5 Max.

R2 = 0.57811.0

12.0

13.0

s)

LV & MV Wear Max.

LV & MV Non Wear Max.

9.0

10.0

(Mic

rons

6 0

7.0

8.0

AFT

5.0

6.0

0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70

#200/Pbe Ratio

Summaryofof

2004 Project Data

AFT Vs SAAFT Vs. SA Contractor Results, Except when OT

(2004 Project Data)

11 011.512.012.5

R2 = 0.7282

9 09.5

10.010.511.0

Mic

rons

)

7 07.58.08.59.0

AFT

(M

6.06.57.0

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

SA (SF/Lb)

AFT vs VMAAFT vs. VMA (2004 Project Data)

13.0

R2 = 0.03411.0

12.0

s)

9.0

10.0

(Mic

rons

6 0

7.0

8.0

AFT

5.0

6.0

13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5

% VMA

Project Average AFTProject Average AFT Mixtures with 3.0% Air Void Design

(2004 Project Data)

11 0

12.0Avg. AFT = 8.6 MicronsAvg. VMA = 14.7%Avg. Vbe = 11.6%

10.0

11.0

rons

)

8.0

9.0

AFT

(Mic

r

7.0

A

6.0

Project Average AFTProject Average AFT Mixtures with 3.5% Air Void Design

(2004 Project Data)

11 0

12.0Avg. AFT = 8.6 MicronsAvg. VMA = 15.0%A Vb 11 5%

10.0

11.0

rons

)

Avg. Vbe = 11.5%

8.0

9.0

AFT

(Mic

r

7.0

A

6.0

Project Average AFTProject Average AFT Mixtures with 4.0 Air Void Design

(2004 Project Data)

11 0

12.0

Avg. AFT = 8.3 MicronsAvg. VMA = 14.9%

10.0

11.0

rons

)

Avg. VMA 14.9%Avg. Vbe = 11.1%

8.0

9.0

AFT

(Mic

r

7.0

A

6.0

“Adjusted” AFT Specificationj p

• Vb does not have to be directly proportional toVbe does not have to be directly proportional to the Aggregate SA (Vbe range less than 6.5%)

• Allows “constant” minimum specification requirements (MA=4 of 8.0 & Indiv of 7.5, etc.)requirements (MA 4 of 8.0 & Indiv of 7.5, etc.) No “steps” required.

• No need for VMA, VFA, or upper limit on P200/Pbe Must maintain Va requirements.P200/Pbe. Must maintain Va requirements.

Wear Course AFT between 7.0 and 9.1

4.0

3.0

3.5

4.0

ng

1.5

2.0

2.5

rface

Rat

in

y = -0.0034x2 + 0.0026x + 4R2 = 0.5448

0.5

1.0Sur

0.00 5 10 15 20 25

Age, years

Wear Course AFT less than 7.0

4.0

y = -0.0182x2 - 0.1051x + 4R2 = 0 80522 5

3.0

3.5

ing

R = 0.8052

1.5

2.0

2.5

rface

Rat

i

0.5

1.0Su

0.00 5 10 15 20 25

Age, years

2 53.03.54.0

atin

g

2 53.03.54.0

atin

g

y = 0.2242Ln(x) + 3.2375R2 = 0.0140.0

0.51.01.52.02.5

5 7 9 11

Adj. Asphalt Film Thickness,

Surf

ace

Ra

y = 0.6914Ln(x) + 2.1961R2 = 0.09730.0

0.51.01.52.02.5

5 7 9 11

Adj. Asphalt Film Thickness,

Surf

ace

Ra

a) 4 years old b) 5 years old

j p ,microns

j p ,microns

3 03.54.0

ng 3 03.54.0

ng

y = 1.1819Ln(x) + 1.0209R2 = 0.1689

0.00.51.01.52.02.53.0

5 7 9 11

Surf

ace

Rat

in

y = 1.6387Ln(x) - 0.0828R2 = 0.2159

0.00.51.01.52.02.53.0

5 7 9 11

Surf

ace

Rat

in

c) 6 years old d) 7 years old

Adj. Asphalt Film Thickness,microns


3 54.0

3 54.0

y = 1.9661Ln(x) - 0.879R2 = 0.2501

0.00.51.01.52.02.53.03.5

5 7 9 11

Surf

ace

Rat

ing

y = 2.7582Ln(x) - 2.5662R2 = 0.4154

0.00.51.01.52.02.53.03.5

5 7 9 11

Surf

ace

Rat

ing

e) 8 years old f) 9 years old

5 7 9 11


5 7 9 11


Summary

f th tof the current

Adjusted AFT Spec.Adjusted AFT Spec.

Mn/DOT’s Adjusted AFT specification is basically a compromise of “straight” AFT y p gand VMA specifications.

