Effect of Mixture Design on Densification
Louay Mohammad
Louisiana Asphalt Technology ConferenceFebruary 23-24, 2005
Shreveport, Louisiana
2
Outline
- Background
- Objective
- Scope
- Mixtures Evaluation
- Results
- Concluding Remarks
3
Objectives of Mix DesignObjectives of Mix Design
• Resist– permanent deformation.– fatigue cracking – repeated load– low temperature cracking– moisture induced damage
• Resist skid• Workability
4
Steps Involved in the Mixture Design
1. Materials Selection1. Materials Selection 2. Design Aggregate Structure2. Design Aggregate Structure
3. Design Binder Content3. Design Binder Content 4. Moisture Sensitivity4. Moisture Sensitivity
TSRTSR
5
Superpave Mixture DesignConcerns:• Minimum VMA Criteria• Difficulties• Differentiate sound from
unsound mixtures• higher VMA mixtures
• Cannot guarantee• Durable• rut resistant
airairasphaltasphalt
aggagg
VOLVOL MASSMASS
VVTT
VMAVMA VVEACEAC
VVVV
6
Superpave Mixture DesignConcerns:• Aggregate Properties/Gradation
selection• 95 percent• Aggregate Specification
• Consensus – ETG• Little research• Aggregate Structure/Mixture Design
and Performance
7
Superpave Mixture DesignImprovement:• Design Aggregate Structure
• Mixture stability• Rational approach to design aggregate
structure • based on principles of aggregate packing
concepts
8
Objective
• Critically examine Superpave mixture design criterion
• Effect of – NMS – Aggregate Gradation and type
9
Scope• Aggregate Types
– Two `• Sandstone, Limestone
• Aggregate Structure– 12.5 mm NMS– 25 mm NMS
• Aggregate gradation– Coarse, Medium, Fine– Bailey Method
• analytical method that enables blending aggregates using engineering principles and packing theory concepts
10
Scope• Compaction Level
– 125 gyrations• Binder Type
– PG 76 – 22M
11
Methodology• Superpave Gyratory Compactor
– Densification Indices, Slope– Locking Point
• Pressure Distribution Analyzer – Frictional Indices, Locking
• Loaded Wheel Tester– PMW
K J I H G F E K J I H G F E D C B A D C B A
Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power
100100
00
% P
assi
ng%
Pas
sing
Combined Blend GradationCombined Blend Gradation
5050
2020
8080
Sieve % PassingA 100B 97C 76D 63E 39F 25G 17H 11I 7J 5K 4.2
1010
3030
4040
6060
7070
9090
CoarseFine
1
2
34
K J I H G F E K J I H G F E D C B A D C B A
Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power
100100
00
% P
assi
ng%
Pas
sing
Combined Blend GradationCombined Blend Gradation
5050
2020
8080
Sieve % PassingA 100B 98C 85D 72E 58F 40G 32H 21I 12J 7K 4.4
1010
3030
4040
6060
7070
9090
1
2
3
4
CoarseFine
14
Aggregate Gradation ½ SS3/4"
1/2"
3/8"
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
Sieve Size
0
10
20
30
40
50
60
70
80
90
100
Perc
ent P
assing
15
Aggregate Gradation 1” LS1.5"
1"3/4"
1/2"
3/8"
No. 4
No. 8
No. 16
No. 30
No. 50
No. 100
No. 200
Sieve Size
0
10
20
30
40
50
60
70
80
90
100
Per
cent
Pas
sing
Mixture Design
11.19.6 10
12
11.1 11.3
9.1
1413.1
8.4 8.5
14
02468
1012141618
1 LS 0.5 LS 0.5 SS
Coarse Medium Fine Specs63.5
58.2 60.5 64.8 62.758.5
