Inter Conversion of Laboratory Measured Dynamic Modulus Results to Field Modulus and Strain

7/25/2019 Inter Conversion of Laboratory Measured Dynamic Modulus Results to Field Modulus and Strain

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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:

"#$!"%&'()$ +,)-..%"/# !#$!"%&'()$ ,)$%"/#



Section S9 Analysis



All NCAT Sections

k = 2"

a = 1

b = 2

.)01!"/23)4

Tave= atmid+ b



Validation Against MnRoads

Stress

Dependency



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



Load with Depth for Moving Load (Stress

Pulse)

Brown Average loadingtime throughout layer

CalMe distribution withdepth

5673!$%&('$%('$%)*5678



Validation of Brown Approach



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

Documents

Inter Conversion of Laboratory Measured Dynamic Modulus Results to Field Modulus and Strain