Whereas the minimum required Vbe in a VMA spec is based on the NominalVMA spec is based on the Nominal Maximum aggregate size, the minimum

i i A j A irequired Vbe in our Adj. AFT spec is based on the calculated Aggregate SA “Index”

Th C t t ’ T i l Mi h ll h• The Contractor’s Trial Mix shall have a minimum Adjusted AFT of 8.5 microns.

• The minimum production Individual• The minimum production IndividualAdjusted AFT requirement is 7.5 microns.

• The minimum production MovingThe minimum production Moving Average (n=4) Adjusted AFT requirement is 8 0 micronsis 8.0 microns.

A gradation and Adjusted AFT calculation are required for each 1000qtons, or portion thereof,

oror at the same rate as the QC Mixture Property (G and G ) tests with aProperty (Gmm and Gmb) tests, with a minimum of one per day.

Aggregate SA AdjustmentAggregate SA Adjustment

Since aggregates with higher Gsb’s will have less gg g g sbSA per pound than those with lower Gsb’s, an Adjusted SA will be calculated as follows for aggregates with minus #4 aggregate Gsb’s less than 2.580, or greater than 2.700.

Adjusted SA = SA*(2.650/-#4Gsb)

There is currently no SA adjustment for aggregates y j gg gwith -#4 Gsb’s between 2.580 and 2.700.

• The JMF limits for the gradation i th th “B dsieves are the same as the “Broad

Band” limits.

• These “Broad Band” limits apply to• These Broad Band limits apply to both Moving Average and Individual

ltresults.

- #8 Individual Sieve Tolerances:

#16 = 4%#30 4%#30 = 4%#50 = 3%#100 = 2%#200 1 2%*#200 = 1.2%*

* T l h b h d f T bl 2360 4M* Tolerance has been changed from Table 2360.4M

• Accurate Gradation results are very• Accurate Gradation results are very important, especially for the #30 thru #200 i i d t t th#200 sieves, in order to meet the required test tolerances

• Hand Washing (rather than Agra• Hand Washing (rather than Agra-Wash) will be required if either

d ti l l t d Adj t d AFTgradation or calculated Adjusted AFT are Out of Tolerance

• The allowable Adjusted AFT calculation tolerance is 1.2 microns.

• If the Adjusted AFT calculation is• If the Adjusted AFT calculation is confirmed to be out of tolerance, the Agency Adjusted AFT will beAgency Adjusted AFT will be Equalized and used for both Individual and Moving AverageIndividual and Moving Average calculations.

• Equalization of the Agency Adjusted q g y jAFT consists of increasing the original Agency value by 0.5 microns.g y y

• This increased value will then be used• This increased value will then be used for acceptance of the test result.

• The minimum Individual Adjusted AFT requirement is 7 5 micronsrequirement is 7.5 microns.

• Material with less than 7 5 but equal to or• Material with less than 7.5, but equal to or greater than 7.0 microns, will receive 90%paypay.

• Material with less than 7 0 but greater than• Material with less than 7.0, but greater than 6.0 microns, will receive 75% pay.

• Material with 6.0 microns, or less, is subject to removal and replacement at thesubject to removal and replacement at the Contractor’s expense.

• The minimum Moving Average (n=4)g g ( )Adjusted AFT requirement is 8.0 microns.

• Generally, all Material which contributed to a MA less than 8 0 microns will receive 80%MA less than 8.0 microns will receive 80% pay.(Exception is Ind. Tests of 8.0 or greater)

• The MA will not be calculated until the 6th

test after the beginning of mix production of a specific mixture. It will include Individual results of Tests 3, 4, 5 and 6.

Th Adj t d AFT S h ll l d• The Adjusted AFT Spec has usually led to mixtures with less -#200, and often more +#8, material.

• The Contractor can make an economic d i i R d AC b idecision: Reduce AC content by using less and cleaner “sand”, or use less +#8 material and more AC.

Conclusion

Our Adjusted AFT Spec is basically a compromise between VMA and “straight” AFT criteriabetween VMA and straight AFT criteria.

I t d f i t V f 4 5% b iInstead of an approximate Vbe range of 4.5% being based on the Maximum Aggregate Size, it is based on the Aggregate SA “Index”the Aggregate SA Index .

Adjusted AFT is an “Index” that represents the V AsAdjusted AFT is an Index that represents the Vbe . As the SA increases, the Vbe must also increase in order to maintain a constant Adjusted AFTj

DensityDensity

Generally, the two most important factors in long term asphalt pavement g p pperformance are adequate (but not too much) asphalt cement and density. ) p y

Adj sted AFT ill not do it alone!Adjusted AFT will not do it alone!

Documents

Why Adjusted AFT.PPT · 2020-03-31 · Why AFT instead of VMA? There is little correlation between the nominal maximum aggregate size and overall gradation, or aggregate surface area