69
50 54
0
20
40
60
80
VFA
1 LS 0.5 LS 0.5 SS
Coarse Medium Fine
3.8
3.0 3.3
5.1
4.0
3.5
5.1
3.6
3.9
0.0
2.0
4.0
6.0
%A
C
1 LS 0.5 LS 0.5 SS
Coarse Medium Fine8 5 . 78 9 .3 8 9 .5 89
8 5 . 1 8 6 . 28 8 89 8 6 . 6 8 6 .4 8 8 89
0
20
40
60
80
100
%G
mm
, Ni
1 LS 0.5 LS 0.5 SS
1775
80
85
90
95
100
0 30 60 90 120 150 180 210
No. Of Gyration
Ht,
mm
SGC
Pressure Distribution Analyzer
12
17
22
0 100 200 300No. of Gyrations
FR, p
siCoarseMediumFine
18
Superpave Gyratory CompactorLocking Point– Number of gyration
• Ht specimen remains constant for three consecutive gyrations
115.4
77
115.4115.4115.5115.5115.6115.6115.7115.7Height, mm
7675747372717069N0. Gyrations
75
80
85
90
95
100
0 30 60 90 120 150 180 210
No. Of Gyration
Ht,
mm
19
115.4
77
115.4115.4115.5115.5115.6115.6115.7115.7Height, mm
7675747372717069N0. Gyrations
Locking Point
Superpave Gyratory CompactorLocking Point
20
80828486889092949698
0.1 1 10 100 1000
No. of Gyrations
% G
mm
% @ % @( ) ( )
Gmm Ndes Gmm NiniLog Ndes Log Nini
−−
Superpave Gyratory CompactorSlope
21
75
80
85
90
95
100
0 50 100 150 200
No. of Gyrations
% G
mm
92%
N=1
CDI
Compaction Densification Index
N=205
TDI
Traffic Densification Index
Superpave Gyratory CompactorCompaction Indices
22
Pressure Distribution Analyzer
• Measures the frictional resistance of mixtures during compaction
• Double plate assembly with 3 load cells equally spaced on the perimeter
23100
300
500
700
900
1100
0 50 100 150 200 250 300
LC1 LC2 LC3
Pressure Distribution Analyzer
24
12
17
22
0 100 200 300No. of Gyrations
FR, p
si
CoarseMediumFine
Pressure Distribution AnalyzerFrictional Resistance
25
Rate of Change of Frictional Resistance
-0.10
0.10.20.30.40.50.6
0 50 100 150 200 250 300
No. of Gyrations
Rate o
f Chan
ge of F
R
-Maximum interlock in the aggregate structure
Number of gyrations corresponding to the point of minimum rate of change in FR
FR Locking Point
- 5
10
15
20
25
0 100 200 300No. of Gyrations
FR, p
si
Coarse Medium Fine
Pressure Distribution AnalyzerLocking Point
26
0
5
10
15
20
25
0 50 100 150 200 250 300
No of Gyrations
Fric
tiona
l Res
ista
nce,
psi
N=1 N@FR Locking Point
Compaction Force Index
200 gyrations
Traffic Force Index
Pressure Distribution AnalyzerIndices
27
Loaded Wheel Tracking Test
28
Four parameters (indices) are measured from the data collected in the HWT test- Post Compaction Consolidation - Inverse Creep Slope
- Stripping Inflection Point
- Stripping Slope
Loaded Wheel Tracking Test
29
020406080
100120140
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS FSpec
Superpave Gyratory CompactorLocking Point
30
0102030405060708090
100
% o
f Nde
s
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C
1" LS M
1" LS F
Superpave Gyratory CompactorLocking Point
31
0123456789
10
1/2"LS C1/2"LS M1/2"LS
1/2" SST C1/2" SST M1/2" SST 1"LS C
1" LS M
1" LS F
Superpave Gyratory CompactorCompaction Slope
32
050
100150200250300350400
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
Superpave Gyratory CompactorCompaction Indices -- CDI
33
0100200300400500600700800
