why adjusted aft.ppt · 2020-03-31 · why aft instead of vma? there is little correlation between...
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WhyAdjusted AFT ?j
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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
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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”.
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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
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• 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
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• 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
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The Primary Difference
betweenbetween
Asphalt Pavement Mixture
and
Aggregate Base
S C
Aggregate Base
is
ASPHALT CEMENT
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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
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Stripping on TH 12
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Stripping on TH 10
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Stripping on TH 101
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More Stripping o e S pp gon TH 101
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Stripping on TH 242
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St i i TH 47Stripping on TH 47
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Stripping on TH 55
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Stripping on TH 7Stripping on TH 7
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More StrippingMore Stripping on TH 7
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Raveling on TH 12
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More Raveling on TH 12
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Raveling on Schmidt Lake Road
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Raveling on TH 21
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More Raveling on TH 21
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E iExcessive
Asphalt Film Thickness (AFT) or
Effective Asphalt Volume (Vbe) p ( be)May Result in
RuttingRutting
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Rutting on TH 41
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Rutting on TH 41
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Rutting on TH 494
Edge of Bridge Shadow
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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)
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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
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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
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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
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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
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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")
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Illustrations of Poor CorrelationIllustrations of Poor Correlationbetween
Maximum Aggregate Size andand
Aggregate Gradation
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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
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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
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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
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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
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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
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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
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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
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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,
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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)
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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
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The calculated aggregate SAThe calculated aggregate SA is not exact,,
b ll blbut generally reasonably represents the gradationrepresents the gradation.
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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 =
![Page 46: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/46.jpg)
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 =
![Page 47: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/47.jpg)
Examples ofExamples of
Aggregate SAvs
% Passing Various Sieves% Passing Various Sieves
![Page 48: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/48.jpg)
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
![Page 49: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/49.jpg)
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
![Page 50: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/50.jpg)
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)
![Page 51: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/51.jpg)
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
![Page 52: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/52.jpg)
SA vs % Passing #8 SieveSA vs. % Passing #8 Sieve (2004 Project Data)
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
![Page 53: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/53.jpg)
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
![Page 54: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/54.jpg)
SA vs % Passing #30 SieveSA vs. % Passing #30 Sieve(2004 Project Data)
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
![Page 55: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/55.jpg)
SA vs % Passing #50 SieveSA vs. % Passing #50 Sieve (2004 Project Data)
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
![Page 56: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/56.jpg)
SA vs % Passing #100 SieveSA vs. % Passing #100 Sieve(2004 Project Data)
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
![Page 57: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/57.jpg)
SA vs % Passing #200 SieveSA vs. % Passing #200 Sieve(2004 Project Data)
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
% Passing #200 Sieve
![Page 58: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/58.jpg)
Another Option besides “SA” that could have been used
to Representto Represent Aggregate Gradation gg g
would have beenFineness Mod l sFineness Modulus
![Page 59: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/59.jpg)
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 )
![Page 60: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/60.jpg)
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"
![Page 61: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/61.jpg)
Asphalt Film Thickness (AFT)i i l this simply the:
Effective AC Volume (Vbe)
Divided by the
Aggregate Surface Area (SA)gg g ( )
![Page 62: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/62.jpg)
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
![Page 63: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/63.jpg)
Examples of
AFTAFT vs
% Passing Various Sieves
![Page 64: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/64.jpg)
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
![Page 65: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/65.jpg)
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
![Page 66: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/66.jpg)
AFT vs % Passing #16 SieveAFT vs. % Passing #16 Sieve (2004 Projects)
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
![Page 67: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/67.jpg)
AFT vs % Passing #30 SieveAFT vs. % Passing #30 Sieve (2004 Projects)
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
![Page 68: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/68.jpg)
AFT vs % Passing #50 SieveAFT vs. % Passing #50 Sieve (2004 Projects)
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
![Page 69: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/69.jpg)
AFT vs % Passing #100 SieveAFT vs. % Passing #100 Sieve (2004 Projects)
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
![Page 70: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/70.jpg)
AFT vs % Passing #200 SieveAFT vs. % Passing #200 Sieve (2004 Projects)
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
% Passing #200 Sieve
![Page 71: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/71.jpg)
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
![Page 72: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/72.jpg)
The Primary Difference
betweenbetween
Asphalt Pavement Mixture
and
Aggregate Base
S C
Aggregate Base
is
ASPHALT CEMENT
![Page 73: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/73.jpg)
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
![Page 74: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/74.jpg)
Approximate AFT’sppof some
1960’, 70’s and 80’s Projects
(Based on Mn/DOT Test Results)(Based on Mn/DOT Test Results)
![Page 75: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/75.jpg)
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.
![Page 76: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/76.jpg)
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.
![Page 77: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/77.jpg)
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 .
![Page 78: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/78.jpg)
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 .
![Page 79: 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](https://reader034.vdocuments.us/reader034/viewer/2022042321/5f0b43017e708231d42fa4cf/html5/thumbnails/79.jpg)
1978 TRIAL MIX AFT (2331 & 2341 Wear)
15.0
16.0
Avg. AFT = 9.3 Microns
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.
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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.
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1980 PROJECT AFT (2331 & 2341 Wear Mixtures)
12 0
13.0
Avg. 2331 & 2341 AFT = 6.8 Microns
10.0
11.0
12.0g
Avg. 2361 AFT = 9.1 Microns
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.
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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.
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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.
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1984 TRIAL MIX AFT (2331 Non Wear)
11 0
12.0
Avg. AFT = 7.4 Microns
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.
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1984 TRIAL MIX AFT(2331 & 2341 Wear)
16.0
17.0
Avg AFT = 9 6 Microns
13.0
14.0
15.0
16.0
cron
s)
Avg. AFT = 9.6 Microns
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.
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1986 TRIAL MIX AFT(2331 Non Wear)
13 0
14.0
Avg AFT = 7 8 Microns
10 0
11.0
12.0
13.0
cron
s)
Avg. AFT = 7.8 Microns
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.
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1986 TRIAL MIX AFT (2331 Shoulder Wear)
13 0
14.0
Avg AFT = 9 3 Microns
10 0
11.0
12.0
13.0
cron
s)
Avg. AFT = 9.3 Microns
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.
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1986 TRIAL MIX AFT(2331 & 2341 Wear)
15 0
16.0Avg. 2331 & 2341 AFT = 9.4 Microns
Avg. 2361 AFT = 13.9 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.
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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
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Some Comments
concerning
VMA AFT and VVMA, AFT and Vbe
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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.
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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
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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
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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")
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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
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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%.
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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%
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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.
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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 )
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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)
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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 )
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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
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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
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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%.
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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
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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
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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.
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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
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Summaryofof
2004 Project Data
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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)
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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
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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
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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
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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
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“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.
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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
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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
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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
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
Adj. Asphalt Film Thickness,microns
5 7 9 11
Adj. Asphalt Film Thickness,microns
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Summary
f th tof the current
Adjusted AFT Spec.Adjusted AFT Spec.
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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”
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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.
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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.
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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.
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• 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.
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- #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
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• 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
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• 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.
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• 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.
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• 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.
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• 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.
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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.
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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
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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!