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Interconversion of Laboratory Measured
Modulus Results to Field Modulus andStrain
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Conversion of Lab to Field
Have we been doing it right for 40 years?
Dynamic modulus is a angular frequency test
Thickness has no effect on strain
Modulus should be determined as function of strain time notstress
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Background
APS-fL has developed a database of Australiandynamic modulus results
Conversion between lab and field is required
This conversion is required for final recommendationson use of database
No recommended method which has been validated
against field modulus and strain
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Data Requirements
No data exist in Australia to currently do theconversion
NCAT extensive database of laboratory modulus,
field modulus and strain
Link has been established between AAPA database
and NCAT testing
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Time Frequency Conversion
Angular Frequency 1/!
= 1/2"t Pulse frequency 1/t
Angular frequency historically used in binders
Pulse historically in some asphalt research
The debate about which conversion to use for
dynamic modulus test is not resolved
AAPA will ignore the debate and subsequent complex
mathematics and instead determine a directconversion based on actual data
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Calibration Plan
Process Data Source
Stage 1- Calibrate lab field
modulus interconversion
Calibrate FrequencyInterconversion
FWD Data NCAT
Calibrate Temperature Profile
Validate findings withWesTrack and MnRoads
FWD WesTrack andMnRoads
Stage 2- Calibratefrequency under moving
load
Calibrate load pulse width
NCAT |E*| and strainCalibrate effect of frequencywith depth
Stage 3- Validate multi-layer asphalt
Validate Multi-layer results NCAT |E*| and strain
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Effective Modulus
Multi layer pavements need to be combined toequivalent single layer
Combine individual dynamic test results by:
"#$!"%&'()$ +,)-..%"/# !#$!"%&'()$ ,)$%"/#
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Section S9 Analysis
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All NCAT Sections
k = 2"
a = 1
b = 2
.)01!"/23)4
Tave= atmid+ b
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Validation Against MnRoads
Stress
Dependency
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FWD are identical to in dynamic modulus results at afrequency of 5.3Hz
Effective Temperature is 2oC higher than mid-layer
temperature
Dynamic modulus needs to be shifted 2"on the
frequency axis to model stain under a field loading
pulse
FWD to Dynamic Modulus
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Load with Depth for Moving Load (Stress
Pulse)
Brown Average loadingtime throughout layer
CalMe distribution withdepth
5673!$%&('$%('$%)*5678
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Validation of Brown Approach
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Validation of CalMe Approach
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Stress Based Approaches
Underestimate Strain
Underestimate of loading time
Overestimate of modulus
9 thickness layers closer to line of equality Is thickness that important?
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Unconstrained Optimisation
a =1.8m
b = 0
3)4 !9+:(/;
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Thickness has no influence on dynamic modulusfrequency
Load Pulse is 1.8m long
Contrary to (Austroads, Brown, CalMe and ME guide)strain pulse should be used, not the current stress
pulse modelling approach.
Frequency With Speed and Depth
(Optimised)
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Coffman 1967
a vehicle acts as a cyclic load with a wave length of 6 feet
using higher frequencies in the upper most layer and lower
frequencies for the lower layers does not appear justified The use of a Strain pulse appears more accurate
than the current use of the Stress pulse
Frequency With Speed and Depth
(Optimised)
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NCAT Time of Loading
Time of approx. 0.1to 0.9 sec
Length of approx. 1.8
to 2m
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Multi Layer Optimisation
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A constant frequency should be used regardless ofasphalt thickness for a given vehicle speed
Strain can accurately be predicted using an
equivalent single asphalt layer
The use of Multi-layers in the Layer Elastic Code
offers no benefit over a single effective layer
Do we need to use multi layer asphalts?
More work is required for sublayer and the temperaturewith depth profile
Conclusions and Recommendations