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
Superpave Gyratory CompactorCompaction Indices -- TDI
34
020406080
100120140
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
Ndes=125
Pressure Distribution AnalyzerFR Locking Point
35
68.860
52.8
67.2 62.456.8
68.8
46.4 46.4
0
20
40
60
80
100%
of N
des
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
Pressure Distribution AnalyzerFR Locking Point
36
Frictional Resistance – Locking Point
0
5
10
15
20
FR, p
si
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS FUSB190 BC
37
0
400
800
1200
1600
2000
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
Pressure Distribution AnalyzerFR -- CFI
38
0
1000
2000
3000
4000
5000
1/2"LS C
1/2"LS M
1/2"LS F
1/2" SST C
1/2" SST M
1/2" SST F
1"LS C
1" LS M
1" LS F
Pressure Distribution AnalyzerFR -- DFI
39
Relationship: No. of Gyrations SGC LP vs. PDA LP
y = 1.0x - 4.0R2 = 0.95
40
50
60
70
80
90
100
40 50 60 70 80 90 100
SGC Locking Point
FR L
ocki
ng P
oint
40
y = 0.70x + 1.65R2 = 0.71
4.6
4.8
5
5.2
5.4
5.6
4.6 4.8 5 5.2 5.4 5.6
VTM at SGC Locking Point, %
VT
M a
t FR
Loc
king
Poi
nt, %
Relationship: VTM SGC LP vs. PDA LP
41
0
100
200
300
400
4 6 8 10 12 14
VMA
CD
I
0
200
400
600
800
4 6 8 10 12 14
VMA
TD
I
Relationship: VMA vs SGC CDI & TDI
• Trends• Increase VMA
• Higher CDI• Lower TDI
• Is there a Min. VMA?
42
R2 = 0.91
600
800
1000
1200
1400
1600
1800
0 100 200 300 400
CDI
CFI
Relationship: Compaction IndicesSGC CDI vs PDA CFI
43
R2 = 0.19
2500
3500
4500
400 600 800
TDI
TFI
Relationship: Compaction IndicesSGC TDI vs PDA TFI
44
R2 = 0.90
800
1000
1200
1400
1600
1800
4 6 8 10 12
Compaction Slope
CFI
Relationship: SCG Compaction Slope vs. CFI
45
LWT Test Results
0
1
2
3
4
5
1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F
46
012345
0 100 200 300 400
CDI
HWT
Rut, m
m
012345
1000 1100 1200 1300 1400 1500 1600 1700 1800
CFI
HW
T R
ut, m
m
Relationship: Rut Dept vs. CDI & CFI
47
012345
400 500 600 700 800
TDI
HWT R
ut, m
m
012345
3600 3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700
TFI
HWT
Rut,
mm
Relationship: Rut Dept vs. TDI & TFI
48
Relationship: Rut Depth vs. FR
00.5
11.5
22.5
33.5
44.5
5
20 20.5 21 21.5 22 22.5 23
FR at Locking Point, psi
HW
T R
ut D
epth
, mm
49
R2 = 0.73
00.5
11.5
22.5
33.5
44.5
5
2 4 6 8 10 12
Compaction Slope
HW
T R
ut, m
m
Relationship: LWT Rut Depth & Compaction Slope
50
Conclusions- SGC densification curves can provide valuable information
about mixtures behavior during compaction- CDI, Slope
• Coarse-grades mixtures had higher SGC LP– 50% - 70% of Ndesign
• Coarse-grades mixtures had higher Compaction Slope:– 6-10
• SGC CDI and PDA CFI indices were higher for Coarse-grades mixtures
• PDA measured LP showed similar ranking as SGC LP– Lower
• FR increased with an increased in the NMS
51
Conclusions
• Good correlation was observed B/W – SGC LP and PDA LP– SGC CDI and PDA CFI– SGC Slope and CDI– SGC Slope and LWT rut depth
• Poor correlation was observed B/W – SGC TDI and PDA TFI
• Mixtures evaluated performed well in the LWT
52
Thank You