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TRANSCRIPT
The Search for the Holy GrailN-DESIGN
January 10, 2007
SUPERPAVE DESIGN COMPATION EFFORT
• Discussion of what is the “true” N-design
• To know where to go, it helps to know where we’ve been
GYRATORY HISTORY
• Texas Four Inch Manual 1930s• Texas Four Inch Motorized 1960• Corps of Engineers 1960 ish• French 1970 ish• Superpave 1992
First Gyratory Compactor• 1939, Texas Highway Department• Texas 4-Inch Gyratory Press• Manually Operated
LCPC Gyratory Compactor
• 1959 visit to Texas
• Developed Protocol– 160 mm – 1º angle– 6 gyrations/min
SUPERPAVE GYRATORY
• N Design Experiment
– Determine number of gyrations to match the road density
N DESIGN RECOMPACTION
85.0%
90.0%
95.0%
100.0%
1 10 100 1000Number of Gyrations
% M
ax T
heor
etic
alG
ravi
ty
119 gyrations
96.5% Existing Density
N DESIGN EXPERIMENT
• Three levels of traffic
– Low, less than three million ESAL’s.
– Medium, more than three million, less than ten million ESAL’s.
– High, more than ten million ESAL’s
N DESIGN EXPERIMENT
• Three high temperature environments
– Cool (monthly temperature < 90 F)
– Warm (monthly temperature > 90 F, < 100 F)
– High (monthly temperature >100 F)
N DESIGN EXPERIMENT
• Two depths of pavement
– Surface, within upper 100 mm of pavement.
– Lower, more than 100 mm from pavement surface.
N DESIGN EXPERIMENT
• Three ages of pavement
– Young, less than three years old.
– Middle age, more than three years, less than twelve years old.
– Old, more than 12 years old.
N DESIGN EXPERIMENT
• In total, 108 cells were required
• Reduced the number of cells to nine and the number of sites to 18.
• In total, 15 sites were obtained and evaluated
CORRELATION
R Square = 0.7944
88.0
90.0
92.0
94.0
96.0
98.0
100.0
88.0 90.0 92.0 94.0 96.0 98.0 100.0Density At 100 Gyrations
Den
sity
Fro
m T
he R
oad
DESIGN GYRATION TABLEAverage High Air
TemperatureESALs <39oC
(millions) Ninitial Ndesign Nmax
< 0.3 7 68 1040.3 - 1 7 76 1171 - 3 7 86 1343 - 10 8 96 15210 - 30 8 109 17430 - 100 9 126 204> 100 9 142 233
N-Design II Experiment
Relate Densityto
Gyrations
%Gmm
Log ESALs
%Gmm
Log Gyrations
1.0E+06 1.0E+10 1.0E+14 1.0E+18
ESAL's
Des
ign
Gyr
atio
ns
10
100
1000
Relate Gyrations To ESAL’s
PG 67-22 Upper Lift
PG 76-22 Upper Lift
90.0
91.0
92.0
93.0
94.0
95.0
96.0
97.0
98.0
0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0ESALs (millions)
Pave
men
t Den
sity
, % G
mm
Winter
TRAFFIC COMPACTIONNdes = 115
Ndes = 70
NCAT Test Track
So What To Do?
Look at the effect of N-design on mixes
• For Same Aggregate SkeletonN Design will cause change in – VMA– Mix Stiffness
19 MM MIXTURES
-2.0%
-1.0%
0.0%
1.0%
2.0%
3.0%
-60 -40 -20 0 20 40 60
Change In Gyrations
Cha
nge
in V
MA
Effect on VMAAggregate Blend Constant
Effect on Stiffness
-
20,000
40,000
60,000
80,000
100,000
120,000
-60 -40 -20 0 20 40 60Change from Design Gyrations
G*(
0.1H
z), k
PaVolumetric Properties Constant
CompactionParameters
EstimatedDesign Traffic
Level(Millions1
ESALs) Ninit Ndes Nmax
< 0.3 6 50 75
0.3 to < 3 7 75 115
3 to < 30 8 100 160
≥ 30 9 125 205
N-Design III Experiment
Relate Densityto
Compaction
%Gmm
Log Gyrations
%Gmm
Log Passes
Relate Gyrations to Passes
Relating Compaction to Locking Point
0
1
2
3
4
5
6
7
0 1 2 3 4 5 6 7 8
Voids at Locking Point
Test
Str
ip V
oids
BUT!!!
• Compaction depends on– Gradation– Lift thickness– Base temperature– Available rollers– Etc.
….SO?…..
• Is our current N-design OK?• Or should we do more research?
• What is the effect of N-design on mixes??
Influence of Ndesign on Aggregate Properties
Property Increased Ndes
Decreased Ndes
Crushed Faces
crush crush
FAA nat sand nat sand
Gradation coarser finer
Influence of Ndesign on Volumetric Properties
Property Increased Ndes
Decreased Ndes
Air Voids none none
VMA (%AC) none* none*
VFA little little
Influence of Ndesign on Mix Properties
Property Increased Ndes
Decreased Ndes
Stiffness increase decrease
Compaction difficult easy
CONCLUSIONS
• Density at end of service life not rational to define N design
• Current spec based on engineering judgment (and is reasonable)
• Test strip density is more rational (would require more research)
